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https://github.com/jart/cosmopolitan.git
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2f48a02b44
Recursive mutexes now go as fast as normal mutexes. The tradeoff is they are no longer safe to use in signal handlers. However you can still have signal safe mutexes if you set your mutex to both recursive and pshared. You can also make functions that use recursive mutexes signal safe using sigprocmask to ensure recursion doesn't happen due to any signal handler The impact of this change is that, on Windows, many functions which edit the file descriptor table rely on recursive mutexes, e.g. open(). If you develop your app so it uses pread() and pwrite() then your app should go very fast when performing a heavily multithreaded and contended workload For example, when scaling to 40+ cores, *NSYNC mutexes can go as much as 1000x faster (in CPU time) than the naive recursive lock implementation. Now recursive will use *NSYNC under the hood when it's possible to do so
102 lines
5.2 KiB
C
102 lines
5.2 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/struct/timespec.h"
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#include "libc/dce.h"
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#include "libc/errno.h"
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#include "libc/sysv/consts/clock.h"
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#include "libc/sysv/consts/timer.h"
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/**
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* Sleeps for particular amount of time.
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*
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* Here's how you could sleep for one second:
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*
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* clock_nanosleep(0, 0, &(struct timespec){1}, 0);
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*
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* Your sleep will be interrupted automatically if you do something like
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* press ctrl-c during the wait. That's an `EINTR` error and it lets you
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* immediately react to status changes. This is always the case, even if
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* you're using `SA_RESTART` since this is a `@norestart` system call.
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*
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* void OnCtrlC(int sig) {} // EINTR only happens after delivery
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* signal(SIGINT, OnCtrlC); // do delivery rather than kill proc
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* printf("save me from sleeping forever by pressing ctrl-c\n");
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* clock_nanosleep(0, 0, &(struct timespec){INT_MAX}, 0);
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* printf("you're my hero\n");
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*
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* If you want to perform an uninterruptible sleep without having to use
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* sigprocmask() to block all signals then this function provides a good
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* solution to that problem. For example:
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*
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* struct timespec rel, now, abs;
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* clock_gettime(CLOCK_REALTIME, &now);
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* rel = timespec_frommillis(100);
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* abs = timespec_add(now, rel);
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* while (clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &abs, 0));
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*
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* will accurately spin on `EINTR` errors. That way you're not impeding
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* signal delivery and you're not loosing precision on the wait timeout.
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* This function has first-class support on Linux, FreeBSD, and NetBSD;
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* on OpenBSD it's good; on XNU it's bad; and on Windows it's ugly.
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*
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* @param clock may be
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* - `CLOCK_REALTIME`
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* - `CLOCK_MONOTONIC`
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* - `CLOCK_REALTIME_COARSE` but is likely to sleep negative time
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* - `CLOCK_MONTONIC_COARSE` but is likely to sleep negative time
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* @param flags can be 0 for relative and `TIMER_ABSTIME` for absolute
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* @param req can be a relative or absolute time, depending on `flags`
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* @param rem shall be updated with the remainder of unslept time when
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* (1) it's non-null; (2) `flags` is 0; and (3) -1 w/ `EINTR` is
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* returned; if this function returns 0 then `rem` is undefined;
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* if flags is `TIMER_ABSTIME` then `rem` is ignored
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* @return 0 on success, or errno on error
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* @raise EINTR when a signal got delivered while we were waiting
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* @raise ECANCELED if thread was cancelled in masked mode
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* @raise ENOTSUP if `clock` is known but we can't use it here
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* @raise EFAULT if `req` or null or bad memory was passed
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* @raise EINVAL if `clock` is unknown to current platform
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* @raise EINVAL if `flags` has an unrecognized value
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* @raise EINVAL if `req->tv_nsec ∉ [0,1000000000)`
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* @raise ENOSYS on bare metal
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* @cancelationpoint
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* @returnserrno
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* @norestart
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*/
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errno_t clock_nanosleep(int clock, int flags, //
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const struct timespec *req, //
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struct timespec *rem) {
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if (IsMetal())
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return ENOSYS;
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if (IsLinux() && clock == CLOCK_REALTIME_COARSE)
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clock = CLOCK_REALTIME;
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if (IsLinux() && clock == CLOCK_MONOTONIC_COARSE)
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clock = CLOCK_MONOTONIC;
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if (clock == 127 || //
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(flags & ~TIMER_ABSTIME) || //
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req->tv_sec < 0 || //
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!(0 <= req->tv_nsec && req->tv_nsec <= 999999999))
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return EINVAL;
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int rc;
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errno_t err, old = errno;
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rc = sys_clock_nanosleep(clock, flags, req, rem);
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err = !rc ? 0 : errno;
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errno = old;
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return err;
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}
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