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https://github.com/xemu-project/xemu.git
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24fa90499f
PTHREAD_MUTEX_ERRORCHECK is completely broken with respect to fork. The way to safely do fork is to bring all threads to a quiescent state by acquiring locks (either in callers---as we do for the iothread mutex---or using pthread_atfork's prepare callbacks) and then release them in the child. The problem is that releasing error-checking locks in the child fails under glibc with EPERM, because the mutex stores a different owner tid than the duplicated thread in the child process. We could make it work for locks acquired via pthread_atfork, by recreating the mutex in the child instead of unlocking it (we know that there are no other threads that could have taken the mutex; but when the lock is acquired in fork's caller that would not be possible. The simplest solution is just to forgo error checking. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
510 lines
11 KiB
C
510 lines
11 KiB
C
/*
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* Wrappers around mutex/cond/thread functions
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*
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* Copyright Red Hat, Inc. 2009
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*
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* Author:
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* Marcelo Tosatti <mtosatti@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <errno.h>
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#include <time.h>
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#include <signal.h>
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#include <stdint.h>
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#include <string.h>
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#include <limits.h>
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#include <unistd.h>
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#include <sys/time.h>
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#ifdef __linux__
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#include <sys/syscall.h>
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#include <linux/futex.h>
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#endif
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#include "qemu/thread.h"
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#include "qemu/atomic.h"
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#include "qemu/notify.h"
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static bool name_threads;
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void qemu_thread_naming(bool enable)
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{
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name_threads = enable;
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#ifndef CONFIG_THREAD_SETNAME_BYTHREAD
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/* This is a debugging option, not fatal */
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if (enable) {
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fprintf(stderr, "qemu: thread naming not supported on this host\n");
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}
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#endif
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}
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static void error_exit(int err, const char *msg)
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{
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fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err));
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abort();
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}
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void qemu_mutex_init(QemuMutex *mutex)
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{
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int err;
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err = pthread_mutex_init(&mutex->lock, NULL);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_mutex_destroy(QemuMutex *mutex)
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{
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int err;
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err = pthread_mutex_destroy(&mutex->lock);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_mutex_lock(QemuMutex *mutex)
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{
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int err;
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err = pthread_mutex_lock(&mutex->lock);
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if (err)
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error_exit(err, __func__);
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}
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int qemu_mutex_trylock(QemuMutex *mutex)
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{
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return pthread_mutex_trylock(&mutex->lock);
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}
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void qemu_mutex_unlock(QemuMutex *mutex)
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{
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int err;
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err = pthread_mutex_unlock(&mutex->lock);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_init(QemuCond *cond)
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{
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int err;
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err = pthread_cond_init(&cond->cond, NULL);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_destroy(QemuCond *cond)
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{
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int err;
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err = pthread_cond_destroy(&cond->cond);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_signal(QemuCond *cond)
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{
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int err;
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err = pthread_cond_signal(&cond->cond);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_broadcast(QemuCond *cond)
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{
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int err;
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err = pthread_cond_broadcast(&cond->cond);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
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{
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int err;
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err = pthread_cond_wait(&cond->cond, &mutex->lock);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_sem_init(QemuSemaphore *sem, int init)
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{
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int rc;
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#if defined(__APPLE__) || defined(__NetBSD__)
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rc = pthread_mutex_init(&sem->lock, NULL);
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if (rc != 0) {
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error_exit(rc, __func__);
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}
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rc = pthread_cond_init(&sem->cond, NULL);
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if (rc != 0) {
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error_exit(rc, __func__);
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}
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if (init < 0) {
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error_exit(EINVAL, __func__);
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}
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sem->count = init;
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#else
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rc = sem_init(&sem->sem, 0, init);
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if (rc < 0) {
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error_exit(errno, __func__);
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}
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#endif
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}
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void qemu_sem_destroy(QemuSemaphore *sem)
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{
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int rc;
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#if defined(__APPLE__) || defined(__NetBSD__)
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rc = pthread_cond_destroy(&sem->cond);
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if (rc < 0) {
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error_exit(rc, __func__);
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}
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rc = pthread_mutex_destroy(&sem->lock);
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if (rc < 0) {
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error_exit(rc, __func__);
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}
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#else
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rc = sem_destroy(&sem->sem);
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if (rc < 0) {
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error_exit(errno, __func__);
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}
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#endif
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}
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void qemu_sem_post(QemuSemaphore *sem)
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{
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int rc;
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#if defined(__APPLE__) || defined(__NetBSD__)
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pthread_mutex_lock(&sem->lock);
