# 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.

- Funções de configuração:

  - `PyImport_AppendInittab()`

  - `PyImport_ExtendInittab()`

  - `PyInitFrozenExtensions()`

  - `PyMem_SetAllocator()`

  - `PyMem_SetupDebugHooks()`

  - `PyObject_SetArenaAllocator()`

  - `Py_SetPath()`

  - `Py_SetProgramName()`

  - `Py_SetPythonHome()`

  - `Py_SetStandardStreamEncoding()`

  - `PySys_AddWarnOption()`

  - `PySys_AddXOption()`

  - `PySys_ResetWarnOptions()`

- Funções informativas:

  - `Py_IsInitialized()`

  - `PyMem_GetAllocator()`

  - `PyObject_GetArenaAllocator()`

  - `Py_GetBuildInfo()`

  - `Py_GetCompiler()`

  - `Py_GetCopyright()`

  - `Py_GetPlatform()`

  - `Py_GetVersion()`

- Utilitários:

  - `Py_DecodeLocale()`

- Alocadores de memória:

  - `PyMem_RawMalloc()`

  - `PyMem_RawRealloc()`

  - `PyMem_RawCalloc()`

  - `PyMem_RawFree()`

Nota

As seguintes funções não devem ser chamadas antes `Py_Initialize()`: `Py_EncodeLocale()`, `Py_GetPath()`, `Py_GetPrefix()`, `Py_GetExecPrefix()`, `Py_GetProgramFullPath()`, `Py_GetPythonHome()`, `Py_GetProgramName()` e `PyEval_InitThreads()`.

## 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`

  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`.

int `Py_DebugFlag`

  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`.

int `Py_DontWriteBytecodeFlag`

  Se definida 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`.

int `Py_FrozenFlag`

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

  Sinalizador privado usado pelos programas `_freeze_importlib` e `frozenmain`.

int `Py_HashRandomizationFlag`

  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.

int `Py_IgnoreEnvironmentFlag`

  Ignora todas as variáveis de ambiente `PYTHON*`, por exemplo `PYTHONPATH` e `PYTHONHOME`, que pode ser definido.

  Definida pelas opções `-E` e `-I`.

int `Py_InspectFlag`

  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`.

int `Py_InteractiveFlag`

  Definida pela opção `-i`.

int `Py_IsolatedFlag`

  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`.

  Novo na versão 3.4.

int `Py_LegacyWindowsFSEncodingFlag`

  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.

int `Py_LegacyWindowsStdioFlag`

  Se o sinalizador for diferente de zero, usa `io.FileIO` em vez de `WindowsConsoleIO` para fluxos padrão `sys`.

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

  Veja a PEP 528 para mais detalhes.

  Disponibilidade: Windows.

int `Py_NoSiteFlag`

  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`.

int `Py_NoUserSiteDirectory`

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

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

int `Py_OptimizeFlag`

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

int `Py_QuietFlag`

  Não exibe as mensagens de direitos autorais e de versão nem mesmo no modo interativo.

  Definida pela opção `-q`.

  Novo na versão 3.2.

int `Py_UnbufferedStdioFlag`

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

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

int `Py_VerboseFlag`

  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`.

## Inicializando e encerrando o interpretador

void `Py_Initialize`()
  Part of the Stable ABI.

  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.

  Nota

  No Windows, altera o modo do console de `O_TEXT` para `O_BINARY`, o que também afetará usos não Python do console usando o Runtime C.

void `Py_InitializeEx`(int initsigs)
  Part of the Stable ABI.

  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.

int `Py_IsInitialized`()
  Part of the Stable ABI.

  Retorna true (diferente de zero) quando o interpretador Python foi inicializado, false (zero) se não. Após `Py_FinalizeEx()` ser chamado, isso retorna false até que `Py_Initialize()` seja chamado novamente.

int `Py_FinalizeEx`()
  Part of the Stable ABI since version 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.

  Esta função é fornecida por vários motivos. Uma aplicação de incorporação pode querer reiniciar o Python sem precisar reiniciar a própria aplicação. Uma aplicação que carregou o interpretador Python de uma biblioteca carregável dinamicamente (ou DLL) pode querer liberar toda a memória alocada pelo Python antes de descarregar a DLL. Durante uma busca por vazamentos de memória em uma aplicação, um desenvolvedor pode querer liberar toda a memória alocada pelo Python antes de sair da aplicação.

  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` sem argumentos.

  Novo na versão 3.6.

void `Py_Finalize`()
  Part of the Stable ABI.

  Esta é uma versão compatível com retrocompatibilidade de `Py_FinalizeEx()` que desconsidera o valor de retorno.

## Process-wide parameters

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

  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).

  Novo na versão 3.4.

void `Py_SetProgramName`(const wchar_t *name)
  Part of the Stable ABI.

  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_*` string.

wchar *`Py_GetProgramName`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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*)
  Part of the Stable ABI since version 3.7.

  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.

const char *`Py_GetVersion`()
  Part of the Stable ABI.

  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`.

const char *`Py_GetPlatform`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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.

  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");

  Novo na versão 3.1.3.

void `PySys_SetArgv`(int argc, wchar_t **argv)
  Part of the Stable ABI.

