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gh-103323: Get the "Current" Thread State from a Thread-Local Variable (gh-103324)

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We replace _PyRuntime.tstate_current with a thread-local variable. As part of this change, we add a _Py_thread_local macro in pyport.h (only for the core runtime) to smooth out the compiler differences. The main motivation here is in support of a per-interpreter GIL, but this change also provides some performance improvement opportunities.

Note that we do not provide a fallback to the thread-local, either falling back to the old tstate_current or to thread-specific storage (PyThread_tss_*()). If that proves problematic then we can circle back. I consider it unlikely, but will run the buildbots to double-check.

Also note that this does not change any of the code related to the GILState API, where it uses a thread state stored in thread-specific storage. I suspect we can combine that with _Py_tss_tstate (from here). However, that can be addressed separately and is not urgent (nor critical).

(While this change was mostly done independently, I did take some inspiration from earlier (~2020) work by @markshannon (main...markshannon:threadstate_in_tls) and @vstinner (#23976).)
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Eric Snow 2023-04-24 11:17:02 -06:00 • committed by GitHub
parent 7ef614c1ad
commit f8abfa3314
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5 changed files with 73 additions and 18 deletions
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26
Include/internal/pycore_pystate.h
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@ -64,17 +64,14 @@ _Py_ThreadCanHandlePendingCalls(void)
/* Variable and macro for in-line access to current thread
and interpreter state */
static inline PyThreadState*
_PyRuntimeState_GetThreadState(_PyRuntimeState *runtime)
{
return (PyThreadState*)_Py_atomic_load_relaxed(&runtime->tstate_current);
}
#if defined(HAVE_THREAD_LOCAL) && !defined(Py_BUILD_CORE_MODULE)
extern _Py_thread_local PyThreadState *_Py_tss_tstate;
#endif
PyAPI_DATA(PyThreadState *) _PyThreadState_GetCurrent(void);
/* Get the current Python thread state.
Efficient macro reading directly the 'tstate_current' atomic
variable. The macro is unsafe: it does not check for error and it can
return NULL.
This function is unsafe: it does not check for error and it can return NULL.
The caller must hold the GIL.
@ -82,9 +79,20 @@ _PyRuntimeState_GetThreadState(_PyRuntimeState *runtime)
static inline PyThreadState*
_PyThreadState_GET(void)
{
return _PyRuntimeState_GetThreadState(&_PyRuntime);
#if defined(HAVE_THREAD_LOCAL) && !defined(Py_BUILD_CORE_MODULE)
return _Py_tss_tstate;
#else
return _PyThreadState_GetCurrent();
#endif
}
static inline PyThreadState*
_PyRuntimeState_GetThreadState(_PyRuntimeState *Py_UNUSED(runtime))
{
return _PyThreadState_GET();
}
static inline void
_Py_EnsureFuncTstateNotNULL(const char *func, PyThreadState *tstate)
{