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if (sem->count == UINT_MAX) {
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rc = EINVAL;
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} else {
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sem->count++;
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rc = pthread_cond_signal(&sem->cond);
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}
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pthread_mutex_unlock(&sem->lock);
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if (rc != 0) {
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error_exit(rc, __func__);
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}
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#else
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rc = sem_post(&sem->sem);
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if (rc < 0) {
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error_exit(errno, __func__);
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}
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#endif
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}
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static void compute_abs_deadline(struct timespec *ts, int ms)
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{
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struct timeval tv;
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gettimeofday(&tv, NULL);
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ts->tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
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ts->tv_sec = tv.tv_sec + ms / 1000;
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if (ts->tv_nsec >= 1000000000) {
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ts->tv_sec++;
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ts->tv_nsec -= 1000000000;
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}
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}
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int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
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{
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int rc;
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struct timespec ts;
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#if defined(__APPLE__) || defined(__NetBSD__)
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rc = 0;
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compute_abs_deadline(&ts, ms);
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pthread_mutex_lock(&sem->lock);
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while (sem->count == 0) {
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rc = pthread_cond_timedwait(&sem->cond, &sem->lock, &ts);
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if (rc == ETIMEDOUT) {
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break;
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}
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if (rc != 0) {
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error_exit(rc, __func__);
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}
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}
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if (rc != ETIMEDOUT) {
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--sem->count;
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}
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pthread_mutex_unlock(&sem->lock);
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return (rc == ETIMEDOUT ? -1 : 0);
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#else
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if (ms <= 0) {
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/* This is cheaper than sem_timedwait. */
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do {
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rc = sem_trywait(&sem->sem);
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} while (rc == -1 && errno == EINTR);
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if (rc == -1 && errno == EAGAIN) {
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return -1;
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}
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} else {
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compute_abs_deadline(&ts, ms);
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do {
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rc = sem_timedwait(&sem->sem, &ts);
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} while (rc == -1 && errno == EINTR);
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if (rc == -1 && errno == ETIMEDOUT) {
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return -1;
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}
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}
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if (rc < 0) {
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error_exit(errno, __func__);
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}
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return 0;
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#endif
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}
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void qemu_sem_wait(QemuSemaphore *sem)
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{
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int rc;
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#if defined(__APPLE__) || defined(__NetBSD__)
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pthread_mutex_lock(&sem->lock);
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while (sem->count == 0) {
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rc = pthread_cond_wait(&sem->cond, &sem->lock);
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if (rc != 0) {
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error_exit(rc, __func__);
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}
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}
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--sem->count;
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pthread_mutex_unlock(&sem->lock);
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#else
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do {
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rc = sem_wait(&sem->sem);
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} while (rc == -1 && errno == EINTR);
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if (rc < 0) {
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error_exit(errno, __func__);
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}
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#endif
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}
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#ifdef __linux__
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#define futex(...) syscall(__NR_futex, __VA_ARGS__)
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static inline void futex_wake(QemuEvent *ev, int n)
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{
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futex(ev, FUTEX_WAKE, n, NULL, NULL, 0);
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}
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static inline void futex_wait(QemuEvent *ev, unsigned val)
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{
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futex(ev, FUTEX_WAIT, (int) val, NULL, NULL, 0);
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}
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#else
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static inline void futex_wake(QemuEvent *ev, int n)
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{
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pthread_mutex_lock(&ev->lock);
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if (n == 1) {
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pthread_cond_signal(&ev->cond);
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} else {
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pthread_cond_broadcast(&ev->cond);
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}
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pthread_mutex_unlock(&ev->lock);
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}
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static inline void futex_wait(QemuEvent *ev, unsigned val)
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{
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pthread_mutex_lock(&ev->lock);
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if (ev->value == val) {
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pthread_cond_wait(&ev->cond, &ev->lock);
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}
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pthread_mutex_unlock(&ev->lock);
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}
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#endif
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/* Valid transitions:
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* - free->set, when setting the event
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* - busy->set, when setting the event, followed by futex_wake
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* - set->free, when resetting the event
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* - free->busy, when waiting
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*
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* set->busy does not happen (it can be observed from the outside but
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* it really is set->free->busy).
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*
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* busy->free provably cannot happen; to enforce it, the set->free transition
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* is done with an OR, which becomes a no-op if the event has concurrently
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* transitioned to free or busy.
