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authorthorpej <thorpej@NetBSD.org>2003-01-18 10:32:11 +0000
committerthorpej <thorpej@NetBSD.org>2003-01-18 10:32:11 +0000
commitc62a74e6d5cfb2fb5034e98b983da7e2fc87709d (patch)
treef1281fd7111ddb57951e4472b342b53a2f56244a /lib/libpthread/pthread_specific.c
parentaf919042eceb8c19f42acd688efa8cf58168af5d (diff)
Merge the nathanw_sa branch.
Diffstat (limited to 'lib/libpthread/pthread_specific.c')
-rw-r--r--lib/libpthread/pthread_specific.c257
1 files changed, 257 insertions, 0 deletions
diff --git a/lib/libpthread/pthread_specific.c b/lib/libpthread/pthread_specific.c
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+/* $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--);
+}