Inicialização, Finalização e Threads

Consulte também Configuração de Inicialização do Python.

Antes da Inicialização do Python

Em uma aplicação que incorpora Python, a função Py_Initialize() deve ser chamada antes de usar qualquer outra função da API Python/C; com exceção de algumas funções e as variáveis globais de configuração.

As seguintes funções podem ser seguramente chamadas antes da inicialização do Python.

Variáveis de configuração global

Python tem variáveis para a configuração global a fim de controlar diferentes características e opções. Por padrão, estes sinalizadores são controlados por opções de linha de comando.

Quando um sinalizador é definido por uma opção, o valor do sinalizador é o número de vezes que a opção foi definida. Por exemplo,``-b`` define Py_BytesWarningFlag para 1 e -bb define Py_BytesWarningFlag para 2.

int Py_BytesWarningFlag

This API is kept for backward compatibility: setting PyConfig.bytes_warning should be used instead, see Python Initialization Configuration.

Emite um aviso ao comparar bytes ou bytearray com str ou bytes com int. Emite um erro se for maior ou igual a 2.

Definida pela opção -b.

Obsoleto desde a versão 3.12.

int Py_DebugFlag

This API is kept for backward compatibility: setting PyConfig.parser_debug should be used instead, see Python Initialization Configuration.

Ativa a saída de depuração do analisador sintático (somente para especialistas, dependendo das opções de compilação).

Definida pela a opção -d e a variável de ambiente PYTHONDEBUG.

Obsoleto desde a versão 3.12.

int Py_DontWriteBytecodeFlag

This API is kept for backward compatibility: setting PyConfig.write_bytecode should be used instead, see Python Initialization Configuration.

Se definido como diferente de zero, o Python não tentará escrever arquivos .pyc na importação de módulos fonte.

Definida pela opção -B e pela variável de ambiente PYTHONDONTWRITEBYTECODE.

Obsoleto desde a versão 3.12.

int Py_FrozenFlag

This API is kept for backward compatibility: setting PyConfig.pathconfig_warnings should be used instead, see Python Initialization Configuration.

Suprime mensagens de erro ao calcular o caminho de pesquisa do módulo em Py_GetPath().

Private flag used by _freeze_module and frozenmain programs.

Obsoleto desde a versão 3.12.

int Py_HashRandomizationFlag

This API is kept for backward compatibility: setting PyConfig.hash_seed and PyConfig.use_hash_seed should be used instead, see Python Initialization Configuration.

Definida como 1 se a variável de ambiente PYTHONHASHSEED estiver definida como uma string não vazia.

Se o sinalizador for diferente de zero, lê a variável de ambiente PYTHONHASHSEED para inicializar a semente de hash secreta.

Obsoleto desde a versão 3.12.

int Py_IgnoreEnvironmentFlag

This API is kept for backward compatibility: setting PyConfig.use_environment should be used instead, see Python Initialization Configuration.

Ignore all PYTHON* environment variables, e.g. PYTHONPATH and PYTHONHOME, that might be set.

Definida pelas opções -E e -I.

Obsoleto desde a versão 3.12.

int Py_InspectFlag

This API is kept for backward compatibility: setting PyConfig.inspect should be used instead, see Python Initialization Configuration.

Quando um script é passado como primeiro argumento ou a opção -c é usada, entre no modo interativo após executar o script ou o comando, mesmo quando sys.stdin não parece ser um terminal.

Definida pela opção -i e pela variável de ambiente PYTHONINSPECT.

Obsoleto desde a versão 3.12.

int Py_InteractiveFlag

This API is kept for backward compatibility: setting PyConfig.interactive should be used instead, see Python Initialization Configuration.

Definida pela opção -i.

Obsoleto desde a versão 3.12.

int Py_IsolatedFlag

This API is kept for backward compatibility: setting PyConfig.isolated should be used instead, see Python Initialization Configuration.

Executa o Python no modo isolado. No modo isolado, sys.path não contém nem o diretório do script nem o diretório de pacotes de sites do usuário.

Definida pela opção -I.

Adicionado na versão 3.4.

Obsoleto desde a versão 3.12.

int Py_LegacyWindowsFSEncodingFlag

This API is kept for backward compatibility: setting PyPreConfig.legacy_windows_fs_encoding should be used instead, see Python Initialization Configuration.

Se o sinalizador for diferente de zero, use a codificação mbcs com o tratador de erros replace, em vez da codificação UTF-8 com o tratador de erros surrogatepass, para a codificação do sistema de arquivos e tratador de erros e codificação do sistema de arquivos.

Definida como 1 se a variável de ambiente PYTHONLEGACYWINDOWSFSENCODING estiver definida como uma string não vazia.

Veja PEP 529 para mais detalhes.

Disponibilidade: Windows.

Obsoleto desde a versão 3.12.

int Py_LegacyWindowsStdioFlag

This API is kept for backward compatibility: setting PyConfig.legacy_windows_stdio should be used instead, see Python Initialization Configuration.

If the flag is non-zero, use io.FileIO instead of io._WindowsConsoleIO for sys standard streams.

Definida como 1 se a variável de ambiente PYTHONLEGACYWINDOWSSTDIO estiver definida como uma string não vazia.

Veja PEP 528 para mais detalhes.

Disponibilidade: Windows.

Obsoleto desde a versão 3.12.

int Py_NoSiteFlag

This API is kept for backward compatibility: setting PyConfig.site_import should be used instead, see Python Initialization Configuration.

Desabilita a importação do módulo site e as manipulações dependentes do site de sys.path que isso acarreta. Também desabilita essas manipulações se site for explicitamente importado mais tarde (chame site.main() se você quiser que eles sejam acionados).

Definida pela opção -S.

Obsoleto desde a versão 3.12.

int Py_NoUserSiteDirectory

This API is kept for backward compatibility: setting PyConfig.user_site_directory should be used instead, see Python Initialization Configuration.

Não adiciona o diretório site-packages de usuário a sys.path.

Definida pelas opções -s e -I, e pela variável de ambiente PYTHONNOUSERSITE.

Obsoleto desde a versão 3.12.

int Py_OptimizeFlag

This API is kept for backward compatibility: setting PyConfig.optimization_level should be used instead, see Python Initialization Configuration.

Definida pela opção -O e pela variável de ambiente PYTHONOPTIMIZE.

Obsoleto desde a versão 3.12.

int Py_QuietFlag

This API is kept for backward compatibility: setting PyConfig.quiet should be used instead, see Python Initialization Configuration.

Não exibe as mensagens de direito autoral e de versão nem mesmo no modo interativo.

Definida pela opção -q.

Adicionado na versão 3.2.

Obsoleto desde a versão 3.12.

int Py_UnbufferedStdioFlag

This API is kept for backward compatibility: setting PyConfig.buffered_stdio should be used instead, see Python Initialization Configuration.

Força os fluxos stdout e stderr a não serem armazenados em buffer.

Definida pela opção -u e pela variável de ambiente PYTHONUNBUFFERED.

Obsoleto desde a versão 3.12.

int Py_VerboseFlag

This API is kept for backward compatibility: setting PyConfig.verbose should be used instead, see Python Initialization Configuration.

Exibe uma mensagem cada vez que um módulo é inicializado, mostrando o local (nome do arquivo ou módulo embutido) de onde ele é carregado. Se maior ou igual a 2, exibe uma mensagem para cada arquivo que é verificado durante a busca por um módulo. Também fornece informações sobre a limpeza do módulo na saída.

Definida pela a opção -v e a variável de ambiente PYTHONVERBOSE.

Obsoleto desde a versão 3.12.

Inicializando e encerrando o interpretador

void Py_Initialize()
Parte da ABI Estável.

Inicializa o interpretador Python. Em uma aplicação que incorpora o Python, isto deve ser chamado antes do uso de qualquer outra função do Python/C API; veja Antes da Inicialização do Python para algumas exceções.

