Compat futex

[urcu.git] / compat_futex.c

diff --git a/compat_futex.c b/compat_futex.c
new file mode 100644 (file)
index 0000000..27fc66b
--- /dev/null
+++ b/compat_futex.c
@@ -0,0 +1,115 @@
+/*
+ * compat_futex.c
+ *
+ * Userspace RCU library - sys_futex compatibility code
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * 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 <urcu/arch.h>
+#include <urcu/urcu-futex.h>
+
+static pthread_mutex_t compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t 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(int *uaddr, int op, int val,
+       const struct timespec *timeout, int *uaddr2, int val3)
+{
+       int ret, i, gret = 0;
+
+       /*
+        * 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.
+        */
+       smp_mb();
+
+       ret = pthread_mutex_lock(&compat_futex_lock);
+       assert(!ret);
+       switch (op) {
+       case FUTEX_WAIT:
+               if (*uaddr != val)
+                       goto end;
+               pthread_cond_wait(&compat_futex_cond, &compat_futex_lock);
+               break;
+       case FUTEX_WAKE:
+               for (i = 0; i < val; i++)
+                       pthread_cond_signal(&compat_futex_cond);
+               break;
+       default:
+               gret = -EINVAL;
+       }
+end:
+       ret = pthread_mutex_unlock(&compat_futex_lock);
+       assert(!ret);
+       return gret;
+}
+
+/*
+ * _ASYNC SIGNAL-SAFE_.
+ * For now, timeout, uaddr2 and val3 are unused.
+ * Waiter will busy-loop trying to read the condition.
+ */
+
+int compat_futex_async(int *uaddr, int op, int val,
+       const struct timespec *timeout, int *uaddr2, int val3)
+{
+       int ret, i;
+
+       /*
+        * 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.
+        */
+       smp_mb();
+
+       switch (op) {
+       case FUTEX_WAIT:
+               while (*uaddr == val)
+                       poll(NULL, 0, 10);
+               break;
+       case FUTEX_WAKE:
+               break;
+       default:
+               return -EINVAL;
+       }
+}