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https://github.com/jart/cosmopolitan.git
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68 lines
3.4 KiB
C
68 lines
3.4 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/blockcancel.internal.h"
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#include "libc/cosmo.h"
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#include "libc/errno.h"
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#include "libc/intrin/atomic.h"
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#include "libc/limits.h"
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#include "libc/thread/thread.h"
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/**
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* Waits for all threads to arrive at barrier.
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*
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* When the barrier is broken, the state becomes reset to what it was
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* when pthread_barrier_init() was called, so that the barrior may be
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* used again in the same way.
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*
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* Unlike pthread_cond_timedwait() this function is not a cancelation
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* point. It is not needed to have cleanup handlers on block cancels.
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*
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* @return 0 on success, `PTHREAD_BARRIER_SERIAL_THREAD` to one lucky
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* thread which was the last arrival, or an errno on error
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* @raise EINVAL if barrier is used incorrectly
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*/
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errno_t pthread_barrier_wait(pthread_barrier_t *barrier) {
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int n;
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// enter barrier
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atomic_fetch_add_explicit(&barrier->_waiters, 1, memory_order_acq_rel);
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n = atomic_fetch_sub_explicit(&barrier->_counter, 1, memory_order_acq_rel);
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n = n - 1;
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// this can only happen on invalid usage
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if (n < 0)
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return EINVAL;
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// reset count and wake waiters if we're last at barrier
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if (!n) {
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atomic_store_explicit(&barrier->_counter, barrier->_count,
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memory_order_release);
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atomic_store_explicit(&barrier->_waiters, 0, memory_order_release);
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cosmo_futex_wake(&barrier->_waiters, INT_MAX, barrier->_pshared);
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return PTHREAD_BARRIER_SERIAL_THREAD;
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}
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// wait for everyone else to arrive at barrier
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BLOCK_CANCELATION;
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while ((n = atomic_load_explicit(&barrier->_waiters, memory_order_acquire)))
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cosmo_futex_wait(&barrier->_waiters, n, barrier->_pshared, 0, 0);
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ALLOW_CANCELATION;
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return 0;
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}
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