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Felix Palmen :freebsd: :c64:Today, I implemented the <a href="https://mastodon.bsd.cafe/tags/async" class="mention hashtag" rel="nofollow noopener" target="_blank">#async</a> / <a href="https://mastodon.bsd.cafe/tags/await" class="mention hashtag" rel="nofollow noopener" target="_blank">#await</a> pattern (as known from <a href="https://mastodon.bsd.cafe/tags/csharp" class="mention hashtag" rel="nofollow noopener" target="_blank">#csharp</a> and meanwhile quite some other languages) ...... in good old <a href="https://mastodon.bsd.cafe/tags/C" class="mention hashtag" rel="nofollow noopener" target="_blank">#C</a>! 😎 Well, at least sort of.* It requires some standard library support, namely <a href="https://mastodon.bsd.cafe/tags/POSIX" class="mention hashtag" rel="nofollow noopener" target="_blank">#POSIX</a> user context switching with <a href="https://mastodon.bsd.cafe/tags/getcontext" class="mention hashtag" rel="nofollow noopener" target="_blank">#getcontext</a> and friends, which was deprecated in POSIX-1.2008. But it's still available on many systems, including <a href="https://mastodon.bsd.cafe/tags/FreeBSD" class="mention hashtag" rel="nofollow noopener" target="_blank">#FreeBSD</a>, <a href="https://mastodon.bsd.cafe/tags/NetBSD" class="mention hashtag" rel="nofollow noopener" target="_blank">#NetBSD</a>, <a href="https://mastodon.bsd.cafe/tags/Linux" class="mention hashtag" rel="nofollow noopener" target="_blank">#Linux</a> (with <a href="https://mastodon.bsd.cafe/tags/glibc" class="mention hashtag" rel="nofollow noopener" target="_blank">#glibc</a>). It's NOT available e.g. on <a href="https://mastodon.bsd.cafe/tags/OpenBSD" class="mention hashtag" rel="nofollow noopener" target="_blank">#OpenBSD</a>, or Linux with some alternative libc.* I can't do anything about the basic language syntax, so some boilerplate comes with using it.* It has some overhead (room for extra stacks, even extra syscalls as getcontext unfortunately also always saves/restores the signal mask)But then ... async/await in C! 🥳 Here are the docs: <a href="https://zirias.github.io/poser/api/latest/class_p_s_c___async_task.html" rel="nofollow noopener" translate="no" target="_blank">https://zirias.github.io/poser/api/latest/class_p_s_c___async_task.html</a><a href="https://mastodon.bsd.cafe/tags/C" class="mention hashtag" rel="nofollow noopener" target="_blank">#C</a> <a href="https://mastodon.bsd.cafe/tags/coding" class="mention hashtag" rel="nofollow noopener" target="_blank">#coding</a>

Felix Palmen :freebsd: :c64:I finally eliminated the need for a dedicated <a href="https://mastodon.bsd.cafe/tags/thread" class="mention hashtag" rel="nofollow noopener" target="_blank">#thread</a> controlling the pam helper <a href="https://mastodon.bsd.cafe/tags/process" class="mention hashtag" rel="nofollow noopener" target="_blank">#process</a> in <a href="https://mastodon.bsd.cafe/tags/swad" class="mention hashtag" rel="nofollow noopener" target="_blank">#swad</a>. 🥳 The building block that was still missing from <a href="https://mastodon.bsd.cafe/tags/poser" class="mention hashtag" rel="nofollow noopener" target="_blank">#poser</a> was a way to await some async I/O task performed on the main thread from a worker thread. So I added a class to allow exactly that. The naive implementation just signals the main thread to carry out the requested task and then waits on a <a href="https://mastodon.bsd.cafe/tags/semaphore" class="mention hashtag" rel="nofollow noopener" target="_blank">#semaphore</a> for completion, which of course blocks the worker thread.Turns out we can actually do better, reaching similar functionality like e.g. <a href="https://mastodon.bsd.cafe/tags/async" class="mention hashtag" rel="nofollow noopener" target="_blank">#async</a> / <a href="https://mastodon.bsd.cafe/tags/await" class="mention hashtag" rel="nofollow noopener" target="_blank">#await</a> in C#: Release the worker thread to do other jobs while waiting. The key to this is user context switching support like offered by <a href="https://mastodon.bsd.cafe/tags/POSIX" class="mention hashtag" rel="nofollow noopener" target="_blank">#POSIX</a>-1.2001 <a href="https://mastodon.bsd.cafe/tags/getcontext" class="mention hashtag" rel="nofollow noopener" target="_blank">#getcontext</a> and friends. Unfortunately it was deprecated in POSIX-1.2008 without an obvious replacement (the docs basically say "use threads", which doesn't work for my scenario), but still lots of systems provide it, e.g. <a href="https://mastodon.bsd.cafe/tags/FreeBSD" class="mention hashtag" rel="nofollow noopener" target="_blank">#FreeBSD</a>, <a href="https://mastodon.bsd.cafe/tags/NetBSD" class="mention hashtag" rel="nofollow noopener" target="_blank">#NetBSD</a>, <a href="https://mastodon.bsd.cafe/tags/Linux" class="mention hashtag" rel="nofollow noopener" target="_blank">#Linux</a> (with <a href="https://mastodon.bsd.cafe/tags/glibc" class="mention hashtag" rel="nofollow noopener" target="_blank">#glibc</a>) ...The posercore lib now offers both implementations, prefering to use user context switching if available. It comes at a price: Every thread job now needs its private stack space (I allocated 64kiB there for now), and of course the switching takes some time as well, but that's very likely better than leaving a task idle waiting. And there's a restriction, resuming must still happen on the same thread that called the "await", so if this thread is currently busy, we have to wait a little bit longer. I still think it's a very nice solution. 😎 In any case, the code for the PAM credential checker module looks much cleaner now (the await "magic" happens on line 174): <a href="https://github.com/Zirias/swad/blob/57eefe93cdad0df55ebede4bd877d22e7be1a7f8/src/bin/swad/cred/pamchecker.c" rel="nofollow noopener" translate="no" target="_blank">https://github.com/Zirias/swad/blob/57eefe93cdad0df55ebede4bd877d22e7be1a7f8/src/bin/swad/cred/pamchecker.c</a><a href="https://mastodon.bsd.cafe/tags/C" class="mention hashtag" rel="nofollow noopener" target="_blank">#C</a> <a href="https://mastodon.bsd.cafe/tags/coding" class="mention hashtag" rel="nofollow noopener" target="_blank">#coding</a>

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