Implement "Key Presence" step in "Encrypted Block Encounted" algorithm in EME.

webkit/media/crypto/proxy_decryptor.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 WEBKIT_MEDIA_CRYPTO_PROXY_DECRYPTOR_H_
 #define WEBKIT_MEDIA_CRYPTO_PROXY_DECRYPTOR_H_
 
 #include <string>
+#include <vector>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "media/base/decryptor.h"
 
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace media {
 class DecryptorClient;
 }
 
 namespace WebKit {
 class WebFrame;
 class WebMediaPlayerClient;
 }
 
 namespace webkit_media {
@@ skipping 22 matching lines @@
   virtual void CancelKeyRequest(const std::string& key_system,
                                 const std::string& session_id) OVERRIDE;
   virtual void Decrypt(const scoped_refptr<media::DecoderBuffer>& encrypted,
                        const DecryptCB& decrypt_cb) OVERRIDE;
 
  private:
   scoped_ptr<media::Decryptor> CreatePpapiDecryptor(
       const std::string& key_system);
   scoped_ptr<media::Decryptor> CreateDecryptor(const std::string& key_system);
 
+  // Helper function that makes sure decryptor_->Decrypt() runs on the
+  // |message_loop|.
+  void DecryptOnMessageLoop(
+      const scoped_refptr<base::MessageLoopProxy>& message_loop_proxy,
+      const scoped_refptr<media::DecoderBuffer>& encrypted,
+      const media::Decryptor::DecryptCB& decrypt_cb);
+
+  // Callback used to pass into decryptor_->Decrypt().
+  void OnBufferDecrypted(
+      const scoped_refptr<base::MessageLoopProxy>& message_loop_proxy,
+      const scoped_refptr<media::DecoderBuffer>& encrypted,
+      const media::Decryptor::DecryptCB& decrypt_cb,
+      media::Decryptor::DecryptStatus status,
+      const scoped_refptr<media::DecoderBuffer>& decrypted);
+
   media::DecryptorClient* client_;
 
   // Needed to create the PpapiDecryptor.
   WebKit::WebMediaPlayerClient* web_media_player_client_;
   WebKit::WebFrame* web_frame_;
 
   // Protects the |decryptor_|. The Decryptor interface specifies that the
   // Decrypt() function will be called on the decoder thread and all other
   // methods on the renderer thread. The |decryptor_| itself is thread safe
   // when this rule is obeyed. This lock is solely to prevent the race condition
   // between setting the |decryptor_| in GenerateKeyRequest() and using it in
   // Decrypt().
-  base::Lock lock_;
+  base::Lock decryptor_lock_;
   scoped_ptr<media::Decryptor> decryptor_;  // Protected by the |lock_|.
 
+  // Protects the |pending_decrypt_closures_|.
+  base::Lock pending_decrypt_closures_lock_;

[scherkus (not reviewing), 2012/07/26 02:06:38]

do you need separate locks?

[xhwang, 2012/07/26 22:16:04]

I was trying to minimize the time of lock blocking. One lock will work for sure
and is actually simpler. Am I doing pre-mature optimization?

[scherkus (not reviewing), 2012/07/28 23:07:19]

Yes.

There are three situations where a lock is required:
  1) GKR()
  2) AddKey()
  3) Decrypt()

1 and 2 are one-off operations as opposed to 3 which is a more frequent
operation. I'm doubtful you'll ever see so much contention between these 3
operations that it necessitates an extra lock.

As you note having a single lock-per-object is also simpler and easier for
others to comprehend.

+  std::vector<base::Closure> pending_decrypt_closures_;
+
   DISALLOW_COPY_AND_ASSIGN(ProxyDecryptor);
 };
 
 }  // namespace webkit_media
 
 #endif  // WEBKIT_MEDIA_CRYPTO_PROXY_DECRYPTOR_H_