cosmopolitan/third_party/nsync/mu_semaphore_sem.c

/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
│ vi: set noet ft=c ts=8 sw=8 fenc=utf-8                                   :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/atomic.h"
#include "libc/calls/cp.internal.h"
#include "libc/calls/struct/timespec.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/errno.h"
#include "libc/intrin/dll.h"
#include "libc/intrin/strace.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/f.h"
#include "libc/sysv/consts/fd.h"
#include "libc/thread/thread.h"
#include "third_party/nsync/mu_semaphore.h"
#include "libc/intrin/atomic.h"
#include "libc/atomic.h"
#include "third_party/nsync/time.h"

/**
 * @fileoverview Semaphores w/ POSIX Semaphores API.
 */

#define ASSERT(x) unassert(x)

struct sem {
	int64_t id;
	struct sem *next;
};

static _Atomic(struct sem *) g_sems;

static nsync_semaphore *sem_big_enough_for_sem = (nsync_semaphore *) (uintptr_t)(1 /
	(sizeof (struct sem) <= sizeof (*sem_big_enough_for_sem)));

static void sems_push (struct sem *f) {
	f->next = atomic_load_explicit (&g_sems, memory_order_relaxed);
	while (!atomic_compare_exchange_weak_explicit (&g_sems, &f->next, f,
						       memory_order_acq_rel,
						       memory_order_relaxed))
		pthread_pause_np ();
}

static bool nsync_mu_semaphore_sem_create (struct sem *f) {
	int rc;
	int lol;
	f->id = 0;
	rc = sys_sem_init (0, &f->id);
	STRACE ("sem_init(0, [%ld]) → %d", f->id, rc);
	if (rc != 0)
		return false;
	lol = __sys_fcntl (f->id, F_DUPFD_CLOEXEC, 50);
	STRACE ("fcntl(%ld, F_DUPFD_CLOEXEC, 50) → %d", f->id, lol);
	if (lol >= 50) {
		rc = sys_close (f->id);
		STRACE ("close(%ld) → %d", f->id, rc);
		f->id = lol;
	}
	return true;
}

static void nsync_mu_semaphore_sem_fork_child (void) {
	struct sem *f;
	for (f = atomic_load_explicit (&g_sems, memory_order_relaxed); f; f = f->next) {
		int rc = sys_close (f->id);
		STRACE ("close(%ld) → %d", f->id, rc);
		ASSERT (nsync_mu_semaphore_sem_create (f));
	}
}

static void nsync_mu_semaphore_sem_init (void) {
	pthread_atfork (0, 0, nsync_mu_semaphore_sem_fork_child);
}

/* Initialize *s; the initial value is 0. */
bool nsync_mu_semaphore_init_sem (nsync_semaphore *s) {
	static atomic_uint once;
	struct sem *f = (struct sem *) s;
	if (!nsync_mu_semaphore_sem_create (f))
		return false;
	cosmo_once (&once, nsync_mu_semaphore_sem_init);
	sems_push(f);
	return true;
}

/* Wait until the count of *s exceeds 0, and decrement it. If POSIX cancellations
   are currently disabled by the thread, then this function always succeeds. When
   they're enabled in MASKED mode, this function may return ECANCELED. Otherwise,
   cancellation will occur by unwinding cleanup handlers pushed to the stack. */
errno_t nsync_mu_semaphore_p_sem (nsync_semaphore *s) {
	int e, rc;
	errno_t result;
	struct sem *f = (struct sem *) s;
	e = errno;
	rc = sys_sem_wait (f->id);
	STRACE ("sem_wait(%ld) → %d% m", f->id, rc);
	if (!rc) {
		result = 0;
	} else {
		result = errno;
		errno = e;
		ASSERT (result == ECANCELED);
	}
	return result;
}

/* Like nsync_mu_semaphore_p() this waits for the count of *s to exceed 0,
   while additionally supporting a time parameter specifying at what point
   in the future ETIMEDOUT should be returned, if neither cancellation, or
   semaphore release happens. */
errno_t nsync_mu_semaphore_p_with_deadline_sem (nsync_semaphore *s, nsync_time abs_deadline) {
	int e, rc;
	errno_t result;
	struct sem *f = (struct sem *) s;
	e = errno;
	rc = sys_sem_timedwait (f->id, &abs_deadline);
	STRACE ("sem_timedwait(%ld, %s) → %d% m", f->id,
		DescribeTimespec(0, &abs_deadline), rc);
	if (!rc) {
		result = 0;
	} else {
		result = errno;
		errno = e;
		ASSERT (result == ETIMEDOUT ||
			result == ECANCELED);
	}
	return result;
}

/* Ensure that the count of *s is at least 1. */
void nsync_mu_semaphore_v_sem (nsync_semaphore *s) {
	struct sem *f = (struct sem *) s;
	ASSERT (!sys_sem_post (f->id));
	STRACE ("sem_post(%ld) → 0% m", f->id);
}