Bug 1070340 (Part 1) - Add ShutdownTracker to imagelib. r=tn

image/build/nsImageModule.cpp

@@ -11,6 +11,7 @@
 
 #include "ImageFactory.h"
 #include "RasterImage.h"
+#include "ShutdownTracker.h"
 #include "SurfaceCache.h"
 
 #include "imgLoader.h"
@@ -85,6 +86,7 @@ static bool sInitialized = false;
 nsresult
 mozilla::image::InitModule()
 {
+  mozilla::image::ShutdownTracker::Initialize();
   mozilla::image::DiscardTracker::Initialize();
   mozilla::image::ImageFactory::Initialize();
   mozilla::image::RasterImage::Initialize();

image/src/ShutdownTracker.cpp

@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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 "ShutdownTracker.h"
+
+#include "mozilla/Services.h"
+#include "nsAutoPtr.h"
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+
+namespace mozilla {
+namespace image {
+
+class ShutdownTrackerImpl;
+
+///////////////////////////////////////////////////////////////////////////////
+// Static Data
+///////////////////////////////////////////////////////////////////////////////
+
+// Whether we've observed shutdown starting yet.
+static bool sShutdownHasStarted = false;
+
+
+///////////////////////////////////////////////////////////////////////////////
+// Implementation
+///////////////////////////////////////////////////////////////////////////////
+
+struct ShutdownObserver : public nsIObserver
+{
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD Observe(nsISupports*, const char* aTopic, const char16_t*)
+  {
+    if (strcmp(aTopic, "xpcom-shutdown") != 0) {
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+    if (os) {
+      os->RemoveObserver(this, "xpcom-shutdown");
+    }
+
+    sShutdownHasStarted = true;
+    return NS_OK;
+  }
+
+private:
+  virtual ~ShutdownObserver() { }
+};
+
+NS_IMPL_ISUPPORTS(ShutdownObserver, nsIObserver)
+
+
+///////////////////////////////////////////////////////////////////////////////
+// Public API
+///////////////////////////////////////////////////////////////////////////////
+
+/* static */ void
+ShutdownTracker::Initialize()
+{
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+  if (os) {
+    os->AddObserver(new ShutdownObserver, "xpcom-shutdown", false);
+  }
+}
+
+/* static */ bool
+ShutdownTracker::ShutdownHasStarted()
+{
+  return sShutdownHasStarted;
+}
+
+} // namespace image
+} // namespace mozilla

image/src/ShutdownTracker.h

@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+/**
+ * ShutdownTracker is an imagelib-global service that allows callers to check
+ * whether shutdown has started.
+ */
+
+#ifndef MOZILLA_IMAGELIB_SHUTDOWNTRACKER_H_
+#define MOZILLA_IMAGELIB_SHUTDOWNTRACKER_H_
+
+namespace mozilla {
+namespace image {
+
+/**
+ * ShutdownTracker is an imagelib-global service that allows callers to check
+ * whether shutdown has started. It exists to avoid the need for registering many
+ * 'xpcom-shutdown' notification observers on short-lived objects, which would
+ * have an unnecessary performance cost.
+ */
+struct ShutdownTracker
+{
+  /**
+   * Initialize static data. Called during imagelib module initialization.
+   */
+  static void Initialize();
+
+  /**
+   * Check whether shutdown has started. Callers can use this to check whether
+   * it's safe to access XPCOM services; if shutdown has started, such calls
+   * must be avoided.
+   *
+   * @return true if shutdown has already started.
+   */
+  static bool ShutdownHasStarted();
+
+private:
+  virtual ~ShutdownTracker() = 0;  // Forbid instantiation.
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // MOZILLA_IMAGELIB_SHUTDOWNTRACKER_H_

image/src/moz.build

@@ -32,6 +32,7 @@ UNIFIED_SOURCES += [
     'imgTools.cpp',
     'OrientedImage.cpp',
     'ScriptedNotificationObserver.cpp',
+    'ShutdownTracker.cpp',
     'SurfaceCache.cpp',
     'SVGDocumentWrapper.cpp',
     'VectorImage.cpp',