This initializes the table of loaded modules (sys.modules), and creates the fundamental modules builtins, __main__ and sys. It also initializes the module search path (sys.path). It does not set sys.argv; use PySys_SetArgvEx() for that. This is a no-op when called for a second time (without calling Py_FinalizeEx() first). There is no return value; it is a fatal error if the initialization fails.

Use the Py_InitializeFromConfig() function to customize the Python Initialization Configuration.

Nota

On Windows, changes the console mode from O_TEXT to O_BINARY, which will also affect non-Python uses of the console using the C Runtime.

void Py_InitializeEx(int initsigs)
Parte da ABI Estável.

This function works like Py_Initialize() if initsigs is 1. If initsigs is 0, it skips initialization registration of signal handlers, which might be useful when Python is embedded.

Use the Py_InitializeFromConfig() function to customize the Python Initialization Configuration.

int Py_IsInitialized()
Parte da ABI Estável.

Return true (nonzero) when the Python interpreter has been initialized, false (zero) if not. After Py_FinalizeEx() is called, this returns false until Py_Initialize() is called again.

int Py_FinalizeEx()
Parte da ABI Estável desde a versão 3.6.

Undo all initializations made by Py_Initialize() and subsequent use of Python/C API functions, and destroy all sub-interpreters (see Py_NewInterpreter() below) that were created and not yet destroyed since the last call to Py_Initialize(). Ideally, this frees all memory allocated by the Python interpreter. This is a no-op when called for a second time (without calling Py_Initialize() again first). Normally the return value is 0. If there were errors during finalization (flushing buffered data), -1 is returned.

This function is provided for a number of reasons. An embedding application might want to restart Python without having to restart the application itself. An application that has loaded the Python interpreter from a dynamically loadable library (or DLL) might want to free all memory allocated by Python before unloading the DLL. During a hunt for memory leaks in an application a developer might want to free all memory allocated by Python before exiting from the application.

Bugs and caveats: The destruction of modules and objects in modules is done in random order; this may cause destructors (__del__() methods) to fail when they depend on other objects (even functions) or modules. Dynamically loaded extension modules loaded by Python are not unloaded. Small amounts of memory allocated by the Python interpreter may not be freed (if you find a leak, please report it). Memory tied up in circular references between objects is not freed. Some memory allocated by extension modules may not be freed. Some extensions may not work properly if their initialization routine is called more than once; this can happen if an application calls Py_Initialize() and Py_FinalizeEx() more than once.

Levanta um evento de auditoria cpython._PySys_ClearAuditHooks com nenhum argumento.

Adicionado na versão 3.6.

void Py_Finalize()
Parte da ABI Estável.

This is a backwards-compatible version of Py_FinalizeEx() that disregards the return value.

Process-wide parameters

int Py_SetStandardStreamEncoding(const char *encoding, const char *errors)

This API is kept for backward compatibility: setting PyConfig.stdio_encoding and PyConfig.stdio_errors should be used instead, see Python Initialization Configuration.

This function should be called before Py_Initialize(), if it is called at all. It specifies which encoding and error handling to use with standard IO, with the same meanings as in str.encode().

It overrides PYTHONIOENCODING values, and allows embedding code to control IO encoding when the environment variable does not work.

encoding and/or errors may be NULL to use PYTHONIOENCODING and/or default values (depending on other settings).

Note that sys.stderr always uses the “backslashreplace” error handler, regardless of this (or any other) setting.

If Py_FinalizeEx() is called, this function will need to be called again in order to affect subsequent calls to Py_Initialize().

Returns 0 if successful, a nonzero value on error (e.g. calling after the interpreter has already been initialized).

Adicionado na versão 3.4.

Obsoleto desde a versão 3.11.

void Py_SetProgramName(const wchar_t *name)
Parte da ABI Estável.

This API is kept for backward compatibility: setting PyConfig.program_name should be used instead, see Python Initialization Configuration.

Esta função deve ser chamada antes de Py_Initialize() ser chamada pela primeira vez, caso seja solicitada. Ela diz ao interpretador o valor do argumento argv[0] para a função main() do programa (convertido em caracteres amplos). Isto é utilizado por Py_GetPath() e algumas outras funções abaixo para encontrar as bibliotecas de tempo de execução relativas ao executável do interpretador. O valor padrão é 'python'. O argumento deve apontar para um caractere string amplo terminado em zero no armazenamento estático, cujo conteúdo não mudará durante a execução do programa. Nenhum código no interpretador Python mudará o conteúdo deste armazenamento.

Use Py_DecodeLocale() to decode a bytes string to get a wchar_t* string.

Obsoleto desde a versão 3.11.

wchar_t *Py_GetProgramName()
Parte da ABI Estável.

Return the program name set with Py_SetProgramName(), or the default. The returned string points into static storage; the caller should not modify its value.

This function should not be called before Py_Initialize(), otherwise it returns NULL.

Alterado na versão 3.10: It now returns NULL if called before Py_Initialize().

wchar_t *Py_GetPrefix()
Parte da ABI Estável.

Return the prefix for installed platform-independent files. This is derived through a number of complicated rules from the program name set with Py_SetProgramName() and some environment variables; for example, if the program name is '/usr/local/bin/python', the prefix is '/usr/local'. The returned string points into static storage; the caller should not modify its value. This corresponds to the prefix variable in the top-level Makefile and the --prefix argument to the configure script at build time. The value is available to Python code as sys.prefix. It is only useful on Unix. See also the next function.

This function should not be called before Py_Initialize(), otherwise it returns NULL.

Alterado na versão 3.10: It now returns NULL if called before Py_Initialize().

wchar_t *Py_GetExecPrefix()
Parte da ABI Estável.

Return the exec-prefix for installed platform-dependent files. This is derived through a number of complicated rules from the program name set with Py_SetProgramName() and some environment variables; for example, if the program name is '/usr/local/bin/python', the exec-prefix is '/usr/local'. The returned string points into static storage; the caller should not modify its value. This corresponds to the exec_prefix variable in the top-level Makefile and the --exec-prefix argument to the configure script at build time. The value is available to Python code as sys.exec_prefix. It is only useful on Unix.

Background: The exec-prefix differs from the prefix when platform dependent files (such as executables and shared libraries) are installed in a different directory tree. In a typical installation, platform dependent files may be installed in the /usr/local/plat subtree while platform independent may be installed in /usr/local.

Generally speaking, a platform is a combination of hardware and software families, e.g. Sparc machines running the Solaris 2.x operating system are considered the same platform, but Intel machines running Solaris 2.x are another platform, and Intel machines running Linux are yet another platform. Different major revisions of the same operating system generally also form different platforms. Non-Unix operating systems are a different story; the installation strategies on those systems are so different that the prefix and exec-prefix are meaningless, and set to the empty string. Note that compiled Python bytecode files are platform independent (but not independent from the Python version by which they were compiled!).

System administrators will know how to configure the mount or automount programs to share /usr/local between platforms while having /usr/local/plat be a different filesystem for each platform.

This function should not be called before Py_Initialize(), otherwise it returns NULL.

Alterado na versão 3.10: It now returns NULL if called before Py_Initialize().

wchar_t *Py_GetProgramFullPath()
Parte da ABI Estável.

Return the full program name of the Python executable; this is computed as a side-effect of deriving the default module search path from the program name (set by Py_SetProgramName() above). The returned string points into static storage; the caller should not modify its value. The value is available to Python code as sys.executable.

This function should not be called before Py_Initialize(), otherwise it returns NULL.

Alterado na versão 3.10: It now returns NULL if called before Py_Initialize().

wchar_t *Py_GetPath()
Parte da ABI Estável.

