timer: add timer_mod_anticipate and timer_mod_anticipate_ns

These let a user anticipate the deadline of a timer, atomically with other sites that call the function. This helps avoiding complicated lock hierarchies. Reviewed-by: Alex Bligh <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
hallyn · Oct 17, 2013 · add40e9 · add40e9
1 parent 0f809e5
commit add40e9
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diff --git a/include/qemu/timer.h b/include/qemu/timer.h
@@ -544,6 +544,19 @@ void timer_del(QEMUTimer *ts);
  */
 void timer_mod_ns(QEMUTimer *ts, int64_t expire_time);
 
+/**
+ * timer_mod_anticipate_ns:
+ * @ts: the timer
+ * @expire_time: the expiry time in nanoseconds
+ *
+ * Modify a timer to expire at @expire_time or the current time,
+ * whichever comes earlier.
+ *
+ * This function is thread-safe but the timer and its timer list must not be
+ * freed while this function is running.
+ */
+void timer_mod_anticipate_ns(QEMUTimer *ts, int64_t expire_time);
+
 /**
  * timer_mod:
  * @ts: the timer
@@ -557,6 +570,19 @@ void timer_mod_ns(QEMUTimer *ts, int64_t expire_time);
  */
 void timer_mod(QEMUTimer *ts, int64_t expire_timer);
 
+/**
+ * timer_mod_anticipate:
+ * @ts: the timer
+ * @expire_time: the expiry time in nanoseconds
+ *
+ * Modify a timer to expire at @expire_time or the current time, whichever
+ * comes earlier, taking into account the scale associated with the timer.
+ *
+ * This function is thread-safe but the timer and its timer list must not be
+ * freed while this function is running.
+ */
+void timer_mod_anticipate(QEMUTimer *ts, int64_t expire_time);
+
 /**
  * timer_pending:
  * @ts: the timer

diff --git a/qemu-timer.c b/qemu-timer.c
@@ -410,11 +410,40 @@ void timer_mod_ns(QEMUTimer *ts, int64_t expire_time)
     }
 }
 
+/* modify the current timer so that it will be fired when current_time
+   >= expire_time or the current deadline, whichever comes earlier.
+   The corresponding callback will be called. */
+void timer_mod_anticipate_ns(QEMUTimer *ts, int64_t expire_time)
+{
+    QEMUTimerList *timer_list = ts->timer_list;
+    bool rearm;
+
+    qemu_mutex_lock(&timer_list->active_timers_lock);
+    if (ts->expire_time == -1 || ts->expire_time > expire_time) {
+        if (ts->expire_time != -1) {
+            timer_del_locked(timer_list, ts);
+        }
+        rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
+    } else {
+        rearm = false;
+    }
+    qemu_mutex_unlock(&timer_list->active_timers_lock);
+
+    if (rearm) {
+        timerlist_rearm(timer_list);
+    }
+}
+
 void timer_mod(QEMUTimer *ts, int64_t expire_time)
 {
     timer_mod_ns(ts, expire_time * ts->scale);
 }
 
+void timer_mod_anticipate(QEMUTimer *ts, int64_t expire_time)
+{
+    timer_mod_anticipate_ns(ts, expire_time * ts->scale);
+}
+
 bool timer_pending(QEMUTimer *ts)
 {
     return ts->expire_time >= 0;