初始化，终结和线程
******************

请参阅 Python 初始化配置 。


在Python初始化之前
==================

在一个植入了 Python 的应用程序中，"Py_Initialize()" 函数必须在任何其他
Python/C API 函数之前被调用；例外的只有个别函数和 全局配置变量。

在初始化Python之前，可以安全地调用以下函数：

* 配置函数：

  * "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()"

* 信息函数：

  * "Py_IsInitialized()"

  * "PyMem_GetAllocator()"

  * "PyObject_GetArenaAllocator()"

  * "Py_GetBuildInfo()"

  * "Py_GetCompiler()"

  * "Py_GetCopyright()"

  * "Py_GetPlatform()"

  * "Py_GetVersion()"

* 工具

  * "Py_DecodeLocale()"

* 内存分配器：

  * "PyMem_RawMalloc()"

  * "PyMem_RawRealloc()"

  * "PyMem_RawCalloc()"

  * "PyMem_RawFree()"

備註:

  以下函数 **不应该** 在 "Py_Initialize()": "Py_EncodeLocale()",
  "Py_GetPath()", "Py_GetPrefix()", "Py_GetExecPrefix()",
  "Py_GetProgramFullPath()", "Py_GetPythonHome()",
  "Py_GetProgramName()" 和 "PyEval_InitThreads()" 前调用。


全局配置变量
============

Python 有负责控制全局配置中不同特性和选项的变量。这些标志默认被 命令行
选项。

当一个选项设置一个旗标时，该旗标的值将是设置选项的次数。 例如，"-b" 会
将 "Py_BytesWarningFlag" 设为 1 而 "-bb" 会将 "Py_BytesWarningFlag" 设
为 2.

int Py_BytesWarningFlag

   当将 "bytes" 或 "bytearray" 与 "str" 比较或者将 "bytes" 与 "int" 比
   较时发出警告。 如果大于等于 "2" 则报错。

   由 "-b" 选项设置。

int Py_DebugFlag

   开启解析器调试输出（限专家使用，依赖于编译选项）。

   由 "-d" 选项和 "PYTHONDEBUG" 环境变量设置。

int Py_DontWriteBytecodeFlag

   如果设置为非零, Python 不会在导入源代码时尝试写入 ".pyc" 文件

   由 "-B" 选项和 "PYTHONDONTWRITEBYTECODE" 环境变量设置。

int Py_FrozenFlag

   当在 "Py_GetPath()" 中计算模块搜索路径时屏蔽错误消息。

   由 "_freeze_importlib" 和 "frozenmain" 程序使用的私有旗标。

int Py_HashRandomizationFlag

   如果 "PYTHONHASHSEED" 环境变量被设为非空字符串则设为 "1"。

   如果该旗标为非零值，则读取 "PYTHONHASHSEED" 环境变量来初始化加密哈
   希种子。

int Py_IgnoreEnvironmentFlag

   忽略所有 "PYTHON*" 环境变量，例如，已设置的 "PYTHONPATH" 和
   "PYTHONHOME"。

   由 "-E"  和 "-I" 选项设置。

int Py_InspectFlag

   当将脚本作为第一个参数传入或是使用了 "-c" 选项时，则会在执行该脚本
   或命令后进入交互模式，即使在 "sys.stdin" 并非一个终端时也是如此。

   由 "-i" 选项和 "PYTHONINSPECT" 环境变量设置。

int Py_InteractiveFlag

   由 "-i" 选项设置。

int Py_IsolatedFlag

   以隔离模式运行 Python. 在隔离模式下 "sys.path" 将不包含脚本的目录或
   用户的 site-packages 目录。

   由 "-I" 选项设置。

   3.4 版新加入.

int Py_LegacyWindowsFSEncodingFlag

   如果该旗标为非零值，则使用 "mbcs" 编码和``replace`` 错误处理句柄，
   而不是 UTF-8 编码和 "surrogatepass" 错误处理句柄作用 *filesystem
   encoding and error handler*。

