/* -------------------------- gl_cond_t datatype -------------------------- */
-/* This implementation is based on the article
- Douglas C. Schmidt, Irfan Pyarali
- "Strategies for Implementing POSIX Condition Variables on Win32"
- <http://www.cs.wustl.edu/~schmidt/win32-cv-1.html> */
+/* In this file, the waitqueues are implemented as linked lists. */
+#define gl_waitqueue_t gl_linked_waitqueue_t
+
+/* All links of a circular list, except the anchor, are of this type, carrying
+ a payload. */
+struct gl_waitqueue_element
+{
+ struct gl_waitqueue_link link; /* must be the first field! */
+ HANDLE event; /* Waiting thread, represented by an event.
+ This field is immutable once initialized. */
+};
+
+static inline void
+gl_waitqueue_init (gl_waitqueue_t *wq)
+{
+ wq->wq_list.wql_next = &wq->wq_list;
+ wq->wq_list.wql_prev = &wq->wq_list;
+}
+
+/* Enqueues the current thread, represented by an event, in a wait queue.
+ Returns NULL if an allocation failure occurs. */
+static struct gl_waitqueue_element *
+gl_waitqueue_add (gl_waitqueue_t *wq)
+{
+ struct gl_waitqueue_element *elt;
+ HANDLE event;
+
+ /* Allocate the memory for the waitqueue element on the heap, not on the
+ thread's stack. If the thread exits unexpectedly, we prefer to leak
+ some memory rather than to access unavailable memory and crash. */
+ elt =
+ (struct gl_waitqueue_element *)
+ malloc (sizeof (struct gl_waitqueue_element));
+ if (elt == NULL)
+ /* No more memory. */
+ return NULL;
+
+ /* Whether the created event is a manual-reset one or an auto-reset one,
+ does not matter, since we will wait on it only once. */
+ event = CreateEvent (NULL, TRUE, FALSE, NULL);
+ if (event == INVALID_HANDLE_VALUE)
+ {
+ /* No way to allocate an event. */
+ free (elt);
+ return NULL;
+ }
+ elt->event = event;
+ /* Insert elt at the end of the circular list. */
+ (elt->link.wql_prev = wq->wq_list.wql_prev)->wql_next = &elt->link;
+ (elt->link.wql_next = &wq->wq_list)->wql_prev = &elt->link;
+ return elt;
+}
+
+/* Removes the current thread, represented by a 'struct gl_waitqueue_element *',
+ from a wait queue.
+ Returns true if is was found and removed, false if it was not present. */
+static inline bool
+gl_waitqueue_remove (gl_waitqueue_t *wq, struct gl_waitqueue_element *elt)
+{
+ if (elt->link.wql_next != NULL && elt->link.wql_prev != NULL)
+ {
+ /* Remove elt from the circular list. */
+ struct gl_waitqueue_link *prev = elt->link.wql_prev;
+ struct gl_waitqueue_link *next = elt->link.wql_next;
+ prev->wql_next = next;
+ next->wql_prev = prev;
+ elt->link.wql_next = NULL;
+ elt->link.wql_prev = NULL;
+ return true;
+ }
+ else
+ return false;
+}
+
+/* Notifies the first thread from a wait queue and dequeues it. */
+static inline void
+gl_waitqueue_notify_first (gl_waitqueue_t *wq)
+{
+ if (wq->wq_list.wql_next != &wq->wq_list)
+ {
+ struct gl_waitqueue_element *elt =
+ (struct gl_waitqueue_element *) wq->wq_list.wql_next;
+ struct gl_waitqueue_link *prev;
+ struct gl_waitqueue_link *next;
+
+ /* Remove elt from the circular list. */
+ prev = &wq->wq_list; /* = elt->link.wql_prev; */
+ next = elt->link.wql_next;
+ prev->wql_next = next;
+ next->wql_prev = prev;
+ elt->link.wql_next = NULL;
+ elt->link.wql_prev = NULL;
+
+ SetEvent (elt->event);
+ /* After the SetEvent, this thread cannot access *elt any more, because
+ the woken-up thread will quickly call free (elt). */
+ }
+}
+
+/* Notifies all threads from a wait queue and dequeues them all. */
+static inline void
+gl_waitqueue_notify_all (gl_waitqueue_t *wq)
