cc583082f4
no waiters, we still increase and decrease count in user mode without entering kernel, once there is a waiter, sem_post will enter kernel to increase count and wake thread up, this is atomicy and allow us to gracefully destroy semaphore after sem_wait returned.
469 lines
9.7 KiB
C
469 lines
9.7 KiB
C
/*
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* Copyright (C) 2010 David Xu <davidxu@freebsd.org>.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice(s), this list of conditions and the following disclaimer as
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* the first lines of this file unmodified other than the possible
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* addition of one or more copyright notices.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice(s), this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#include "namespace.h"
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#include <sys/types.h>
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#include <sys/queue.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <errno.h>
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#include <machine/atomic.h>
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#include <sys/umtx.h>
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#include <limits.h>
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#include <fcntl.h>
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#include <pthread.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <semaphore.h>
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#include <unistd.h>
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#include "un-namespace.h"
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#include "libc_private.h"
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__weak_reference(_sem_close, sem_close);
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__weak_reference(_sem_destroy, sem_destroy);
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__weak_reference(_sem_getvalue, sem_getvalue);
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__weak_reference(_sem_init, sem_init);
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__weak_reference(_sem_open, sem_open);
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__weak_reference(_sem_post, sem_post);
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__weak_reference(_sem_timedwait, sem_timedwait);
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__weak_reference(_sem_trywait, sem_trywait);
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__weak_reference(_sem_unlink, sem_unlink);
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__weak_reference(_sem_wait, sem_wait);
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#define SEM_PREFIX "/tmp/SEMD"
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#define SEM_MAGIC1 ((u_int32_t)0x73656d31)
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#define SEM_MAGIC ((u_int32_t)0x73656d32)
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struct sem_nameinfo {
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int open_count;
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char *name;
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sem_t *sem;
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LIST_ENTRY(sem_nameinfo) next;
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};
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static pthread_once_t once = PTHREAD_ONCE_INIT;
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static pthread_mutex_t sem_llock;
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static LIST_HEAD(,sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
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static void
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sem_prefork()
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{
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_pthread_mutex_lock(&sem_llock);
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}
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static void
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sem_postfork()
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{
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_pthread_mutex_unlock(&sem_llock);
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}
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static void
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sem_child_postfork()
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{
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_pthread_mutex_unlock(&sem_llock);
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}
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static void
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sem_module_init(void)
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{
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pthread_mutexattr_t ma;
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_pthread_mutexattr_init(&ma);
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_pthread_mutexattr_settype(&ma, PTHREAD_MUTEX_RECURSIVE);
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_pthread_mutex_init(&sem_llock, &ma);
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_pthread_mutexattr_destroy(&ma);
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_pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
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}
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static inline int
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sem_check_validity(sem_t *sem)
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{
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if (sem->_magic == SEM_MAGIC || sem->_magic == SEM_MAGIC1)
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return (0);
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else {
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errno = EINVAL;
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return (-1);
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}
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}
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int
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_sem_init(sem_t *sem, int pshared, unsigned int value)
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{
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if (value > SEM_VALUE_MAX) {
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errno = EINVAL;
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return (-1);
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}
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bzero(sem, sizeof(sem_t));
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sem->_magic = SEM_MAGIC;
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sem->_kern._count = (u_int32_t)value;
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sem->_kern._has_waiters = 0;
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sem->_kern._flags = (pshared ? USYNC_PROCESS_SHARED : 0) | SEM_VER2;
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return (0);
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}
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sem_t *
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_sem_open(const char *name, int flags, ...)
