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libdispatch-187.5 (coming soon!)
by Mark Heily 05 Aug '11

05 Aug '11

I just checked out http://opensource.apple.com, and was excited to see the sources for 10.7 have been released. Unfortunately, it was just a tease as the sources for libdispatch are not available yet. I know that there are folks within Apple working on merging the changes from the Apple private branch into the public MacOSforge branch, and I'm wondering how that is going. Would it be possible to get the unmodified libdispatch sources from the 10.7 build so I could try to put together a "portability patchset" that would add the Autoconf stuff and everything needed to build on other platforms? This would probably be easier and faster than having someone at Apple backport the changes from 10.7 into the MacOSforge repo. Think of it as "forward porting" the changes from MacOSforge branch instead of backporting changes the other direction. I believe this is the methodology that OpenSSH has used successfully, where the core OpenSSH team develops strictly for OpenBSD, and a separate team maintains a "portable OpenSSH" branch using a pile of patches that are applied to the upstream releases. As a suggestion, a very kind person from Apple could upload the raw 10.7 sources into the SVN tags directory at this URL: http://svn.macosforge.org/repository/libdispatch/tags/OSX_10_7 Thanks a lot! - Mark

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Re: [libdispatch-dev] The results of your email commands
by Antonio Carlos de faria 21 Jul '11

21 Jul '11

From: carlos.faria01(a)hotmail.com To: carlos.faria01(a)hotmail.com; libdispatch-dev-owner(a)lists.macosforge.org Subject: RE: The results of your email commands Date: Tue, 19 Jul 2011 23:18:04 +0300 From: carlos.faria01(a)hotmail.com To: libdispatch-dev-owner(a)lists.macosforge.org Subject: RE: The results of your email commands Date: Tue, 19 Jul 2011 23:17:04 +0300 Subject: The results of your email commands From: libdispatch-dev-owner(a)lists.macosforge.org To: carlos.faria01(a)hotmail.com Date: Mon, 18 Jul 2011 17:40:17 -0700 The results of your email command are provided below. Attached is your original message. - Results: Ignoring non-text/plain MIME parts - Unprocessed: Eu gostaria de adicioná-lo à minha rede profissional no LinkedIn. -Antonio Carlos de Antonio Carlos de Faria Profissional independente de Administração de serviços São Paulo Area, Brazil Confirm that you know Antonio Carlos de Faria https://www.linkedin.com/e/33697e-gqa4zs8l-1k/isd/3122561631/WOZR4KjD/ -- (c) 2011, LinkedIn Corporation - Done. --Anexo de Mensagem Encaminhado-- Date: Tue, 19 Jul 2011 00:40:16 +0000 From: carlos.faria01(a)hotmail.com To: libdispatch-dev-request(a)lists.macosforge.org Subject: Faça parte da minha rede no LinkedIn LinkedIn Eu gostaria de adicioná-lo à minha rede profissional no LinkedIn. -Antonio Carlos de Antonio Carlos de Faria Profissional independente de Administração de serviços São Paulo Area, Brazil Confirm that you know Antonio Carlos de © 2011, LinkedIn Corporation

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Re: [libdispatch-dev] The results of your email commands
by Antonio Carlos de faria 19 Jul '11