Return the default module search path; this is computed from the program name (set by Py_SetProgramName() above) and some environment variables. The returned string consists of a series of directory names separated by a platform dependent delimiter character. The delimiter character is ':' on Unix and macOS, ';' on Windows. The returned string points into static storage; the caller should not modify its value. The list sys.path is initialized with this value on interpreter startup; it can be (and usually is) modified later to change the search path for loading modules.

This function should not be called before Py_Initialize(), otherwise it returns NULL.

Alterado na versão 3.10: It now returns NULL if called before Py_Initialize().

void Py_SetPath(const wchar_t*)
Parte da ABI Estável desde a versão 3.7.

This API is kept for backward compatibility: setting PyConfig.module_search_paths and PyConfig.module_search_paths_set should be used instead, see Python Initialization Configuration.

Set the default module search path. If this function is called before Py_Initialize(), then Py_GetPath() won’t attempt to compute a default search path but uses the one provided instead. This is useful if Python is embedded by an application that has full knowledge of the location of all modules. The path components should be separated by the platform dependent delimiter character, which is ':' on Unix and macOS, ';' on Windows.

This also causes sys.executable to be set to the program full path (see Py_GetProgramFullPath()) and for sys.prefix and sys.exec_prefix to be empty. It is up to the caller to modify these if required after calling Py_Initialize().

Use Py_DecodeLocale() to decode a bytes string to get a wchar_* string.

O argumento caminho é copiado internamente, então o chamador pode liberá-lo depois da finalização da chamada.

Alterado na versão 3.8: O caminho completo do programa agora é utilizado para sys.executable, em vez do nome do programa.

Obsoleto desde a versão 3.11.

const char *Py_GetVersion()
Parte da ABI Estável.

Retorna a verão deste interpretador Python. Esta é uma string que se parece com

"3.0a5+ (py3k:63103M, May 12 2008, 00:53:55) \n[GCC 4.2.3]"

The first word (up to the first space character) is the current Python version; the first characters are the major and minor version separated by a period. The returned string points into static storage; the caller should not modify its value. The value is available to Python code as sys.version.

See also the Py_Version constant.

const char *Py_GetPlatform()
Parte da ABI Estável.

Return the platform identifier for the current platform. On Unix, this is formed from the “official” name of the operating system, converted to lower case, followed by the major revision number; e.g., for Solaris 2.x, which is also known as SunOS 5.x, the value is 'sunos5'. On macOS, it is 'darwin'. On Windows, it is 'win'. The returned string points into static storage; the caller should not modify its value. The value is available to Python code as sys.platform.

const char *Py_GetCopyright()
Parte da ABI Estável.

Retorna a string oficial de direitos autoriais para a versão atual do Python, por exemplo

'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'

The returned string points into static storage; the caller should not modify its value. The value is available to Python code as sys.copyright.

const char *Py_GetCompiler()
Parte da ABI Estável.

Retorna uma indicação do compilador usado para construir a atual versão do Python, em colchetes, por exemplo:

"[GCC 2.7.2.2]"

The returned string points into static storage; the caller should not modify its value. The value is available to Python code as part of the variable sys.version.

const char *Py_GetBuildInfo()
Parte da ABI Estável.

Retorna informação sobre o número de sequência e a data e hora da construção da instância atual do interpretador Python, por exemplo

"#67, Aug  1 1997, 22:34:28"

The returned string points into static storage; the caller should not modify its value. The value is available to Python code as part of the variable sys.version.

void PySys_SetArgvEx(int argc, wchar_t **argv, int updatepath)
Parte da ABI Estável.

This API is kept for backward compatibility: setting PyConfig.argv, PyConfig.parse_argv and PyConfig.safe_path should be used instead, see Python Initialization Configuration.

Set sys.argv based on argc and argv. These parameters are similar to those passed to the program’s main() function with the difference that the first entry should refer to the script file to be executed rather than the executable hosting the Python interpreter. If there isn’t a script that will be run, the first entry in argv can be an empty string. If this function fails to initialize sys.argv, a fatal condition is signalled using Py_FatalError().

Se updatepath é zero, isto é tudo o que a função faz. Se updatepath não é zero, a função também modifica sys.path de acordo com o seguinte algoritmo:

  • If the name of an existing script is passed in argv[0], the absolute path of the directory where the script is located is prepended to sys.path.

  • Otherwise (that is, if argc is 0 or argv[0] doesn’t point to an existing file name), an empty string is prepended to sys.path, which is the same as prepending the current working directory (".").

Use Py_DecodeLocale() to decode a bytes string to get a wchar_* string.

See also PyConfig.orig_argv and PyConfig.argv members of the Python Initialization Configuration.

Nota

It is recommended that applications embedding the Python interpreter for purposes other than executing a single script pass 0 as updatepath, and update sys.path themselves if desired. See CVE-2008-5983.

On versions before 3.1.3, you can achieve the same effect by manually popping the first sys.path element after having called PySys_SetArgv(), for example using:

PyRun_SimpleString("import sys; sys.path.pop(0)\n");

Adicionado na versão 3.1.3.

Obsoleto desde a versão 3.11.

void PySys_SetArgv(int argc, wchar_t **argv)
Parte da ABI Estável.

This API is kept for backward compatibility: setting PyConfig.argv and PyConfig.parse_argv should be used instead, see Python Initialization Configuration.

This function works like PySys_SetArgvEx() with updatepath set to 1 unless the python interpreter was started with the -I.

Use Py_DecodeLocale() to decode a bytes string to get a wchar_* string.

See also PyConfig.orig_argv and PyConfig.argv members of the Python Initialization Configuration.

Alterado na versão 3.4: The updatepath value depends on -I.

Obsoleto desde a versão 3.11.

void Py_SetPythonHome(const wchar_t *home)
Parte da ABI Estável.

This API is kept for backward compatibility: setting PyConfig.home should be used instead, see Python Initialization Configuration.

Set the default “home” directory, that is, the location of the standard Python libraries. See PYTHONHOME for the meaning of the argument string.

The argument should point to a zero-terminated character string in static storage whose contents will not change for the duration of the program’s execution. No code in the Python interpreter will change the contents of this storage.

Use Py_DecodeLocale() to decode a bytes string to get a wchar_* string.

Obsoleto desde a versão 3.11.

wchar_t *Py_GetPythonHome()
Parte da ABI Estável.

Return the default “home”, that is, the value set by a previous call to Py_SetPythonHome(), or the value of the PYTHONHOME environment variable if it is set.

This function should not be called before Py_Initialize(), otherwise it returns NULL.

Alterado na versão 3.10: It now returns NULL if called before Py_Initialize().

Thread State and the Global Interpreter Lock

The Python interpreter is not fully thread-safe. In order to support multi-threaded Python programs, there’s a global lock, called the global interpreter lock or GIL, that must be held by the current thread before it can safely access Python objects. Without the lock, even the simplest operations could cause problems in a multi-threaded program: for example, when two threads simultaneously increment the reference count of the same object, the reference count could end up being incremented only once instead of twice.

Therefore, the rule exists that only the thread that has acquired the GIL may operate on Python objects or call Python/C API functions. In order to emulate concurrency of execution, the interpreter regularly tries to switch threads (see sys.setswitchinterval()). The lock is also released around potentially blocking I/O operations like reading or writing a file, so that other Python threads can run in the meantime.

The Python interpreter keeps some thread-specific bookkeeping information inside a data structure called PyThreadState. There’s also one global variable pointing to the current PyThreadState: it can be retrieved using PyThreadState_Get().

Releasing the GIL from extension code

A maioria dos códigos de extensão que manipulam o GIL tem a seguinte estrutura:

Save the thread state in a local variable.
Release the global interpreter lock.
... Do some blocking I/O operation ...
Reacquire the global interpreter lock.
Restore the thread state from the local variable.

