diff options
Diffstat (limited to 'lib/libc/gen/sem.c')
-rw-r--r-- | lib/libc/gen/sem.c | 458 |
1 files changed, 458 insertions, 0 deletions
diff --git a/lib/libc/gen/sem.c b/lib/libc/gen/sem.c new file mode 100644 index 0000000..e9ae669 --- /dev/null +++ b/lib/libc/gen/sem.c @@ -0,0 +1,458 @@ +/* + * Copyright (C) 2010 David Xu <davidxu@freebsd.org>. + * Copyright (C) 2000 Jason Evans <jasone@freebsd.org>. + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice(s), this list of conditions and the following disclaimer as + * the first lines of this file unmodified other than the possible + * addition of one or more copyright notices. + * 2. Redistributions in binary form must reproduce the above copyright + * notice(s), this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY + * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR + * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, + * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE + * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, + * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + * + * $FreeBSD$ + */ + +/* + * Some notes about this implementation. + * + * This is mostly a simple implementation of POSIX semaphores that + * does not need threading. Any semaphore created is a kernel-based + * semaphore regardless of the pshared attribute. This is necessary + * because libc's stub for pthread_cond_wait() doesn't really wait, + * and it is not worth the effort impose this behavior on libc. + * + * All functions here are designed to be thread-safe so that a + * threads library need not provide wrappers except to make + * sem_wait() and sem_timedwait() cancellation points or to + * provide a faster userland implementation for non-pshared + * semaphores. + * + * Also, this implementation of semaphores cannot really support + * real pshared semaphores. The sem_t is an allocated object + * and can't be seen by other processes when placed in shared + * memory. It should work across forks as long as the semaphore + * is created before any forks. + * + * The function sem_init() should be overridden by a threads + * library if it wants to provide a different userland version + * of semaphores. The functions sem_wait() and sem_timedwait() + * need to be wrapped to provide cancellation points. The function + * sem_post() may need to be wrapped to be signal-safe. + */ +#include "namespace.h" +#include <sys/types.h> +#include <sys/queue.h> +#include <machine/atomic.h> +#include <errno.h> +#include <sys/umtx.h> +#include <sys/_semaphore.h> +#include <limits.h> +#include <fcntl.h> +#include <pthread.h> +#include <stdarg.h> +#include <stdlib.h> +#include <time.h> +#include "un-namespace.h" +#include "libc_private.h" + +/* + * Old semaphore definitions. + */ +struct sem { +#define SEM_MAGIC ((u_int32_t) 0x09fa4012) + u_int32_t magic; + pthread_mutex_t lock; + pthread_cond_t gtzero; + u_int32_t count; + u_int32_t nwaiters; +#define SEM_USER (NULL) + semid_t semid; /* semaphore id if kernel (shared) semaphore */ + int syssem; /* 1 if kernel (shared) semaphore */ + LIST_ENTRY(sem) entry; + struct sem **backpointer; +}; + +typedef struct sem* sem_t; + +#define SEM_FAILED ((sem_t *)0) +#define SEM_VALUE_MAX __INT_MAX + +#define SYM_FB10(sym) __CONCAT(sym, _fb10) +#define WEAK_REF(sym, alias) __weak_reference(sym, alias) +#define SYM_COMPAT(sym, impl, ver) __sym_compat(sym, impl, ver) + +#define FB10_COMPAT(func, sym) \ + WEAK_REF(func, SYM_FB10(sym)); \ + SYM_COMPAT(sym, SYM_FB10(sym), FBSD_1.0) + +static sem_t sem_alloc(unsigned int value, semid_t semid, int system_sem); +static void sem_free(sem_t