From c0b92e301ea3878faaa1bc6cc7de8d75e39333a7 Mon Sep 17 00:00:00 2001
From: Jonathan Kew <jfkthame@gmail.com>
Date: Fri, 13 Jan 2012 11:37:46 +0000
Subject: [PATCH] bug 708075 - observe memory-pressure notification and discard
 cached gfxShapedWord records. r=roc

---
 gfx/thebes/gfxFont.cpp | 49 ++++++++++++++++++++++++++++++++++++++++++
 gfx/thebes/gfxFont.h   | 12 +++++++++++
 2 files changed, 61 insertions(+)

diff --git a/gfx/thebes/gfxFont.cpp b/gfx/thebes/gfxFont.cpp
index dedb16fae04..ad11bce8c30 100644
--- a/gfx/thebes/gfxFont.cpp
+++ b/gfx/thebes/gfxFont.cpp
@@ -69,6 +69,7 @@
 #include "nsCompressedCharMap.h"
 #include "nsStyleConsts.h"
 #include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
 
 #include "cairo.h"
 #include "gfxFontTest.h"
@@ -81,6 +82,7 @@
 
 using namespace mozilla;
 using namespace mozilla::gfx;
+using mozilla::services::GetObserverService;
 
 gfxFontCache *gfxFontCache::gGlobalCache = nsnull;
 
@@ -954,6 +956,39 @@ gfxFontFamily::FindFont(const nsAString& aPostscriptName)
     return nsnull;
 }
 
+/*
+ * gfxFontCache - global cache of gfxFont instances.
+ * Expires unused fonts after a short interval;
+ * notifies fonts to age their cached shaped-word records;
+ * observes memory-pressure notification and tells fonts to clear their
+ * shaped-word caches to free up memory.
+ */
+
+// Observer for the memory-pressure notification, to trigger
+// flushing of the shaped-word caches
+class MemoryPressureObserver : public nsIObserver,
+                               public nsSupportsWeakReference
+{
+public:
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIOBSERVER
+};
+
+NS_IMPL_ISUPPORTS2(MemoryPressureObserver, nsIObserver, nsISupportsWeakReference)
+
+NS_IMETHODIMP
+MemoryPressureObserver::Observe(nsISupports *aSubject,
+                                const char *aTopic,
+                                const PRUnichar *someData)
+{
+    if (!nsCRT::strcmp(aTopic, "memory-pressure")) {
+        gfxFontCache *fontCache = gfxFontCache::GetCache();
+        if (fontCache) {
+            fontCache->FlushShapedWordCaches();
+        }
+    }
+    return NS_OK;
+}
 
 nsresult
 gfxFontCache::Init()
@@ -986,6 +1021,12 @@ gfxFontCache::gfxFontCache()
     : nsExpirationTracker<gfxFont,3>(FONT_TIMEOUT_SECONDS * 1000)
 {
     mFonts.Init();
+
+    nsCOMPtr<nsIObserverService> obs = GetObserverService();
+    if (obs) {
+        obs->AddObserver(new MemoryPressureObserver, "memory-pressure", false);
+    }
+
     mWordCacheExpirationTimer = do_CreateInstance("@mozilla.org/timer;1");
     if (mWordCacheExpirationTimer) {
         mWordCacheExpirationTimer->
@@ -1102,6 +1143,14 @@ gfxFontCache::WordCacheExpirationTimerCallback(nsITimer* aTimer, void* aCache)
     cache->mFonts.EnumerateEntries(AgeCachedWordsForFont, nsnull);
 }
 
+/*static*/
+PLDHashOperator
+gfxFontCache::ClearCachedWordsForFont(HashEntry* aHashEntry, void* aUserData)
+{
+    aHashEntry->mFont->ClearCachedWords();
+    return PL_DHASH_NEXT;
+}
+
 void
 gfxFont::RunMetrics::CombineWith(const RunMetrics& aOther, bool aOtherIsOnLeft)
 {
diff --git a/gfx/thebes/gfxFont.h b/gfx/thebes/gfxFont.h
index 65139b69ba4..a3fe6bd3d44 100644
--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@@ -732,6 +732,10 @@ public:
         AgeAllGenerations();
     }
 
+    void FlushShapedWordCaches() {
+        mFonts.EnumerateEntries(ClearCachedWordsForFont, nsnull);
+    }
+
 protected:
     void DestroyFont(gfxFont *aFont);
 
@@ -767,6 +771,7 @@ protected:
 
     nsTHashtable<HashEntry> mFonts;
 
+    static PLDHashOperator ClearCachedWordsForFont(HashEntry* aHashEntry, void*);
     static PLDHashOperator AgeCachedWordsForFont(HashEntry* aHashEntry, void*);
     static void WordCacheExpirationTimerCallback(nsITimer* aTimer, void* aCache);
     nsCOMPtr<nsITimer>      mWordCacheExpirationTimer;
@@ -1405,6 +1410,13 @@ public:
         }
     }
 
+    // Discard all cached word records; called on memory-pressure notification.
+    void ClearCachedWords() {
+        if (mWordCache.IsInitialized()) {
+            mWordCache.Clear();
+        }
+    }
+
 protected:
     // Call the appropriate shaper to generate glyphs for aText and store
     // them into aShapedWord.