RFR: 8074211: javax.sound.midi: Error with send System Exclusive messages of different length [v3]

[Phil Race]

On Sun, 29 Oct 2023 14:29:45 GMT, Alec Su <duke at openjdk.org> wrote:

>> JVM attempts to reuse the buffer for sending MIDI out data when the buffer size is enough. It use `dwBytesRecorded` in `MIDIHDR` structure to indicate the actual size of the data. However, `midiOutLongMsg()` ignores `dwBytesRecorded`, although it did not mentioned in the documentation. I've tested on Windows 7, 10 and 11. All of them have the same behavior.
>> 
>> The bug cannot be easily reproduced because some MIDI drivers filter out any malformed MIDI data. The example code below create a special case to make sure all MIDI data are legally when the bug is triggered.
>> 
>> 
>> import javax.sound.midi.*;
>> 
>> public class MidiTest {
>>     public static class RawMidiMessage extends MidiMessage {
>>         public RawMidiMessage(byte[] data) {
>>             super(data);
>>         }
>> 
>>         @Override
>>         public Object clone() {
>>             return new RawMidiMessage(this.getMessage());
>>         }
>>     }
>> 
>>     public static void main(String[] args) {
>>         var deviceInfos = MidiSystem.getMidiDeviceInfo();
>>         for (var info : deviceInfos) {
>>             try (MidiDevice device = MidiSystem.getMidiDevice(info)) {
>>                 if (device.getMaxReceivers() != 0) {
>>                     System.out.println("Open MIDI port: " + info.getName());
>>                     device.open();
>>                     Receiver receiver = device.getReceiver();
>>                     // Send two sysex messages at once
>>                     receiver.send(new RawMidiMessage(new byte[]{
>>                             (byte) 0xF0, 0x7D, 0x01, (byte) 0xF7,
>>                             (byte) 0xF0, 0x7D, 0x02, (byte) 0xF7
>>                         }), -1);
>>                     // Send another sysex message
>>                     receiver.send(new RawMidiMessage(new byte[]{(byte) 0xF0, 0x7D, 0x03, (byte) 0xF7}), -1);
>>                 }
>>             } catch (MidiUnavailableException e) {
>>                 e.printStackTrace();
>>             }
>>         }
>>     }
>> }
>> 
>> 
>> The expected messages received should be the following three messages
>> 
>> F0 7D 01 F7
>> F0 7D 02 F7
>> F0 7D 03 F7
>> 
>> 
>> But acually four messages was received with the second message repeated twice.
>> 
>> F0 7D 01 F7
>> F0 7D 02 F7
>> F0 7D 03 F7
>> F0 7D 02 F7
>> 
>> 
>> To resolve the issue, I add a new variable to backup the actual buffer size and set `dwBufferLength` of `MIDIHDR` structure to the size of MIDI data. After calling `midiOutLongMsg()`, I restore the original buffer size if the buf...
>
> Alec Su has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Code cleanup

test/jdk/javax/sound/midi/Devices/OutputBuffer.java line 33:

> 31:  *          is sent again with the next sysex message
> 32:  * @comment This test does not fail when the bug occurs. It requires manual
> 33:  *          monitoring of the output.

The fix seems reasonable. but this test comment is odd. I'm not sure I understand what you can mean by manual monitoring of the output. The test doesn't seem useful unless it can detect failure.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16399#discussion_r1383994508