610 lines
16 KiB
C
610 lines
16 KiB
C
/* $NetBSD: pthread_mutex.c,v 1.54 2012/08/16 04:49:47 matt Exp $ */
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/*-
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* Copyright (c) 2001, 2003, 2006, 2007, 2008 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Nathan J. Williams, by Jason R. Thorpe, and by Andrew Doran.
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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, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE 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 BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* To track threads waiting for mutexes to be released, we use lockless
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* lists built on atomic operations and memory barriers.
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*
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* A simple spinlock would be faster and make the code easier to
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* follow, but spinlocks are problematic in userspace. If a thread is
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* preempted by the kernel while holding a spinlock, any other thread
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* attempting to acquire that spinlock will needlessly busy wait.
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*
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* There is no good way to know that the holding thread is no longer
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* running, nor to request a wake-up once it has begun running again.
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* Of more concern, threads in the SCHED_FIFO class do not have a
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* limited time quantum and so could spin forever, preventing the
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* thread holding the spinlock from getting CPU time: it would never
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* be released.
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*/
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#include <sys/cdefs.h>
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__RCSID("$NetBSD: pthread_mutex.c,v 1.54 2012/08/16 04:49:47 matt Exp $");
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#include <sys/types.h>
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#include <sys/lwpctl.h>
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#include <sys/lock.h>
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#include <errno.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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#include "pthread.h"
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#include "pthread_int.h"
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#define MUTEX_WAITERS_BIT ((uintptr_t)0x01)
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#define MUTEX_RECURSIVE_BIT ((uintptr_t)0x02)
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#define MUTEX_DEFERRED_BIT ((uintptr_t)0x04)
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#define MUTEX_THREAD ((uintptr_t)-16L)
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#define MUTEX_HAS_WAITERS(x) ((uintptr_t)(x) & MUTEX_WAITERS_BIT)
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#define MUTEX_RECURSIVE(x) ((uintptr_t)(x) & MUTEX_RECURSIVE_BIT)
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#define MUTEX_OWNER(x) ((uintptr_t)(x) & MUTEX_THREAD)
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#if __GNUC_PREREQ__(3, 0)
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#define NOINLINE __attribute ((noinline))
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#else
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#define NOINLINE /* nothing */
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#endif
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static void pthread__mutex_wakeup(pthread_t, pthread_mutex_t *);
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static int pthread__mutex_lock_slow(pthread_mutex_t *);
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static int pthread__mutex_unlock_slow(pthread_mutex_t *);
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static void pthread__mutex_pause(void);
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int _pthread_mutex_held_np(pthread_mutex_t *);
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pthread_t _pthread_mutex_owner_np(pthread_mutex_t *);
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__weak_alias(pthread_mutex_held_np,_pthread_mutex_held_np)
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__weak_alias(pthread_mutex_owner_np,_pthread_mutex_owner_np)
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__strong_alias(__libc_mutex_init,pthread_mutex_init)
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__strong_alias(__libc_mutex_lock,pthread_mutex_lock)
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__strong_alias(__libc_mutex_trylock,pthread_mutex_trylock)
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__strong_alias(__libc_mutex_unlock,pthread_mutex_unlock)
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__strong_alias(__libc_mutex_destroy,pthread_mutex_destroy)
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__strong_alias(__libc_mutexattr_init,pthread_mutexattr_init)
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__strong_alias(__libc_mutexattr_destroy,pthread_mutexattr_destroy)
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__strong_alias(__libc_mutexattr_settype,pthread_mutexattr_settype)
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int
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pthread_mutex_init(pthread_mutex_t *ptm, const pthread_mutexattr_t *attr)
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{
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intptr_t type;
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if (attr == NULL)
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type = PTHREAD_MUTEX_NORMAL;
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else
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type = (intptr_t)attr->ptma_private;
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switch (type) {
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case PTHREAD_MUTEX_ERRORCHECK:
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__cpu_simple_lock_set(&ptm->ptm_errorcheck);
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ptm->ptm_owner = NULL;
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break;
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case PTHREAD_MUTEX_RECURSIVE:
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__cpu_simple_lock_clear(&ptm->ptm_errorcheck);
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ptm->ptm_owner = (void *)MUTEX_RECURSIVE_BIT;
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break;
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default:
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__cpu_simple_lock_clear(&ptm->ptm_errorcheck);
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ptm->ptm_owner = NULL;
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break;
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}
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ptm->ptm_magic = _PT_MUTEX_MAGIC;
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ptm->ptm_waiters = NULL;
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ptm->ptm_recursed = 0;
