245 lines
7.2 KiB
C
245 lines
7.2 KiB
C
/*
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* This file contains the old semaphore code that we need to
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* preserve for glibc-2.0 backwards compatibility. Port to glibc 2.1
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* done by Cristian Gafton.
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*/
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/* Linuxthreads - a simple clone()-based implementation of Posix */
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/* threads for Linux. */
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/* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
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/* */
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/* This program is free software; you can redistribute it and/or */
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/* modify it under the terms of the GNU Library General Public License */
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/* as published by the Free Software Foundation; either version 2 */
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/* of the License, or (at your option) any later version. */
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/* */
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/* This program is distributed in the hope that it will be useful, */
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/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
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/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
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/* GNU Library General Public License for more details. */
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/* Semaphores a la POSIX 1003.1b */
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#include <shlib-compat.h>
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#if SHLIB_COMPAT(libpthread, GLIBC_2_0, GLIBC_2_1)
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#include <errno.h>
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#include "pthread.h"
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#include "internals.h"
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#include "spinlock.h"
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#include "restart.h"
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#include "queue.h"
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typedef struct {
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long int sem_status;
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int sem_spinlock;
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} old_sem_t;
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extern int __old_sem_init (old_sem_t *__sem, int __pshared, unsigned int __value);
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extern int __old_sem_wait (old_sem_t *__sem);
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extern int __old_sem_trywait (old_sem_t *__sem);
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extern int __old_sem_post (old_sem_t *__sem);
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extern int __old_sem_getvalue (old_sem_t *__sem, int *__sval);
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extern int __old_sem_destroy (old_sem_t *__sem);
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/* Maximum value the semaphore can have. */
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#define SEM_VALUE_MAX ((int) ((~0u) >> 1))
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static inline int sem_compare_and_swap(old_sem_t *sem, long oldval, long newval)
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{
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return compare_and_swap(&sem->sem_status, oldval, newval, &sem->sem_spinlock);
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}
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/* The state of a semaphore is represented by a long int encoding
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either the semaphore count if >= 0 and no thread is waiting on it,
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or the head of the list of threads waiting for the semaphore.
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To distinguish the two cases, we encode the semaphore count N
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as 2N+1, so that it has the lowest bit set.
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A sequence of sem_wait operations on a semaphore initialized to N
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result in the following successive states:
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2N+1, 2N-1, ..., 3, 1, &first_waiting_thread, &second_waiting_thread, ...
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*/
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static void sem_restart_list(pthread_descr waiting);
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int __old_sem_init(old_sem_t *sem, int pshared, unsigned int value)
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{
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if (value > SEM_VALUE_MAX) {
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errno = EINVAL;
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return -1;
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}
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if (pshared) {
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errno = ENOSYS;
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return -1;
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}
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sem->sem_spinlock = LT_SPINLOCK_INIT;
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sem->sem_status = ((long)value << 1) + 1;
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return 0;
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}
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/* Function called by pthread_cancel to remove the thread from
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waiting inside __old_sem_wait. Here we simply unconditionally
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indicate that the thread is to be woken, by returning 1. */
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static int old_sem_extricate_func(void *obj, pthread_descr th)
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{
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return 1;
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}
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int __old_sem_wait(old_sem_t * sem)
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{
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long oldstatus, newstatus;
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volatile pthread_descr self = thread_self();
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pthread_descr * th;
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pthread_extricate_if extr;
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/* Set up extrication interface */
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extr.pu_object = 0;
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extr.pu_extricate_func = old_sem_extricate_func;
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while (1) {
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/* Register extrication interface */
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__pthread_set_own_extricate_if(self, &extr);
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do {
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oldstatus = sem->sem_status;
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if ((oldstatus & 1) && (oldstatus != 1))
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newstatus = oldstatus - 2;
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else {
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newstatus = (long) self;
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self->p_nextwaiting = (pthread_descr) oldstatus;
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}
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}
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while (! sem_compare_and_swap(sem, oldstatus, newstatus));
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if (newstatus & 1) {
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/* We got the semaphore. */
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__pthread_set_own_extricate_if(self, 0);
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return 0;
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}
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/* Wait for sem_post or cancellation */
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suspend(self);
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__pthread_set_own_extricate_if(self, 0);
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/* This is a cancellation point */
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if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
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/* Remove ourselves from the waiting list if we're still on it */
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/* First check if we're at the head of the list. */
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do {
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oldstatus = sem->sem_status;
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if (oldstatus != (long) self) break;
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newstatus = (long) self->p_nextwaiting;
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}
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while (! sem_compare_and_swap(sem, oldstatus, newstatus));
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/* Now, check if we're somewhere in the list.
