Make image_decoder a Leaky LazyInstance

chrome/browser/image_decoder.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_IMAGE_DECODER_H_
 #define CHROME_BROWSER_IMAGE_DECODER_H_
 
+#include <map>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/lazy_instance.h"
 #include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
 #include "base/threading/sequenced_worker_pool.h"
+#include "base/timer/timer.h"
+#include "content/public/browser/utility_process_host.h"
 #include "content/public/browser/utility_process_host_client.h"
 
 class SkBitmap;
 
-// Decodes an image in a sandboxed process.
+// This is a helper class for decoding images safely in a utility process. To
+// use this, call ImageDecoder::Start(...) or
+// ImageDecoder::StartWithOptions(...) on any thread.
+//
+// Internally, most of the work happens on the IO thread, and then
+// the callback (ImageRequest::OnImageDecoded or
+// ImageRequest::OnDecodeImageFailed) is posted back to the |task_runner_|
+// associated with the ImageRequest.
+// The Cancel() method does not run on the IO thread. |map_lock_| is used to

[Lei Zhang, 2015/03/25 23:28:38]

Can you document what thread Cancel() runs on?

[Theresa, 2015/03/25 23:54:09]

Done.

+// protect the data that is accessed from multiple threads.
 class ImageDecoder : public content::UtilityProcessHostClient {
  public:
-  class Delegate {
+  class ImageRequest {
    public:
     // Called when image is decoded.
-    // |decoder| is used to identify the image in case of decoding several
-    // images simultaneously.
-    virtual void OnImageDecoded(const ImageDecoder* decoder,
-                                const SkBitmap& decoded_image) = 0;
+    virtual void OnImageDecoded(const SkBitmap& decoded_image) = 0;
 
-    // Called when decoding image failed. Delegate can do some cleanup in
+    // Called when decoding image failed. ImageRequest can do some cleanup in
     // this handler.
-    virtual void OnDecodeImageFailed(const ImageDecoder* decoder) {}
+    virtual void OnDecodeImageFailed() {}
+
+    base::SequencedTaskRunner* task_runner() const {
+      return task_runner_.get();
+    }
 
    protected:
-    virtual ~Delegate() {}
+    explicit ImageRequest(
+        const scoped_refptr<base::SequencedTaskRunner>& task_runner);
+    virtual ~ImageRequest();
+
+   private:
+    // The thread to post OnImageDecoded or OnDecodeImageFailed once the
+    // the image has been decoded.
+    const scoped_refptr<base::SequencedTaskRunner> task_runner_;
   };
 
   enum ImageCodec {
     DEFAULT_CODEC = 0,  // Uses WebKit image decoding (via WebImage).
     ROBUST_JPEG_CODEC,  // Restrict decoding to robust jpeg codec.
   };
 
-  ImageDecoder(Delegate* delegate,
-               const std::string& image_data,
-               ImageCodec image_codec);
-
-  ImageDecoder(Delegate* delegate,
-               const std::vector<char>& image_data,
-               ImageCodec image_codec);
+  // Calls StartWithOptions with ImageCodec::DEFAULT_CODEC and
+  // shrink_to_fit = false.
+  static void Start(ImageRequest* image_request,
+                    const std::string& image_data);
 
   // Starts asynchronous image decoding. Once finished, the callback will be
-  // posted back to |task_runner|.
-  void Start(scoped_refptr<base::SequencedTaskRunner> task_runner);
+  // posted back to image_request's task_runner_.
+  static void StartWithOptions(ImageRequest* image_request,
+                               const std::string& image_data,
+                               ImageCodec image_codec,
+                               bool shrink_to_fit);
 
-  const std::vector<unsigned char>& get_image_data() const {
-    return image_data_;
-  }
-
-  void set_delegate(Delegate* delegate) { delegate_ = delegate; }
-  void set_shrink_to_fit(bool shrink_to_fit) { shrink_to_fit_ = shrink_to_fit; }
+  // Removes all instances of image_request from image_request_id_map_,
+  // ensuring callbacks are not made to the image_request after it is destroyed.
+  static void Cancel(ImageRequest* image_request);
 
  private:
+  friend struct base::DefaultLazyInstanceTraits<ImageDecoder>;
+
+  ImageDecoder();
   // It's a reference counted object, so destructor is private.
   ~ImageDecoder() override;
 
-  // Overidden from UtilityProcessHostClient:
+  // Sends a request to the sandboxed process to decode the image. Starts
+  // batch mode if necessary.
+  void DecodeImageInSandbox(ImageRequest* image_request,
+                            const std::vector<unsigned char>& image_data,
+                            ImageCodec image_codec,
+                            bool shrink_to_fit);
+
+  void CancelImpl(ImageRequest* image_request);
+
+  using RequestMap = std::map<int, ImageRequest*>;
+
+  // Starts UtilityProcessHost in batch mode and starts batch_mode_timer_.
+  void StartBatchMode();
+
+  // Stops batch mode if no requests have come in since kBatchModeTimeout.
+  void StopBatchMode();
+
+  // Overidden from UtilityProcessHostClient.
   bool OnMessageReceived(const IPC::Message& message) override;
 
   // IPC message handlers.
-  void OnDecodeImageSucceeded(const SkBitmap& decoded_image);
-  void OnDecodeImageFailed();
+  void OnDecodeImageSucceeded(const SkBitmap& decoded_image, int request_id);
+  void OnDecodeImageFailed(int request_id);
 
-  // Launches sandboxed process that will decode the image.
-  void DecodeImageInSandbox(const std::vector<unsigned char>& image_data);
+  // id to use for the next Start request that comes in.
+  int image_request_id_counter_;
 
-  Delegate* delegate_;
-  std::vector<unsigned char> image_data_;
-  const ImageCodec image_codec_;
-  scoped_refptr<base::SequencedTaskRunner> task_runner_;
-  bool shrink_to_fit_; // if needed for IPC msg size limit
+  // Map of request id's to ImageRequests.
+  RequestMap image_request_id_map_;
+
+  // Protects image_request_id_map_ and image_request_id_counter_.
+  base::Lock map_lock_;
+
+  // The UtilityProcessHost requests are sent to.
+  base::WeakPtr<content::UtilityProcessHost> utility_process_host_;
+
+  // Calls StopBatchMode after kBatchModeTimeout has elapsed.
+  base::RepeatingTimer<ImageDecoder> batch_mode_timer_;
+
+  // The time Start was last called.
+  base::TimeTicks last_request_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
 };
 
 #endif  // CHROME_BROWSER_IMAGE_DECODER_H_