19 Jul '11

From: carlos.faria01(a)hotmail.com To: carlos.faria01(a)hotmail.com; libdispatch-dev-owner(a)lists.macosforge.org Subject: RE: The results of your email commands Date: Tue, 19 Jul 2011 23:18:04 +0300 From: carlos.faria01(a)hotmail.com To: libdispatch-dev-owner(a)lists.macosforge.org Subject: RE: The results of your email commands Date: Tue, 19 Jul 2011 23:17:04 +0300 Subject: The results of your email commands From: libdispatch-dev-owner(a)lists.macosforge.org To: carlos.faria01(a)hotmail.com Date: Mon, 18 Jul 2011 17:40:17 -0700 The results of your email command are provided below. Attached is your original message. - Results: Ignoring non-text/plain MIME parts - Unprocessed: Eu gostaria de adicioná-lo à minha rede profissional no LinkedIn. -Antonio Carlos de Antonio Carlos de Faria Profissional independente de Administração de serviços São Paulo Area, Brazil Confirm that you know Antonio Carlos de Faria https://www.linkedin.com/e/33697e-gqa4zs8l-1k/isd/3122561631/WOZR4KjD/ -- (c) 2011, LinkedIn Corporation - Done. --Anexo de Mensagem Encaminhado-- Date: Tue, 19 Jul 2011 00:40:16 +0000 From: carlos.faria01(a)hotmail.com To: libdispatch-dev-request(a)lists.macosforge.org Subject: Faça parte da minha rede no LinkedIn LinkedIn Eu gostaria de adicioná-lo à minha rede profissional no LinkedIn. -Antonio Carlos de Antonio Carlos de Faria Profissional independente de Administração de serviços São Paulo Area, Brazil Confirm that you know Antonio Carlos de © 2011, LinkedIn Corporation

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Faça parte da minha rede no LinkedIn
by Antonio Carlos de Faria 19 Jul '11

19 Jul '11

LinkedIn ------------ Eu gostaria de adicioná-lo à minha rede profissional no LinkedIn. -Antonio Carlos de Antonio Carlos de Faria Profissional independente de Administração de serviços São Paulo Area, Brazil Confirm that you know Antonio Carlos de Faria https://www.linkedin.com/e/-jkkfhg-gqa61jy9-41/isd/3577532546/4qPnP3Q3/ -- (c) 2011, LinkedIn Corporation

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Faça parte da minha rede no LinkedIn
by Antonio Carlos de Faria 19 Jul '11

19 Jul '11

LinkedIn ------------ Eu gostaria de adicioná-lo à minha rede profissional no LinkedIn. -Antonio Carlos de Antonio Carlos de Faria Profissional independente de Administração de serviços São Paulo e redondezas, Brasil Confirme que você conhece Antonio Carlos de Faria https://www.linkedin.com/e/-jkkfhg-gqa4zvtp-36/isd/3577532546/4qPnP3Q3/ -- (c) 2011, LinkedIn Corporation

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What's with this sigsuspend stuff?
by DrPizza 08 Jul '11

08 Jul '11

I'm trying to understand the purpose of _dispatch_sigsuspend() [1], but for the life of me, I cannot see what it is. To the best of my knowledge, sigsuspend() blocks a single thread (not an entire process, per POSIX [2]), suspending it until one of the signals in the sigset_t is sent to that thread. sigsuspend() requires that the sigset_t be properly initialized (using either sigemptyset() or sigfillset()) and then, optionally, modified (using sigaddset() or sigdelset()). The behaviour is undefined if this does not occur. _dispatch_sigsuspend() does not properly initialize the sigset_t, instead passing it straight to sigsuspend(). So whatever the purpose of this function is, it probably isn't doing it properly. But then, what is that purpose? _dispatch_sigsuspend() is sent to the normal priority, non-overcommitting queue. This is a multithreaded queue, and the block is only sent once. The function loops forever; even if the sigsuspend() returns, it gets called again immediately. So the net result is surely that one of the threads in the workqueue will just be stuck forever? Clearly I'm missing something here; can anyone enlighten me? Regards, Peter [1]: http://libdispatch.macosforge.org/trac/browser/trunk/src/queue.c#L953 [2]: http://pubs.opengroup.org/onlinepubs/007908799/xsh/sigsuspend.html

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Possible race in _dispatch_logv when DISPATCH_DEBUG is defined?
by DrPizza 05 Jul '11

