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Issue #15038: Optimize python Locks on Windows
Extract cross-platform condition variable support into a separate file and provide user-mode non-recursive locks for Windows.
This commit is contained in:
Kristján Valur Jónsson
parent
633c4d9199
commit
e75ff35af2
6 changed files with 497 additions and 192 deletions
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@ -59,213 +59,49 @@ static unsigned long gil_interval = DEFAULT_INTERVAL;
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(Note: this mechanism is enabled with FORCE_SWITCHING above)
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*/
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#ifndef _POSIX_THREADS
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/* This means pthreads are not implemented in libc headers, hence the macro
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not present in unistd.h. But they still can be implemented as an external
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library (e.g. gnu pth in pthread emulation) */
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# ifdef HAVE_PTHREAD_H
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# include <pthread.h> /* _POSIX_THREADS */
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# endif
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#include "condvar.h"
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#ifndef Py_HAVE_CONDVAR
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#error You need either a POSIX-compatible or a Windows system!
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#endif
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#ifdef _POSIX_THREADS
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/*
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* POSIX support
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*/
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#include <pthread.h>
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#define ADD_MICROSECONDS(tv, interval) \
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do { \
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tv.tv_usec += (long) interval; \
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tv.tv_sec += tv.tv_usec / 1000000; \
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tv.tv_usec %= 1000000; \
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} while (0)
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/* We assume all modern POSIX systems have gettimeofday() */
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#ifdef GETTIMEOFDAY_NO_TZ
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#define GETTIMEOFDAY(ptv) gettimeofday(ptv)
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#else
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#define GETTIMEOFDAY(ptv) gettimeofday(ptv, (struct timezone *)NULL)
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#endif
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#define MUTEX_T pthread_mutex_t
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#define MUTEX_T PyMUTEX_T
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#define MUTEX_INIT(mut) \
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if (pthread_mutex_init(&mut, NULL)) { \
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Py_FatalError("pthread_mutex_init(" #mut ") failed"); };
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if (PyMUTEX_INIT(&(mut))) { \
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Py_FatalError("PyMUTEX_INIT(" #mut ") failed"); };
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#define MUTEX_FINI(mut) \
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if (pthread_mutex_destroy(&mut)) { \
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Py_FatalError("pthread_mutex_destroy(" #mut ") failed"); };
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if (PyMUTEX_FINI(&(mut))) { \
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Py_FatalError("PyMUTEX_FINI(" #mut ") failed"); };
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#define MUTEX_LOCK(mut) \
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if (pthread_mutex_lock(&mut)) { \
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Py_FatalError("pthread_mutex_lock(" #mut ") failed"); };
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if (PyMUTEX_LOCK(&(mut))) { \
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Py_FatalError("PyMUTEX_LOCK(" #mut ") failed"); };
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#define MUTEX_UNLOCK(mut) \
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if (pthread_mutex_unlock(&mut)) { \
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Py_FatalError("pthread_mutex_unlock(" #mut ") failed"); };
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if (PyMUTEX_UNLOCK(&(mut))) { \
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Py_FatalError("PyMUTEX_UNLOCK(" #mut ") failed"); };
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#define COND_T pthread_cond_t
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#define COND_T PyCOND_T
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#define COND_INIT(cond) \
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if (pthread_cond_init(&cond, NULL)) { \
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Py_FatalError("pthread_cond_init(" #cond ") failed"); };
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if (PyCOND_INIT(&(cond))) { \
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Py_FatalError("PyCOND_INIT(" #cond ") failed"); };
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#define COND_FINI(cond) \
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if (pthread_cond_destroy(&cond)) { \
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Py_FatalError("pthread_cond_destroy(" #cond ") failed"); };
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if (PyCOND_FINI(&(cond))) { \
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Py_FatalError("PyCOND_FINI(" #cond ") failed"); };
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#define COND_SIGNAL(cond) \
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if (pthread_cond_signal(&cond)) { \
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Py_FatalError("pthread_cond_signal(" #cond ") failed"); };
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if (PyCOND_SIGNAL(&(cond))) { \
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Py_FatalError("PyCOND_SIGNAL(" #cond ") failed"); };
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#define COND_WAIT(cond, mut) \
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if (pthread_cond_wait(&cond, &mut)) { \
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Py_FatalError("pthread_cond_wait(" #cond ") failed"); };
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if (PyCOND_WAIT(&(cond), &(mut))) { \
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Py_FatalError("PyCOND_WAIT(" #cond ") failed"); };
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#define COND_TIMED_WAIT(cond, mut, microseconds, timeout_result) \
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{ \
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int r; \
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struct timespec ts; \
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struct timeval deadline; \
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\
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GETTIMEOFDAY(&deadline); \
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ADD_MICROSECONDS(deadline, microseconds); \
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ts.tv_sec = deadline.tv_sec; \
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ts.tv_nsec = deadline.tv_usec * 1000; \
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\
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r = pthread_cond_timedwait(&cond, &mut, &ts); \
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if (r == ETIMEDOUT) \
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int r = PyCOND_TIMEDWAIT(&(cond), &(mut), (microseconds)); \
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if (r < 0) \
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Py_FatalError("PyCOND_WAIT(" #cond ") failed"); \
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if (r) /* 1 == timeout, 2 == impl. can't say, so assume timeout */ \
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timeout_result = 1; \
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else if (r) \
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Py_FatalError("pthread_cond_timedwait(" #cond ") failed"); \
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else \
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timeout_result = 0; \
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} \
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#elif defined(NT_THREADS)
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/*
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* Windows (2000 and later, as well as (hopefully) CE) support
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*/
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#include <windows.h>
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#define MUTEX_T CRITICAL_SECTION
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#define MUTEX_INIT(mut) do { \
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if (!(InitializeCriticalSectionAndSpinCount(&(mut), 4000))) \
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Py_FatalError("CreateMutex(" #mut ") failed"); \
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} while (0)
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#define MUTEX_FINI(mut) \
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DeleteCriticalSection(&(mut))
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#define MUTEX_LOCK(mut) \
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EnterCriticalSection(&(mut))
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#define MUTEX_UNLOCK(mut) \
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LeaveCriticalSection(&(mut))
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/* We emulate condition variables with a semaphore.
