sf: avoid lock on main thread during luma calc

The luma calculation operation was previously done while holding
a lock that was also used to protect the request to collect the
next sample. When the main thread would request the next sample,
it could stall waiting on the longer luma calculation to complete.

This patch refactors the sampling request locking mechanisms so
sampling request signalling is protected by one lock, and the members
needed during the sampling thread operations are protected by another
lock.

Fixes: http://b/132110951
Test: collect traces during during problematic animation (agsa
initial query for info) and verify problem went away
Test: visually inspect jank during agsa continued conversation
Test: libgui#RegionSamplingTest
Test: monkey 6000 event inject
Change-Id: I291d6bcb80d0588f2e1f3689bfdd4b3434132e90

1 files changed, 11 insertions, 12 deletions

diff --git a/services/surfaceflinger/RegionSamplingThread.h b/services/surfaceflinger/RegionSamplingThread.h
index 72b20420ef..08134e6acd 100644
--- a/services/surfaceflinger/RegionSamplingThread.h
+++ b/services/surfaceflinger/RegionSamplingThread.h
@@ -100,7 +100,7 @@ private:
     void binderDied(const wp<IBinder>& who) override;
     void checkForStaleLuma();
 
-    void captureSample() REQUIRES(mMutex);
+    void captureSample();
     void threadMain();
 
     SurfaceFlinger& mFlinger;
@@ -110,19 +110,18 @@ private:
 
     std::unique_ptr<SamplingOffsetCallback> const mPhaseCallback;
 
-    std::mutex mThreadMutex;
-    std::thread mThread GUARDED_BY(mThreadMutex);
+    std::thread mThread;
 
-    std::mutex mMutex;
+    std::mutex mThreadControlMutex;
     std::condition_variable_any mCondition;
-    bool mRunning GUARDED_BY(mMutex) = true;
-    bool mSampleRequested GUARDED_BY(mMutex) = false;
-
-    std::unordered_map<wp<IBinder>, Descriptor, WpHash> mDescriptors GUARDED_BY(mMutex);
-    std::chrono::nanoseconds lastSampleTime GUARDED_BY(mMutex);
-    bool mDiscardedFrames GUARDED_BY(mMutex) = false;
-
-    sp<GraphicBuffer> mCachedBuffer GUARDED_BY(mMutex) = nullptr;
+    bool mRunning GUARDED_BY(mThreadControlMutex) = true;
+    bool mSampleRequested GUARDED_BY(mThreadControlMutex) = false;
+    bool mDiscardedFrames GUARDED_BY(mThreadControlMutex) = false;
+    std::chrono::nanoseconds lastSampleTime GUARDED_BY(mThreadControlMutex);
+
+    std::mutex mSamplingMutex;
+    std::unordered_map<wp<IBinder>, Descriptor, WpHash> mDescriptors GUARDED_BY(mSamplingMutex);
+    sp<GraphicBuffer> mCachedBuffer GUARDED_BY(mSamplingMutex) = nullptr;
 };
 
 } // namespace android