From 453116079c5b8417f4ee4eb5ba8b924ad74c1655 Mon Sep 17 00:00:00 2001
From: Joe Drew <joe@drew.ca>
Date: Wed, 26 Sep 2012 11:33:06 -0400
Subject: [PATCH] Bug 786444 - Part 2 - Make imgFrame's lock status a count,
 not a boolean, so you can lock it multiple times and still be correct.
 r=jlebar

Also add a bunch of NS_ABORT_IF_FALSEs that verify that the lock status is
always valid.

--HG--
extra : rebase_source : 70cce5ed671586529e7d698e4bcdc86f5c748aa5
---
 image/src/imgFrame.cpp | 48 ++++++++++++++++++++++++++++++------------
 image/src/imgFrame.h   |  5 +++--
 2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/image/src/imgFrame.cpp b/image/src/imgFrame.cpp
index bf7146a1f937..9fab64a1e9cd 100644
--- a/image/src/imgFrame.cpp
+++ b/image/src/imgFrame.cpp
@@ -109,6 +109,7 @@ imgFrame::imgFrame() :
   mSinglePixelColor(0),
   mTimeout(100),
   mDisposalMethod(0), /* imgIContainer::kDisposeNotSpecified */
+  mLockCount(0),
   mBlendMethod(1), /* imgIContainer::kBlendOver */
   mSinglePixel(false),
   mNeverUseDeviceSurface(false),
@@ -118,7 +119,6 @@ imgFrame::imgFrame() :
 #ifdef USE_WIN_SURFACE
   mIsDDBSurface(false),
 #endif
-  mLocked(false),
   mInformedDiscardTracker(false)
 {
   static bool hasCheckedOptimize = false;
@@ -578,6 +578,8 @@ uint32_t imgFrame::GetImageDataLength() const
 
 void imgFrame::GetImageData(uint8_t **aData, uint32_t *length) const
 {
+  NS_ABORT_IF_FALSE(mLockCount != 0, "Can't GetImageData unless frame is locked");
+
   if (mImageSurface)
     *aData = mImageSurface->Data();
   else if (mPalettedImageData)
@@ -600,6 +602,8 @@ bool imgFrame::GetHasAlpha() const
 
 void imgFrame::GetPaletteData(uint32_t **aPalette, uint32_t *length) const
 {
+  NS_ABORT_IF_FALSE(mLockCount != 0, "Can't GetPaletteData unless frame is locked");
+
   if (!mPalettedImageData) {
     *aPalette = nullptr;
     *length = 0;
@@ -611,14 +615,21 @@ void imgFrame::GetPaletteData(uint32_t **aPalette, uint32_t *length) const
 
 nsresult imgFrame::LockImageData()
 {
-  if (mPalettedImageData)
-    return NS_ERROR_NOT_AVAILABLE;
-
-  NS_ABORT_IF_FALSE(!mLocked, "Trying to lock already locked image data.");
-  if (mLocked) {
+  NS_ABORT_IF_FALSE(mLockCount >= 0, "Unbalanced locks and unlocks");
+  if (mLockCount < 0) {
     return NS_ERROR_FAILURE;
   }
-  mLocked = true;
+
+  mLockCount++;
+
+  // If we are not the first lock, there's nothing to do.
+  if (mLockCount != 1) {
+    return NS_OK;
+  }
+
+  // Paletted images don't have surfaces, so there's nothing to do.
+  if (mPalettedImageData)
+    return NS_OK;
 
   if ((mOptSurface || mSinglePixel) && !mImageSurface) {
     // Recover the pixels
@@ -659,15 +670,26 @@ nsresult imgFrame::LockImageData()
 
 nsresult imgFrame::UnlockImageData()
 {
-  if (mPalettedImageData)
-    return NS_ERROR_NOT_AVAILABLE;
-
-  NS_ABORT_IF_FALSE(mLocked, "Unlocking an unlocked image!");
-  if (!mLocked) {
+  NS_ABORT_IF_FALSE(mLockCount != 0, "Unlocking an unlocked image!");
+  if (mLockCount == 0) {
     return NS_ERROR_FAILURE;
   }
 
-  mLocked = false;
+  mLockCount--;
+
+  NS_ABORT_IF_FALSE(mLockCount >= 0, "Unbalanced locks and unlocks");
+  if (mLockCount < 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // If we are not the last lock, there's nothing to do.
+  if (mLockCount != 0) {
+    return NS_OK;
+  }
+
+  // Paletted images don't have surfaces, so there's nothing to do.
+  if (mPalettedImageData)
+    return NS_OK;
 
   // Assume we've been written to.
   if (mImageSurface)
diff --git a/image/src/imgFrame.h b/image/src/imgFrame.h
index b6d434239cb9..afad17059513 100644
--- a/image/src/imgFrame.h
+++ b/image/src/imgFrame.h
@@ -157,6 +157,9 @@ private: // data
   int32_t      mTimeout; // -1 means display forever
   int32_t      mDisposalMethod;
 
+  /** Indicates how many readers currently have locked this frame */
+  int32_t mLockCount;
+
   gfxASurface::gfxImageFormat mFormat;
   uint8_t      mPaletteDepth;
   int8_t       mBlendMethod;
@@ -165,8 +168,6 @@ private: // data
   bool mFormatChanged;
   bool mCompositingFailed;
   bool mNonPremult;
-  /** Indicates if the image data is currently locked */
-  bool mLocked;
 
   /** Have we called DiscardTracker::InformAllocation()? */
   bool mInformedDiscardTracker;