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.
diff --git a/Python/condvar.h b/Python/condvar.h
new file mode 100644
index 0000000..8d3c595
--- /dev/null
+++ b/Python/condvar.h
@@ -0,0 +1,353 @@
+/*
+ * Portable condition variable support for windows and pthreads.
+ * Everything is inline, this header can be included where needed.
+ *
+ * APIs generally return 0 on success and non-zero on error,
+ * and the caller needs to use its platform's error mechanism to
+ * discover the error (errno, or GetLastError())
+ *
+ * Note that some implementations cannot distinguish between a
+ * condition variable wait time-out and successful wait. Most often
+ * the difference is moot anyway since the wait condition must be
+ * re-checked.
+ * PyCOND_TIMEDWAIT, in addition to returning negative on error,
+ * thus returns 0 on regular success, 1 on timeout
+ * or 2 if it can't tell.
+ */
+
+#ifndef _CONDVAR_H_
+#define _CONDVAR_H_
+
+#include "Python.h"
+
+#ifndef _POSIX_THREADS
+/* This means pthreads are not implemented in libc headers, hence the macro
+ not present in unistd.h. But they still can be implemented as an external
+ library (e.g. gnu pth in pthread emulation) */
+# ifdef HAVE_PTHREAD_H
+# include <pthread.h> /* _POSIX_THREADS */
+# endif
+#endif
+
+#ifdef _POSIX_THREADS
+/*
+ * POSIX support
+ */
+#define Py_HAVE_CONDVAR
+
+#include <pthread.h>
+
+#define PyCOND_ADD_MICROSECONDS(tv, interval) \
+do { \
+ tv.tv_usec += (long) interval; \
+ tv.tv_sec += tv.tv_usec / 1000000; \
+ tv.tv_usec %= 1000000; \
+} while (0)
+
+/* We assume all modern POSIX systems have gettimeofday() */
+#ifdef GETTIMEOFDAY_NO_TZ
+#define PyCOND_GETTIMEOFDAY(ptv) gettimeofday(ptv)
+#else
+#define PyCOND_GETTIMEOFDAY(ptv) gettimeofday(ptv, (struct timezone *)NULL)
+#endif
+
+/* The following functions return 0 on success, nonzero on error */
+#define PyMUTEX_T pthread_mutex_t
+#define PyMUTEX_INIT(mut) pthread_mutex_init((mut), NULL)
+#define PyMUTEX_FINI(mut) pthread_mutex_destroy(mut)
+#define PyMUTEX_LOCK(mut) pthread_mutex_lock(mut)
+#define PyMUTEX_UNLOCK(mut) pthread_mutex_unlock(mut)
+
+#define PyCOND_T pthread_cond_t
+#define PyCOND_INIT(cond) pthread_cond_init((cond), NULL)
+#define PyCOND_FINI(cond) pthread_cond_destroy(cond)
+#define PyCOND_SIGNAL(cond) pthread_cond_signal(cond)
+#define PyCOND_BROADCAST(cond) pthread_cond_broadcast(cond)
+#define PyCOND_WAIT(cond, mut) pthread_cond_wait((cond), (mut))
+
+/* return 0 for success, 1 on timeout, -1 on error */
+Py_LOCAL_INLINE(int)
+PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, long us)
+{
+ int r;
+ struct timespec ts;
+ struct timeval deadline;
+
+ PyCOND_GETTIMEOFDAY(&deadline);
+ PyCOND_ADD_MICROSECONDS(deadline, us);
+ ts.tv_sec = deadline.tv_sec;
+ ts.tv_nsec = deadline.tv_usec * 1000;
+
+ r = pthread_cond_timedwait((cond), (mut), &ts);
+ if (r == ETIMEDOUT)
+ return 1;
+ else if (r)
+ return -1;
+ else
+ return 0;
+}
+
+#elif defined(NT_THREADS)
+/*
+ * Windows (XP, 2003 server and later, as well as (hopefully) CE) support
+ *
+ * Emulated condition variables ones that work with XP and later, plus
+ * example native support on VISTA and onwards.
+ */
+#define Py_HAVE_CONDVAR
+
+
+/* include windows if it hasn't been done before */
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+/* options */
+/* non-emulated condition variables are provided for those that want
+ * to target Windows Vista. Modify this macro to enable them.
+ */
+#ifndef _PY_EMULATED_WIN_CV
+#define _PY_EMULATED_WIN_CV 1 /* use emulated condition variables */
+#endif
+
+/* fall back to emulation if not targeting Vista */
+#if !defined NTDDI_VISTA || NTDDI_VERSION < NTDDI_VISTA
+#undef _PY_EMULATED_WIN_CV
+#define _PY_EMULATED_WIN_CV 1
+#endif
+
+
+#if _PY_EMULATED_WIN_CV
+
+/* The mutex is a CriticalSection object and
+ The condition variables is emulated with the help of a semaphore.
+ Semaphores are available on Windows XP (2003 server) and later.
+ We use a Semaphore rather than an auto-reset event, because although
+ an auto-resent event might appear to solve the lost-wakeup bug (race
+ condition between releasing the outer lock and waiting) because it
+ maintains state even though a wait hasn't happened, there is still
+ a lost wakeup problem if more than one thread are interrupted in the
+ critical place. A semaphore solves that, because its state is counted,
+ not Boolean.
+ Because it is ok to signal a condition variable with no one
+ waiting, we need to keep track of the number of
+ waiting threads. Otherwise, the semaphore's state could rise
+ without bound. This also helps reduce the number of "spurious wakeups"
+ that would otherwise happen.