sem); + +static LIST_HEAD(, sem) named_sems = LIST_HEAD_INITIALIZER(named_sems); +static pthread_mutex_t named_sems_mtx = PTHREAD_MUTEX_INITIALIZER; + +FB10_COMPAT(_libc_sem_init_compat, sem_init); +FB10_COMPAT(_libc_sem_destroy_compat, sem_destroy); +FB10_COMPAT(_libc_sem_open_compat, sem_open); +FB10_COMPAT(_libc_sem_close_compat, sem_close); +FB10_COMPAT(_libc_sem_unlink_compat, sem_unlink); +FB10_COMPAT(_libc_sem_wait_compat, sem_wait); +FB10_COMPAT(_libc_sem_trywait_compat, sem_trywait); +FB10_COMPAT(_libc_sem_timedwait_compat, sem_timedwait); +FB10_COMPAT(_libc_sem_post_compat, sem_post); +FB10_COMPAT(_libc_sem_getvalue_compat, sem_getvalue); + +static inline int +sem_check_validity(sem_t *sem) +{ + + if ((sem != NULL) && ((*sem)->magic == SEM_MAGIC)) + return (0); + else { + errno = EINVAL; + return (-1); + } +} + +static void +sem_free(sem_t sem) +{ + + sem->magic = 0; + free(sem); +} + +static sem_t +sem_alloc(unsigned int value, semid_t semid, int system_sem) +{ + sem_t sem; + + if (value > SEM_VALUE_MAX) { + errno = EINVAL; + return (NULL); + } + + sem = (sem_t)malloc(sizeof(struct sem)); + if (sem == NULL) { + errno = ENOSPC; + return (NULL); + } + + sem->count = (u_int32_t)value; + sem->nwaiters = 0; + sem->magic = SEM_MAGIC; + sem->semid = semid; + sem->syssem = system_sem; + return (sem); +} + +int +_libc_sem_init_compat(sem_t *sem, int pshared, unsigned int value) +{ + semid_t semid; + + /* + * We always have to create the kernel semaphore if the + * threads library isn't present since libc's version of + * pthread_cond_wait() is just a stub that doesn't really + * wait. + */ + semid = (semid_t)SEM_USER; + if ((pshared != 0) && ksem_init(&semid, value) != 0) + return (-1); + + *sem = sem_alloc(value, semid, pshared); + if ((*sem) == NULL) { + if (pshared != 0) + ksem_destroy(semid); + return (-1); + } + return (0); +} + +int +_libc_sem_destroy_compat(sem_t *sem) +{ + int retval; + + if (sem_check_validity(sem) != 0) + return (-1); + + /* + * If this is a system semaphore let the kernel track it otherwise + * make sure there are no waiters. + */ + if ((*sem)->syssem != 0) + retval = ksem_destroy((*sem)->semid); + else if ((*sem)->nwaiters > 0) { + errno = EBUSY; + retval = -1; + } + else { + retval = 0; + (*sem)->magic = 0; + } + + if (retval == 0) + sem_free(*sem); + return (retval); +} + +sem_t * +_libc_sem_open_compat(const char *name, int oflag, ...) +{ + sem_t *sem; + sem_t s; + semid_t semid; + mode_t mode; + unsigned int value; + + mode = 0; + value = 0; + + if ((oflag & O_CREAT) != 0) { + va_list ap; + + va_start(ap, oflag); + mode = va_arg(ap, int); + value = va_arg(ap, unsigned int); + va_end(ap); + } + /* + * we can be lazy and let the kernel handle the "oflag", + * we'll just merge duplicate IDs into our list. + */ + if (ksem_open(&semid, name, oflag, mode, value) == -1) + return (SEM_FAILED); + /* + * search for a duplicate ID, we must return the same sem_t * + * if we locate one. + */ + _pthread_mutex_lock(&named_sems_mtx); + LIST_FOREACH(s, &named_sems, entry) { + if (s->semid == semid) { + sem = s->backpointer; + _pthread_mutex_unlock(&named_sems_mtx); + return (sem); + } + } + sem = (sem_t *)malloc(sizeof(*sem)); + if (sem == NULL) + goto err; + *sem = sem_alloc(value, semid, 1); + if ((*sem) == NULL) + goto err; + LIST_INSERT_HEAD(&named_sems, *sem, entry); + (*sem)->backpointer = sem; + _pthread_mutex_unlock(&named_sems_mtx); + return (sem); +err: + _pthread_mutex_unlock(&named_sems_mtx); + ksem_close(semid); + if (sem != NULL) { + if (*sem != NULL) + sem_free(*sem); + else + errno = ENOSPC; + free(sem); + } else { + errno = ENOSPC; + } + return (SEM_FAILED); +} + +int +_libc_sem_close_compat(sem_t *sem) +{ + + if (sem_check_validity(sem) != 0) + return (-1); + + if ((*sem)->syssem == 0) { + errno = EINVAL; + return (-1); + } + + _pthread_mutex_lock(&named_sems_mtx); + if (ksem_close((*sem)->semid) != 0) { + _pthread_mutex_unlock(&named_sems_mtx); + return (-1); + } + LIST_REMOVE((*sem), entry); + _pthread_mutex_unlock(&named_sems_mtx); + sem_free(*sem); + *sem = NULL; + free(sem); + return (0); +} + +int +_libc_sem_unlink_compat(const char *name) +{ + + return (ksem_unlink(name)); +} + +static int +_umtx_wait_uint(volatile unsigned *mtx, unsigned id, const struct timespec *timeout) +{ + if (timeout && (timeout->tv_sec < 0 || (timeout->tv_sec == 0 && + timeout->tv_nsec <= 0))) { + errno = ETIMEDOUT; + return (-1); + } + return _umtx_op(__DEVOLATILE(void *, mtx), + UMTX_OP_WAIT_UINT_PRIVATE, id, NULL, __DECONST(void*, timeout)); +} + +static int +_umtx_wake(volatile void *mtx) +{ + return _umtx_op(__DEVOLATILE(void *, mtx), UMTX_OP_WAKE_PRIVATE, + 1, NULL, NULL); +} + +#define TIMESPEC_SUB(dst, src, val) \ + do { \ + (dst)->tv_sec = (src)->tv_sec - (val)->tv_sec; \ + (dst)->tv_nsec = (src)->tv_nsec - (val)->tv_nsec; \ + if ((dst)->tv_nsec < 0) { \ + (dst)->tv_sec--; \ + (dst)->tv_nsec += 1000000000; \ + } \ + } while (0) + + +static void +sem_cancel_handler(void *arg) +{ + sem_t *sem = arg; + + atomic_add_int(&(*sem)->nwaiters, -1); + if ((*sem)->nwaiters && (*sem)->count) + _umtx_wake(&(*sem)->count); +} + +int +_libc_sem_timedwait_compat(sem_t * __restrict sem, + const struct timespec * __restrict abstime) +{ + struct timespec ts, ts2; + int val, retval; + + if (sem_check_validity(sem) != 0) + return (-1); + + if ((*sem)->syssem != 0) { + _pthread_cancel_enter(1); + retval = ksem_wait((*sem)->semid); /* XXX no timeout */ + _pthread_cancel_leave(retval == -1); + return (retval); + } + + retval = 0; + _pthread_testcancel(); + for (;;) { + while ((val = (*sem)->count) > 0) { + if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1)) + return (0); + } + if (retval) { + _pthread_testcancel(); + break; + } + if (abstime) { + if (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0) { + errno = EINVAL; + return (-1); + } + clock_gettime(CLOCK_REALTIME, &ts); + TIMESPEC_SUB(&ts2, abstime, &ts); + } + atomic_add_int(&(*sem)->nwaiters, 1); + pthread_cleanup_push(sem_cancel_handler, sem); + _pthread_cancel_enter(1); + retval = _umtx_wait_uint(&(*sem)->count, 0, abstime ? &ts2 : NULL); + _pthread_cancel_leave(0); + pthread_cleanup_pop(0); + atomic_add_int(&(*sem)->nwaiters, -1); + } + return (retval); +} + +int +_libc_sem_wait_compat(sem_t *sem) +{ + return _libc_sem_timedwait_compat(sem, NULL); +} + +int +_libc_sem_trywait_compat(sem_t *sem) +{ + int val; + + if (sem_check_validity(sem) != 0) + return (-1); + + if ((*sem)->syssem != 0) + return ksem_trywait((*sem)->semid); + + while ((val = (*sem)->count) > 0) { + if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1)) + return (0); + } + errno = EAGAIN; + return (-1); +} + +int +_libc_sem_post_compat(sem_t *sem) +{ + + if (sem_check_validity(sem) != 0) + return (-1); + + if ((*sem)->syssem != 0) + return ksem_post((*sem)->semid); + + atomic_add_rel_int(&(*sem)->count, 1); + + if ((*sem)->nwaiters) + return _umtx_wake(&(*sem)->count); + return (0); +} + +int +_libc_sem_getvalue_compat(sem_t * __restrict sem, int * __restrict sval) +{ + int retval; + + if (sem_check_validity(sem) != 0) + return (-1); + + if ((*sem)->syssem != 0) + retval = ksem_getvalue((*sem)->semid, sval); + else { + *sval = (int)(*sem)->count; + retval = 0; + } + return (retval); +} |