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{
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char path[PATH_MAX];
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struct stat sb;
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va_list ap;
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struct sem_nameinfo *ni = NULL;
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sem_t *sem = NULL;
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int fd = -1, mode, len, errsave;
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int value = 0;
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if (name[0] != '/') {
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errno = EINVAL;
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return (SEM_FAILED);
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}
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name++;
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if (flags & ~(O_CREAT|O_EXCL)) {
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errno = EINVAL;
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return (SEM_FAILED);
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}
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_pthread_once(&once, sem_module_init);
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_pthread_mutex_lock(&sem_llock);
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LIST_FOREACH(ni, &sem_list, next) {
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if (strcmp(name, ni->name) == 0) {
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ni->open_count++;
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sem = ni->sem;
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_pthread_mutex_unlock(&sem_llock);
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return (sem);
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}
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}
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if (flags & O_CREAT) {
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va_start(ap, flags);
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mode = va_arg(ap, int);
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value = va_arg(ap, int);
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va_end(ap);
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}
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len = sizeof(*ni) + strlen(name) + 1;
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ni = (struct sem_nameinfo *)malloc(len);
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if (ni == NULL) {
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errno = ENOSPC;
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goto error;
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}
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ni->name = (char *)(ni+1);
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strcpy(ni->name, name);
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strcpy(path, SEM_PREFIX);
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if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
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errno = ENAMETOOLONG;
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goto error;
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}
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fd = _open(path, flags|O_RDWR, mode);
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if (fd == -1)
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goto error;
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if (flock(fd, LOCK_EX) == -1)
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goto error;
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if (_fstat(fd, &sb)) {
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flock(fd, LOCK_UN);
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goto error;
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}
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if (sb.st_size < sizeof(sem_t)) {
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sem_t tmp;
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tmp._magic = SEM_MAGIC;
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tmp._kern._has_waiters = 0;
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tmp._kern._count = value;
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tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED | SEM_VER2;
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if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) {
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flock(fd, LOCK_UN);
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goto error;
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}
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}
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flock(fd, LOCK_UN);
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sem = (sem_t *)mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE,
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MAP_SHARED|MAP_NOSYNC, fd, 0);
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if (sem == MAP_FAILED) {
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sem = NULL;
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if (errno == ENOMEM)
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errno = ENOSPC;
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goto error;
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}
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if (sem->_magic != SEM_MAGIC) {
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errno = EINVAL;
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goto error;
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}
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ni->open_count = 1;
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ni->sem = sem;
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LIST_INSERT_HEAD(&sem_list, ni, next);
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_pthread_mutex_unlock(&sem_llock);
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_close(fd);
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return (sem);
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error:
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errsave = errno;
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_pthread_mutex_unlock(&sem_llock);
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if (fd != -1)
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_close(fd);
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if (sem != NULL)
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munmap(sem, sizeof(sem_t));
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free(ni);
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errno = errsave;
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return (SEM_FAILED);
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}
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int
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_sem_close(sem_t *sem)
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{
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struct sem_nameinfo *ni;
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if (sem_check_validity(sem) != 0)
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return (-1);
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if (!(sem->_kern._flags & SEM_NAMED)) {
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errno = EINVAL;
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return (-1);
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}
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_pthread_once(&once, sem_module_init);
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_pthread_mutex_lock(&sem_llock);
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LIST_FOREACH(ni, &sem_list, next) {
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if (sem == ni->sem) {
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if (--ni->open_count > 0) {
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_pthread_mutex_unlock(&sem_llock);
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return (0);
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}
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else
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break;
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}
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}
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if (ni) {
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LIST_REMOVE(ni, next);
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_pthread_mutex_unlock(&sem_llock);
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munmap(sem, sizeof(*sem));
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free(ni);
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return (0);
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}
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_pthread_mutex_unlock(&sem_llock);
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errno = EINVAL;
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return (-1);
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}
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int
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_sem_unlink(const char *name)
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{
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char path[PATH_MAX];
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if (name[0] != '/') {
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errno = ENOENT;
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return -1;
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}
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name++;
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strcpy(path, SEM_PREFIX);
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if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
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errno = ENAMETOOLONG;
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return (-1);
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}
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return unlink(path);
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}