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return 0;
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}
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int
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pthread_mutex_destroy(pthread_mutex_t *ptm)
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{
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pthread__error(EINVAL, "Invalid mutex",
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ptm->ptm_magic == _PT_MUTEX_MAGIC);
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pthread__error(EBUSY, "Destroying locked mutex",
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MUTEX_OWNER(ptm->ptm_owner) == 0);
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ptm->ptm_magic = _PT_MUTEX_DEAD;
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return 0;
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}
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int
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pthread_mutex_lock(pthread_mutex_t *ptm)
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{
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pthread_t self;
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void *val;
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self = pthread__self();
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val = atomic_cas_ptr(&ptm->ptm_owner, NULL, self);
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if (__predict_true(val == NULL)) {
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#ifndef PTHREAD__ATOMIC_IS_MEMBAR
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membar_enter();
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#endif
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return 0;
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}
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return pthread__mutex_lock_slow(ptm);
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}
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/* We want function call overhead. */
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NOINLINE static void
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pthread__mutex_pause(void)
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{
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pthread__smt_pause();
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}
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/*
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* Spin while the holder is running. 'lwpctl' gives us the true
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* status of the thread. pt_blocking is set by libpthread in order
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* to cut out system call and kernel spinlock overhead on remote CPUs
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* (could represent many thousands of clock cycles). pt_blocking also
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* makes this thread yield if the target is calling sched_yield().
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*/
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NOINLINE static void *
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pthread__mutex_spin(pthread_mutex_t *ptm, pthread_t owner)
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{
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pthread_t thread;
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unsigned int count, i;
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for (count = 2;; owner = ptm->ptm_owner) {
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thread = (pthread_t)MUTEX_OWNER(owner);
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if (thread == NULL)
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break;
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if (thread->pt_lwpctl->lc_curcpu == LWPCTL_CPU_NONE ||
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thread->pt_blocking)
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break;
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if (count < 128)
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count += count;
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for (i = count; i != 0; i--)
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pthread__mutex_pause();
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}
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return owner;
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}
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NOINLINE static int
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pthread__mutex_lock_slow(pthread_mutex_t *ptm)
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{
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void *waiters, *new, *owner, *next;
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pthread_t self;
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pthread__error(EINVAL, "Invalid mutex",
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ptm->ptm_magic == _PT_MUTEX_MAGIC);
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owner = ptm->ptm_owner;
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self = pthread__self();
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/* Recursive or errorcheck? */
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if (MUTEX_OWNER(owner) == (uintptr_t)self) {
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if (MUTEX_RECURSIVE(owner)) {
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if (ptm->ptm_recursed == INT_MAX)
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return EAGAIN;
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ptm->ptm_recursed++;
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return 0;
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}
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if (__SIMPLELOCK_LOCKED_P(&ptm->ptm_errorcheck))
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return EDEADLK;
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}
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for (;; owner = ptm->ptm_owner) {
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/* Spin while the owner is running. */
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owner = pthread__mutex_spin(ptm, owner);
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/* If it has become free, try to acquire it again. */
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if (MUTEX_OWNER(owner) == 0) {
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do {
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new = (void *)
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((uintptr_t)self | (uintptr_t)owner);
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next = atomic_cas_ptr(&ptm->ptm_owner, owner,
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new);
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if (next == owner) {
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#ifndef PTHREAD__ATOMIC_IS_MEMBAR
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membar_enter();
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#endif
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return 0;
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}
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owner = next;
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} while (MUTEX_OWNER(owner) == 0);
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/*
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* We have lost the race to acquire the mutex.