+
+ Generic emulations of the pthread_cond_* API using
+ earlier Win32 functions can be found on the Web.
+ The following read can be edificating (or not):
+ http://www.cse.wustl.edu/~schmidt/win32-cv-1.html
+*/
+
+typedef CRITICAL_SECTION PyMUTEX_T;
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_INIT(PyMUTEX_T *cs)
+{
+ InitializeCriticalSection(cs);
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_FINI(PyMUTEX_T *cs)
+{
+ DeleteCriticalSection(cs);
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_LOCK(PyMUTEX_T *cs)
+{
+ EnterCriticalSection(cs);
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_UNLOCK(PyMUTEX_T *cs)
+{
+ LeaveCriticalSection(cs);
+ return 0;
+}
+
+/* The ConditionVariable object. From XP onwards it is easily emulated with
+ * a Semaphore
+ */
+
+typedef struct _PyCOND_T
+{
+ HANDLE sem;
+ int waiting;
+} PyCOND_T;
+
+Py_LOCAL_INLINE(int)
+PyCOND_INIT(PyCOND_T *cv)
+{
+ /* A semaphore with a "large" max value, The positive value
+ * is only needed to catch those "lost wakeup" events and
+ * race conditions when a timed wait elapses.
+ */
+ cv->sem = CreateSemaphore(NULL, 0, 100000, NULL);
+ if (cv->sem==NULL)
+ return -1;
+ cv->waiting = 0;
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_FINI(PyCOND_T *cv)
+{
+ return CloseHandle(cv->sem) ? 0 : -1;
+}
+
+/* this implementation can detect a timeout. Returns 1 on timeout,
+ * 0 otherwise (and -1 on error)
+ */
+Py_LOCAL_INLINE(int)
+_PyCOND_WAIT_MS(PyCOND_T *cv, PyMUTEX_T *cs, DWORD ms)
+{
+ DWORD wait;
+ cv->waiting++;
+ PyMUTEX_UNLOCK(cs);
+ /* "lost wakeup bug" would occur if the caller were interrupted here,
+ * but we are safe because we are using a semaphore wich has an internal
+ * count.
+ */
+ wait = WaitForSingleObject(cv->sem, ms);
+ PyMUTEX_LOCK(cs);
+ if (wait != WAIT_OBJECT_0)
+ --cv->waiting;
+ /* Here we have a benign race condition with PyCOND_SIGNAL.
+ * When failure occurs or timeout, it is possible that
+ * PyCOND_SIGNAL also decrements this value
+ * and signals releases the mutex. This is benign because it
+ * just means an extra spurious wakeup for a waiting thread.
+ */
+
+ if (wait == WAIT_FAILED)
+ return -1;
+ /* return 0 on success, 1 on timeout */
+ return wait != WAIT_OBJECT_0;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_WAIT(PyCOND_T *cv, PyMUTEX_T *cs)
+{
+ int result = _PyCOND_WAIT_MS(cv, cs, INFINITE);
+ return result >= 0 ? 0 : result;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long us)
+{
+ return _PyCOND_WAIT_MS(cv, cs, us/1000);
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_SIGNAL(PyCOND_T *cv)
+{
+ if (cv->waiting) {
+ /* notifying thread decreases the cv->waiting count so that
+ * a delay between notify and wakeup doesn't cause a number
+ * of extra ReleaseSemaphore calls
+ */
+ cv->waiting--;
+ return ReleaseSemaphore(cv->sem, 1, NULL) ? 0 : -1;
+ }
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_BROADCAST(PyCOND_T *cv)
+{
+ if (cv->waiting) {
+ return ReleaseSemaphore(cv->sem, cv->waiting, NULL) ? 0 : -1;
+ cv->waiting = 0;
+ }
+ return 0;
+}
+
+#else
+
+/* Use native Win7 primitives if build target is Win7 or higher */
+
+/* SRWLOCK is faster and better than CriticalSection */
+typedef SRWLOCK PyMUTEX_T;
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_INIT(PyMUTEX_T *cs)
+{
+ InitializeSRWLock(cs);
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_FINI(PyMUTEX_T *cs)
+{
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_LOCK(PyMUTEX_T *cs)
+{
+ AcquireSRWLockExclusive(cs);
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyMUTEX_UNLOCK(PyMUTEX_T *cs)
+{
+ ReleaseSRWLockExclusive(cs);
+ return 0;
+}
+
+
+typedef CONDITION_VARIABLE PyCOND_T;
+
+Py_LOCAL_INLINE(int)
+PyCOND_INIT(PyCOND_T *cv)
+{
+ InitializeConditionVariable(cv);
+ return 0;
+}
+Py_LOCAL_INLINE(int)
+PyCOND_FINI(PyCOND_T *cv)
+{
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_WAIT(PyCOND_T *cv, PyMUTEX_T *cs)
+{
+ return SleepConditionVariableSRW(cv, cs, INFINITE, 0) ? 0 : -1;
+}
+
+/* This implementation makes no distinction about timeouts. Signal
+ * 2 to indicate that we don't know.
+ */
+Py_LOCAL_INLINE(int)
+PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long us)
+{
+ return SleepConditionVariableSRW(cv, cs, us/1000, 0) ? 2 : -1;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_SIGNAL(PyCOND_T *cv)
+{
+ WakeConditionVariable(cv);
+ return 0;
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_BROADCAST(PyCOND_T *cv)
+{
+ WakeAllConditionVariable(cv);
+ return 0;
+}
+
+
+#endif /* _PY_EMULATED_WIN_CV */
+
+#endif /* _POSIX_THREADS, NT_THREADS */
+
+#endif /* _CONDVAR_H_ */