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*/
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#define EV_SET 0
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#define EV_FREE 1
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#define EV_BUSY -1
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void qemu_event_init(QemuEvent *ev, bool init)
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{
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#ifndef __linux__
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pthread_mutex_init(&ev->lock, NULL);
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pthread_cond_init(&ev->cond, NULL);
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#endif
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ev->value = (init ? EV_SET : EV_FREE);
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}
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void qemu_event_destroy(QemuEvent *ev)
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{
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#ifndef __linux__
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pthread_mutex_destroy(&ev->lock);
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pthread_cond_destroy(&ev->cond);
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#endif
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}
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void qemu_event_set(QemuEvent *ev)
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{
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if (atomic_mb_read(&ev->value) != EV_SET) {
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if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
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/* There were waiters, wake them up. */
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futex_wake(ev, INT_MAX);
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}
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}
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}
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void qemu_event_reset(QemuEvent *ev)
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{
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if (atomic_mb_read(&ev->value) == EV_SET) {
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/*
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* If there was a concurrent reset (or even reset+wait),
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* do nothing. Otherwise change EV_SET->EV_FREE.
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*/
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atomic_or(&ev->value, EV_FREE);
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}
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}
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void qemu_event_wait(QemuEvent *ev)
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{
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unsigned value;
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value = atomic_mb_read(&ev->value);
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if (value != EV_SET) {
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if (value == EV_FREE) {
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/*
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* Leave the event reset and tell qemu_event_set that there
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* are waiters. No need to retry, because there cannot be
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* a concurent busy->free transition. After the CAS, the
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* event will be either set or busy.
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*/
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if (atomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
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return;
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}
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}
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futex_wait(ev, EV_BUSY);
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}
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}
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static pthread_key_t exit_key;
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union NotifierThreadData {
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void *ptr;
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NotifierList list;
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};
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QEMU_BUILD_BUG_ON(sizeof(union NotifierThreadData) != sizeof(void *));
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void qemu_thread_atexit_add(Notifier *notifier)
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{
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union NotifierThreadData ntd;
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ntd.ptr = pthread_getspecific(exit_key);
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notifier_list_add(&ntd.list, notifier);
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pthread_setspecific(exit_key, ntd.ptr);
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}
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void qemu_thread_atexit_remove(Notifier *notifier)
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{
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union NotifierThreadData ntd;
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ntd.ptr = pthread_getspecific(exit_key);
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notifier_remove(notifier);
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pthread_setspecific(exit_key, ntd.ptr);
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}
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static void qemu_thread_atexit_run(void *arg)
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{
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union NotifierThreadData ntd = { .ptr = arg };
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notifier_list_notify(&ntd.list, NULL);
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}
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static void __attribute__((constructor)) qemu_thread_atexit_init(void)
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{
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pthread_key_create(&exit_key, qemu_thread_atexit_run);
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}
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/* Attempt to set the threads name; note that this is for debug, so
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* we're not going to fail if we can't set it.
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*/
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static void qemu_thread_set_name(QemuThread *thread, const char *name)
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{
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#ifdef CONFIG_PTHREAD_SETNAME_NP
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pthread_setname_np(thread->thread, name);
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#endif
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}
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void qemu_thread_create(QemuThread *thread, const char *name,
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void *(*start_routine)(void*),
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void *arg, int mode)
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{
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sigset_t set, oldset;
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int err;
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pthread_attr_t attr;
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err = pthread_attr_init(&attr);
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if (err) {
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error_exit(err, __func__);
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}
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if (mode == QEMU_THREAD_DETACHED) {
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err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
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if (err) {
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error_exit(err, __func__);
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}
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}
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/* Leave signal handling to the iothread. */
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sigfillset(&set);
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pthread_sigmask(SIG_SETMASK, &set, &oldset);
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err = pthread_create(&thread->thread, &attr, start_routine, arg);
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if (err)
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error_exit(err, __func__);
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if (name_threads) {
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qemu_thread_set_name(thread, name);
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}
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pthread_sigmask(SIG_SETMASK, &oldset, NULL);
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pthread_attr_destroy(&attr);
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}
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void qemu_thread_get_self(QemuThread *thread)
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{
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thread->thread = pthread_self();
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}
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bool qemu_thread_is_self(QemuThread *thread)
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{
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return pthread_equal(pthread_self(), thread->thread);
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}
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void qemu_thread_exit(void *retval)
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{
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pthread_exit(retval);
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}
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void *qemu_thread_join(QemuThread *thread)
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{
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int err;
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void *ret;
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err = pthread_join(thread->thread, &ret);
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if (err) {
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error_exit(err, __func__);
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}
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return ret;
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}
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