   如果 "PYTHONLEGACYWINDOWSFSENCODING" 环境变量被设为非空字符串则设为
   "1"。

   更多詳情請見 **PEP 529**。

   適用：Windows。

int Py_LegacyWindowsStdioFlag

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

   如果 "PYTHONLEGACYWINDOWSSTDIO" 环境变量被设为非空字符串则设为 "1"
   。

   更多詳情請見 **PEP 528**。

   適用：Windows。

int Py_NoSiteFlag

   禁用 "site" 的导入及其所附带的基于站点对 "sys.path" 的操作。 如果
   "site" 会在稍后被显式地导入也会禁用这些操作 (如果你希望触发它们则应
   调用 "site.main()")。

   由 "-S" 选项设置。

int Py_NoUserSiteDirectory

   不要将 "用户 site-packages 目录" 添加到 "sys.path"。

   由 "-s" 和 "-I" 选项以及 "PYTHONNOUSERSITE" 环境变量设置。

int Py_OptimizeFlag

   由 "-O" 选项和 "PYTHONOPTIMIZE" 环境变量设置。

int Py_QuietFlag

   即使在交互模式下也不显示版权和版本信息。

   由 "-q" 选项设置。

   3.2 版新加入.

int Py_UnbufferedStdioFlag

   强制 stdout 和 stderr 流不带缓冲。

   由 "-u" 选项和 "PYTHONUNBUFFERED" 环境变量设置。

int Py_VerboseFlag

   每次初始化模块时打印一条消息，显示加载模块的位置（文件名或内置模块
   ）。 如果大于或等于 "2"，则为搜索模块时检查的每个文件打印一条消息。
   此外还会在退出时提供模块清理信息。

   由 "-v" 选项和 "PYTHONVERBOSE" 环境变量设置。


初始化和最终化解释器
====================

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

   初始化 Python 解释器。 在嵌入 Python 的应用程序中，它应当在使用任何
   其他 Python/C API 函数之前被调用；请参阅 在 Python 初始化之前 了解
   少数的例外情况。

   这将初始化已加载模块表 ("sys.modules")，并创建基本模块 "builtins"、
   "__main__" 和 "sys"。 它还会初始化模块搜索路径 ("sys.path")。 它不
   会设置 "sys.argv"；如有需要请使用 "PySys_SetArgvEx()"。 当第二次调
   用时 (在未事先调用 "Py_FinalizeEx()" 的情况下) 将不会执行任何操作。
   它没有返回值；如果初始化失败则会发生致命错误。

   備註:

     在 Windows 上，将控制台模式从 "O_TEXT" 改为 "O_BINARY"，这还将影
     响使用 C 运行时的非 Python 的控制台使用。

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

   如果 *initsigs* 为 "1" 则该函数的工作方式与 "Py_Initialize()" 类似
   。 如果 *initsigs* 为 "0"，它将跳过信号处理句柄的初始化注册，这在嵌
   入 Python 时可能会很有用处。

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

   如果 Python 解释器已初始化，则返回真值（非零）；否则返回假值（零）
   。 在调用 "Py_FinalizeEx()" 之后，此函数将返回假值直到
   "Py_Initialize()" 再次被调用。

int Py_FinalizeEx()
    * Part of the Stable ABI since version 3.6.*

   撤销 "Py_Initialize()" 所做的所有初始化操作和后续对 Python/C API 函
   数的使用，并销毁自上次调用 "Py_Initialize()" 以来创建但尚未销毁的所
   有子解释器（参见下文 "Py_NewInterpreter()" 一节)。 在理想情况下，这
   会释放 Python 解释器分配的所有内存。 当第二次调用时（在未再次调用
   "Py_Initialize()" 的情况下），这将不执行任何操作。 正常情况下返回值
   是 "0"。 如果在最终化（刷新缓冲数据）过程中出现错误，则返回 "-1"。

   提供此函数的原因有很多。嵌入应用程序可能希望重新启动Python，而不必
   重新启动应用程序本身。从动态可加载库（或DLL）加载Python解释器的应用
   程序可能希望在卸载DLL之前释放Python分配的所有内存。在搜索应用程序内
   存泄漏的过程中，开发人员可能希望在退出应用程序之前释放Python分配的
   所有内存。

   **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.

   引发一个 审计事件 "cpython._PySys_ClearAuditHooks"，不附带任何参数
   。

   3.6 版新加入.