This is so common that a pair of macros exists to simplify it:

Py_BEGIN_ALLOW_THREADS
... Do some blocking I/O operation ...
Py_END_ALLOW_THREADS

A macro Py_BEGIN_ALLOW_THREADS abre um novo bloco e declara uma variável local oculta; a macro Py_END_ALLOW_THREADS fecha o bloco.

The block above expands to the following code:

PyThreadState *_save;

_save = PyEval_SaveThread();
... Do some blocking I/O operation ...
PyEval_RestoreThread(_save);

Here is how these functions work: the global interpreter lock is used to protect the pointer to the current thread state. When releasing the lock and saving the thread state, the current thread state pointer must be retrieved before the lock is released (since another thread could immediately acquire the lock and store its own thread state in the global variable). Conversely, when acquiring the lock and restoring the thread state, the lock must be acquired before storing the thread state pointer.

Nota

Calling system I/O functions is the most common use case for releasing the GIL, but it can also be useful before calling long-running computations which don’t need access to Python objects, such as compression or cryptographic functions operating over memory buffers. For example, the standard zlib and hashlib modules release the GIL when compressing or hashing data.

Non-Python created threads

When threads are created using the dedicated Python APIs (such as the threading module), a thread state is automatically associated to them and the code showed above is therefore correct. However, when threads are created from C (for example by a third-party library with its own thread management), they don’t hold the GIL, nor is there a thread state structure for them.

If you need to call Python code from these threads (often this will be part of a callback API provided by the aforementioned third-party library), you must first register these threads with the interpreter by creating a thread state data structure, then acquiring the GIL, and finally storing their thread state pointer, before you can start using the Python/C API. When you are done, you should reset the thread state pointer, release the GIL, and finally free the thread state data structure.

The PyGILState_Ensure() and PyGILState_Release() functions do all of the above automatically. The typical idiom for calling into Python from a C thread is:

PyGILState_STATE gstate;
gstate = PyGILState_Ensure();

/* Perform Python actions here. */
result = CallSomeFunction();
/* evaluate result or handle exception */

/* Release the thread. No Python API allowed beyond this point. */
PyGILState_Release(gstate);

Note that the PyGILState_* functions assume there is only one global interpreter (created automatically by Py_Initialize()). Python supports the creation of additional interpreters (using Py_NewInterpreter()), but mixing multiple interpreters and the PyGILState_* API is unsupported.

Cuidados com o uso de fork()

Another important thing to note about threads is their behaviour in the face of the C fork() call. On most systems with fork(), after a process forks only the thread that issued the fork will exist. This has a concrete impact both on how locks must be handled and on all stored state in CPython’s runtime.

The fact that only the “current” thread remains means any locks held by other threads will never be released. Python solves this for os.fork() by acquiring the locks it uses internally before the fork, and releasing them afterwards. In addition, it resets any Lock Objects in the child. When extending or embedding Python, there is no way to inform Python of additional (non-Python) locks that need to be acquired before or reset after a fork. OS facilities such as pthread_atfork() would need to be used to accomplish the same thing. Additionally, when extending or embedding Python, calling fork() directly rather than through os.fork() (and returning to or calling into Python) may result in a deadlock by one of Python’s internal locks being held by a thread that is defunct after the fork. PyOS_AfterFork_Child() tries to reset the necessary locks, but is not always able to.

The fact that all other threads go away also means that CPython’s runtime state there must be cleaned up properly, which os.fork() does. This means finalizing all other PyThreadState objects belonging to the current interpreter and all other PyInterpreterState objects. Due to this and the special nature of the “main” interpreter, fork() should only be called in that interpreter’s “main” thread, where the CPython global runtime was originally initialized. The only exception is if exec() will be called immediately after.

High-level API

Estes são os tipos e as funções mais comumente usados na escrita de um código de extensão em C, ou ao incorporar o interpretador Python:

type PyInterpreterState
Parte da API Limitada (como uma estrutura opaca).

This data structure represents the state shared by a number of cooperating threads. Threads belonging to the same interpreter share their module administration and a few other internal items. There are no public members in this structure.

Threads belonging to different interpreters initially share nothing, except process state like available memory, open file descriptors and such. The global interpreter lock is also shared by all threads, regardless of to which interpreter they belong.

type PyThreadState
Parte da API Limitada (como uma estrutura opaca).

This data structure represents the state of a single thread. The only public data member is:

PyInterpreterState *interp

This thread’s interpreter state.

void PyEval_InitThreads()
Parte da ABI Estável.

Função descontinuada que não faz nada.

In Python 3.6 and older, this function created the GIL if it didn’t exist.

Alterado na versão 3.9: The function now does nothing.

Alterado na versão 3.7: Esta função agora é chamada por Py_Initialize(), então não há mais necessidade de você chamá-la.

Alterado na versão 3.2: Esta função não pode mais ser chamada antes de Py_Initialize().

Obsoleto desde a versão 3.9.

int PyEval_ThreadsInitialized()
Parte da ABI Estável.

Returns a non-zero value if PyEval_InitThreads() has been called. This function can be called without holding the GIL, and therefore can be used to avoid calls to the locking API when running single-threaded.

Alterado na versão 3.7: The GIL is now initialized by Py_Initialize().

Obsoleto desde a versão 3.9.

PyThreadState *PyEval_SaveThread()
Parte da ABI Estável.

Release the global interpreter lock (if it has been created) and reset the thread state to NULL, returning the previous thread state (which is not NULL). If the lock has been created, the current thread must have acquired it.

void PyEval_RestoreThread(PyThreadState *tstate)
Parte da ABI Estável.

Acquire the global interpreter lock (if it has been created) and set the thread state to tstate, which must not be NULL. If the lock has been created, the current thread must not have acquired it, otherwise deadlock ensues.

Nota

Calling this function from a thread when the runtime is finalizing will terminate the thread, even if the thread was not created by Python. You can use _Py_IsFinalizing() or sys.is_finalizing() to check if the interpreter is in process of being finalized before calling this function to avoid unwanted termination.

PyThreadState *PyThreadState_Get()
Parte da ABI Estável.

Return the current thread state. The global interpreter lock must be held. When the current thread state is NULL, this issues a fatal error (so that the caller needn’t check for NULL).

PyThreadState *PyThreadState_Swap(PyThreadState *tstate)
Parte da ABI Estável.

Swap the current thread state with the thread state given by the argument tstate, which may be NULL. The global interpreter lock must be held and is not released.

The following functions use thread-local storage, and are not compatible with sub-interpreters:

PyGILState_STATE PyGILState_Ensure()
Parte da ABI Estável.

Certifique-se de que a thread atual esteja pronta para chamar a API Python C, independentemente do estado atual do Python ou do bloqueio global do interpretador (GIL). Isso pode ser chamado quantas vezes desejar por uma thread, desde que cada chamada corresponda a uma chamada para PyGILState_Release(). Em geral, outras APIs relacionadas a threads podem ser usadas entre chamadas PyGILState_Ensure() e PyGILState_Release() desde que o estado da thread seja restaurado ao seu estado anterior antes de Release(). Por exemplo, o uso normal das macros Py_BEGIN_ALLOW_THREADS e Py_END_ALLOW_THREADS é aceitável.

The return value is an opaque “handle” to the thread state when PyGILState_Ensure() was called, and must be passed to PyGILState_Release() to ensure Python is left in the same state. Even though recursive calls are allowed, these handles cannot be shared - each unique call to PyGILState_Ensure() must save the handle for its call to PyGILState_Release().

When the function returns, the current thread will hold the GIL and be able to call arbitrary Python code. Failure is a fatal error.

Nota

Calling this function from a thread when the runtime is finalizing will terminate the thread, even if the thread was not created by Python. You can use _Py_IsFinalizing() or sys.is_finalizing() to check if the interpreter is in process of being finalized before calling this function to avoid unwanted termination.

void PyGILState_Release(PyGILState_STATE)
Parte da ABI Estável.

