From 7c2def154017148d1634b6ec2e283ea1b536bb29 Mon Sep 17 00:00:00 2001
From: Andrew Osmond <aosmond@mozilla.com>
Date: Tue, 19 Sep 2017 08:19:48 -0400
Subject: [PATCH] Bug 1380649 - Part 2. Ensure SourceSurfaceVolatileData does
 not forget its purged state. r=jrmuizel

Currently if SourceSurfaceVolatileData::Map fails due to being purged,
we expect that the surface will be discarded by the caller. This has not
consistently been the case, and as such, we should ensure we do not
forget if a buffer was previously purged when we reacquire it. Since we
do not at this time support repopulating an already allocated buffer
with new data, we cannot reset this state once it has been set.
---
 gfx/layers/SourceSurfaceVolatileData.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gfx/layers/SourceSurfaceVolatileData.h b/gfx/layers/SourceSurfaceVolatileData.h
index 7641733621a6..a97bf08ee73c 100644
--- a/gfx/layers/SourceSurfaceVolatileData.h
+++ b/gfx/layers/SourceSurfaceVolatileData.h
@@ -32,6 +32,7 @@ public:
     , mStride(0)
     , mMapCount(0)
     , mFormat(SurfaceFormat::UNKNOWN)
+    , mWasPurged(false)
   {
   }
 
@@ -66,10 +67,14 @@ public:
   bool Map(MapType, MappedSurface *aMappedSurface) override
   {
     MutexAutoLock lock(mMutex);
+    if (mWasPurged) {
+      return false;
+    }
     if (mMapCount == 0) {
       mVBufPtr = mVBuf;
     }
     if (mVBufPtr.WasBufferPurged()) {
+      mWasPurged = true;
       return false;
     }
     aMappedSurface->mData = mVBufPtr;
@@ -82,6 +87,7 @@ public:
   {
     MutexAutoLock lock(mMutex);
     MOZ_ASSERT(mMapCount > 0);
+    MOZ_ASSERT(!mWasPurged);
     if (--mMapCount == 0) {
       mVBufPtr = nullptr;
     }
@@ -100,6 +106,7 @@ private:
   RefPtr<VolatileBuffer> mVBuf;
   VolatileBufferPtr<uint8_t> mVBufPtr;
   SurfaceFormat mFormat;
+  bool mWasPurged;
 };
 
 } // namespace gfx