[BACK]Return to pthread_tsd.c CVS log [TXT][DIR] Up to [cvs.NetBSD.org] / src / lib / libpthread

File: [cvs.NetBSD.org] / src / lib / libpthread / pthread_tsd.c (download)

Revision 1.11.8.1, Tue Nov 24 17:37:16 2015 UTC (4 years, 4 months ago) by martin
Branch: netbsd-7
CVS Tags: netbsd-7-nhusb-base-20170116, netbsd-7-nhusb-base, netbsd-7-nhusb, netbsd-7-2-RELEASE, netbsd-7-1-RELEASE, netbsd-7-1-RC2, netbsd-7-1-RC1, netbsd-7-1-2-RELEASE, netbsd-7-1-1-RELEASE, netbsd-7-1
Changes since 1.11: +56 -13 lines

Pull up following revision(s) (requested by manu in ticket #829):
	lib/libpthread_dbg/pthread_dbg.c: revision 1.43 (via patch)
	lib/libpthread/pthread_int.h: revision 1.91-1.92 (via patch)
	lib/libc/stdlib/jemalloc.c: revision 1.37-1.38
	lib/libpthread/pthread_tsd.c: revision 1.12-1.14 (via patch)
	include/limits.h: revision 1.34 (via patch)
	lib/libpthread/pthread.c: revision 1.146-1.147 (via patch)
	lib/libpthread/pthread_key_create.3: revision 1.7 (via patch)

libpthread:

Make PTHREAD_KEYS_MAX dynamically adjustable
NetBSD's PTHREAD_KEYS_MAX is set to 256, which is low compared to
other systems like Linux (1024) or MacOS X (512). As a result some
setups tested on Linux will exhibit problems on NetBSD because of
pthread_keys usage beyond the limit. This happens for instance on
Apache with various module loaded, and in this case no particular
developper can be blamed for going beyond the limit, since several
modules from different sources contribute to the problem.
This patch makes the limit conigurable through the PTHREAD_KEYS_MAX
environement variable. If undefined, the default remains unchanged
(256). In any case, the value cannot be lowered below POSIX-mandated
_POSIX_THREAD_KEYS_MAX (128).

While there:
- use EXIT_FAILURE instead of 1 when calling err(3) in libpthread.
- Reset _POSIX_THREAD_KEYS_MAX to POSIX mandated 128, instead of 256.

Fix previous: Can't use calloc/malloc before we complete initialization
of the thread library, because malloc uses pthread_foo_specific, and it will
end up initializing itself incorrectly.

Thanks rump for not letting us use even mmap during initialization.

libc/jemalloc:

Fix non _REENTRANT build.
Defer using pthread keys until we are threaded.
From Christos, fixes PR port-arm/50087 by allowing malloc calls prior
to libpthread initialization.

/*	$NetBSD: pthread_tsd.c,v 1.11.8.1 2015/11/24 17:37:16 martin Exp $	*/

/*-
 * Copyright (c) 2001, 2007 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Nathan J. Williams, by Andrew Doran, and by Christos Zoulas.
 *
 * 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.
 *
 * 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.
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: pthread_tsd.c,v 1.11.8.1 2015/11/24 17:37:16 martin Exp $");

/* Functions and structures dealing with thread-specific data */
#include <errno.h>
#include <sys/mman.h>

#include "pthread.h"
#include "pthread_int.h"
#include "reentrant.h"

int pthread_keys_max;
static pthread_mutex_t tsd_mutex = PTHREAD_MUTEX_INITIALIZER;
static int nextkey;

PTQ_HEAD(pthread__tsd_list, pt_specific) *pthread__tsd_list = NULL;
void (**pthread__tsd_destructors)(void *) = NULL;

__strong_alias(__libc_thr_keycreate,pthread_key_create)
__strong_alias(__libc_thr_keydelete,pthread_key_delete)

static void
/*ARGSUSED*/
null_destructor(void *p)
{
}

#include <err.h>
#include <stdlib.h>
#include <stdio.h>

/* Can't use mmap directly so early in the process because rump hijacks it */
void *_mmap(void *, size_t, int, int, int, off_t);

void *
pthread_tsd_init(size_t *tlen)
{
	char *pkm;
	size_t alen;
	char *arena;

	if ((pkm = pthread__getenv("PTHREAD_KEYS_MAX")) != NULL) {
		pthread_keys_max = (int)strtol(pkm, NULL, 0);
		if (pthread_keys_max < _POSIX_THREAD_KEYS_MAX)
			pthread_keys_max = _POSIX_THREAD_KEYS_MAX;
	} else {
		pthread_keys_max = PTHREAD_KEYS_MAX;
	}

	/*
	 * Can't use malloc here yet, because malloc will use the fake
	 * libc thread functions to initialize itself, so mmap the space.
	 */
	*tlen = sizeof(struct __pthread_st)
	    + pthread_keys_max * sizeof(struct pt_specific);
	alen = *tlen
	    + sizeof(*pthread__tsd_list) * pthread_keys_max
	    + sizeof(*pthread__tsd_destructors) * pthread_keys_max;

	arena = _mmap(NULL, alen, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
	if (arena == MAP_FAILED) {
		pthread_keys_max = 0;
		return NULL;
	}

	pthread__tsd_list = (void *)arena;
	arena += sizeof(*pthread__tsd_list) * pthread_keys_max;
	pthread__tsd_destructors = (void *)arena;
	arena += sizeof(*pthread__tsd_destructors) * pthread_keys_max;
	return arena;
}

int
pthread_key_create(pthread_key_t *key, void (*destructor)(void *))
{
	int i;

	if (__predict_false(__uselibcstub))
		return __libc_thr_keycreate_stub(key, destructor);