  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.

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

void `Py_SetPythonHome`(const wchar_t *home)
  Part of the Stable ABI.

  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.

wchar_t *`Py_GetPythonHome`()
  Part of the Stable ABI.

  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()`.

## Estado de thread e a trava global do interpretador

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.

Portanto, existe a regra de que somente a thread que adquiriu a GIL pode operar em objetos Python ou chamar funções da API C/Python. Para emular a simultaneidade de execução, o interpretador tenta alternar threads regularmente (consulte `sys.setswitchinterval()`). A trava também é liberada em operações de E/S potencialmente bloqueantes, como ler ou escrever um arquivo, para que outras threads Python possam ser executadas enquanto isso.

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 a 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.

Isso é tão comum que existe um par de macros para simplificá-lo:

    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.

O bloco acima se expande para o seguinte código:

    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`
  Part of the Limited API (as an opaque struct).

  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`
  Part of the Limited API (as an opaque struct).

  This data structure represents the state of a single thread. The only public data member is `interp` (`PyInterpreterState*`), which points to this thread’s interpreter state.

void `PyEval_InitThreads`()
  Part of the Stable ABI.

  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()`.

  Deprecated since version 3.9, will be removed in version 3.11.

int `PyEval_ThreadsInitialized`()
  Part of the Stable ABI.

  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()`.

  Deprecated since version 3.9, will be removed in version 3.11.

PyThreadState *`PyEval_SaveThread`()
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  Certifique-se de que a thread atual esteja pronta para chamar a API Python C, independentemente do estado atual do Python ou da trava 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)
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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.

  Novo 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`
  Part of the Stable ABI.

  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`
  Part of the Stable ABI.

  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`
  Part of the Stable ABI.

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

`Py_UNBLOCK_THREADS`
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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` sem argumentos.

void `PyInterpreterState_Clear`(PyInterpreterState *interp)
  Part of the Stable ABI.

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

  Levanta um evento de auditoria `cpython.PyInterpreterState_Clear` sem argumentos.

void `PyInterpreterState_Delete`(PyInterpreterState *interp)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI since version 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`.

  Novo na versão 3.9.

uint64_t `PyThreadState_GetID`(PyThreadState *tstate)
  Part of the Stable ABI since version 3.10.

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

  tstate must not be `NULL`.

  Novo na versão 3.9.

PyInterpreterState *`PyThreadState_GetInterpreter`(PyThreadState *tstate)
  Part of the Stable ABI since version 3.10.

  Get the interpreter of the Python thread state tstate.

  tstate must not be `NULL`.

  Novo na versão 3.9.

PyInterpreterState *`PyInterpreterState_Get`(void)
  Part of the Stable ABI since version 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.

  Novo na versão 3.9.

int64_t `PyInterpreterState_GetID`(PyInterpreterState *interp)
  Part of the Stable ABI since version 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.

  Novo na versão 3.7.

PyObject *`PyInterpreterState_GetDict`(PyInterpreterState *interp)
  Part of the Stable ABI since version 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.

  Novo na versão 3.8.

typedef PyObject *(*`_PyFrameEvalFunction`)(PyThreadState *tstate, PyFrameObject *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.

_PyFrameEvalFunction `_PyInterpreterState_GetEvalFrameFunc`(PyInterpreterState *interp)

  Get the frame evaluation function.

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

  Novo 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”.

  Novo na versão 3.9.

PyObject *`PyThreadState_GetDict`()
  Retorna valor: Referência emprestada. Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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)
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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`()
  Part of the Stable ABI.

  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:

PyThreadState *`Py_NewInterpreter`()
  Part of the Stable ABI.

  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 return value points 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, `NULL` is returned; 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; however, unlike most other Python/C API functions, there needn’t be a current thread state on entry.)

  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.

void `Py_EndInterpreter`(PyThreadState *tstate)
  Part of the Stable ABI.

  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 must be held before calling this function and is still held when it returns.) `Py_FinalizeEx()` will destroy all sub-interpreters that haven’t been explicitly destroyed at that point.

### 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, )
  Part of the Stable ABI.

  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:

  - on a bytecode boundary;

  - with the main thread holding the global interpreter lock (func can therefore use the full C API).

  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.

  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.

  Novo na versão 3.1.

## 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`.

  The caller must hold the GIL.

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.

  The caller must hold the GIL.

## 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.

Novo 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`()
  Part of the Stable ABI since version 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)
  Part of the Stable ABI since version 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)
  Part of the Stable ABI since version 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)
  Part of the Stable ABI since version 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)
  Part of the Stable ABI since version 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)
  Part of the Stable ABI since version 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)
  Part of the Stable ABI since version 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`()
  Part of the Stable ABI.

void `PyThread_delete_key`(int key)
  Part of the Stable ABI.

int `PyThread_set_key_value`(int key, void *value)
  Part of the Stable ABI.

void *`PyThread_get_key_value`(int key)
  Part of the Stable ABI.

void `PyThread_delete_key_value`(int key)
  Part of the Stable ABI.

void `PyThread_ReInitTLS`()
  Part of the Stable ABI.