commit 8f8374d75ab17be5d168fea14d3f8e2a40ca3c66
author Dan Stoza <stoza@google.com> Tue Apr 19 10:03:46 2016 -0700
committer Dan Stoza <stoza@google.com> Tue Apr 19 10:03:46 2016 -0700
tree 056a1bd07580255d0cbd0f949e98ea3eb6f3d230
parent 6328134d8f3969e5cf345bec84b2c6455afc6a34

DispSync: Actually wait forever

When computeNextEventTimeLocked returns INT64_MAX (because there are
currently no listeners), wait until the condition variable is
signaled instead of waiting for a long timeout. Since the condition
variable timeout is specified using CLOCK_REALTIME behind the scenes,
we can receive false wakeups in the presence of large system clock
changes.

Bug: 28152577
Change-Id: I88dbab5d5d0776cb25dea76a4574db055b308fd1

services/surfaceflinger/DispSync.cpp

diff --git a/services/surfaceflinger/DispSync.cpp b/services/surfaceflinger/DispSync.cpp
index 4cf9370..37b6420 100644
--- a/services/surfaceflinger/DispSync.cpp
+++ b/services/surfaceflinger/DispSync.cpp
@@ -97,7 +97,6 @@
     virtual bool threadLoop() {
         status_t err;
         nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
-        nsecs_t nextEventTime = 0;
 
         while (true) {
             Vector<CallbackInvocation> callbackInvocations;
@@ -127,16 +126,21 @@
                     continue;
                 }
 
-                nextEventTime = computeNextEventTimeLocked(now);
-                targetTime = nextEventTime;
+                targetTime = computeNextEventTimeLocked(now);
 
                 bool isWakeup = false;
 
                 if (now < targetTime) {
-                    ALOGV("[%s] Waiting until %" PRId64, mName,
-                            ns2us(targetTime));
                     if (kTraceDetailedInfo) ATRACE_NAME("DispSync waiting");
-                    err = mCond.waitRelative(mMutex, targetTime - now);
+
+                    if (targetTime == INT64_MAX) {
+                        ALOGV("[%s] Waiting forever", mName);
+                        err = mCond.wait(mMutex);
+                    } else {
+                        ALOGV("[%s] Waiting until %" PRId64, mName,
+                                ns2us(targetTime));
+                        err = mCond.waitRelative(mMutex, targetTime - now);
+                    }
 
                     if (err == TIMED_OUT) {
                         isWakeup = true;