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

   这是一个不考虑返回值的 "Py_FinalizeEx()" 的向下兼容版本。


进程级参数
==========

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

   如果要调用该函数，应当在 "Py_Initialize()" 之前调用。 它指定了标准
   IO 使用的编码格式和错误处理方式，其含义与 "str.encode()" 中的相同。

   它覆盖了 "PYTHONIOENCODING" 的值，并允许嵌入代码以便在环境变量不起
   作用时控制 IO 编码格式。

   *encoding* 和/或 *errors* 可以为 "NULL" 以使用 "PYTHONIOENCODING"
   和/或默认值（取决于其他设置）。

   请注意无论是否有此设置（或任何其他设置），"sys.stderr" 都会使用
   "backslashreplace" 错误处理句柄。

   如果调用了 "Py_FinalizeEx()"，则需要再次调用该函数以便影响对
   "Py_Initialize()" 的后续调用。

   成功时返回 "0"，出错时返回非零值（例如在解释器已被初始化后再调用）
   。

   3.4 版新加入.

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

   如果要调用该函数，应当在首次调用 "Py_Initialize()" 之前调用它。 它
   将告诉解释器程序的 "main()" 函数的 "argv[0]" 参数的值（转换为宽字符
   ）。 "Py_GetPath()" 和下面的某些其他函数会使用它在相对于解释器的位
   置上查找可执行文件的 Python 运行时库。 默认值是 "'python'"。 参数应
   当指向静态存储中的一个以零值结束的宽字符串，其内容在程序执行期间不
   会发生改变。 Python 解释器中的任何代码都不会改变该存储的内容。

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

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

   返回用 "Py_SetProgramName()" 设置的程序名称，或默认的名称。 返回的
   字符串指向静态存储；调用者不应修改其值。

   此函数不应在 "Py_Initialize()" 之前被调用，否则将返回 "NULL"。

   3.10 版更變: 现在如果它在 "Py_Initialize()" 之前被调用将返回 "NULL"
   。

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.

   此函数不应在 "Py_Initialize()" 之前被调用，否则将返回 "NULL"。

   3.10 版更變: 现在如果它在 "Py_Initialize()" 之前被调用将返回 "NULL"
   。

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.

   此函数不应在 "Py_Initialize()" 之前被调用，否则将返回 "NULL"。

   3.10 版更變: 现在如果它在 "Py_Initialize()" 之前被调用将返回 "NULL"
   。

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".

   此函数不应在 "Py_Initialize()" 之前被调用，否则将返回 "NULL"。

   3.10 版更變: 现在如果它在 "Py_Initialize()" 之前被调用将返回 "NULL"
   。

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.

   此函数不应在 "Py_Initialize()" 之前被调用，否则将返回 "NULL"。

   3.10 版更變: 现在如果它在 "Py_Initialize()" 之前被调用将返回 "NULL"
   。

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.

   The path argument is copied internally, so the caller may free it
   after the call completes.

   3.8 版更變: The program full path is now used for "sys.executable",
   instead of the program name.

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

   Return the version of this Python interpreter.  This is a string
   that looks something like

      "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.*

   Return the official copyright string for the current Python
   version, for example

   "'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'"

   返回的字符串指向静态存储；调用者不应修改其值。 Python 代码可通过
   "sys.copyright" 获取该值。

const char *Py_GetCompiler()
    * Part of the Stable ABI.*

   返回用于编译当前 Python 版本的编译器指令，为带方括号的形式，例如:

      "[GCC 2.7.2.2]"

   返回的字符串指向静态存储；调用者不应修改其值。 Python 代码可以从变
   量 "sys.version" 中获取该值。

const char *Py_GetBuildInfo()
    * Part of the Stable ABI.*

   返回有关当前Python解释器实例的序列号和构建日期和时间的信息，例如：

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

   返回的字符串指向静态存储；调用者不应修改其值。 Python 代码可以从变
   量 "sys.version" 中获取该值。

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()".

