From 6fc9eaab4accdf77989dd3ba775c7083b5d2b16f Mon Sep 17 00:00:00 2001
From: David Anderson <danderson@mozilla.com>
Date: Wed, 2 Aug 2017 11:37:31 -0700
Subject: [PATCH] Don't flush async paints on the main thread. (bug 1386517,
 r=mattwoodrow)

---
 gfx/layers/client/TextureClient.cpp | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/gfx/layers/client/TextureClient.cpp b/gfx/layers/client/TextureClient.cpp
index 0abee6bdfc20..9990cddfc7ef 100644
--- a/gfx/layers/client/TextureClient.cpp
+++ b/gfx/layers/client/TextureClient.cpp
@@ -543,22 +543,23 @@ TextureClient::Unlock()
   }
 
   if (mBorrowedDrawTarget) {
-    if (mOpenMode & OpenMode::OPEN_WRITE) {
-      mBorrowedDrawTarget->Flush();
-      if (mReadbackSink && !mData->ReadBack(mReadbackSink)) {
-        // Fallback implementation for reading back, because mData does not
-        // have a backend-specific implementation and returned false.
-        RefPtr<SourceSurface> snapshot = mBorrowedDrawTarget->Snapshot();
-        RefPtr<DataSourceSurface> dataSurf = snapshot->GetDataSurface();
-        mReadbackSink->ProcessReadback(dataSurf);
+    if (!(mOpenMode & OpenMode::OPEN_ASYNC_WRITE)) {
+      if (mOpenMode & OpenMode::OPEN_WRITE) {
+        mBorrowedDrawTarget->Flush();
+        if (mReadbackSink && !mData->ReadBack(mReadbackSink)) {
+          // Fallback implementation for reading back, because mData does not
+          // have a backend-specific implementation and returned false.
+          RefPtr<SourceSurface> snapshot = mBorrowedDrawTarget->Snapshot();
+          RefPtr<DataSourceSurface> dataSurf = snapshot->GetDataSurface();
+          mReadbackSink->ProcessReadback(dataSurf);
+        }
       }
-    }
 
-    mBorrowedDrawTarget->DetachAllSnapshots();
-    // If this assertion is hit, it means something is holding a strong reference
-    // to our DrawTarget externally, which is not allowed.
-    MOZ_ASSERT_IF(!(mOpenMode & OpenMode::OPEN_ASYNC_WRITE),
-                  mBorrowedDrawTarget->refCount() <= mExpectedDtRefs);
+      mBorrowedDrawTarget->DetachAllSnapshots();
+      // If this assertion is hit, it means something is holding a strong reference
+      // to our DrawTarget externally, which is not allowed.
+      MOZ_ASSERT(mBorrowedDrawTarget->refCount() <= mExpectedDtRefs);
+    }
 
     mBorrowedDrawTarget = nullptr;
   }