diff options
| author | thorpej <thorpej@NetBSD.org> | 2003-01-18 10:32:11 +0000 |
|---|---|---|
| committer | thorpej <thorpej@NetBSD.org> | 2003-01-18 10:32:11 +0000 |
| commit | c62a74e6d5cfb2fb5034e98b983da7e2fc87709d (patch) | |
| tree | f1281fd7111ddb57951e4472b342b53a2f56244a /lib/libpthread/pthread_specific.c | |
| parent | af919042eceb8c19f42acd688efa8cf58168af5d (diff) | |
Merge the nathanw_sa branch.
Diffstat (limited to 'lib/libpthread/pthread_specific.c')
| -rw-r--r-- | lib/libpthread/pthread_specific.c | 257 |
1 files changed, 257 insertions, 0 deletions
diff --git a/lib/libpthread/pthread_specific.c b/lib/libpthread/pthread_specific.c new file mode 100644 index 00000000000..be7d2e93ed2 --- /dev/null +++ b/lib/libpthread/pthread_specific.c @@ -0,0 +1,257 @@ +/* $NetBSD: pthread_specific.c,v 1.2 2003/01/18 10:34:16 thorpej Exp $ */ + +/*- + * Copyright (c) 2001 The NetBSD Foundation, Inc. + * All rights reserved. + * + * This code is derived from software contributed to The NetBSD Foundation + * by Nathan J. Williams. + * + * 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, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the NetBSD + * Foundation, Inc. and its contributors. + * 4. Neither the name of The NetBSD Foundation nor the names of its + * contributors may be used to endorse or promote products derived + * from this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS + * ``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 FOUNDATION OR CONTRIBUTORS + * 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. + */ + +/* Functions and structures dealing with thread-specific data */ +#include <assert.h> +#include <errno.h> +#include <sys/cdefs.h> + +#include "pthread.h" +#include "pthread_int.h" + +static pthread_mutex_t tsd_mutex = PTHREAD_MUTEX_INITIALIZER; +static int nextkey; +int pthread__tsd_alloc[PTHREAD_KEYS_MAX]; +void (*pthread__tsd_destructors[PTHREAD_KEYS_MAX])(void *); + +__strong_alias(__libc_thr_keycreate,pthread_key_create) +__strong_alias(__libc_thr_setspecific,pthread_setspecific) +__strong_alias(__libc_thr_getspecific,pthread_getspecific) +__strong_alias(__libc_thr_keydelete,pthread_key_delete) + +int +pthread_key_create(pthread_key_t *key, void (*destructor)(void *)) +{ + int i; + + /* Get a lock on the allocation list */ + pthread_mutex_lock(&tsd_mutex); + + /* Find an avaliable slot */ + /* 1. Search from "nextkey" to the end of the list. */ + for (i = nextkey; i < PTHREAD_KEYS_MAX; i++) + if (pthread__tsd_alloc[i] == 0) + break; + + if (i == PTHREAD_KEYS_MAX) { + /* 2. If that didn't work, search from the start + * of the list back to "nextkey". + */ + for (i = 0; i < nextkey; i++) + if (pthread__tsd_alloc[i] == 0) + break; + + if (i == nextkey) { + /* If we didn't find one here, there isn't one + * to be found. + */ + pthread_mutex_unlock(&tsd_mutex); + return EAGAIN; + } + } + + /* Got one. */ + pthread__tsd_alloc[i] = 1; + nextkey = (i + 1) % PTHREAD_KEYS_MAX; + pthread__tsd_destructors[i] = destructor; + pthread_mutex_unlock(&tsd_mutex); + *key = i; + + return 0; +} + +int +pthread_key_delete(pthread_key_t key) +{ + + /* + * This is tricky. The standard says of pthread_key_create() + * that new keys have the value NULL associated with them in + * all threads. According to people who were present at the + * standardization meeting, that requirement was written + * before pthread_key_delete() was introduced, and not + * reconsidered when it was. + * + * See David Butenhof's article in comp.programming.threads: + * Subject: Re: TSD key reusing issue + * Message-ID: <u97d8.29$fL6.200@news.cpqcorp.net> + * Date: Thu, 21 Feb 2002 09:06:17 -0500 + * http://groups.google.com/groups?hl=en&selm=u97d8.29%24fL6.200%40news.cpqcorp.net + * + * Given: + * + * 1: Applications are not required to clear keys in all + * threads before calling pthread_key_delete(). + * 2: Clearing pointers without running destructors is a + * memory leak. + * 3: The pthread_key_delete() function is expressly forbidden + * to run any destructors. + * + * Option 1: Make this function effectively a no-op and + * prohibit key reuse. This is a possible resource-exhaustion + * problem given that we have a static storage area for keys, + * but having a non-static storage area would make + * pthread_setspecific() expensive (might need to realloc the + * TSD array). + * + * Option 2: Ignore the specified behavior of + * pthread_key_create() and