05 Jul '11

The intended pattern in _dispatch_logv is to have a static FILE* logfile for the log file, lazily initialized by the first thread to call the function. To avoid locking, every thread that sees that logfile is empty opens the log file in a private per-thread FILE*, and then tries to cmpxchg that into the static value. Any thread that loses the race just closes its private copy and uses the shared one. However, tmp has been marked static too, which means that if several threads are executing _dispatch_logv simultaneously, they'll clobber each other's tmp. That seems of dubious value to me; I think tmp should be non-static. Peter

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[PATCH] libdispatch-r197_v2
by Mark Heily 29 Jun '11

29 Jun '11

See attached for a small update to the portability patch I sent out awhile back. This fixes a crash on Linux caused by a glibc bug in the pause() function. See below for the diff between v1 and v2 of the patch. Regards, - Mark @@ -115,8 +119,9 @@ sigfillset(&mask); pthread_sigmask(SIG_SETMASK, &mask, NULL); - pause(); - DISPATCH_CRASH("pause() returned"); + for (;;) { + pause(); + } #else /* !defined(__linux__) */ pthread_exit(NULL); DISPATCH_CRASH("pthread_exit() returned");

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Clarification on default target_queue for custom serial queues
by Daniel Shusta 27 Jun '11

27 Jun '11

When reading about libdispatch, I get the sense that I can create serial queues en masse and it’ll just work out, because the queues will be limited to a system-determined number of threads. The reason behind this: > In fact, serial queues are scheduled using the global queues. Each serial queue has a target queue, which is initially set to the default priority concurrent queue. When a block is first added to an empty serial queue, the queue itself is added to the target queue. -- GCD technical brief, formerly linked from http://developer.apple.com/technologies/mac/snowleopard/gcd.html but is now a dead link. There’s a backup at http://www.ctestlabs.org/hughes_multicore/documents/GrandCentral_TB_brief_2… This information is repeated at the WWDC session talks (#210, about 10 and a half minutes into the video available to developers). Essentially, global queues are limited to a handful of threads, and since serial queues run on the global queues, they're also all funneled down to that handful of threads. But libdispatch doesn’t actually seem to do this. Example code (tested on iOS 4.3, also shows this behavior on Snow Leopard 10.6.7, 10.6.0, and Lion dev previews): NSUInteger queueCount = 50; dispatch_queue_t queueArray[queueCount]; for ( NSUInteger i = 0; i < queueCount; ++i ) queueArray[i] = dispatch_queue_create("com.some.queue", DISPATCH_QUEUE_SERIAL); // Then enqueue expensive blocks on each of these with a dispatch group, wait for the group to finish, and clean up. The process will just go ahead and create 50 threads. On a dual-core machine, this isn’t really what I was hoping for. But two lines of adjustments… NSUInteger queueCount = 50; dispatch_queue_t queueArray[queueCount]; dispatch_queue_t defaultGlobalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); for ( NSUInteger i = 0; i < queueCount; ++i ) { queueArray[i] = dispatch_queue_create("com.some.queue", DISPATCH_QUEUE_SERIAL); dispatch_set_target_queue(queueArray[i], defaultGlobalQueue); } // Then enqueue expensive blocks on each of these with a dispatch group, wait for the group to finish, and clean up. …will limit it to a couple of threads. According to the documentation quoted above, these two code samples should produce identical results -- serial queues should already target the default global queue. Yet the actual behaviors are very different. Is this intentional? Am I misunderstanding something? Thanks for your time and whatever response you can give, --Daniel Shusta === PS. this is specific to custom serial queues. Custom concurrent queues in iOS 4.3+ funnel down to a couple of threads. PPS. In libdispatch's queue.c, it does seem like the target queue is supposed to be the default global queue. In _dispatch_queue_init() we see dq->do_targetq = _dispatch_get_root_queue(0, true);

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When do the NDAs expire?
by DrPizza 24 Jun '11

24 Jun '11

I'm not covered by the NDAs (not a registered developer, never agreed to them), but am interested in details of the new I/O mechanisms. The barrier API is also very welcome. When will people be able to talk about these, and when (if ever) will source code be available? Peter

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