There is however a (badly formatted version) of the discussion on freelists. Here is one link:
//www.freelists.org/post/wdmaudiodev/Problem-capturing-midi-on-multiprocessor-SMP-XP-machines,2 Hope that helps. Thanks. Devendra.ps: If you need the better formatted version, please email me off the list, and I'll copy paste from the Yahoo group archive.
On 8/17/10 4:19 AM, Evert van der Poll wrote:
Hi Tobias, Maybe I wasn't entirely clear.But would not the race-condition persist?The MIDI data is returned by calling IAllocatorMXF::PutMessage(), not by the return value from the function. That is right. But if the queue is empty, the call to IMXF::PutMessage() will return to PortCls without having submitted new data. PortCls will only call IAllocatorMXF::PutMessage() after it has processed all previous data. So in this last call it is safe to set your "not running anymore" flag, knowing that you already emptied your queue in the previous call and that there is not going to be any processing on PortCls's side since there is no new data. There is no race-condition in this scenario.I was still wondering if it is safe to call PutMessage on the Allocator of the IPortDMus within The PutMessage() of the render-stream for example.Actually I don't use a spinlock on my capture stream. If you look closely at the DDK sample you will see that it also doesn't use a spinlock there. The call to SourceEvtsToPort() from the PutMessageLocked() function is actually bogus. You won't call this from your DPC because that is handling your render stream. The capture stream is entirely driven by PortCls. The only place where I call IAllocatorMXF::PutMessage() while holding a spinlock is on my render stream. This looks safe to me. You're only recycling a used event. There is not going to be any processing on it on PortCls's side. Regards, Evert -----Original Message----- From: wdmaudiodev-bounce@xxxxxxxxxxxxx [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx]On Behalf Of Tobias Erichsen Sent: Monday, August 16, 2010 2:00 PM To: wdmaudiodev@xxxxxxxxxxxxx Subject: [wdmaudiodev] AW: Re: AW: Re: Possible problem in IPortDMus::Notify and servicegroup dispatching? Hi Evert,This is indeed an annoying problem and probably easy to fix if youhave the source code of PortCls. But somehow I doubtthat is going to happen. Is PortCls even supported still? I know thatMicrosoft pulled the plug for DirectMusic some time ago. AFAIK the PortCls is still part of the complete audio-framework up to Windows 7, so I hope it is still supported ;-)The problem is not with IAllocatorMXF::PutMessage() orIAllocatorMXF::GetMessage(). My Syser aided investigation showed thatthe deadlock occurs AFTER you return to PortCls fromIMXF::PutMessage() on a capture filter. That was also what I figured, but apart from this current freezing-issue, I was still wondering if it is safe to call PutMessage on the Allocator of the IPortDMus within The PutMessage() of the render-stream for example. It is done in the sample, so I would consider it safe (but we all know that there have been locking-issues in early versions of the sample - hence the split into PutMessage and PutMessageLocked ;-) And the same question goes for the capture-stream: can I call GetMessage and PutMessage on the Allocator of the IPortDMus while holding my private locks to secure my internal fifo?My guess about what happens is this: IMXF::PutMessage() is called on acapture filter to retrieve MIDI data from it. It is aresponse to calling IPortDMus::Notify() on your capture port. PortClswill continue to call IMXF::PutMessage() until thatfunction returns NULL, meaning there is no more data.I thought that the PutMessage returns an NTSTATUS - what result-code would tell the PortCls to call me again?The processing that PortCls does after receiving data fromIMXF::PutMessage() needs to acquire two spinlocks. About the sametime IPortDMus::Notify() needs to acquire the same two spinlocks butin reversed order; a classic deadlock scenario.The important thing in the above sentence is that, if there is no datareturned from IMXF::PutMessage() there will be noprocessing and hence no need to acquire the spinlocks. That is why mysolution will work; because there will be no newIPortDMus::Notify() call until IMXF::PutMessage() returns NULL.But would not the race-condition persist? When the last thing you do in your PutMessage method is to reset a state-variable to "not running anymore", you return and at that point PortCls will do the PostProcessing with the necessity to lock ist Spins and at the same time the place where you call the Notify() will also know that the "not running anymore" is true and issue a Notify?However, I tested this extensively with MidiTest (another one of thoseindispensible tools ;)) I really love this tool - used it to test my driver (together with MIDI-OX) extensively.So, don't worry!Unfortunately I'm the worrying kind ;-) Tobias ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.com/
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