Fix crash with MIDI send for MidiManagerAlsa

media/midi/midi_manager.cc

 // Copyright (c) 2013 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.
 
 #include "media/midi/midi_manager.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 131 matching lines @@
   ReportUsage(Usage::SESSION_ENDED);
 
   // At this point, |client| can be in the destruction process, and calling
   // any method of |client| is dangerous.
   base::AutoLock auto_lock(lock_);
   clients_.erase(client);
   pending_clients_.erase(client);
 }
 
 void MidiManager::AccumulateMidiBytesSent(MidiManagerClient* client, size_t n) {
-  {
-    base::AutoLock auto_lock(lock_);
-    if (clients_.find(client) == clients_.end())
-      return;
-  }
+  base::AutoLock auto_lock(lock_);
+  if (clients_.find(client) == clients_.end())
+    return;
+
   client->AccumulateMidiBytesSent(n);

[Takashi Toyoshima, 2015/12/07 06:00:28]

Good catch.

Can you add a comment here?

We are likely to unlock any mutex before calling a callback as possible. Without
any comment, someone may be revert this fix unexpectedly to avoid a potential
deadlock.

 }
 
 void MidiManager::DispatchSendMidiData(MidiManagerClient* client,
                                        uint32 port_index,
                                        const std::vector<uint8>& data,
                                        double timestamp) {
   NOTREACHED();
 }
 
 void MidiManager::StartInitialization() {
@@ skipping 92 matching lines @@
   base::AutoLock auto_lock(lock_);
   finalized_ = true;
 
   // Detach all clients so that they do not call MidiManager methods any more.
   for (auto client : clients_)
     client->Detach();
 }
 
 }  // namespace midi
 }  // namespace media