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* The new owner could be running on another
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* CPU, in which case we should spin and avoid
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* the overhead of blocking.
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*/
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continue;
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}
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/*
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* Nope, still held. Add thread to the list of waiters.
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* Issue a memory barrier to ensure mutexwait/mutexnext
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* are visible before we enter the waiters list.
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*/
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self->pt_mutexwait = 1;
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for (waiters = ptm->ptm_waiters;; waiters = next) {
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self->pt_mutexnext = waiters;
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membar_producer();
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next = atomic_cas_ptr(&ptm->ptm_waiters, waiters, self);
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if (next == waiters)
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break;
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}
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/*
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* Set the waiters bit and block.
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*
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* Note that the mutex can become unlocked before we set
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* the waiters bit. If that happens it's not safe to sleep
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* as we may never be awoken: we must remove the current
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* thread from the waiters list and try again.
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*
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* Because we are doing this atomically, we can't remove
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* one waiter: we must remove all waiters and awken them,
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* then sleep in _lwp_park() until we have been awoken.
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*
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* Issue a memory barrier to ensure that we are reading
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* the value of ptm_owner/pt_mutexwait after we have entered
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* the waiters list (the CAS itself must be atomic).
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*/
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membar_consumer();
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for (owner = ptm->ptm_owner;; owner = next) {
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if (MUTEX_HAS_WAITERS(owner))
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break;
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if (MUTEX_OWNER(owner) == 0) {
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pthread__mutex_wakeup(self, ptm);
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break;
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}
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new = (void *)((uintptr_t)owner | MUTEX_WAITERS_BIT);
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next = atomic_cas_ptr(&ptm->ptm_owner, owner, new);
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if (next == owner) {
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/*
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* pthread_mutex_unlock() can do a
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* non-interlocked CAS. We cannot
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* know if our attempt to set the
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* waiters bit has succeeded while
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* the holding thread is running.
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* There are many assumptions; see
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* sys/kern/kern_mutex.c for details.
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* In short, we must spin if we see
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* that the holder is running again.
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*/
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membar_sync();
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next = pthread__mutex_spin(ptm, owner);
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}
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}
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/*
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* We may have been awoken by the current thread above,
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* or will be awoken by the current holder of the mutex.
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* The key requirement is that we must not proceed until
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* told that we are no longer waiting (via pt_mutexwait
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* being set to zero). Otherwise it is unsafe to re-enter
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* the thread onto the waiters list.
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*/
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while (self->pt_mutexwait) {
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self->pt_blocking++;
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(void)_lwp_park(NULL, self->pt_unpark,
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__UNVOLATILE(&ptm->ptm_waiters),
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__UNVOLATILE(&ptm->ptm_waiters));
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self->pt_unpark = 0;
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self->pt_blocking--;
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membar_sync();
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}
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}
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}
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int
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pthread_mutex_trylock(pthread_mutex_t *ptm)
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{
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pthread_t self;
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void *val, *new, *next;
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self = pthread__self();
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val = atomic_cas_ptr(&ptm->ptm_owner, NULL, self);
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if (__predict_true(val == NULL)) {
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#ifndef PTHREAD__ATOMIC_IS_MEMBAR
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membar_enter();
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#endif
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return 0;
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}
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if (MUTEX_RECURSIVE(val)) {
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if (MUTEX_OWNER(val) == 0) {
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new = (void *)((uintptr_t)self | (uintptr_t)val);
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next = atomic_cas_ptr(&ptm->ptm_owner, val, new);
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if (__predict_true(next == val)) {
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#ifndef PTHREAD__ATOMIC_IS_MEMBAR
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membar_enter();
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#endif
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return 0;
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}
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}
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if (MUTEX_OWNER(val) == (uintptr_t)self) {
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if (ptm->ptm_recursed == INT_MAX)
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return EAGAIN;
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ptm->ptm_recursed++;
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return 0;
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}
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}
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return EBUSY;
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}
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int
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pthread_mutex_unlock(pthread_mutex_t *ptm)
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{
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pthread_t self;
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void *value;
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/*
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* Note this may be a non-interlocked CAS. See lock_slow()
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* above and sys/kern/kern_mutex.c for details.
