use pthread_condattr_setclock to avoid race conditions with the clock

2006-07-12 01:47:10 +00:00
parent 22dc123b35
commit 6e245f46ae
1 changed files with 105 additions and 18 deletions
@@ -209,10 +209,92 @@ MutexImpl *MakeMutex( RageMutex *pParent )
 	return new MutexImpl_Pthreads( pParent );
 }

+/* Check if condattr_setclock is supported, and supports the clock that RageTimer
+ * selected. */
+#if defined(UNIX)
+#include <dlfcn.h>
+#include "arch/ArchHooks/ArchHooks_Unix.h"
+#endif
+namespace
+{
+	typedef int (* CONDATTR_SET_CLOCK)( pthread_condattr_t *attr, clockid_t clock_id );
+	CONDATTR_SET_CLOCK g_CondattrSetclock = NULL;
+	bool bInitialized = false;
+
+#if defined(UNIX)
+	clockid_t GetClock()
+	{
+		return ArchHooks_Unix::GetClock();
+	}
+
+	void InitMonotonic()
+	{
+		if( bInitialized )
+			return;
+		bInitialized = true;
+
+		void *pLib = NULL;
+
+		do {
+			{
+				pLib = dlopen( NULL, RTLD_LAZY );
+				if( pLib == NULL )
+					break;
+
+				g_CondattrSetclock = (CONDATTR_SET_CLOCK) dlsym( pLib, "pthread_condattr_setclock" );
+
+				if( g_CondattrSetclock == NULL )
+					break;
+			}
+
+			/* Make sure that we can set up the clock attribute. */
+			pthread_condattr_t condattr;
+			pthread_condattr_init( &condattr );
+
+			if( g_CondattrSetclock(&condattr, GetClock()) != 0 )
+			{
+				printf( "pthread_condattr_setclock failed\n" );
+				pthread_condattr_destroy( &condattr );
+				break;
+			}
+			pthread_condattr_destroy( &condattr );
+
+			/* Everything seems to work. */
+			return;
+		} while(0);
+
+		g_CondattrSetclock = NULL;
+		if( pLib != NULL )
+			dlclose( pLib );
+		pLib = NULL;
+	}
+#else
+	void InitMonotonic()
+	{
+		bInitialized = true;
+	}
+
+	clockid_t GetClock()
+	{
+		return CLOCK_REALTIME;
+	}
+#endif
+};
+
 EventImpl_Pthreads::EventImpl_Pthreads( MutexImpl_Pthreads *pParent )
 {
 	m_pParent = pParent;
-	pthread_cond_init( &m_Cond, NULL );
+
+	InitMonotonic();
+       
+	pthread_condattr_t condattr;
+	pthread_condattr_init( &condattr );
+
+	if( g_CondattrSetclock != NULL )
+		g_CondattrSetclock( &condattr, GetClock() );
+
+	pthread_cond_init( &m_Cond, &condattr );
+	pthread_condattr_destroy( &condattr );
 }

 EventImpl_Pthreads::~EventImpl_Pthreads()
@@ -229,29 +311,34 @@ bool EventImpl_Pthreads::Wait( RageTimer *pTimeout )
 		return true;
 	}

-#if 1
-	float fSecondsInFuture = -pTimeout->Ago();
-
-	RageTimer timeofday;
+	/* If the clock is not CLOCK_MONOTONIC, or we can't change the wait clock (no
+	 * condattr_setclock), pthread_cond_timedwait has an inherent race condition:
+	 * the system clock may change before we call it. */
+	timespec abstime;
+	if( g_CondattrSetclock != NULL || GetClock() == CLOCK_REALTIME )
 	{
+		/* If we support condattr_setclock, we'll set the condition to use the same
+		 * clock as RageTimer and can use it directly.  If the clock is CLOCK_REALTIME,
+		 * that's the default anyway. */
+		abstime.tv_sec = pTimeout->m_secs;
+		abstime.tv_nsec = pTimeout->m_us * 1000;
+	}
+	else
+	{
+		/* The RageTimer clock is different than the wait clock; convert it. */
 		timeval tv;
 		gettimeofday( &tv, NULL );
+
+		RageTimer timeofday;
 		timeofday.m_secs = tv.tv_sec;
 		timeofday.m_us = tv.tv_usec;
-	}
-	timeofday += fSecondsInFuture;
-	

-	timespec abstime;
-	abstime.tv_sec = timeofday.m_secs;
-	abstime.tv_nsec = timeofday.m_us * 1000;
-#else
-	/* XXX: This is how it should look for CLOCK_MONOTONIC: simply use the
-	 * time directly.  This requires that the condition be set to that clock,
-	 * which requires pthread_condattr_setclock(). */
-	abstime.tv_sec = pTimeout->m_secs;
-	abstime.tv_nsec = pTimeout->m_us * 1000;
-#endif
+		float fSecondsInFuture = -pTimeout->Ago();
+		timeofday += fSecondsInFuture;
+
+		abstime.tv_sec = timeofday.m_secs;
+		abstime.tv_nsec = timeofday.m_us * 1000;
+	}

 	int iRet = pthread_cond_timedwait( &m_Cond, &m_pParent->mutex, &abstime );
 	return iRet != ETIMEDOUT;