CoreMIDI MidiReceived Issue - macos

Question

I have a thread in my OSX app where I process midi messages stored in a packetList and send them using MIDIReceived(deviceEndpoint, packetList) to a virtual instrument;
As part of my program, I send 16 note-off messages at one time to tell the virtual instrument to stop playing all 16 notes.
There's something strange - if I enable the debug message NSLog(#"Num Packets %d", packetList->numPackets); the code works fine.
However, if I take NSLog(#"Num Packets %d", packetList->numPackets); away, some notes do not get turned off some times. It's almost as if some messages were skipped over because the thread runs too fast or something.
Could someone explain to me why this is happening? Thanks a lot.
- (void) processMIDIThread:(NSObject*)param {
#autoreleasepool {
MAIN:
for (;;) {
if([[NSThread currentThread] isCancelled]) {
NSLog(#"Thread has been cancelled");
goto END;
}
int pktToTrigger = 0;
if (midiMode==kKeyboardMode)
pktToTrigger = 1; // in case note off message is lost
else
pktToTrigger = 3;
// Queue processing starts here
if (packetList->numPackets >= pktToTrigger) {
NSLog(#"Num Packets %d", packetList->numPackets);
OSStatus res = MIDIReceived(deviceEndpoint, packetList);
if (res)
NSLog(#"Problem sending midi packets to virtual device");
// NSLog(#"Sent %d %d %d" ,(int)packetList->packet->data[0],(int)packetList->packet->data[1],(int)packetList->packet->data[2]);
[self clearPacketList];
}
}
}
END: [NSThread exit];
NSLog(#"Exited current thread.");
;
}
The add packet function
- (void) addPacketToPacketList:(Byte*) data ofLength:(int) len {
if (_midiDeviceMode==kMidiOut) {
//NSLog(#"length %d", len);
//NSLog(#"%lld", mach_absolute_time());
//NSLog(#"Insert %d %d %d" ,(int)data[0],(int)data[1],(int)data[2]);
currentPacket = MIDIPacketListAdd(packetList, PACKETLIST_SIZE, currentPacket, mach_absolute_time(), len, data);
//packetReady = YES;
if (!currentPacket) exit(1);
}
}
The calling function from another class
-(void) sendAllNoteOffs {
NSMutableArray* noteZoneArray = [_keyboardView noteZoneArray];
for (int i=0; i < noteZoneArray.count; i++) {
NoteZone* nz = [noteZoneArray objectAtIndex:i];
if ([nz lastNotePlayed]) {
NotePacket* note = [NotePacket initWithLeapValue:127 forNote:[nz noteValue] noteOn:NO forChan:_keyboardChannel];
[_virtualMIDIDevice addPacketToPacketList:note->data ofLength:note->length];
// [_virtualMIDIDevice addPacketToPacketList:note->data ofLength:note->length];
[nz setLastNotePlayed:NO];
}
[nz setHighlightedOn:NO];
}
[_virtualMIDIDevice setAllNotesOffSent:YES];
}
Update :
Replacing the debug statement with the following seems to work as well.
[NSThread sleepForTimeInterval:0.0000001];
But I still don't have a good explanation for it. While not noticeable this means there's a delay in between notes.