   If *updatepath* is zero, this is all the function does.  If
   *updatepath* is non-zero, the function also modifies "sys.path"
   according to the following algorithm:

   * 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.

   備註:

     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");

   3.1.3 版新加入.

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.

   3.4 版更變: 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.

   此函数不应在 "Py_Initialize()" 之前被调用，否则将返回 "NULL"。

   3.10 版更變: 现在如果它在 "Py_Initialize()" 之前被调用将返回 "NULL"
   。


线程状态和全局解释器锁
======================

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()".


从扩展扩展代码中释放 GIL
------------------------

大多数操作 *GIL* 的扩展代码具有以下简单结构：

   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.

这是如此常用因此增加了一对宏来简化它:

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

"Py_BEGIN_ALLOW_THREADS" 宏将打开一个新块并声明一个隐藏的局部变量；
"Py_END_ALLOW_THREADS" 宏将关闭这个块。

上面的代码块可扩展为下面的代码:

   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.

備註:

  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.


非Python创建的线程
------------------

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.


Cautions about 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 锁对象 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.


高阶 API
--------

These are the most commonly used types and functions when writing C
extension code, or when embedding the Python interpreter:

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.*

   不执行任何操作的已弃用函数。

   在 Python 3.6 及更老的版本中，此函数会在 GIL 不存在时创建它。

   3.9 版更變: 此函数现在不执行任何操作。

   3.7 版更變: 该函数现在由 "Py_Initialize()" 调用，因此你无需再自行调
   用它。

   3.2 版更變: This function cannot be called before "Py_Initialize()"
   anymore.

   自從版本 3.9 後不推薦使用，將會自版本 3.11 中移除。.

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.

   3.7 版更變: The *GIL* is now initialized by "Py_Initialize()".

   自從版本 3.9 後不推薦使用，將會自版本 3.11 中移除。.

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.

   備註:

     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.*

   Ensure that the current thread is ready to call the Python C API
   regardless of the current state of Python, or of the global
   interpreter lock. This may be called as many times as desired by a
   thread as long as each call is matched with a call to
   "PyGILState_Release()". In general, other thread-related APIs may
   be used between "PyGILState_Ensure()" and "PyGILState_Release()"
   calls as long as the thread state is restored to its previous state
   before the Release().  For example, normal usage of the
   "Py_BEGIN_ALLOW_THREADS" and "Py_END_ALLOW_THREADS" macros is
   acceptable.

   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.

   備註:

     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.

   3.4 版新加入.

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.*

   This macro expands to "{ PyThreadState *_save; _save =
   PyEval_SaveThread();". Note that it contains an opening brace; it
   must be matched with a following "Py_END_ALLOW_THREADS" macro.  See
   above for further discussion of this macro.

Py_END_ALLOW_THREADS
    * Part of the Stable ABI.*

   此宏扩展为 "PyEval_RestoreThread(_save); }"。 注意它包含一个右花括
   号；它必须与之前的 "Py_BEGIN_ALLOW_THREADS" 宏匹配。 请参阅上文以进
   一步讨论此宏。

Py_BLOCK_THREADS
    * Part of the Stable ABI.*

   这个宏扩展为 "PyEval_RestoreThread(_save);": 它等价于没有关闭花括号
   的 "Py_END_ALLOW_THREADS"。

Py_UNBLOCK_THREADS
    * Part of the Stable ABI.*

   这个宏扩展为 "_save = PyEval_SaveThread();": 它等价于没有开始花括号
   和变量声明的 "Py_BEGIN_ALLOW_THREADS"。


底层级 API
----------

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

3.7 版更變: "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.

   Raises an auditing event "cpython.PyInterpreterState_New" with no
   arguments.

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.

   Raises an auditing event "cpython.PyInterpreterState_Clear" with no
   arguments.

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.*

   创建属于给定解释器对象的新线程状态对象。全局解释器锁不需要保持，但
   如果需要序列化对此函数的调用，则可以保持。

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.

   3.9 版更變: 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.

   也請見 "PyEval_GetFrame()"。

   *tstate* 不可為 "NULL"。

   3.9 版新加入.

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* 不可為 "NULL"。

   3.9 版新加入.

