Web MIDI: fix multi-threading problem around message buffer handling

media/midi/midi_manager_mac.h

 // 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.
 
 #ifndef MEDIA_MIDI_MIDI_MANAGER_MAC_H_
 #define MEDIA_MIDI_MIDI_MANAGER_MAC_H_
 
 #include <CoreMIDI/MIDIServices.h>
 #include <map>
 #include <string>
+#include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "media/midi/midi_manager.h"
 #include "media/midi/midi_port_info.h"
 
 namespace media {
 
 class MEDIA_EXPORT MIDIManagerMac : public MIDIManager {
  public:
   MIDIManagerMac();
   virtual ~MIDIManagerMac();
 
   // MIDIManager implementation.
   virtual bool Initialize() OVERRIDE;
   virtual void SendMIDIData(MIDIManagerClient* client,
-                            int port_index,
-                            const uint8* data,
-                            size_t length,
+                            unsigned int port_index,

[scherkus (not reviewing), 2013/08/21 17:46:29]

nit: while unsigned is prevalent in blink, this should be size_t

[Takashi Toyoshima, 2013/08/22 05:47:45]

Done.

[palmer, 2013/08/22 18:25:41]

There is a fun thing here. It can often make sense, as a space optimization, to
implement a size_t interface with an unsigned int type that is not as wide as a
size_t. E.g., on a 64-bit machine:

// We create tons of these, and they don't
// need to have more than 2 ** 32 - 1 bytes,
// so save 4 bytes by using uint32_t. (On
// 64-bit, size_t would be 8 bytes.) Plus,
// very short strings, which are common,
// now fit into a single 64-bit word! Yay.
//
// sizeof(String) will be 8 on most systems.
typedef struct String {
    uint32_t count;
    uint8_t bytes[1];
} String;

// Although we have taken a short-cut in the
// implementation, expose the correct interface
// in case we need to go big someday.
String* newString(uint8_t* bytes, size_t count) {
    // Check that we are not caught in our lie!
    // We do this to be safe, even while
    // presenting a not-quite-true but future-proof
    // interface.
    assert(count < UINT32_T_MAX);

    // ...
}

That general idea is behind a lot of Blink/WebKit code. You could argue that the
interfaces should exactly match their implementations --- newString(uint8_t*
bytes, uint32_t count) --- but then you'd be making all the callers do the
safety checks (callers are likely to use size_t, as they should), and the
interface would not be able to transparently grow someday in the future.

+                            const std::vector<uint8>& data,
                             double timestamp) OVERRIDE;
 
  private:
   // CoreMIDI callback for MIDI data.
   // Each callback can contain multiple packets, each of which can contain
   // multiple MIDI messages.
   static void ReadMidiDispatch(
       const MIDIPacketList *pktlist,
       void *read_proc_refcon,
       void *src_conn_refcon);
@@ skipping 21 matching lines @@
 
   // Keeps track of all destinations.
   std::vector<MIDIEndpointRef> destinations_;
 
   DISALLOW_COPY_AND_ASSIGN(MIDIManagerMac);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_MIDI_MIDI_MANAGER_MAC_H_