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*/
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#ifndef PTHREAD__ATOMIC_IS_MEMBAR
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membar_exit();
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#endif
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self = pthread__self();
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value = atomic_cas_ptr_ni(&ptm->ptm_owner, self, NULL);
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if (__predict_true(value == self)) {
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pthread__smt_wake();
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return 0;
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}
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return pthread__mutex_unlock_slow(ptm);
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}
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NOINLINE static int
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pthread__mutex_unlock_slow(pthread_mutex_t *ptm)
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{
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pthread_t self, owner, new;
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int weown, error, deferred;
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pthread__error(EINVAL, "Invalid mutex",
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ptm->ptm_magic == _PT_MUTEX_MAGIC);
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self = pthread__self();
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owner = ptm->ptm_owner;
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weown = (MUTEX_OWNER(owner) == (uintptr_t)self);
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deferred = (int)((uintptr_t)owner & MUTEX_DEFERRED_BIT);
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error = 0;
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if (__SIMPLELOCK_LOCKED_P(&ptm->ptm_errorcheck)) {
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if (!weown) {
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error = EPERM;
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new = owner;
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} else {
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new = NULL;
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}
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} else if (MUTEX_RECURSIVE(owner)) {
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if (!weown) {
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error = EPERM;
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new = owner;
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} else if (ptm->ptm_recursed) {
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ptm->ptm_recursed--;
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new = owner;
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} else {
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new = (pthread_t)MUTEX_RECURSIVE_BIT;
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}
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} else {
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pthread__error(EPERM,
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"Unlocking unlocked mutex", (owner != NULL));
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pthread__error(EPERM,
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"Unlocking mutex owned by another thread", weown);
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new = NULL;
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}
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/*
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* Release the mutex. If there appear to be waiters, then
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* wake them up.
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*/
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if (new != owner) {
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owner = atomic_swap_ptr(&ptm->ptm_owner, new);
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if (MUTEX_HAS_WAITERS(owner) != 0) {
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pthread__mutex_wakeup(self, ptm);
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return 0;
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}
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}
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/*
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* There were no waiters, but we may have deferred waking
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* other threads until mutex unlock - we must wake them now.
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*/
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if (!deferred)
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return error;
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if (self->pt_nwaiters == 1) {
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/*
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* If the calling thread is about to block, defer
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* unparking the target until _lwp_park() is called.
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*/
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if (self->pt_willpark && self->pt_unpark == 0) {
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self->pt_unpark = self->pt_waiters[0];
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} else {
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(void)_lwp_unpark(self->pt_waiters[0],
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__UNVOLATILE(&ptm->ptm_waiters));
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}
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} else {
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(void)_lwp_unpark_all(self->pt_waiters, self->pt_nwaiters,
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__UNVOLATILE(&ptm->ptm_waiters));
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}
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self->pt_nwaiters = 0;
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return error;
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}
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static void
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pthread__mutex_wakeup(pthread_t self, pthread_mutex_t *ptm)
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{
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pthread_t thread, next;
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ssize_t n, rv;
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/*
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* Take ownership of the current set of waiters. No
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* need for a memory barrier following this, all loads
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* are dependent upon 'thread'.
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*/
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thread = atomic_swap_ptr(&ptm->ptm_waiters, NULL);
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pthread__smt_wake();
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for (;;) {
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/*
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* Pull waiters from the queue and add to our list.
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* Use a memory barrier to ensure that we safely
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* read the value of pt_mutexnext before 'thread'
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* sees pt_mutexwait being cleared.
