Modify the code to avoid potential deadlocks.
If the signal to dump a thread is never delivered, then it's
possible for a deadlock. The signal handler is responsible for
unlocking and deleting the ThreadEntry created for the pid/tid
combination. This means if the signal is lost, the ThreadEntry
gets stuck locked and never deleted. If a second attempt to get
a backtrace of this thread occurs, there is a deadlock.
Also, decrease the timeout from 10 seconds to 5 seconds. The original
10 seconds was because the unwind was actually done in the signal
handler. Now the signal handler does nothing but copy the ucontext
structure and let the caller do the unwind.
Bug: 21086132
(cherry picked from commit 2d09171758b7d98c77f27e439a4caf35dd84c311)
Change-Id: I414c500eb08983a5017caf3fce4f499465575a9d
diff --git a/libbacktrace/ThreadEntry.cpp b/libbacktrace/ThreadEntry.cpp
index e8b60c8..084c1aa 100644
--- a/libbacktrace/ThreadEntry.cpp
+++ b/libbacktrace/ThreadEntry.cpp
@@ -69,7 +69,7 @@
}
void ThreadEntry::Remove(ThreadEntry* entry) {
- pthread_mutex_unlock(&entry->mutex_);
+ entry->Unlock();
pthread_mutex_lock(&ThreadEntry::list_mutex_);
if (--entry->ref_count_ == 0) {
@@ -96,20 +96,24 @@
pthread_cond_destroy(&wait_cond_);
}
-void ThreadEntry::Wait(int value) {
+bool ThreadEntry::Wait(int value) {
timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
- ts.tv_sec += 10;
+ ts.tv_sec += 5;
+ bool wait_completed = true;
pthread_mutex_lock(&wait_mutex_);
while (wait_value_ != value) {
int ret = pthread_cond_timedwait(&wait_cond_, &wait_mutex_, &ts);
if (ret != 0) {
- BACK_LOGW("pthread_cond_timedwait failed: %s", strerror(ret));
+ BACK_LOGW("pthread_cond_timedwait for value %d failed: %s", value, strerror(ret));
+ wait_completed = false;
break;
}
}
pthread_mutex_unlock(&wait_mutex_);
+
+ return wait_completed;
}
void ThreadEntry::Wake() {