Release any resources previously acquired. After this call, Python’s state will be the same as it was prior to the corresponding PyGILState_Ensure() call (but generally this state will be unknown to the caller, hence the use of the GILState API).

Every call to PyGILState_Ensure() must be matched by a call to PyGILState_Release() on the same thread.

PyThreadState *PyGILState_GetThisThreadState()
Parte da ABI Estável.

Get the current thread state for this thread. May return NULL if no GILState API has been used on the current thread. Note that the main thread always has such a thread-state, even if no auto-thread-state call has been made on the main thread. This is mainly a helper/diagnostic function.

int PyGILState_Check()

Return 1 if the current thread is holding the GIL and 0 otherwise. This function can be called from any thread at any time. Only if it has had its Python thread state initialized and currently is holding the GIL will it return 1. This is mainly a helper/diagnostic function. It can be useful for example in callback contexts or memory allocation functions when knowing that the GIL is locked can allow the caller to perform sensitive actions or otherwise behave differently.

Adicionado na versão 3.4.

The following macros are normally used without a trailing semicolon; look for example usage in the Python source distribution.

Py_BEGIN_ALLOW_THREADS
Parte da ABI Estável.

Esta macro se expande para { PyThreadState *_save; _save = PyEval_SaveThread();. Observe que ele contém uma chave de abertura; ele deve ser combinado com a seguinte macro Py_END_ALLOW_THREADS. Veja acima para uma discussão mais aprofundada desta macro.

Py_END_ALLOW_THREADS
Parte da ABI Estável.

Esta macro se expande para PyEval_RestoreThread(_save); }. Observe que ele contém uma chave de fechamento; ele deve ser combinado com uma macro Py_BEGIN_ALLOW_THREADS anterior. Veja acima para uma discussão mais aprofundada desta macro.

Py_BLOCK_THREADS
Parte da ABI Estável.

Esta macro se expande para PyEval_RestoreThread(_save);: é equivalente a Py_END_ALLOW_THREADS sem a chave de fechamento.

Py_UNBLOCK_THREADS
Parte da ABI Estável.

Esta macro se expande para _save = PyEval_SaveThread();: é equivalente a Py_BEGIN_ALLOW_THREADS sem a chave de abertura e declaração de variável.

Low-level API

All of the following functions must be called after Py_Initialize().

Alterado na versão 3.7: Py_Initialize() now initializes the GIL.

PyInterpreterState *PyInterpreterState_New()
Parte da ABI Estável.

Create a new interpreter state object. The global interpreter lock need not be held, but may be held if it is necessary to serialize calls to this function.

Levanta um evento de auditoria cpython.PyInterpreterState_New com nenhum argumento.

void PyInterpreterState_Clear(PyInterpreterState *interp)
Parte da ABI Estável.

Reset all information in an interpreter state object. The global interpreter lock must be held.

Levanta um evento de auditoria cpython.PyInterpreterState_Clear com nenhum argumento.

void PyInterpreterState_Delete(PyInterpreterState *interp)
Parte da ABI Estável.

Destroy an interpreter state object. The global interpreter lock need not be held. The interpreter state must have been reset with a previous call to PyInterpreterState_Clear().

PyThreadState *PyThreadState_New(PyInterpreterState *interp)
Parte da ABI Estável.

Create a new thread state object belonging to the given interpreter object. The global interpreter lock need not be held, but may be held if it is necessary to serialize calls to this function.

void PyThreadState_Clear(PyThreadState *tstate)
Parte da ABI Estável.

Reset all information in a thread state object. The global interpreter lock must be held.

Alterado na versão 3.9: This function now calls the PyThreadState.on_delete callback. Previously, that happened in PyThreadState_Delete().

void PyThreadState_Delete(PyThreadState *tstate)
Parte da ABI Estável.

Destroy a thread state object. The global interpreter lock need not be held. The thread state must have been reset with a previous call to PyThreadState_Clear().

void PyThreadState_DeleteCurrent(void)

Destroy the current thread state and release the global interpreter lock. Like PyThreadState_Delete(), the global interpreter lock need not be held. The thread state must have been reset with a previous call to PyThreadState_Clear().

PyFrameObject *PyThreadState_GetFrame(PyThreadState *tstate)
Parte da ABI Estável desde a versão 3.10.

Get the current frame of the Python thread state tstate.

Return a strong reference. Return NULL if no frame is currently executing.

See also PyEval_GetFrame().

tstate must not be NULL.

Adicionado na versão 3.9.

uint64_t PyThreadState_GetID(PyThreadState *tstate)
Parte da ABI Estável desde a versão 3.10.

Get the unique thread state identifier of the Python thread state tstate.

tstate must not be NULL.

Adicionado na versão 3.9.

PyInterpreterState *PyThreadState_GetInterpreter(PyThreadState *tstate)
Parte da ABI Estável desde a versão 3.10.

Get the interpreter of the Python thread state tstate.

tstate must not be NULL.

Adicionado na versão 3.9.

void PyThreadState_EnterTracing(PyThreadState *tstate)

Suspend tracing and profiling in the Python thread state tstate.

Resume them using the PyThreadState_LeaveTracing() function.

Adicionado na versão 3.11.

void PyThreadState_LeaveTracing(PyThreadState *tstate)

Resume tracing and profiling in the Python thread state tstate suspended by the PyThreadState_EnterTracing() function.

See also PyEval_SetTrace() and PyEval_SetProfile() functions.

Adicionado na versão 3.11.

PyInterpreterState *PyInterpreterState_Get(void)
Parte da ABI Estável desde a versão 3.9.

Get the current interpreter.

Issue a fatal error if there no current Python thread state or no current interpreter. It cannot return NULL.

The caller must hold the GIL.

Adicionado na versão 3.9.

int64_t PyInterpreterState_GetID(PyInterpreterState *interp)
Parte da ABI Estável desde a versão 3.7.

Return the interpreter’s unique ID. If there was any error in doing so then -1 is returned and an error is set.

The caller must hold the GIL.

Adicionado na versão 3.7.

PyObject *PyInterpreterState_GetDict(PyInterpreterState *interp)
Parte da ABI Estável desde a versão 3.8.

Return a dictionary in which interpreter-specific data may be stored. If this function returns NULL then no exception has been raised and the caller should assume no interpreter-specific dict is available.

This is not a replacement for PyModule_GetState(), which extensions should use to store interpreter-specific state information.

Adicionado na versão 3.8.

typedef PyObject *(*_PyFrameEvalFunction)(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag)

Type of a frame evaluation function.

The throwflag parameter is used by the throw() method of generators: if non-zero, handle the current exception.

Alterado na versão 3.9: The function now takes a tstate parameter.

Alterado na versão 3.11: The frame parameter changed from PyFrameObject* to _PyInterpreterFrame*.

_PyFrameEvalFunction _PyInterpreterState_GetEvalFrameFunc(PyInterpreterState *interp)

Get the frame evaluation function.

See the PEP 523 “Adding a frame evaluation API to CPython”.

Adicionado na versão 3.9.

void _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState *interp, _PyFrameEvalFunction eval_frame)

Set the frame evaluation function.

See the PEP 523 “Adding a frame evaluation API to CPython”.

Adicionado na versão 3.9.

PyObject *PyThreadState_GetDict()
Retorna valor: Referência emprestada. Parte da ABI Estável.

Return a dictionary in which extensions can store thread-specific state information. Each extension should use a unique key to use to store state in the dictionary. It is okay to call this function when no current thread state is available. If this function returns NULL, no exception has been raised and the caller should assume no current thread state is available.

int PyThreadState_SetAsyncExc(unsigned long id, PyObject *exc)
Parte da ABI Estável.

