[Qemu-devel] [PATCH 4/4] timer: make qemu_clock_enable sync between disable and timer's cb

[Liu Ping Fan <pingfank@linux.vnet.ibm.com>]

After disabling the QemuClock, we should make sure that no QemuTimers
are still in flight. To implement that with light overhead, we resort
to QemuEvent. The caller of disabling will wait on QemuEvent of each
timerlist.

Note, qemu_clock_enable(foo,false) can _not_ be called from timer's cb.
And the callers of qemu_clock_enable() should be sync by themselves,
not protected by this patch.

Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
---
 include/qemu/timer.h |  1 +
 qemu-timer.c         | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 1363316..ca09ba2 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -85,6 +85,7 @@ int64_t timerlistgroup_deadline_ns(QEMUTimerListGroup tlg);
 
 int qemu_timeout_ns_to_ms(int64_t ns);
 int qemu_poll_ns(GPollFD *fds, uint nfds, int64_t timeout);
+/* The disable of clock can not be called in timer's cb */
 void qemu_clock_enable(QEMUClock *clock, bool enabled);
 void qemu_clock_warp(QEMUClock *clock);
 
diff --git a/qemu-timer.c b/qemu-timer.c
index ebe7597..5828107 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -71,6 +71,8 @@ struct QEMUTimerList {
     QLIST_ENTRY(QEMUTimerList) list;
     QEMUTimerListNotifyCB *notify_cb;
     void *notify_opaque;
+    /* light weight method to mark the end of timerlist's running */
+    QemuEvent ev;
 };
 
 struct QEMUTimer {
@@ -92,6 +94,7 @@ static QEMUTimerList *timerlist_new_from_clock(QEMUClock *clock)
     QEMUTimerList *tl;
 
     tl = g_malloc0(sizeof(QEMUTimerList));
+    qemu_event_init(&tl->ev, false);
     tl->clock = clock;
     QLIST_INSERT_HEAD(&clock->timerlists, tl, list);
     return tl;
@@ -145,12 +148,18 @@ void qemu_clock_notify(QEMUClock *clock)
     }
 }
 
+/* The disable of clock can _not_ be called from timer's cb */
 void qemu_clock_enable(QEMUClock *clock, bool enabled)
 {
+    QEMUTimerList *tl;
     bool old = clock->enabled;
     clock->enabled = enabled;
     if (enabled && !old) {
         qemu_clock_notify(clock);
+    } else if (!enabled && old) {
+        QLIST_FOREACH(tl, &clock->timerlists, list) {
+            qemu_event_wait(&tl->ev);
+        }
     }
 }
 
@@ -419,6 +428,7 @@ bool timerlist_run_timers(QEMUTimerList *tl)
     }
 
     current_time = qemu_get_clock_ns(tl->clock);
+    qemu_event_reset(&tl->ev);
     for(;;) {
         ts = tl->active_timers;
         if (!qemu_timer_expired_ns(ts, current_time)) {
@@ -432,6 +442,7 @@ bool timerlist_run_timers(QEMUTimerList *tl)
         ts->cb(ts->opaque);
         progress = true;
     }
+    qemu_event_set(&tl->ev);
     return progress;
 }
 
-- 
1.8.1.4