Re: Who owns MIDIPacketList memory supplied to MIDISend
Re: Who owns MIDIPacketList memory supplied to MIDISend
- Subject: Re: Who owns MIDIPacketList memory supplied to MIDISend
- From: Eric Kampman <email@hidden>
- Date: Sun, 05 Jun 2011 12:40:30 -0700
Thanks Brian,
But the issue is still unresolved, because
1) if the data is copied, it doesn't matter where the "copied from" location is, stack or heap,
2) if I use a global or some other more "permanant" memory, then if the data is NOT copied then I must ensure that I don't overwrite the data before it goes out the door.
Another active thread here has to do with modifying MIDI data that's already been submitted, and a statement was made that once CoreMIDI has it it can't be modified, which also makes me believe it's copied.
So I'd still like to know the answer. I'll keep fishing on the list archive too.
Thanks,
Eric
On Jun 5, 2011, at 12:07 PM, Brian Willoughby wrote:
> I do not recall whether the data is copied or not, but the key is that you should not allocate the data on the stack. There are many ways to allocate the packet and packet list in Standard C, Objective C, or C++, so just avoid the stack and you'll be fine. If you've found sample code that allocates on the stack, then it's simply bad sample code.
>
> By the way, the code snippet that you excerpted could possibly work if the context of the lines were changed, i.e. static globals or instance variables.
>
> Brian Willoughby
> Sound Consulting
>
>
> On Jun 5, 2011, at 11:51, Eric Kampman wrote:
>> <QUOTE>
>> MIDIPacketList the_packet_list ;
>> MIDIPacketList* packet_list = &the_packet_list ;
>> MIDIPacket* current_packet = MIDIPacketListInit (packet_list) ;
>> </UNQUOTE>
>>
>> OK, I get that -- it looks like a MIDIPacket defaults to having 256 bytes available.
>>
>> But the_packet_list is on the stack, and it doesn't look to me like MIDISend is a synchronous (blocking) call (since the timestamp can be non-zero), so ... does the MIDI data get copied? The inference I think is that the data DOES get copied, otherwise the above code would often behave badly.
>
>
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