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 buffer
hasn't been freed due to an error.
It seems that the patch may also resolve JDK-8250667. The extra bytes in the
second sysex message is the same issue as JDK-8074211. I didn't figure out how
the scrambled data generated in the third sysex message, but all the messages
are correct after applying the patch.
-------------
Commit messages:
- Resolve the message size issue when sending SysexMessage on Windows
Changes: https://git.openjdk.org/jdk/pull/16399/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16399&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8074211
Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
Patch: https://git.openjdk.org/jdk/pull/16399.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/16399/head:pull/16399
PR: https://git.openjdk.org/jdk/pull/16399