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int
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_sem_destroy(sem_t *sem)
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{
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if (sem_check_validity(sem) != 0)
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return (-1);
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if (sem->_kern._flags & SEM_NAMED) {
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errno = EINVAL;
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return (-1);
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}
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sem->_magic = 0;
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return (0);
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}
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int
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_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
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{
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if (sem_check_validity(sem) != 0)
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return (-1);
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*sval = (int)sem->_kern._count & ~SEM_WAITERS;
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return (0);
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}
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static __inline int
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usem_wait(struct _usem *sem, const struct timespec *abstime)
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{
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struct _umtx_time *tm_p, timeout;
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size_t tm_size;
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if (abstime == NULL) {
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tm_p = NULL;
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tm_size = 0;
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} else {
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timeout._clockid = CLOCK_REALTIME;
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timeout._flags = UMTX_ABSTIME;
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timeout._timeout = *abstime;
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tm_p = &timeout;
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tm_size = sizeof(timeout);
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}
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return _umtx_op(sem, UMTX_OP_SEM_WAIT, 0,
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(void *)tm_size, __DECONST(void*, tm_p));
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}
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static inline int
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_trywait(sem_t *sem)
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{
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int count;
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if ((sem->_kern._flags & SEM_VER2) != 0) {
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while (((count = sem->_kern._count) & ~SEM_WAITERS) > 0) {
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if (atomic_cmpset_acq_int(&sem->_kern._count, count, count - 1))
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return (0);
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}
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} else {
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while ((count = sem->_kern._count) > 0) {
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if (atomic_cmpset_acq_int(&sem->_kern._count, count, count - 1))
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return (0);
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}
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}
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return (EAGAIN);
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}
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int
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_sem_trywait(sem_t *sem)
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{
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int status;
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if (sem_check_validity(sem) != 0)
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return (-1);
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if ((status = _trywait(sem)) == 0)
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return (0);
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errno = status;
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return (-1);
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}
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int
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_sem_timedwait(sem_t * __restrict sem,
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const struct timespec * __restrict abstime)
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{
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int retval;
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if (sem_check_validity(sem) != 0)
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return (-1);
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retval = 0;
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for (;;) {
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if (_trywait(sem) == 0)
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return (0);
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if (retval) {
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_pthread_testcancel();
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break;
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}
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/*
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* The timeout argument is only supposed to
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* be checked if the thread would have blocked.
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*/
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if (abstime != NULL) {
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if (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0) {
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errno = EINVAL;
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return (-1);
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}
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}
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_pthread_cancel_enter(1);
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retval = usem_wait(&sem->_kern, abstime);
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_pthread_cancel_leave(0);
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}
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return (retval);
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}
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int
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_sem_wait(sem_t *sem)
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{
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return _sem_timedwait(sem, NULL);
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}
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/*
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* POSIX:
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* The sem_post() interface is reentrant with respect to signals and may be
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* invoked from a signal-catching function.
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* The implementation does not use lock, so it should be safe.
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*/
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int
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_sem_post(sem_t *sem)
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{
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int count;
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if (sem_check_validity(sem) != 0)
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return (-1);
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if ((sem->_kern._flags & SEM_VER2) != 0) {
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for (;;) {
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count = sem->_kern._count;
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if ((count & SEM_WAITERS) == 0) {
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if (__predict_false(count == SEM_VALUE_MAX)) {
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errno = ERANGE;
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return (-1);
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}
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if (atomic_cmpset_rel_int(&sem->_kern._count, count, count+1))
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return (0);
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} else {
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return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
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}
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}
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} else {
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do {
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count = sem->_kern._count;
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if (__predict_false(count == SEM_VALUE_MAX)) {
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errno = ERANGE;
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return (-1);
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}
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} while (!atomic_cmpset_rel_int(&sem->_kern._count, count, count+1));
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rmb();
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if (!sem->_kern._has_waiters)
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return (0);
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return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
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}
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}
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