	/* Get a lock on the allocation list */
	pthread_mutex_lock(&tsd_mutex);
	
	/* Find an available slot:
	 * The condition for an available slot is one with the destructor
	 * not being NULL. If the desired destructor is NULL we set it to 
	 * our own internal destructor to satisfy the non NULL condition.
	 */
	/* 1. Search from "nextkey" to the end of the list. */
	for (i = nextkey; i < pthread_keys_max; i++)
		if (pthread__tsd_destructors[i] == NULL)
			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_destructors[i] == NULL)
				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__assert(PTQ_EMPTY(&pthread__tsd_list[i]));
	pthread__tsd_destructors[i] = destructor ? destructor : null_destructor;

	nextkey = (i + 1) % pthread_keys_max;
	pthread_mutex_unlock(&tsd_mutex);
	*key = i;

	return 0;
}

/*
 * Each thread holds an array of pthread_keys_max pt_specific list
 * elements. When an element is used it is inserted into the appropriate
 * key bucket of pthread__tsd_list. This means that ptqe_prev == NULL,
 * means that the element is not threaded, ptqe_prev != NULL it is
 * already part of the list. When we set to a NULL value we delete from the
 * list if it was in the list, and when we set to non-NULL value, we insert
 * in the list if it was not already there.
 *
 * We keep this global array of lists of threads that have called
 * pthread_set_specific with non-null values, for each key so that
 * we don't have to check all threads for non-NULL values in
 * pthread_key_destroy
 *
 * We could keep an accounting of the number of specific used
 * entries per thread, so that we can update pt_havespecific when we delete
 * the last one, but we don't bother for now
 */
int
pthread__add_specific(pthread_t self, pthread_key_t key, const void *value)
{
	struct pt_specific *pt;

	pthread__assert(key >= 0 && key < pthread_keys_max);

	pthread_mutex_lock(&tsd_mutex);
	pthread__assert(pthread__tsd_destructors[key] != NULL);
	pt = &self->pt_specific[key];
	self->pt_havespecific = 1;
	if (value) {
		if (pt->pts_next.ptqe_prev == NULL)
			PTQ_INSERT_HEAD(&pthread__tsd_list[key], pt, pts_next);
	} else {
		if (pt->pts_next.ptqe_prev != NULL) {
			PTQ_REMOVE(&pthread__tsd_list[key], pt, pts_next);
			pt->pts_next.ptqe_prev = NULL;
		}
	}
	pt->pts_value = __UNCONST(value);
	pthread_mutex_unlock(&tsd_mutex);

	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 the argument doesn't
	 * apply in general, just to this implementation.
	 */

	/*
	 * We do option 3; we find the list of all pt_specific structures
	 * threaded on the key we are deleting, unthread them, and set the
	 * pointer to NULL. Finally we unthread the entry, freeing it for
	 * further use.
	 *
	 * We don't call the destructor here, it is the responsibility
	 * of the application to cleanup the storage:
	 * 	http://pubs.opengroup.org/onlinepubs/9699919799/functions/\
	 *	pthread_key_delete.html
	 */
	struct pt_specific *pt;

	if (__predict_false(__uselibcstub))
		return __libc_thr_keydelete_stub(key);

	pthread__assert(key >= 0 && key < pthread_keys_max);

	pthread_mutex_lock(&tsd_mutex);

	pthread__assert(pthread__tsd_destructors[key] != NULL);

	while ((pt = PTQ_FIRST(&pthread__tsd_list[key])) != NULL) {
		PTQ_REMOVE(&pthread__tsd_list[key], pt, pts_next);
		pt->pts_value = NULL;
		pt->pts_next.ptqe_prev = NULL;
	}

	pthread__tsd_destructors[key] = NULL;
	pthread_mutex_unlock(&tsd_mutex);

	return 0;
}

/* 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 *);

	if (!self->pt_havespecific)
		return;
	pthread_mutex_unlock(&self->pt_lock);

	/* 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 = 4; /* We're not required to try very hard */
	do {
		done = 1;
		for (i = 0; i < pthread_keys_max; i++) {
			struct pt_specific *pt = &self->pt_specific[i];
			if (pt->pts_next.ptqe_prev == NULL)
				continue;
			pthread_mutex_lock(&tsd_mutex);

			if (pt->pts_next.ptqe_prev != NULL)  {
				PTQ_REMOVE(&pthread__tsd_list[i], pt, pts_next);
				val = pt->pts_value;
				pt->pts_value = NULL;
				pt->pts_next.ptqe_prev = NULL;
				destructor = pthread__tsd_destructors[i];
			} else
				destructor = NULL;

			pthread_mutex_unlock(&tsd_mutex);
			if (destructor != NULL) {
				done = 0;
				(*destructor)(val);
			}
		}
	} while (!done && iterations--);

	self->pt_havespecific = 0;
	pthread_mutex_lock(&self->pt_lock);
}