+{
+ struct gl_waitqueue_link *l;
+
+ for (l = wq->wq_list.wql_next; l != &wq->wq_list; )
+ {
+ struct gl_waitqueue_element *elt = (struct gl_waitqueue_element *) l;
+ struct gl_waitqueue_link *prev;
+ struct gl_waitqueue_link *next;
+
+ /* Remove elt from the circular list. */
+ prev = &wq->wq_list; /* = elt->link.wql_prev; */
+ next = elt->link.wql_next;
+ prev->wql_next = next;
+ next->wql_prev = prev;
+ elt->link.wql_next = NULL;
+ elt->link.wql_prev = NULL;
+
+ SetEvent (elt->event);
+ /* After the SetEvent, this thread cannot access *elt any more, because
+ the woken-up thread will quickly call free (elt). */
+
+ l = next;
+ }
+ if (!(wq->wq_list.wql_next == &wq->wq_list
+ && wq->wq_list.wql_prev == &wq->wq_list))
+ abort ();
+}
int
glthread_cond_init_func (gl_cond_t *cond)
{
InitializeCriticalSection (&cond->lock);
- /* Create a manual-reset event. */
- cond->event = CreateEvent (NULL, TRUE, FALSE, NULL);
- cond->waiters_count = 0;
- cond->release_count = 0;
- cond->wait_generation_count = 0;
+ gl_waitqueue_init (&cond->waiters);
cond->guard.done = 1;
-
return 0;
}
Sleep (0);
}
+ EnterCriticalSection (&cond->lock);
{
- unsigned old_generation_count;
- HANDLE event;
-
- EnterCriticalSection (&cond->lock);
- /* Increment waiters_count,
- and get a copy of the current wait_generation_count. */
- cond->waiters_count++;
- old_generation_count = cond->wait_generation_count;
- event = cond->event;
+ struct gl_waitqueue_element *elt = gl_waitqueue_add (&cond->waiters);
LeaveCriticalSection (&cond->lock);
-
- {
- /* Now release the lock and let any other thread take it. */
- int err = glthread_lock_unlock (lock);
- if (err != 0)
- {
- EnterCriticalSection (&cond->lock);
- cond->waiters_count--;
- LeaveCriticalSection (&cond->lock);
- return err;
- }
-
+ if (elt == NULL)
{
- /* Wait until another thread signals this event. */
+ /* Allocation failure. Weird. */
+ return EAGAIN;
+ }
+ else
+ {
+ HANDLE event = elt->event;
+ int err;
DWORD result;
- for (;;)
+ /* Now release the lock and let any other thread take it. */
+ err = glthread_lock_unlock (lock);
+ if (err != 0)
{
- bool wait_done;
-
- result = WaitForSingleObject (event, INFINITE);
- if (result != WAIT_OBJECT_0)
- break;
- /* Distingish intended from spurious wakeups. */
EnterCriticalSection (&cond->lock);
- wait_done =
- (cond->release_count > 0
- && cond->wait_generation_count != old_generation_count);
+ gl_waitqueue_remove (&cond->waiters, elt);
LeaveCriticalSection (&cond->lock);
- if (wait_done)
- break;
+ CloseHandle (event);
+ free (elt);
+ return err;
}
-
- /* Take the lock again. It does not matter whether this is done
- before or after the bookkeeping. */
- err = glthread_lock_lock (lock);
-
- /* Do the bookkeeping. */
- EnterCriticalSection (&cond->lock);
- cond->waiters_count--;
- if (result == WAIT_OBJECT_0)
- {
- /* The wait terminated because the event was signaled.
- Acknowledge the receipt. */
- if (--cond->release_count == 0)
- {
- /* The last waiting thread to be notified has to reset
- the event. */
- ResetEvent (cond->event);
- }
- }
- LeaveCriticalSection (&cond->lock);
-
- return (err ? err :
- result == WAIT_OBJECT_0 ? 0 :
- /* WAIT_FAILED shouldn't happen */ EAGAIN);
+ /* POSIX says:
+ "If another thread is able to acquire the mutex after the
+ about-to-block thread has released it, then a subsequent call to
+ pthread_cond_broadcast() or pthread_cond_signal() in that thread
+ shall behave as if it were issued after the about-to-block thread
+ has blocked."
