mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 11:37:35 +00:00
3f0bcdc3ef
- Exhaustively document cancellation points - Rename SIGCANCEL to SIGTHR just like BSDs - Further improve POSIX thread cancellations - Ensure asynchronous cancellations work correctly - Elevate the quality of getrandom() and getentropy() - Make futexes cancel correctly on OpenBSD 6.x and 7.x - Add reboot.com and shutdown.com to examples directory - Remove underscore prefix from awesome timespec_*() APIs - Create assertions that help verify our cancellation points - Remove bad timespec APIs (cmp generalizes eq/ne/gt/gte/lt/lte)
130 lines
4.9 KiB
C
130 lines
4.9 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net 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/assert.h"
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#include "libc/calls/cp.internal.h"
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#include "libc/calls/struct/timespec.h"
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#include "libc/calls/struct/timespec.internal.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/sysv/errfuns.h"
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#include "libc/thread/semaphore.h"
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#include "libc/thread/thread.h"
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#include "third_party/nsync/futex.internal.h"
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static void sem_delay(int n) {
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volatile int i;
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for (i = 0; i != 1 << n; i++) donothing;
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}
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// TODO(jart): This should be abstracted by polyfill.
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static struct timespec *sem_timeout(struct timespec *memory,
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const struct timespec *abstime) {
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struct timespec now;
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if (!abstime) {
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return 0;
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} else if (FUTEX_TIMEOUT_IS_ABSOLUTE) {
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*memory = *abstime;
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return memory;
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} else {
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now = timespec_real();
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if (timespec_cmp(now, *abstime) > 0) {
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*memory = (struct timespec){0};
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} else {
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*memory = timespec_sub(*abstime, now);
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}
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return memory;
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}
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}
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static void sem_timedwait_cleanup(void *arg) {
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sem_t *sem = arg;
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_unassert(atomic_fetch_add_explicit(&sem->sem_waiters, -1,
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memory_order_acq_rel) > 0);
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}
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/**
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* Locks semaphore w/ deadline.
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*
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* @param abstime is absolute deadline or null to wait forever
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* @return 0 on success, or -1 w/ errno
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* @raise ECANCELED if calling thread was cancelled in masked mode
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* @raise EINTR if signal was delivered instead
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* @raise EDEADLK if deadlock was detected
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* @raise ETIMEDOUT if deadline expired
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* @raise EINVAL if `sem` is invalid
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* @cancellationpoint
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*/
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int sem_timedwait(sem_t *sem, const struct timespec *abstime) {
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int e, i, v, rc;
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struct timespec ts;
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e = errno;
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for (i = 0; i < 7; ++i) {
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rc = sem_trywait(sem);
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if (!rc) {
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return rc;
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} else if (errno == EAGAIN) {
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errno = e;
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sem_delay(i);
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} else {
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return rc;
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}
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}
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BEGIN_CANCELLATION_POINT;
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_unassert(atomic_fetch_add_explicit(&sem->sem_waiters, +1,
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memory_order_acq_rel) >= 0);
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pthread_cleanup_push(sem_timedwait_cleanup, sem);
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do {
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if (!(v = atomic_load_explicit(&sem->sem_value, memory_order_relaxed))) {
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rc = nsync_futex_wait_(&sem->sem_value, v, sem->sem_pshared,
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sem_timeout(&ts, abstime));
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if (rc == -EINTR || rc == -ECANCELED) {
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errno = -rc;
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rc = -1;
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} else if (rc == -EAGAIN || rc == -EWOULDBLOCK) {
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rc = 0;
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} else if (rc == -ETIMEDOUT) {
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_npassert(abstime);
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if (timespec_cmp(*abstime, timespec_real()) <= 0) {
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rc = etimedout();
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} else {
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rc = 0;
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}
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} else {
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_npassert(!rc);
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rc = 0;
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}
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} else if (v > 0) {
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rc = 0;
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} else {
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_unassert(v > INT_MIN);
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rc = einval();
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}
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} while (!rc && (!v || !atomic_compare_exchange_weak_explicit(
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&sem->sem_value, &v, v - 1, memory_order_acquire,
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memory_order_relaxed)));
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pthread_cleanup_pop(1);
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END_CANCELLATION_POINT;
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return rc;
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}
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