From 996c02e7e2de9bcdbcc23fc3dae6bd8b73a9cd47 Mon Sep 17 00:00:00 2001
From: Justin Lebar <justin.lebar@gmail.com>
Date: Fri, 9 Mar 2012 17:21:01 -0500
Subject: [PATCH] Bug 731419 - Part 2: Discard image data immediately on tab
 close, DOM changes. r=bz

---
 content/base/src/nsDocument.cpp | 37 +++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/content/base/src/nsDocument.cpp b/content/base/src/nsDocument.cpp
index 9cbbd96a346c..ed5066747c2c 100644
--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -3247,6 +3247,14 @@ nsIDocument::TakeFrameRequestCallbacks(FrameRequestCallbackList& aCallbacks)
   mFrameRequestCallbacks.Clear();
 }
 
+PLDHashOperator RequestDiscardEnumerator(imgIRequest* aKey,
+                                         PRUint32 aData,
+                                         void* userArg)
+{
+  aKey->RequestDiscard();
+  return PL_DHASH_NEXT;
+}
+
 void
 nsDocument::DeleteShell()
 {
@@ -3255,6 +3263,11 @@ nsDocument::DeleteShell()
     RevokeAnimationFrameNotifications();
   }
 
+  // When our shell goes away, request that all our images be immediately
+  // discarded, so we don't carry around decoded image data for a document we
+  // no longer intend to paint.
+  mImageTracker.EnumerateRead(RequestDiscardEnumerator, nsnull);
+
   mPresShell = nsnull;
 }
 
@@ -8309,26 +8322,32 @@ nsDocument::RemoveImage(imgIRequest* aImage)
 
   // If the count is now zero, remove from the tracker.
   // Otherwise, set the new value.
-  if (count == 0) {
-    mImageTracker.Remove(aImage);
-  } else {
+  if (count != 0) {
     mImageTracker.Put(aImage, count);
+    return NS_OK;
   }
 
+  mImageTracker.Remove(aImage);
+
   nsresult rv = NS_OK;
 
-  // If we removed the image from the tracker and we're locking images, unlock
-  // this image.
-  if (count == 0 && mLockingImages)
+  // Now that we're no longer tracking this image, unlock it if we'd
+  // previously locked it.
+  if (mLockingImages) {
     rv = aImage->UnlockImage();
+  }
 
-  // If we removed the image from the tracker and we're animating images,
-  // remove our request to animate this image.
-  if (count == 0 && mAnimatingImages) {
+  // If we're animating images, remove our request to animate this one.
+  if (mAnimatingImages) {
     nsresult rv2 = aImage->DecrementAnimationConsumers();
     rv = NS_SUCCEEDED(rv) ? rv2 : rv;
   }
 
+  // Request that the image be discarded if nobody else holds a lock on it.
+  // Do this even if !mLockingImages, because even if we didn't just unlock
+  // this image, it might still be a candidate for discarding.
+  aImage->RequestDiscard();
+
   return rv;
 }