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*/
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for (n = self->pt_nwaiters, self->pt_nwaiters = 0;
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n < pthread__unpark_max && thread != NULL;
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thread = next) {
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next = thread->pt_mutexnext;
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if (thread != self) {
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self->pt_waiters[n++] = thread->pt_lid;
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membar_sync();
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}
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thread->pt_mutexwait = 0;
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/* No longer safe to touch 'thread' */
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}
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switch (n) {
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case 0:
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return;
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case 1:
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/*
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* If the calling thread is about to block,
|
|
* defer unparking the target until _lwp_park()
|
|
* is called.
|
|
*/
|
|
if (self->pt_willpark && self->pt_unpark == 0) {
|
|
self->pt_unpark = self->pt_waiters[0];
|
|
return;
|
|
}
|
|
rv = (ssize_t)_lwp_unpark(self->pt_waiters[0],
|
|
__UNVOLATILE(&ptm->ptm_waiters));
|
|
if (rv != 0 && errno != EALREADY && errno != EINTR &&
|
|
errno != ESRCH) {
|
|
pthread__errorfunc(__FILE__, __LINE__,
|
|
__func__, "_lwp_unpark failed");
|
|
}
|
|
return;
|
|
default:
|
|
rv = _lwp_unpark_all(self->pt_waiters, (size_t)n,
|
|
__UNVOLATILE(&ptm->ptm_waiters));
|
|
if (rv != 0 && errno != EINTR) {
|
|
pthread__errorfunc(__FILE__, __LINE__,
|
|
__func__, "_lwp_unpark_all failed");
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
int
|
|
pthread_mutexattr_init(pthread_mutexattr_t *attr)
|
|
{
|
|
|
|
attr->ptma_magic = _PT_MUTEXATTR_MAGIC;
|
|
attr->ptma_private = (void *)PTHREAD_MUTEX_DEFAULT;
|
|
return 0;
|
|
}
|
|
|
|
int
|
|
pthread_mutexattr_destroy(pthread_mutexattr_t *attr)
|
|
{
|
|
|
|
pthread__error(EINVAL, "Invalid mutex attribute",
|
|
attr->ptma_magic == _PT_MUTEXATTR_MAGIC);
|
|
|
|
return 0;
|
|
}
|
|
|
|
int
|
|
pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *typep)
|
|
{
|
|
|
|
pthread__error(EINVAL, "Invalid mutex attribute",
|
|
attr->ptma_magic == _PT_MUTEXATTR_MAGIC);
|
|
|
|
*typep = (int)(intptr_t)attr->ptma_private;
|
|
return 0;
|
|
}
|
|
|
|
int
|
|
pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type)
|
|
{
|
|
|
|
pthread__error(EINVAL, "Invalid mutex attribute",
|
|
attr->ptma_magic == _PT_MUTEXATTR_MAGIC);
|
|
|
|
switch (type) {
|
|
case PTHREAD_MUTEX_NORMAL:
|
|
case PTHREAD_MUTEX_ERRORCHECK:
|
|
case PTHREAD_MUTEX_RECURSIVE:
|
|
attr->ptma_private = (void *)(intptr_t)type;
|
|
return 0;
|
|
default:
|
|
return EINVAL;
|
|
}
|
|
}
|
|
|
|
void
|
|
pthread__mutex_deferwake(pthread_t self, pthread_mutex_t *ptm)
|
|
{
|
|
|
|
if (__predict_false(ptm == NULL ||
|
|
MUTEX_OWNER(ptm->ptm_owner) != (uintptr_t)self)) {
|
|
(void)_lwp_unpark_all(self->pt_waiters, self->pt_nwaiters,
|
|
__UNVOLATILE(&ptm->ptm_waiters));
|
|
self->pt_nwaiters = 0;
|
|
} else {
|
|
atomic_or_ulong((volatile unsigned long *)
|
|
(uintptr_t)&ptm->ptm_owner,
|
|
(unsigned long)MUTEX_DEFERRED_BIT);
|
|
}
|
|
}
|
|
|
|
int
|
|
_pthread_mutex_held_np(pthread_mutex_t *ptm)
|
|
{
|
|
|
|
return MUTEX_OWNER(ptm->ptm_owner) == (uintptr_t)pthread__self();
|
|
}
|
|
|
|
pthread_t
|
|
_pthread_mutex_owner_np(pthread_mutex_t *ptm)
|
|
{
|
|
|
|
return (pthread_t)MUTEX_OWNER(ptm->ptm_owner);
|
|
}
|