[RFC 2/2] sem-posix: use monotonic clock instead

[Longpeng(Mike)]

Use CLOCK_MONOTONIC, so the timeout isn't affected by changes
to the system time. It depends on the pthread_condattr_setclock(),
while some systems(e.g. mac os) do not support it,  the behavior
won't change in these systems.

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
 include/qemu/thread-posix.h |  1 +
 meson.build                 | 11 +++++++++++
 util/qemu-thread-posix.c    | 32 +++++++++++++++++++++++++++++---
 3 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/include/qemu/thread-posix.h b/include/qemu/thread-posix.h
index 5466608..cc77000 100644
--- a/include/qemu/thread-posix.h
+++ b/include/qemu/thread-posix.h
@@ -29,6 +29,7 @@ struct QemuCond {
 struct QemuSemaphore {
     pthread_mutex_t lock;
     pthread_cond_t cond;
+    pthread_condattr_t attr;
     unsigned int count;
     bool initialized;
 };
diff --git a/meson.build b/meson.build
index 3ccb110..2bab94f 100644
--- a/meson.build
+++ b/meson.build
@@ -1688,6 +1688,17 @@ config_host_data.set('CONFIG_PTHREAD_SETNAME_NP_WO_TID', 
cc.links(gnu_source_pre
     pthread_create(&thread, 0, f, 0);
     return 0;
   }''', dependencies: threads))
+config_host_data.set('CONFIG_PTHREAD_CONDATTR_SETCLOCK', 
cc.links(gnu_source_prefix + '''
+  #include <pthread.h>
+  #include <time.h>
+
+  int main(void)
+  {
+    pthread_condattr_t attr
+    pthread_condattr_init(&attr);
+    pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
+    return 0;
+  }''', dependencies: threads))
 
 config_host_data.set('CONFIG_SIGNALFD', cc.links(gnu_source_prefix + '''
   #include <sys/signalfd.h>
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index 1ad2503..d3a7c54 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -40,10 +40,22 @@ static void error_exit(int err, const char *msg)
 
 static void compute_abs_deadline(struct timespec *ts, int ms)
 {
+    time_t now_sec;
+    long now_nsec;
+#ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
+    struct timespec now;
+    clock_gettime(CLOCK_MONOTONIC, &now);
+    now_sec = now.tv_sec;
+    now_nsec = now.tv_nsec;
+#else
     struct timeval tv;
     gettimeofday(&tv, NULL);
-    ts->tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
-    ts->tv_sec = tv.tv_sec + ms / 1000;
+    now_sec = tv.tv_sec;
+    now_nsec = tv.tv_usec * 1000;
+#endif
+
+    ts->tv_nsec = now_nsec + (ms % 1000) * 1000000;
+    ts->tv_sec = now_sec + ms / 1000;
     if (ts->tv_nsec >= 1000000000) {
         ts->tv_sec++;
         ts->tv_nsec -= 1000000000;
@@ -223,7 +235,17 @@ void qemu_sem_init(QemuSemaphore *sem, int init)
     if (rc != 0) {
         error_exit(rc, __func__);
     }
-    rc = pthread_cond_init(&sem->cond, NULL);
+    rc = pthread_condattr_init(&sem->attr);
+    if (rc != 0) {
+        error_exit(rc, __func__);
+    }
+#ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
+    rc = pthread_condattr_setclock(&sem->attr, CLOCK_MONOTONIC);
+    if (rc != 0) {
+        error_exit(rc, __func__);
+    }
+#endif
+    rc = pthread_cond_init(&sem->cond, &sem->attr);
     if (rc != 0) {
         error_exit(rc, __func__);
     }
@@ -248,6 +270,10 @@ void qemu_sem_destroy(QemuSemaphore *sem)
     if (rc < 0) {
         error_exit(rc, __func__);
     }
+    rc = pthread_condattr_destroy(&sem->attr);
+    if (rc < 0) {
+        error_exit(rc, __func__);
+    }
 }
 
 void qemu_sem_post(QemuSemaphore *sem)
-- 
1.8.3.1