leave the old values. If an + * application deletes a key that still has non-NULL values in + * some threads... it's probably a memory leak and hence + * incorrect anyway, and we're within our rights to let the + * application lose. However, it's possible (if unlikely) that + * the application is storing pointers to non-heap data, or + * non-pointers that have been wedged into a void pointer, so + * we can't entirely write off such applications as incorrect. + * This could also lead to running (new) destructors on old + * data that was never supposed to be associated with that + * destructor. + * + * Option 3: Follow the specified behavior of + * pthread_key_create(). Either pthread_key_create() or + * pthread_key_delete() would then have to clear the values in + * every thread's slot for that key. In order to guarantee the + * visibility of the NULL value in other threads, there would + * have to be synchronization operations in both the clearer + * and pthread_getspecific(). Putting synchronization in + * pthread_getspecific() is a big performance lose. But in + * reality, only (buggy) reuse of an old key would require + * this synchronization; for a new key, there has to be a + * memory-visibility propagating event between the call to + * pthread_key_create() and pthread_getspecific() with that + * key, so setting the entries to NULL without synchronization + * will work, subject to problem (2) above. However, it's kind + * of slow. + * + * Note that the argument in option 3 only applies because we + * keep TSD in ordinary memory which follows the pthreads + * visibility rules. The visibility rules are not required by + * the standard to apply to TSD, so this arguemnt doesn't + * apply in general, just to this implementation. + */ + + /* For the momemt, we're going with option 1. */ + pthread_mutex_lock(&tsd_mutex); + pthread__tsd_destructors[key] = NULL; + pthread_mutex_unlock(&tsd_mutex); + + return 0; +} + +int +pthread_setspecific(pthread_key_t key, const void *value) +{ + pthread_t self; + + if (pthread__tsd_alloc[key] == 0) + return EINVAL; + + self = pthread__self(); + /* + * We can't win here on constness. Having been given a + * "const void *", we can only assign it to other const void *, + * and return it from functions that are const void *, without + * generating a warning. + */ + self->pt_specific[key] = (void *) value; + + return 0; +} + +void* +pthread_getspecific(pthread_key_t key) +{ + pthread_t self; + + if (pthread__tsd_alloc[key] == 0) + return NULL; + + self = pthread__self(); + return (self->pt_specific[key]); +} + +/* Perform thread-exit-time destruction of thread-specific data. */ +void +pthread__destroy_tsd(pthread_t self) +{ + int i, done, iterations; + void *val; + void (*destructor)(void *); + + /* Butenhof, section 5.4.2 (page 167): + * + * ``Also, Pthreads sets the thread-specific data value for a + * key to NULL before calling that key's destructor (passing + * the previous value of the key) when a thread terminates [*]. + * ... + * [*] That is, unfortunately, not what the standard + * says. This is one of the problems with formal standards - + * they say what they say, not what they were intended to + * say. Somehow, an error crept in, and the sentence + * specifying that "the implementation clears the + * thread-specific data value before calling the destructor" + * was deleted. Nobody noticed, and the standard was approved + * with the error. So the standard says (by omission) that if + * you want to write a portable application using + * thread-specific data, that will not hang on thread + * termination, you must call pthread_setspecific within your + * destructor function to change the value to NULL. This would + * be silly, and any serious implementation of Pthreads will + * violate the standard in this respect. Of course, the + * standard will be fixed, probably by the 1003.1n amendment + * (assorted corrections to 1003.1c-1995), but that will take + * a while.'' + */ + + iterations = PTHREAD_DESTRUCTOR_ITERATIONS; + do { + done = 1; + for (i = 0; i < PTHREAD_KEYS_MAX; i++) { + pthread_mutex_lock(&tsd_mutex); + destructor = pthread__tsd_destructors[i]; + pthread_mutex_unlock(&tsd_mutex); + if ((self->pt_specific[i] != NULL) && + destructor != NULL) { + done = 0; + val = self->pt_specific[i]; + self->pt_specific[i] = NULL; /* see above */ + (*destructor)(val); + } + } + } while (!done && iterations--); +} |