Asynchronously raise an exception in a thread. The id argument is the thread id of the target thread; exc is the exception object to be raised. This function does not steal any references to exc. To prevent naive misuse, you must write your own C extension to call this. Must be called with the GIL held. Returns the number of thread states modified; this is normally one, but will be zero if the thread id isn’t found. If exc is NULL, the pending exception (if any) for the thread is cleared. This raises no exceptions.

Alterado na versão 3.7: The type of the id parameter changed from long to unsigned long.

void PyEval_AcquireThread(PyThreadState *tstate)
Parte da ABI Estável.

Acquire the global interpreter lock and set the current thread state to tstate, which must not be NULL. The lock must have been created earlier. If this thread already has the lock, deadlock ensues.

Nota

Calling this function from a thread when the runtime is finalizing will terminate the thread, even if the thread was not created by Python. You can use _Py_IsFinalizing() or sys.is_finalizing() to check if the interpreter is in process of being finalized before calling this function to avoid unwanted termination.

Alterado na versão 3.8: Updated to be consistent with PyEval_RestoreThread(), Py_END_ALLOW_THREADS(), and PyGILState_Ensure(), and terminate the current thread if called while the interpreter is finalizing.

PyEval_RestoreThread() is a higher-level function which is always available (even when threads have not been initialized).

void PyEval_ReleaseThread(PyThreadState *tstate)
Parte da ABI Estável.

Reset the current thread state to NULL and release the global interpreter lock. The lock must have been created earlier and must be held by the current thread. The tstate argument, which must not be NULL, is only used to check that it represents the current thread state — if it isn’t, a fatal error is reported.

PyEval_SaveThread() is a higher-level function which is always available (even when threads have not been initialized).

void PyEval_AcquireLock()
Parte da ABI Estável.

Acquire the global interpreter lock. The lock must have been created earlier. If this thread already has the lock, a deadlock ensues.

Obsoleto desde a versão 3.2: This function does not update the current thread state. Please use PyEval_RestoreThread() or PyEval_AcquireThread() instead.

Nota

Calling this function from a thread when the runtime is finalizing will terminate the thread, even if the thread was not created by Python. You can use _Py_IsFinalizing() or sys.is_finalizing() to check if the interpreter is in process of being finalized before calling this function to avoid unwanted termination.

Alterado na versão 3.8: Updated to be consistent with PyEval_RestoreThread(), Py_END_ALLOW_THREADS(), and PyGILState_Ensure(), and terminate the current thread if called while the interpreter is finalizing.

void PyEval_ReleaseLock()
Parte da ABI Estável.

Release the global interpreter lock. The lock must have been created earlier.

Obsoleto desde a versão 3.2: This function does not update the current thread state. Please use PyEval_SaveThread() or PyEval_ReleaseThread() instead.

Sub-interpreter support

While in most uses, you will only embed a single Python interpreter, there are cases where you need to create several independent interpreters in the same process and perhaps even in the same thread. Sub-interpreters allow you to do that.

The “main” interpreter is the first one created when the runtime initializes. It is usually the only Python interpreter in a process. Unlike sub-interpreters, the main interpreter has unique process-global responsibilities like signal handling. It is also responsible for execution during runtime initialization and is usually the active interpreter during runtime finalization. The PyInterpreterState_Main() function returns a pointer to its state.

You can switch between sub-interpreters using the PyThreadState_Swap() function. You can create and destroy them using the following functions:

type PyInterpreterConfig

Structure containing most parameters to configure a sub-interpreter. Its values are used only in Py_NewInterpreterFromConfig() and never modified by the runtime.

Adicionado na versão 3.12.

Campos de estrutura:

int use_main_obmalloc

If this is 0 then the sub-interpreter will use its own “object” allocator state. Otherwise it will use (share) the main interpreter’s.

If this is 0 then check_multi_interp_extensions must be 1 (non-zero). If this is 1 then gil must not be PyInterpreterConfig_OWN_GIL.

int allow_fork

If this is 0 then the runtime will not support forking the process in any thread where the sub-interpreter is currently active. Otherwise fork is unrestricted.

Note that the subprocess module still works when fork is disallowed.

int allow_exec

If this is 0 then the runtime will not support replacing the current process via exec (e.g. os.execv()) in any thread where the sub-interpreter is currently active. Otherwise exec is unrestricted.

Note that the subprocess module still works when exec is disallowed.

int allow_threads

If this is 0 then the sub-interpreter’s threading module won’t create threads. Otherwise threads are allowed.

int allow_daemon_threads

If this is 0 then the sub-interpreter’s threading module won’t create daemon threads. Otherwise daemon threads are allowed (as long as allow_threads is non-zero).

int check_multi_interp_extensions

If this is 0 then all extension modules may be imported, including legacy (single-phase init) modules, in any thread where the sub-interpreter is currently active. Otherwise only multi-phase init extension modules (see PEP 489) may be imported. (Also see Py_mod_multiple_interpreters.)

This must be 1 (non-zero) if use_main_obmalloc is 0.

int gil

This determines the operation of the GIL for the sub-interpreter. It may be one of the following:

PyInterpreterConfig_DEFAULT_GIL

Use the default selection (PyInterpreterConfig_SHARED_GIL).

PyInterpreterConfig_SHARED_GIL

Use (share) the main interpreter’s GIL.

PyInterpreterConfig_OWN_GIL

Use the sub-interpreter’s own GIL.

If this is PyInterpreterConfig_OWN_GIL then PyInterpreterConfig.use_main_obmalloc must be 0.

PyStatus Py_NewInterpreterFromConfig(PyThreadState **tstate_p, const PyInterpreterConfig *config)

Create a new sub-interpreter. This is an (almost) totally separate environment for the execution of Python code. In particular, the new interpreter has separate, independent versions of all imported modules, including the fundamental modules builtins, __main__ and sys. The table of loaded modules (sys.modules) and the module search path (sys.path) are also separate. The new environment has no sys.argv variable. It has new standard I/O stream file objects sys.stdin, sys.stdout and sys.stderr (however these refer to the same underlying file descriptors).

The given config controls the options with which the interpreter is initialized.

Upon success, tstate_p will be set to the first thread state created in the new sub-interpreter. This thread state is made in the current thread state. Note that no actual thread is created; see the discussion of thread states below. If creation of the new interpreter is unsuccessful, tstate_p is set to NULL; no exception is set since the exception state is stored in the current thread state and there may not be a current thread state.

Like all other Python/C API functions, the global interpreter lock must be held before calling this function and is still held when it returns. Likewise a current thread state must be set on entry. On success, the returned thread state will be set as current. If the sub-interpreter is created with its own GIL then the GIL of the calling interpreter will be released. When the function returns, the new interpreter’s GIL will be held by the current thread and the previously interpreter’s GIL will remain released here.

Adicionado na versão 3.12.

Sub-interpreters are most effective when isolated from each other, with certain functionality restricted:

PyInterpreterConfig config = {
    .use_main_obmalloc = 0,
    .allow_fork = 0,
    .allow_exec = 0,
    .allow_threads = 1,
    .allow_daemon_threads = 0,
    .check_multi_interp_extensions = 1,
    .gil = PyInterpreterConfig_OWN_GIL,
};
PyThreadState *tstate = Py_NewInterpreterFromConfig(&config);

Note that the config is used only briefly and does not get modified. During initialization the config’s values are converted into various PyInterpreterState values. A read-only copy of the config may be stored internally on the PyInterpreterState.

Extension modules are shared between (sub-)interpreters as follows:

  • For modules using multi-phase initialization, e.g. PyModule_FromDefAndSpec(), a separate module object is created and initialized for each interpreter. Only C-level static and global variables are shared between these module objects.

