X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=src%2Fcompat_futex.c;fp=src%2Fcompat_futex.c;h=9e918fe8e2aac035dc39e6e23868410348d02627;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332

diff --git a/src/compat_futex.c b/src/compat_futex.c
new file mode 100644
index 0000000..9e918fe
--- /dev/null
+++ b/src/compat_futex.c
@@ -0,0 +1,154 @@
+/*
+ * compat_futex.c
+ *
+ * Userspace RCU library - sys_futex compatibility code
+ *
+ * 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
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdio.h>
+#include <pthread.h>
+#include <signal.h>
+#include <assert.h>
+#include <errno.h>
+#include <poll.h>
+#include <stdint.h>
+
+#include <urcu/arch.h>
+#include <urcu/futex.h>
+#include <urcu/system.h>
+
+/*
+ * 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.
+ * For now, timeout, uaddr2 and val3 are unused.
+ * Waiter will relinquish the CPU until woken up.
+ */
+
+int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
+	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
+{
+	int ret = 0, lockret;
+
+	/*
+	 * Check if NULL. Don't let users expect that they are taken into
+	 * account.
+	 */
+	assert(!timeout);
+	assert(!uaddr2);
+	assert(!val3);
+
+	/*
+	 * memory barriers to serialize with the previous uaddr modification.
+	 */
+	cmm_smp_mb();
+
+	lockret = pthread_mutex_lock(&__urcu_compat_futex_lock);
+	if (lockret) {
+		errno = lockret;
+		ret = -1;
+		goto end;
+	}
+	switch (op) {
+	case FUTEX_WAIT:
+		/*
+		 * 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:
+		/*
+		 * 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:
+		errno = EINVAL;
+		ret = -1;
+	}
+	lockret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
+	if (lockret) {
+		errno = lockret;
+		ret = -1;
+	}
+end:
+	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(int32_t *uaddr, int op, int32_t val,
+	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
+{
+	int ret = 0;
+
+	/*
+	 * Check if NULL. Don't let users expect that they are taken into
+	 * account.
+	 */
+	assert(!timeout);
+	assert(!uaddr2);
+	assert(!val3);
+
+	/*
+	 * Ensure previous memory operations on uaddr have completed.
+	 */
+	cmm_smp_mb();
+
+	switch (op) {
+	case FUTEX_WAIT:
+		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:
+		errno = EINVAL;
+		ret = -1;
+	}
+end:
+	return ret;
+}