1 files changed, 390 insertions, 0 deletions
diff --git a/Python/condvar.h b/Python/condvar.h
new file mode 100644
index 0000000000..19474ef21f
--- /dev/null
+++ b/Python/condvar.h
@@ -0,0 +1,390 @@
+/* 
+ * 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.
+ *
+ * There are at least two caveats with using these condition variables,
+ * due to the fact that they may be emulated with Semaphores on
+ * Windows:
+ * 1) While PyCOND_SIGNAL() will wake up at least one thread, we
+ *    cannot currently guarantee that it will be one of the threads
+ *    already waiting in a PyCOND_WAIT() call.  It _could_ cause
+ *    the wakeup of a subsequent thread to try a PyCOND_WAIT(),
+ *    including the thread doing the PyCOND_SIGNAL() itself.
+ *    The same applies to PyCOND_BROADCAST(), if N threads are waiting
+ *    then at least N threads will be woken up, but not necessarily
+ *    those already waiting.
+ *    For this reason, don't make the scheduling assumption that a
+ *    specific other thread will get the wakeup signal
+ * 2) The _mutex_ must be held when calling PyCOND_SIGNAL() and
+ *    PyCOND_BROADCAST().
+ *    While e.g. the posix standard strongly recommends that the mutex
+ *    associated with the condition variable is held when a
+ *    pthread_cond_signal() call is made, this is not a hard requirement,
+ *    although scheduling will not be "reliable" if it isn't.  Here
+ *    the mutex is used for internal synchronization of the emulated
+ *    Condition Variable.
+ */
+
+#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 { /* TODO: add overflow and truncation checks */ \
+    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, PY_LONG_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.
+
+   This implementation still has the problem that the threads woken
+   with a "signal" aren't necessarily those that are already
+   waiting.  It corresponds to listing 2 in:
+   http://birrell.org/andrew/papers/ImplementingCVs.pdf
+
+   Generic emulations of the pthread_cond_* API using
+   earlier Win32 functions can be found on the Web.
+   The following read can be give background information to these issues,
+   but the implementations are all broken in some way.
+   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; /* to allow PyCOND_SIGNAL to be a no-op */
+} 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.
+         * ('waiting' corresponds to the semaphore's "negative" count and
+         * we may end up with e.g. (waiting == -1 && sem.count == 1).  When
+         * a new thread comes along, it will pass right throuhgh, having
+         * adjusted it to (waiting == 0 && sem.count == 0).
+         */
+         
+    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, PY_LONG_LONG us)
+{
+    return _PyCOND_WAIT_MS(cv, cs, (DWORD)(us/1000));
+}
+
+Py_LOCAL_INLINE(int)
+PyCOND_SIGNAL(PyCOND_T *cv)
+{
+    /* this test allows PyCOND_SIGNAL to be a no-op unless required
+     * to wake someone up, thus preventing an unbounded increase of
+     * the semaphore's internal counter.
+     */
+    if (cv->waiting > 0) {
+        /* notifying thread decreases the cv->waiting count so that
+         * a delay between notify and actual wakeup of the target thread
+         * 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)
+{
+    int waiting = cv->waiting;
+    if (waiting > 0) {
+        cv->waiting = 0;
+        return ReleaseSemaphore(cv->sem, waiting, NULL) ? 0 : -1;
+    }
+    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, PY_LONG_LONG us)
+{
+    return SleepConditionVariableSRW(cv, cs, (DWORD)(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_ */