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We use a Semaphore rather than an auto-reset event, because although
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an auto-resent event might appear to solve the lost-wakeup bug (race
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condition between releasing the outer lock and waiting) because it
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maintains state even though a wait hasn't happened, there is still
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a lost wakeup problem if more than one thread are interrupted in the
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critical place. A semaphore solves that.
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Because it is ok to signal a condition variable with no one
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waiting, we need to keep track of the number of
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waiting threads. Otherwise, the semaphore's state could rise
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without bound.
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Generic emulations of the pthread_cond_* API using
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Win32 functions can be found on the Web.
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The following read can be edificating (or not):
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http://www.cse.wustl.edu/~schmidt/win32-cv-1.html
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*/
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typedef struct COND_T
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{
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HANDLE sem; /* the semaphore */
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int n_waiting; /* how many are unreleased */
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} COND_T;
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__inline static void _cond_init(COND_T *cond)
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{
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/* A semaphore with a large max value, The positive value
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* is only needed to catch those "lost wakeup" events and
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* race conditions when a timed wait elapses.
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*/
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if (!(cond->sem = CreateSemaphore(NULL, 0, 1000, NULL)))
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Py_FatalError("CreateSemaphore() failed");
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cond->n_waiting = 0;
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}
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__inline static void _cond_fini(COND_T *cond)
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{
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BOOL ok = CloseHandle(cond->sem);
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if (!ok)
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Py_FatalError("CloseHandle() failed");
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}
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__inline static void _cond_wait(COND_T *cond, MUTEX_T *mut)
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{
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++cond->n_waiting;
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MUTEX_UNLOCK(*mut);
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/* "lost wakeup bug" would occur if the caller were interrupted here,
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* but we are safe because we are using a semaphore wich has an internal
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* count.
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*/
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if (WaitForSingleObject(cond->sem, INFINITE) == WAIT_FAILED)
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Py_FatalError("WaitForSingleObject() failed");
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MUTEX_LOCK(*mut);
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}
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__inline static int _cond_timed_wait(COND_T *cond, MUTEX_T *mut,
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int us)
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{
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DWORD r;
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++cond->n_waiting;
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MUTEX_UNLOCK(*mut);
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r = WaitForSingleObject(cond->sem, us / 1000);
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if (r == WAIT_FAILED)
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Py_FatalError("WaitForSingleObject() failed");
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MUTEX_LOCK(*mut);
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if (r == WAIT_TIMEOUT)
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--cond->n_waiting;
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/* Here we have a benign race condition with _cond_signal. If the
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* wait operation has timed out, but before we can acquire the
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* mutex again to decrement n_waiting, a thread holding the mutex
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* still sees a positive n_waiting value and may call
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* ReleaseSemaphore and decrement n_waiting.
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* This will cause n_waiting to be decremented twice.
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* This is benign, though, because ReleaseSemaphore will also have
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* been called, leaving the semaphore state positive. We may
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* thus end up with semaphore in state 1, and n_waiting == -1, and
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* the next time someone calls _cond_wait(), that thread will
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* pass right through, decrementing the semaphore state and
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* incrementing n_waiting, thus correcting the extra _cond_signal.
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*/
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return r == WAIT_TIMEOUT;
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}
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__inline static void _cond_signal(COND_T *cond) {
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/* NOTE: This must be called with the mutex held */
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if (cond->n_waiting > 0) {
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if (!ReleaseSemaphore(cond->sem, 1, NULL))
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Py_FatalError("ReleaseSemaphore() failed");
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--cond->n_waiting;
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}
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}
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#define COND_INIT(cond) \
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_cond_init(&(cond))
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#define COND_FINI(cond) \
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_cond_fini(&(cond))
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#define COND_SIGNAL(cond) \
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_cond_signal(&(cond))
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#define COND_WAIT(cond, mut) \
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_cond_wait(&(cond), &(mut))
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#define COND_TIMED_WAIT(cond, mut, us, timeout_result) do { \
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(timeout_result) = _cond_timed_wait(&(cond), &(mut), us); \
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} while (0)
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#else
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#error You need either a POSIX-compatible or a Windows system!
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#endif /* _POSIX_THREADS, NT_THREADS */
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/* Whether the GIL is already taken (-1 if uninitialized). This is atomic
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@ -356,13 +192,13 @@ static void drop_gil(PyThreadState *tstate)
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MUTEX_LOCK(switch_mutex);
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/* Not switched yet => wait */
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if (_Py_atomic_load_relaxed(&gil_last_holder) == tstate) {
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RESET_GIL_DROP_REQUEST();
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RESET_GIL_DROP_REQUEST();
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/* NOTE: if COND_WAIT does not atomically start waiting when
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releasing the mutex, another thread can run through, take
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the GIL and drop it again, and reset the condition
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before we even had a chance to wait for it. */
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COND_WAIT(switch_cond, switch_mutex);
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}
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}
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MUTEX_UNLOCK(switch_mutex);
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}
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#endif
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