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

   Get the interpreter of the Python thread state *tstate*.

   *tstate* 不可為 "NULL"。

   3.9 版新加入.

PyInterpreterState *PyInterpreterState_Get(void)
    * Part of the Stable ABI since version 3.9.*

   获取当前解释器。

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

   调用时必须携带GIL。

   3.9 版新加入.

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.

   调用时必须携带GIL。

   3.7 版新加入.

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.

   3.8 版新加入.

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

   帧评估函数的类型

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

   3.9 版更變: 此函数现在可接受一个 *tstate* 形参。

_PyFrameEvalFunction _PyInterpreterState_GetEvalFrameFunc(PyInterpreterState *interp)

   Get the frame evaluation function.

   See the **PEP 523** "Adding a frame evaluation API to CPython".

   3.9 版新加入.

void _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState *interp, _PyFrameEvalFunction eval_frame)

   Set the frame evaluation function.

   See the **PEP 523** "Adding a frame evaluation API to CPython".

   3.9 版新加入.

PyObject *PyThreadState_GetDict()
    *返回值：借入的引用。** 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.

   3.7 版更變: 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.

   備註:

     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.

   3.8 版更變: 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.*

   获取全局解释器锁。锁必须是先前创建的。如果该线程已经拥有锁，则会出
   现死锁。

   3.2 版後已棄用: This function does not update the current thread
   state.  Please use "PyEval_RestoreThread()" or
   "PyEval_AcquireThread()" instead.

   備註:

     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.

   3.8 版更變: 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.

   3.2 版後已棄用: This function does not update the current thread
   state.  Please use "PyEval_SaveThread()" or
   "PyEval_ReleaseThread()" instead.


子解释器支持
============

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.


错误和警告
----------

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.


异步通知
========

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.

   警告:

     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.

   3.9 版更變: 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.

   3.1 版新加入.


分析和跟踪
==========

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*:

   +--------------------------------+------------------------------------------+
   | *what* 的值                    | *arg* 的含义                             |
   |================================|==========================================|
   | "PyTrace_CALL"                 | 总是 "Py_None".                          |
   +--------------------------------+------------------------------------------+
   | "PyTrace_EXCEPTION"            | "sys.exc_info()" 返回的异常信息。        |
   +--------------------------------+------------------------------------------+
   | "PyTrace_LINE"                 | 总是 "Py_None".                          |
   +--------------------------------+------------------------------------------+
   | "PyTrace_RETURN"               | 返回给调用方的值，或者如果是由异常导致的 |
   |                                | 则返回 "NULL"。                          |
   +--------------------------------+------------------------------------------+
   | "PyTrace_C_CALL"               | 正在调用函数对象。                       |
   +--------------------------------+------------------------------------------+
   | "PyTrace_C_EXCEPTION"          | 正在调用函数对象。                       |
   +--------------------------------+------------------------------------------+
   | "PyTrace_C_RETURN"             | 正在调用函数对象。                       |
   +--------------------------------+------------------------------------------+
   | "PyTrace_OPCODE"               | 总是 "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*.


高级调试器支持
==============

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()

   返回主解释器状态对象。

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.


线程本地存储支持
================

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.

備註:

  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.

3.7 版新加入.

也參考: "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.

   When Py_LIMITED_API is not defined, static allocation of this type
   by "Py_tss_NEEDS_INIT" is allowed.

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.


Dynamic Allocation
~~~~~~~~~~~~~~~~~~

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.*

   Return a value which is the same state as a value initialized with
   "Py_tss_NEEDS_INIT", or "NULL" in the case of dynamic allocation
   failure.

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".

   備註:

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


方法
~~~~

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.*

   Return a zero value on successful initialization of a TSS key.  The
   behavior is undefined if the value pointed to by the *key* argument
   is not initialized by "Py_tss_NEEDS_INIT".  This function can be
   called repeatedly on the same key -- calling it on an already
   initialized key is a no-op and immediately returns success.

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
------------------------------

3.7 版後已棄用: This API is superseded by Thread Specific Storage
(TSS) API.

備註:

  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.

由于上面提到的兼容性问题，不应在新代码中使用此版本的API。

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.*
