X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=compat_futex.c;h=9e918fe8e2aac035dc39e6e23868410348d02627;hp=27fc66bb4ff7e1318f6bde0788498505319ff02e;hb=b2633d211b186cb201be327ded53ecf523ecf0bd;hpb=49617de1d80d771ac9a1d45b1710b16fac65e0aa

diff --git a/compat_futex.c b/compat_futex.c
index 27fc66b..9e918fe 100644
--- a/compat_futex.c
+++ b/compat_futex.c
@@ -3,7 +3,7 @@
  *
  * Userspace RCU library - sys_futex compatibility code
  *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -26,12 +26,24 @@
 #include <assert.h>
 #include <errno.h>
 #include <poll.h>
+#include <stdint.h>
 
 #include <urcu/arch.h>
-#include <urcu/urcu-futex.h>
+#include <urcu/futex.h>
+#include <urcu/system.h>
 
-static pthread_mutex_t compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
-static pthread_cond_t compat_futex_cond = PTHREAD_COND_INITIALIZER;
+/*
+ * Using attribute "weak" for __urcu_compat_futex_lock and
+ * __urcu_compat_futex_cond. Those are globally visible by the entire
+ * program, even though many shared objects may have their own version.
+ * The first version that gets loaded will be used by the entire program
+ * (executable and all shared objects).
+ */
+
+__attribute__((weak))
+pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
+__attribute__((weak))
+pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;
 
 /*
  * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
@@ -39,14 +51,14 @@ static pthread_cond_t compat_futex_cond = PTHREAD_COND_INITIALIZER;
  * Waiter will relinquish the CPU until woken up.
  */
 
-int compat_futex_noasync(int *uaddr, int op, int val,
-	const struct timespec *timeout, int *uaddr2, int val3)
+int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
+	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 {
-	int ret, i, gret = 0;
+	int ret = 0, lockret;
 
 	/*
 	 * Check if NULL. Don't let users expect that they are taken into
-	 * account. 
+	 * account.
 	 */
 	assert(!timeout);
 	assert(!uaddr2);
@@ -55,43 +67,62 @@ int compat_futex_noasync(int *uaddr, int op, int val,
 	/*
 	 * memory barriers to serialize with the previous uaddr modification.
 	 */
-	smp_mb();
+	cmm_smp_mb();
 
-	ret = pthread_mutex_lock(&compat_futex_lock);
-	assert(!ret);
+	lockret = pthread_mutex_lock(&__urcu_compat_futex_lock);
+	if (lockret) {
+		errno = lockret;
+		ret = -1;
+		goto end;
+	}
 	switch (op) {
 	case FUTEX_WAIT:
-		if (*uaddr != val)
-			goto end;
-		pthread_cond_wait(&compat_futex_cond, &compat_futex_lock);
+		/*
+		 * Wait until *uaddr is changed to something else than "val".
+		 * Comparing *uaddr content against val figures out which
+		 * thread has been awakened.
+		 */
+		while (CMM_LOAD_SHARED(*uaddr) == val)
+			pthread_cond_wait(&__urcu_compat_futex_cond,
+				&__urcu_compat_futex_lock);
 		break;
 	case FUTEX_WAKE:
-		for (i = 0; i < val; i++)
-			pthread_cond_signal(&compat_futex_cond);
+		/*
+		 * Each wake is sending a broadcast, thus attempting wakeup of
+		 * all awaiting threads, independently of their respective
+		 * uaddr.
+		 */
+		pthread_cond_broadcast(&__urcu_compat_futex_cond);
 		break;
 	default:
-		gret = -EINVAL;
+		errno = EINVAL;
+		ret = -1;
+	}
+	lockret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
+	if (lockret) {
+		errno = lockret;
+		ret = -1;
 	}
 end:
-	ret = pthread_mutex_unlock(&compat_futex_lock);
-	assert(!ret);
-	return gret;
+	return ret;
 }
 
 /*
  * _ASYNC SIGNAL-SAFE_.
  * For now, timeout, uaddr2 and val3 are unused.
  * Waiter will busy-loop trying to read the condition.
+ * It is OK to use compat_futex_async() on a futex address on which
+ * futex() WAKE operations are also performed.
  */
 
-int compat_futex_async(int *uaddr, int op, int val,
-	const struct timespec *timeout, int *uaddr2, int val3)
+int compat_futex_async(int32_t *uaddr, int op, int32_t val,
+	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 {
-	int ret, i;
+	int ret = 0;
 
 	/*
 	 * Check if NULL. Don't let users expect that they are taken into
-	 * account. 
+	 * account.
 	 */
 	assert(!timeout);
 	assert(!uaddr2);
@@ -100,16 +131,24 @@ int compat_futex_async(int *uaddr, int op, int val,
 	/*
 	 * Ensure previous memory operations on uaddr have completed.
 	 */
-	smp_mb();
+	cmm_smp_mb();
 
 	switch (op) {
 	case FUTEX_WAIT:
-		while (*uaddr == val)
-			poll(NULL, 0, 10);
+		while (CMM_LOAD_SHARED(*uaddr) == val) {
+			if (poll(NULL, 0, 10) < 0) {
+				ret = -1;
+				/* Keep poll errno. Caller handles EINTR. */
+				goto end;
+			}
+		}
 		break;
 	case FUTEX_WAKE:
 		break;
 	default:
-		return -EINVAL;
+		errno = EINVAL;
+		ret = -1;
 	}
+end:
+	return ret;
 }