TransactionCompletedListener: Mutex for getInstance

We have always needed this technically, since otherwise
calling getInstance from multiple threads could fail. It seems
before we were lucky enough to not actually do that, until
the situation in the attached bug arose.

Bug: 226882766
Test: Existing tests pass
Change-Id: I648f6fa48296599a0c0e0d00a07fb71d9330880d

1 files changed, 2 insertions, 0 deletions

diff --git a/libs/gui/SurfaceComposerClient.cpp b/libs/gui/SurfaceComposerClient.cpp
index 6c197c457c..88872f8610 100644
--- a/libs/gui/SurfaceComposerClient.cpp
+++ b/libs/gui/SurfaceComposerClient.cpp
@@ -206,12 +206,14 @@ int64_t TransactionCompletedListener::getNextIdLocked() {
 }
 
 sp<TransactionCompletedListener> TransactionCompletedListener::sInstance = nullptr;
+static std::mutex sListenerInstanceMutex;
 
 void TransactionCompletedListener::setInstance(const sp<TransactionCompletedListener>& listener) {
     sInstance = listener;
 }
 
 sp<TransactionCompletedListener> TransactionCompletedListener::getInstance() {
+    std::lock_guard<std::mutex> lock(sListenerInstanceMutex);
     if (sInstance == nullptr) {
         sInstance = new TransactionCompletedListener;
     }