Implement futex wait scheme

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/libust/lttng-ust-comm.c b/libust/lttng-ust-comm.c
index 93f48940edb9a162f205686b066f1f9eb9bbc4e9..a5f2b0b0069de494f0fb44dd14fdde78537002e6 100644 (file)
--- a/libust/lttng-ust-comm.c
+++ b/libust/lttng-ust-comm.c
@@ -19,6 +19,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#define _LGPL_SOURCE
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/prctl.h>
@@ -35,6 +36,7 @@
 #include <assert.h>
 #include <signal.h>
 #include <urcu/uatomic.h>
+#include <urcu/futex.h>
 
 #include <lttng-ust-comm.h>
 #include <ust/usterr-signal-safe.h>
@@ -477,6 +479,8 @@ error:
 static
 void wait_for_sessiond(struct sock_info *sock_info)
 {
+       int ret;
+
        ust_lock();
        if (lttng_ust_comm_should_quit) {
                goto quit;
@@ -489,9 +493,19 @@ void wait_for_sessiond(struct sock_info *sock_info)
        ust_unlock();
 
        DBG("Waiting for %s apps sessiond", sock_info->name);
-       /* Wait for futex wakeup TODO */
-       sleep(5);
-
+       /* Wait for futex wakeup */
+       if (uatomic_read((int32_t *) sock_info->wait_shm_mmap) == 0) {
+               ret = futex_async((int32_t *) sock_info->wait_shm_mmap,
+                       FUTEX_WAIT, 0, NULL, NULL, 0);
+               /*
+                * FIXME: Currently, futexes on read-only shm seems to
+                * EFAULT.
+                */
+               if (ret < 0) {
+                       PERROR("futex");
+                       sleep(5);
+               }
+       }
        return;
 
 quit: