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raspberrypi / picamera2

New libcamera based python library
BSD 2-Clause "Simplified" License
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[BUG] Hanging at constructor, rather than throwing exception when 2+ interpreters try to initialise picamera2 #229

Closed chrisruk closed 2 years ago

chrisruk commented 2 years ago

Describe the bug

If you run two interpreters both with: p = Picamera2()

The second interpreter will hang on this call.

Expected behaviour

An exception should be produced in the second call to picamera2.

See also #223

davidplowman commented 2 years ago

I'm suspicious that this may actually be a libcamera bug. The 2nd instance realises that it can't lock all the media devices, and therefore decides to unlock them all again and give up: here.

Only that very call to unlock() causes it to try to re-acquire the mutex (lock_) that it already has, causing it to hang. Not sure what the best fix is there... give up lock_ first? have a version of unlock() that doesn't re-take the lock? make lock_ itself a re-entrant kind of a mutex?

@kbingham Does this sound right? Any thoughts on the best course of action?

kbingham commented 2 years ago

Could you try testing with this patch please? https://patchwork.libcamera.org/patch/16728/

It sounds like something I reported on IPU3 recently, and Laurent posted that as a fix.

davidplowman commented 2 years ago

Ah yes, that does indeed fix it for me! I see the "unlocking" bit that happens when it fails is now removed from being under the mutex.

So what's the ETA for this one...? Thanks!!

kbingham commented 2 years ago

Could you reply to the patch saying it fixes an issue for you please? (+RB/TB tags :D)

It fixes the IPU3 for me - but breaks CTS (chrome camera test suite) because now it lets two cameras run, and that breaks - but that's not /your/ problem. So I'm holding up the patch ... but if it solves a problem for you we should look to merge it.

kbingham commented 2 years ago

Now merged at https://git.libcamera.org/libcamera/libcamera.git/commit/?id=dfc6d711c9f7f0a9868afa5158aa2089163bded3

davidplowman commented 2 years ago

@kbingham Fabulous, thank you!

I'm going to close this one as it will go away when we pick up the latest libcamera for our next release. Thanks everyone!