Bug 823610: Make discarding GL contexts of foreground pages on memory pressure pref-able, and pref off for b2g. r=jgilbert,jlebar

b2g/app/b2g.js

@@ -615,3 +615,7 @@ pref("wap.UAProf.tagname", "x-wap-profile");
 
 // Wait up to this much milliseconds when orientation changed
 pref("layers.orientation.sync.timeout", 1000);
+
+// Don't discard WebGL contexts for foreground apps on memory
+// pressure.
+pref("webgl.can-lose-context-in-foreground", false);

content/canvas/src/WebGLContext.cpp

@@ -45,12 +45,14 @@
 #include "mozilla/Services.h"
 #include "mozilla/dom/WebGLRenderingContextBinding.h"
 #include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/ipc/ProcessPriorityManager.h"
 
 #include "Layers.h"
 
 using namespace mozilla;
 using namespace mozilla::gl;
 using namespace mozilla::dom;
+using namespace mozilla::dom::ipc;
 using namespace mozilla::layers;
 
 NS_IMETHODIMP
@@ -63,7 +65,10 @@ WebGLMemoryPressureObserver::Observe(nsISupports* aSubject,
 
     bool wantToLoseContext = true;
 
-    if (!nsCRT::strcmp(aSomeData, NS_LITERAL_STRING("heap-minimize").get()))
+    if (!mContext->mCanLoseContextInForeground && CurrentProcessIsForeground())
+        wantToLoseContext = false;
+    else if (!nsCRT::strcmp(aSomeData,
+                            NS_LITERAL_STRING("heap-minimize").get()))
         wantToLoseContext = mContext->mLoseContextOnHeapMinimize;
 
     if (wantToLoseContext)
@@ -179,6 +184,7 @@ WebGLContext::WebGLContext()
     mContextStatus = ContextStable;
     mContextLostErrorSet = false;
     mLoseContextOnHeapMinimize = false;
+    mCanLoseContextInForeground = true;
 
     mAlreadyGeneratedWarnings = 0;
     mAlreadyWarnedAboutFakeVertexAttrib0 = false;

content/canvas/src/WebGLContext.h

@@ -843,6 +843,7 @@ protected:
     bool mHasRobustness;
     bool mIsMesa;
     bool mLoseContextOnHeapMinimize;
+    bool mCanLoseContextInForeground;
 
     template<typename WebGLObjectType>
     void DeleteWebGLObjectsArray(nsTArray<WebGLObjectType>& array);

content/canvas/src/WebGLContextValidate.cpp

@@ -858,6 +858,7 @@ WebGLContext::InitAndValidateGL()
     mMinCapability = Preferences::GetBool("webgl.min_capability_mode", false);
     mDisableExtensions = Preferences::GetBool("webgl.disable-extensions", false);
     mLoseContextOnHeapMinimize = Preferences::GetBool("webgl.lose-context-on-heap-minimize", false);
+    mCanLoseContextInForeground = Preferences::GetBool("webgl.can-lose-context-in-foreground", true);
 
     mActiveTexture = 0;
     mWebGLError = LOCAL_GL_NO_ERROR;

dom/ipc/ProcessPriorityManager.cpp

@@ -4,6 +4,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "mozilla/ClearOnShutdown.h"
 #include "mozilla/dom/ipc/ProcessPriorityManager.h"
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/dom/TabChild.h"
@@ -26,6 +27,7 @@
 #include "nsIDOMEventTarget.h"
 #include "nsIDOMDocument.h"
 #include "nsPIDOMWindow.h"
+#include "StaticPtr.h"
 
 #ifdef XP_WIN
 #include <process.h>
@@ -42,6 +44,8 @@ namespace ipc {
 
 namespace {
 static bool sInitialized = false;
+class ProcessPriorityManager;
+static StaticRefPtr<ProcessPriorityManager> sManager;
 
 // Some header defines a LOG macro, but we don't want it here.
 #ifdef LOG
@@ -127,6 +131,8 @@ public:
   NS_DECL_NSIOBSERVER
   NS_DECL_NSIDOMEVENTLISTENER
 
+  ProcessPriority GetPriority() const { return mProcessPriority; }
+
 private:
   void SetPriority(ProcessPriority aPriority);
   void OnContentDocumentGlobalCreated(nsISupports* aOuterWindow);
@@ -389,9 +395,15 @@ InitProcessPriorityManager()
     return;
   }
 
-  // This object is held alive by the observer service.
-  nsRefPtr<ProcessPriorityManager> mgr = new ProcessPriorityManager();
-  mgr->Init();
+  sManager = new ProcessPriorityManager();
+  sManager->Init();
+  ClearOnShutdown(&sManager);
+}
+
+bool
+CurrentProcessIsForeground()
+{
+  return sManager->GetPriority() >= PROCESS_PRIORITY_FOREGROUND;
 }
 
 } // namespace ipc

dom/ipc/ProcessPriorityManager.h

@@ -26,6 +26,13 @@ namespace ipc {
  */
 void InitProcessPriorityManager();
 
+/**
+ * True iff the current process has foreground or higher priority as
+ * computed by DOM visibility.  The returned answer may not match the
+ * actual OS process priority, for short intervals.
+ */
+bool CurrentProcessIsForeground();
+
 } // namespace ipc
 } // namespace dom
 } // namespace mozilla

hal/HalTypes.h

@@ -70,6 +70,9 @@ typedef Observer<SwitchEvent> SwitchObserver;
 enum ProcessPriority {
   PROCESS_PRIORITY_BACKGROUND,
   PROCESS_PRIORITY_BACKGROUND_HOMESCREEN,
+  // Any priority greater than or equal to FOREGROUND is considered
+  // "foreground" for the purposes of priority testing, for example
+  // CurrentProcessIsForeground().
   PROCESS_PRIORITY_FOREGROUND,
   PROCESS_PRIORITY_MASTER,
   NUM_PROCESS_PRIORITY

modules/libpref/src/init/all.js

@@ -3706,6 +3706,7 @@ pref("webgl.prefer-16bpp", false);
 pref("webgl.default-no-alpha", false);
 pref("webgl.force-layers-readback", false);
 pref("webgl.lose-context-on-heap-minimize", false);
+pref("webgl.can-lose-context-in-foreground", true);
 
 // Stagefright prefs
 pref("stagefright.force-enabled", false);