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There's a race condition with sem_post here, but it does not matter:
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the net result is that at the time pthread_exit is called,
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self is no longer reachable from sem->sem_status. */
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if (oldstatus != (long) self && (oldstatus & 1) == 0) {
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for (th = &(((pthread_descr) oldstatus)->p_nextwaiting);
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*th != NULL && *th != (pthread_descr) 1;
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th = &((*th)->p_nextwaiting)) {
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if (*th == self) {
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*th = self->p_nextwaiting;
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break;
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}
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}
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}
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pthread_exit(PTHREAD_CANCELED);
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}
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}
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}
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int __old_sem_trywait(old_sem_t * sem)
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{
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long oldstatus, newstatus;
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do {
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oldstatus = sem->sem_status;
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if ((oldstatus & 1) == 0 || (oldstatus == 1)) {
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errno = EAGAIN;
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return -1;
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}
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newstatus = oldstatus - 2;
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}
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while (! sem_compare_and_swap(sem, oldstatus, newstatus));
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return 0;
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}
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int __old_sem_post(old_sem_t * sem)
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{
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long oldstatus, newstatus;
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do {
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oldstatus = sem->sem_status;
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if ((oldstatus & 1) == 0)
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newstatus = 3;
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else {
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if (oldstatus >= SEM_VALUE_MAX) {
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/* Overflow */
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errno = ERANGE;
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return -1;
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}
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newstatus = oldstatus + 2;
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}
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}
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while (! sem_compare_and_swap(sem, oldstatus, newstatus));
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if ((oldstatus & 1) == 0)
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sem_restart_list((pthread_descr) oldstatus);
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return 0;
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}
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int __old_sem_getvalue(old_sem_t * sem, int * sval)
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{
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long status = sem->sem_status;
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if (status & 1)
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*sval = (int)((unsigned long) status >> 1);
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else
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*sval = 0;
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return 0;
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}
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int __old_sem_destroy(old_sem_t * sem)
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{
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if ((sem->sem_status & 1) == 0) {
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errno = EBUSY;
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return -1;
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}
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return 0;
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}
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/* Auxiliary function for restarting all threads on a waiting list,
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in priority order. */
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static void sem_restart_list(pthread_descr waiting)
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{
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pthread_descr th, towake, *p;
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/* Sort list of waiting threads by decreasing priority (insertion sort) */
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towake = NULL;
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while (waiting != (pthread_descr) 1) {
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th = waiting;
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waiting = waiting->p_nextwaiting;
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p = &towake;
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while (*p != NULL && th->p_priority < (*p)->p_priority)
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p = &((*p)->p_nextwaiting);
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th->p_nextwaiting = *p;
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*p = th;
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}
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/* Wake up threads in priority order */
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while (towake != NULL) {
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th = towake;
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towake = towake->p_nextwaiting;
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th->p_nextwaiting = NULL;
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restart(th);
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}
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}
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compat_symbol (libpthread, __old_sem_init, sem_init, GLIBC_2_0);
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compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
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compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
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compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
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compat_symbol (libpthread, __old_sem_getvalue, sem_getvalue, GLIBC_2_0);
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compat_symbol (libpthread, __old_sem_destroy, sem_destroy, GLIBC_2_0);
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#endif
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