From ce9337c8d9ea9b1f26a5f77274aebd49c81bba86 Mon Sep 17 00:00:00 2001
From: "Unknown W. Brackets" <checkins@unknownbrackets.org>
Date: Sun, 6 Jul 2014 16:16:38 -0700
Subject: [PATCH] Try to approximate condvars on win xp better.

---
 base/mutex.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/base/mutex.h b/base/mutex.h
index fb0affa384..99b4260657 100644
--- a/base/mutex.h
+++ b/base/mutex.h
@@ -235,6 +235,7 @@ public:
 		InitializeConditionVariable(&cond_);
 #else
 		sema_ = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
+		waiting_ = 0;
 #endif
 #else
 		pthread_cond_init(&event_, NULL);
@@ -256,7 +257,10 @@ public:
 #ifdef _M_X64
 		WakeConditionVariable(&cond_);
 #else
-		ReleaseSemaphore(sema_, 1, NULL);
+		// Should be locked at this time.
+		if (waiting_ != 0) {
+			ReleaseSemaphore(sema_, 1, NULL);
+		}
 #endif
 #else
 		pthread_cond_signal(&event_);
@@ -275,9 +279,11 @@ public:
 		// Since a semaphore keeps a count, the window between unlock and lock won't cause us to deadlock.
 		// However, we could wake early incorrectly (if the semaphore is signalled already.)
 		// That's better than deadlocking or forgetting to wake.
+		waiting_++;
 		mtx.unlock();
 		WaitForSingleObject(sema_, INFINITE);
 		mtx.lock();
+		waiting_--;
 #endif
 #else
 		pthread_cond_wait(&event_, &mtx.native_handle());
@@ -292,9 +298,11 @@ public:
 		// Since a semaphore keeps a count, the window between unlock and lock won't cause us to deadlock.
 		// However, we could wake early incorrectly (if the semaphore is signalled already.)
 		// That's better than deadlocking or forgetting to wake.
+		waiting_++;
 		mtx.unlock();
 		WaitForSingleObject(sema_, milliseconds);
 		mtx.lock();
+		waiting_--;
 #endif
 #else
 		timespec timeout;
@@ -318,6 +326,7 @@ private:
 	CONDITION_VARIABLE cond_;
 #else
 	HANDLE sema_;
+	volatile int waiting_;
 #endif
 #else
 	pthread_cond_t event_;