+ This is fulfilled here, because the thread signalling is done
+ through SetEvent, not PulseEvent. */
+ /* Wait until another thread signals this event. */
+ result = WaitForSingleObject (event, INFINITE);
+ if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
+ abort ();
+ CloseHandle (event);
+ free (elt);
+ /* The thread which signalled the event already did the bookkeeping:
+ removed us from the waiters. */
+ return glthread_lock_lock (lock);
}
- }
}
}
Sleep (0);
}
+ EnterCriticalSection (&cond->lock);
{
- unsigned old_generation_count;
- HANDLE event;
-
- EnterCriticalSection (&cond->lock);
- /* Increment waiters_count,
- and get a copy of the current wait_generation_count. */
- cond->waiters_count++;
- old_generation_count = cond->wait_generation_count;
- event = cond->event;
+ struct gl_waitqueue_element *elt = gl_waitqueue_add (&cond->waiters);
LeaveCriticalSection (&cond->lock);
-
- {
- /* Now release the lock and let any other thread take it. */
- int err = glthread_lock_unlock (lock);
- if (err != 0)
- {
- EnterCriticalSection (&cond->lock);
- cond->waiters_count--;
- LeaveCriticalSection (&cond->lock);
- return err;
- }
-
+ if (elt == NULL)
{
- /* Wait until another thread signals this event or until the abstime
- passes. */
+ /* Allocation failure. Weird. */
+ return EAGAIN;
+ }
+ else
+ {
+ HANDLE event = elt->event;
+ int err;
+ DWORD timeout;
DWORD result;
- for (;;)
+ /* Now release the lock and let any other thread take it. */
+ err = glthread_lock_unlock (lock);
+ if (err != 0)
{
- DWORD timeout;
- bool wait_done;
-
- gettimeofday (&currtime, NULL);
- if (currtime.tv_sec > abstime->tv_sec)
- timeout = 0;
+ EnterCriticalSection (&cond->lock);
+ gl_waitqueue_remove (&cond->waiters, elt);
+ LeaveCriticalSection (&cond->lock);
+ CloseHandle (event);
+ free (elt);
+ return err;
+ }
+ /* POSIX says:
+ "If another thread is able to acquire the mutex after the
+ about-to-block thread has released it, then a subsequent call to
+ pthread_cond_broadcast() or pthread_cond_signal() in that thread
+ shall behave as if it were issued after the about-to-block thread
+ has blocked."
+ This is fulfilled here, because the thread signalling is done
+ through SetEvent, not PulseEvent. */
+ /* Wait until another thread signals this event or until the abstime
+ passes. */
+ gettimeofday (&currtime, NULL);
+ if (currtime.tv_sec > abstime->tv_sec)
+ timeout = 0;
+ else
+ {
+ unsigned long seconds = abstime->tv_sec - currtime.tv_sec;
+ timeout = seconds * 1000;
+ if (timeout / 1000 != seconds) /* overflow? */
+ timeout = INFINITE;
else
{
- unsigned long seconds = abstime->tv_sec - currtime.tv_sec;
- timeout = seconds * 1000;
- if (timeout / 1000 != seconds) /* overflow? */
- timeout = INFINITE;
+ long milliseconds =
+ abstime->tv_nsec / 1000000 - currtime.tv_usec / 1000;
+ if (milliseconds >= 0)
+ {
+ timeout += milliseconds;
+ if (timeout < milliseconds) /* overflow? */
+ timeout = INFINITE;
+ }
else
{
- long milliseconds =
- abstime->tv_nsec / 1000000 - currtime.tv_usec / 1000;
- if (milliseconds >= 0)
- {
- timeout += milliseconds;
- if (timeout < milliseconds) /* overflow? */
- timeout = INFINITE;
- }
+ if (timeout >= - milliseconds)
+ timeout -= (- milliseconds);
else
- {
- if (timeout >= - milliseconds)
- timeout -= (- milliseconds);
- else
- timeout = 0;
- }
+ timeout = 0;
}
}
-
- result = WaitForSingleObject (event, timeout);
- if (result != WAIT_OBJECT_0)
- break;
- /* Distingish intended from spurious wakeups. */
- EnterCriticalSection (&cond->lock);
- wait_done =
- (cond->release_count > 0
- && cond->wait_generation_count != old_generation_count);
- LeaveCriticalSection (&cond->lock);
- if (wait_done)
- break;
}
-
- /* Take the lock again. It does not matter whether this is done
- before or after the bookkeeping. */
- err = glthread_lock_lock (lock);
-
- /* Do the bookkeeping. */
- EnterCriticalSection (&cond->lock);
- cond->waiters_count--;
- if (result == WAIT_OBJECT_0)
+ result = WaitForSingleObject (event, timeout);
+ if (result == WAIT_FAILED)
+ abort ();
+ if (result == WAIT_TIMEOUT)
{
- /* The wait terminated because the event was signaled.