  • For modules using single-phase initialization, e.g. PyModule_Create(), the first time a particular extension is imported, it is initialized normally, and a (shallow) copy of its module’s dictionary is squirreled away. When the same extension is imported by another (sub-)interpreter, a new module is initialized and filled with the contents of this copy; the extension’s init function is not called. Objects in the module’s dictionary thus end up shared across (sub-)interpreters, which might cause unwanted behavior (see Bugs and caveats below).

    Note that this is different from what happens when an extension is imported after the interpreter has been completely re-initialized by calling Py_FinalizeEx() and Py_Initialize(); in that case, the extension’s initmodule function is called again. As with multi-phase initialization, this means that only C-level static and global variables are shared between these modules.

PyThreadState *Py_NewInterpreter(void)
Parte da ABI Estável.

Create a new sub-interpreter. This is essentially just a wrapper around Py_NewInterpreterFromConfig() with a config that preserves the existing behavior. The result is an unisolated sub-interpreter that shares the main interpreter’s GIL, allows fork/exec, allows daemon threads, and allows single-phase init modules.

void Py_EndInterpreter(PyThreadState *tstate)
Parte da ABI Estável.

Destroy the (sub-)interpreter represented by the given thread state. The given thread state must be the current thread state. See the discussion of thread states below. When the call returns, the current thread state is NULL. All thread states associated with this interpreter are destroyed. The global interpreter lock used by the target interpreter must be held before calling this function. No GIL is held when it returns.

Py_FinalizeEx() will destroy all sub-interpreters that haven’t been explicitly destroyed at that point.

A Per-Interpreter GIL

Using Py_NewInterpreterFromConfig() you can create a sub-interpreter that is completely isolated from other interpreters, including having its own GIL. The most important benefit of this isolation is that such an interpreter can execute Python code without being blocked by other interpreters or blocking any others. Thus a single Python process can truly take advantage of multiple CPU cores when running Python code. The isolation also encourages a different approach to concurrency than that of just using threads. (See PEP 554.)

Using an isolated interpreter requires vigilance in preserving that isolation. That especially means not sharing any objects or mutable state without guarantees about thread-safety. Even objects that are otherwise immutable (e.g. None, (1, 5)) can’t normally be shared because of the refcount. One simple but less-efficient approach around this is to use a global lock around all use of some state (or object). Alternately, effectively immutable objects (like integers or strings) can be made safe in spite of their refcounts by making them “immortal”. In fact, this has been done for the builtin singletons, small integers, and a number of other builtin objects.

If you preserve isolation then you will have access to proper multi-core computing without the complications that come with free-threading. Failure to preserve isolation will expose you to the full consequences of free-threading, including races and hard-to-debug crashes.

Aside from that, one of the main challenges of using multiple isolated interpreters is how to communicate between them safely (not break isolation) and efficiently. The runtime and stdlib do not provide any standard approach to this yet. A future stdlib module would help mitigate the effort of preserving isolation and expose effective tools for communicating (and sharing) data between interpreters.

Adicionado na versão 3.12.

Bugs and caveats

Because sub-interpreters (and the main interpreter) are part of the same process, the insulation between them isn’t perfect — for example, using low-level file operations like os.close() they can (accidentally or maliciously) affect each other’s open files. Because of the way extensions are shared between (sub-)interpreters, some extensions may not work properly; this is especially likely when using single-phase initialization or (static) global variables. It is possible to insert objects created in one sub-interpreter into a namespace of another (sub-)interpreter; this should be avoided if possible.

Special care should be taken to avoid sharing user-defined functions, methods, instances or classes between sub-interpreters, since import operations executed by such objects may affect the wrong (sub-)interpreter’s dictionary of loaded modules. It is equally important to avoid sharing objects from which the above are reachable.

Also note that combining this functionality with PyGILState_* APIs is delicate, because these APIs assume a bijection between Python thread states and OS-level threads, an assumption broken by the presence of sub-interpreters. It is highly recommended that you don’t switch sub-interpreters between a pair of matching PyGILState_Ensure() and PyGILState_Release() calls. Furthermore, extensions (such as ctypes) using these APIs to allow calling of Python code from non-Python created threads will probably be broken when using sub-interpreters.

Notificações assíncronas

A mechanism is provided to make asynchronous notifications to the main interpreter thread. These notifications take the form of a function pointer and a void pointer argument.

int Py_AddPendingCall(int (*func)(void*), void *arg)
Parte da ABI Estável.

Schedule a function to be called from the main interpreter thread. On success, 0 is returned and func is queued for being called in the main thread. On failure, -1 is returned without setting any exception.

When successfully queued, func will be eventually called from the main interpreter thread with the argument arg. It will be called asynchronously with respect to normally running Python code, but with both these conditions met:

func must return 0 on success, or -1 on failure with an exception set. func won’t be interrupted to perform another asynchronous notification recursively, but it can still be interrupted to switch threads if the global interpreter lock is released.

This function doesn’t need a current thread state to run, and it doesn’t need the global interpreter lock.

To call this function in a subinterpreter, the caller must hold the GIL. Otherwise, the function func can be scheduled to be called from the wrong interpreter.

Aviso

This is a low-level function, only useful for very special cases. There is no guarantee that func will be called as quick as possible. If the main thread is busy executing a system call, func won’t be called before the system call returns. This function is generally not suitable for calling Python code from arbitrary C threads. Instead, use the PyGILState API.

Adicionado na versão 3.1.

Alterado na versão 3.9: If this function is called in a subinterpreter, the function func is now scheduled to be called from the subinterpreter, rather than being called from the main interpreter. Each subinterpreter now has its own list of scheduled calls.

Profiling and Tracing

The Python interpreter provides some low-level support for attaching profiling and execution tracing facilities. These are used for profiling, debugging, and coverage analysis tools.

This C interface allows the profiling or tracing code to avoid the overhead of calling through Python-level callable objects, making a direct C function call instead. The essential attributes of the facility have not changed; the interface allows trace functions to be installed per-thread, and the basic events reported to the trace function are the same as had been reported to the Python-level trace functions in previous versions.

typedef int (*Py_tracefunc)(PyObject *obj, PyFrameObject *frame, int what, PyObject *arg)

The type of the trace function registered using PyEval_SetProfile() and PyEval_SetTrace(). The first parameter is the object passed to the registration function as obj, frame is the frame object to which the event pertains, what is one of the constants PyTrace_CALL, PyTrace_EXCEPTION, PyTrace_LINE, PyTrace_RETURN, PyTrace_C_CALL, PyTrace_C_EXCEPTION, PyTrace_C_RETURN, or PyTrace_OPCODE, and arg depends on the value of what:

Value of what

Meaning of arg

PyTrace_CALL

Always Py_None.

PyTrace_EXCEPTION

Exception information as returned by sys.exc_info().

PyTrace_LINE

Always Py_None.

PyTrace_RETURN

Value being returned to the caller, or NULL if caused by an exception.

PyTrace_C_CALL

Function object being called.

PyTrace_C_EXCEPTION

Function object being called.

PyTrace_C_RETURN

Function object being called.

PyTrace_OPCODE

Always Py_None.

int PyTrace_CALL

The value of the what parameter to a Py_tracefunc function when a new call to a function or method is being reported, or a new entry into a generator. Note that the creation of the iterator for a generator function is not reported as there is no control transfer to the Python bytecode in the corresponding frame.

int PyTrace_EXCEPTION

The value of the what parameter to a Py_tracefunc function when an exception has been raised. The callback function is called with this value for what when after any bytecode is processed after which the exception becomes set within the frame being executed. The effect of this is that as exception propagation causes the Python stack to unwind, the callback is called upon return to each frame as the exception propagates. Only trace functions receives these events; they are not needed by the profiler.

int PyTrace_LINE

The value passed as the what parameter to a Py_tracefunc function (but not a profiling function) when a line-number event is being reported. It may be disabled for a frame by setting f_trace_lines to 0 on that frame.

int PyTrace_RETURN

The value for the what parameter to Py_tracefunc functions when a call is about to return.

int PyTrace_C_CALL

The value for the what parameter to Py_tracefunc functions when a C function is about to be called.

int PyTrace_C_EXCEPTION

The value for the what parameter to Py_tracefunc functions when a C function has raised an exception.

int PyTrace_C_RETURN

The value for the what parameter to Py_tracefunc functions when a C function has returned.

int PyTrace_OPCODE

The value for the what parameter to Py_tracefunc functions (but not profiling functions) when a new opcode is about to be executed. This event is not emitted by default: it must be explicitly requested by setting f_trace_opcodes to 1 on the frame.

void PyEval_SetProfile(Py_tracefunc func, PyObject *obj)

Set the profiler function to func. The obj parameter is passed to the function as its first parameter, and may be any Python object, or NULL. If the profile function needs to maintain state, using a different value for obj for each thread provides a convenient and thread-safe place to store it. The profile function is called for all monitored events except PyTrace_LINE PyTrace_OPCODE and PyTrace_EXCEPTION.

See also the sys.setprofile() function.

The caller must hold the GIL.

void PyEval_SetProfileAllThreads(Py_tracefunc func, PyObject *obj)

Like PyEval_SetProfile() but sets the profile function in all running threads belonging to the current interpreter instead of the setting it only on the current thread.

The caller must hold the GIL.

As PyEval_SetProfile(), this function ignores any exceptions raised while setting the profile functions in all threads.

Adicionado na versão 3.12.

void PyEval_SetTrace(Py_tracefunc func, PyObject *obj)

Set the tracing function to func. This is similar to PyEval_SetProfile(), except the tracing function does receive line-number events and per-opcode events, but does not receive any event related to C function objects being called. Any trace function registered using PyEval_SetTrace() will not receive PyTrace_C_CALL, PyTrace_C_EXCEPTION or PyTrace_C_RETURN as a value for the what parameter.

See also the sys.settrace() function.

The caller must hold the GIL.

void PyEval_SetTraceAllThreads(Py_tracefunc func, PyObject *obj)

Like PyEval_SetTrace() but sets the tracing function in all running threads belonging to the current interpreter instead of the setting it only on the current thread.

The caller must hold the GIL.

As PyEval_SetTrace(), this function ignores any exceptions raised while setting the trace functions in all threads.

Adicionado na versão 3.12.

Advanced Debugger Support

These functions are only intended to be used by advanced debugging tools.

PyInterpreterState *PyInterpreterState_Head()

Return the interpreter state object at the head of the list of all such objects.

PyInterpreterState *PyInterpreterState_Main()

Return the main interpreter state object.

PyInterpreterState *PyInterpreterState_Next(PyInterpreterState *interp)

Return the next interpreter state object after interp from the list of all such objects.

PyThreadState *PyInterpreterState_ThreadHead(PyInterpreterState *interp)

Return the pointer to the first PyThreadState object in the list of threads associated with the interpreter interp.

PyThreadState *PyThreadState_Next(PyThreadState *tstate)

Return the next thread state object after tstate from the list of all such objects belonging to the same PyInterpreterState object.

Thread Local Storage Support

The Python interpreter provides low-level support for thread-local storage (TLS) which wraps the underlying native TLS implementation to support the Python-level thread local storage API (threading.local). The CPython C level APIs are similar to those offered by pthreads and Windows: use a thread key and functions to associate a void* value per thread.

The GIL does not need to be held when calling these functions; they supply their own locking.

Note that Python.h does not include the declaration of the TLS APIs, you need to include pythread.h to use thread-local storage.

Nota

None of these API functions handle memory management on behalf of the void* values. You need to allocate and deallocate them yourself. If the void* values happen to be PyObject*, these functions don’t do refcount operations on them either.

Thread Specific Storage (TSS) API

TSS API is introduced to supersede the use of the existing TLS API within the CPython interpreter. This API uses a new type Py_tss_t instead of int to represent thread keys.

Adicionado na versão 3.7.

Ver também

“A New C-API for Thread-Local Storage in CPython” (PEP 539)

type Py_tss_t

This data structure represents the state of a thread key, the definition of which may depend on the underlying TLS implementation, and it has an internal field representing the key’s initialization state. There are no public members in this structure.

Quando Py_LIMITED_API não é definido, a alocação estática deste tipo por Py_tss_NEEDS_INIT é permitida.

Py_tss_NEEDS_INIT

This macro expands to the initializer for Py_tss_t variables. Note that this macro won’t be defined with Py_LIMITED_API.

Alocação dinâmica

Dynamic allocation of the Py_tss_t, required in extension modules built with Py_LIMITED_API, where static allocation of this type is not possible due to its implementation being opaque at build time.

Py_tss_t *PyThread_tss_alloc()
Parte da ABI Estável desde a versão 3.7.

Retorna um valor que é o mesmo estado de um valor inicializado com Py_tss_NEEDS_INIT, ou NULL no caso de falha de alocação dinâmica.

void PyThread_tss_free(Py_tss_t *key)
Parte da ABI Estável desde a versão 3.7.

Free the given key allocated by PyThread_tss_alloc(), after first calling PyThread_tss_delete() to ensure any associated thread locals have been unassigned. This is a no-op if the key argument is NULL.

Nota

A freed key becomes a dangling pointer. You should reset the key to NULL.

Métodos

The parameter key of these functions must not be NULL. Moreover, the behaviors of PyThread_tss_set() and PyThread_tss_get() are undefined if the given Py_tss_t has not been initialized by PyThread_tss_create().

int PyThread_tss_is_created(Py_tss_t *key)
Parte da ABI Estável desde a versão 3.7.

Return a non-zero value if the given Py_tss_t has been initialized by PyThread_tss_create().

int PyThread_tss_create(Py_tss_t *key)
Parte da ABI Estável desde a versão 3.7.

Retorna um valor zero na inicialização bem-sucedida de uma chave TSS. O comportamento é indefinido se o valor apontado pelo argumento key não for inicializado por Py_tss_NEEDS_INIT. Essa função pode ser chamada repetidamente na mesma tecla – chamá-la em uma tecla já inicializada não funciona e retorna imediatamente com sucesso.

void PyThread_tss_delete(Py_tss_t *key)
Parte da ABI Estável desde a versão 3.7.

Destroy a TSS key to forget the values associated with the key across all threads, and change the key’s initialization state to uninitialized. A destroyed key is able to be initialized again by PyThread_tss_create(). This function can be called repeatedly on the same key – calling it on an already destroyed key is a no-op.

int PyThread_tss_set(Py_tss_t *key, void *value)
Parte da ABI Estável desde a versão 3.7.

Return a zero value to indicate successfully associating a void* value with a TSS key in the current thread. Each thread has a distinct mapping of the key to a void* value.

void *PyThread_tss_get(Py_tss_t *key)
Parte da ABI Estável desde a versão 3.7.

Return the void* value associated with a TSS key in the current thread. This returns NULL if no value is associated with the key in the current thread.

Thread Local Storage (TLS) API

Obsoleto desde a versão 3.7: This API is superseded by Thread Specific Storage (TSS) API.

Nota

This version of the API does not support platforms where the native TLS key is defined in a way that cannot be safely cast to int. On such platforms, PyThread_create_key() will return immediately with a failure status, and the other TLS functions will all be no-ops on such platforms.

Due to the compatibility problem noted above, this version of the API should not be used in new code.

int PyThread_create_key()
Parte da ABI Estável.
void PyThread_delete_key(int key)
Parte da ABI Estável.
int PyThread_set_key_value(int key, void *value)
Parte da ABI Estável.
void *PyThread_get_key_value(int key)
Parte da ABI Estável.
void PyThread_delete_key_value(int key)
Parte da ABI Estável.
void PyThread_ReInitTLS()
Parte da ABI Estável.