- Acknowledge the receipt. */
- if (--cond->release_count == 0)
+ EnterCriticalSection (&cond->lock);
+ if (gl_waitqueue_remove (&cond->waiters, elt))
+ {
+ /* The event was not signaled between the WaitForSingleObject
+ call and the EnterCriticalSection call. */
+ if (!(WaitForSingleObject (event, 0) == WAIT_TIMEOUT))
+ abort ();
+ }
+ else
{
- /* The last waiting thread to be notified has to reset
- the event. */
- ResetEvent (cond->event);
+ /* The event was signaled between the WaitForSingleObject
+ call and the EnterCriticalSection call. */
+ if (!(WaitForSingleObject (event, 0) == WAIT_OBJECT_0))
+ abort ();
+ /* Produce the right return value. */
+ result = WAIT_OBJECT_0;
}
+ LeaveCriticalSection (&cond->lock);
}
- LeaveCriticalSection (&cond->lock);
-
+ else
+ {
+ /* The thread which signalled the event already did the
+ bookkeeping: removed us from the waiters. */
+ }
+ CloseHandle (event);
+ free (elt);
+ /* Take the lock again. It does not matter whether this is done
+ before or after the bookkeeping for WAIT_TIMEOUT. */
+ err = glthread_lock_lock (lock);
return (err ? err :
result == WAIT_OBJECT_0 ? 0 :
result == WAIT_TIMEOUT ? ETIMEDOUT :
/* WAIT_FAILED shouldn't happen */ EAGAIN);
}
- }
}
}
EnterCriticalSection (&cond->lock);
/* POSIX says:
"The pthread_cond_broadcast() and pthread_cond_signal() functions shall
- have no effect if there are no threads currently blocked on cond."
- Also, if waiters_count == release_count > 0, all blocked threads will
- be unblocked soon anyway; do nothing in this case as well. */
- if (cond->waiters_count > cond->release_count)
- {
- /* Signal the manual-reset event. */
- SetEvent (cond->event);
- /* ... and reset it is soon as one of the currently waiting threads has
- acknowledged the receipt of the signal. */
- cond->release_count++;
- cond->wait_generation_count++;
- }
+ have no effect if there are no threads currently blocked on cond." */
+ if (cond->waiters.wq_list.wql_next != &cond->waiters.wq_list)
+ gl_waitqueue_notify_first (&cond->waiters);
LeaveCriticalSection (&cond->lock);
return 0;
EnterCriticalSection (&cond->lock);
/* POSIX says:
"The pthread_cond_broadcast() and pthread_cond_signal() functions shall
- have no effect if there are no threads currently blocked on cond." */
- if (cond->waiters_count > 0)
- {
- /* Signal the manual-reset event. */
- SetEvent (cond->event);
- /* ... and reset it only after all currently waiting threads have
- acknowledged the receipt of the signal. */
- cond->release_count = cond->waiters_count;
- cond->wait_generation_count++;
- }
+ have no effect if there are no threads currently blocked on cond."
+ gl_waitqueue_notify_all is a nop in this case. */
+ gl_waitqueue_notify_all (&cond->waiters);
LeaveCriticalSection (&cond->lock);
return 0;
{
if (!cond->guard.done)
return EINVAL;
- if (cond->waiters_count > 0)
+ if (cond->waiters.wq_list.wql_next != &cond->waiters.wq_list)
return EBUSY;
- CloseHandle (cond->event);
DeleteCriticalSection (&cond->lock);
cond->guard.done = 0;
return 0;
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