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/*
* This file contains the old semaphore code that we need to
* preserve for glibc-2.0 backwards compatibility. Port to glibc 2.1
* done by Cristian Gafton.
*/
/* Linuxthreads - a simple clone()-based implementation of Posix */
/* threads for Linux. */
/* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
/* */
/* This program is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Library General Public License */
/* as published by the Free Software Foundation; either version 2 */
/* of the License, or (at your option) any later version. */
/* */
/* This program is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
/* GNU Library General Public License for more details. */
/* Semaphores a la POSIX 1003.1b */
#include <errno.h>
#include "pthread.h"
#include "internals.h"
#include "spinlock.h"
#include "restart.h"
#include "queue.h"
typedef struct {
long int sem_status;
int sem_spinlock;
} old_sem_t;
/* Maximum value the semaphore can have. */
#define SEM_VALUE_MAX ((int) ((~0u) >> 1))
static inline int sem_compare_and_swap(old_sem_t *sem, long oldval, long newval)
{
return compare_and_swap(&sem->sem_status, oldval, newval, &sem->sem_spinlock);
}
/* The state of a semaphore is represented by a long int encoding
either the semaphore count if >= 0 and no thread is waiting on it,
or the head of the list of threads waiting for the semaphore.
To distinguish the two cases, we encode the semaphore count N
as 2N+1, so that it has the lowest bit set.
A sequence of sem_wait operations on a semaphore initialized to N
result in the following successive states:
2N+1, 2N-1, ..., 3, 1, &first_waiting_thread, &second_waiting_thread, ...
*/
static void sem_restart_list(pthread_descr waiting);
int __old_sem_init(old_sem_t *sem, int pshared, unsigned int value)
{
if (value > SEM_VALUE_MAX) {
errno = EINVAL;
return -1;
}
if (pshared) {
errno = ENOSYS;
return -1;
}
sem->sem_spinlock = 0;
sem->sem_status = ((long)value << 1) + 1;
return 0;
}
/* Function called by pthread_cancel to remove the thread from
waiting inside __old_sem_wait. Here we simply unconditionally
indicate that the thread is to be woken, by returning 1. */
static int old_sem_extricate_func(void *obj, pthread_descr th)
{
return 1;
}
int __old_sem_wait(old_sem_t * sem)
{
long oldstatus, newstatus;
volatile pthread_descr self = thread_self();
pthread_descr * th;
pthread_extricate_if extr;
/* Set up extrication interface */
extr.pu_object = 0;
extr.pu_extricate_func = old_sem_extricate_func;
while (1) {
/* Register extrication interface */
__pthread_set_own_extricate_if(self, &extr);
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) && (oldstatus != 1))
newstatus = oldstatus - 2;
else {
newstatus = (long) self;
self->p_nextwaiting = (pthread_descr) oldstatus;
}
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
if (newstatus & 1) {
/* We got the semaphore. */
__pthread_set_own_extricate_if(self, 0);
return 0;
}
/* Wait for sem_post or cancellation */
suspend(self);
__pthread_set_own_extricate_if(self, 0);
/* This is a cancellation point */
if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
/* Remove ourselves from the waiting list if we're still on it */
/* First check if we're at the head of the list. */
do {
oldstatus = sem->sem_status;
if (oldstatus != (long) self) break;
newstatus = (long) self->p_nextwaiting;
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
/* Now, check if we're somewhere in the list.
There's a race condition with sem_post here, but it does not matter:
the net result is that at the time pthread_exit is called,
self is no longer reachable from sem->sem_status. */
if (oldstatus != (long) self && (oldstatus & 1) == 0) {
for (th = &(((pthread_descr) oldstatus)->p_nextwaiting);
*th != NULL && *th != (pthread_descr) 1;
th = &((*th)->p_nextwaiting)) {
if (*th == self) {
*th = self->p_nextwaiting;
break;
}
}
}
pthread_exit(PTHREAD_CANCELED);
}
}
}
int __old_sem_trywait(old_sem_t * sem)
{
long oldstatus, newstatus;
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) == 0 || (oldstatus == 1)) {
errno = EAGAIN;
return -1;
}
newstatus = oldstatus - 2;
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
return 0;
}
int __old_sem_post(old_sem_t * sem)
{
long oldstatus, newstatus;
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) == 0)
newstatus = 3;
else {
if (oldstatus >= SEM_VALUE_MAX) {
/* Overflow */
errno = ERANGE;
return -1;
}
newstatus = oldstatus + 2;
}
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
if ((oldstatus & 1) == 0)
sem_restart_list((pthread_descr) oldstatus);
return 0;
}
int __old_sem_getvalue(old_sem_t * sem, int * sval)
{
long status = sem->sem_status;
if (status & 1)
*sval = (int)((unsigned long) status >> 1);
else
*sval = 0;
return 0;
}
int __old_sem_destroy(old_sem_t * sem)
{
if ((sem->sem_status & 1) == 0) {
errno = EBUSY;
return -1;
}
return 0;
}
/* Auxiliary function for restarting all threads on a waiting list,
in priority order. */
static void sem_restart_list(pthread_descr waiting)
{
pthread_descr th, towake, *p;
/* Sort list of waiting threads by decreasing priority (insertion sort) */
towake = NULL;
while (waiting != (pthread_descr) 1) {
th = waiting;
waiting = waiting->p_nextwaiting;
p = &towake;
while (*p != NULL && th->p_priority < (*p)->p_priority)
p = &((*p)->p_nextwaiting);
th->p_nextwaiting = *p;
*p = th;
}
/* Wake up threads in priority order */
while (towake != NULL) {
th = towake;
towake = towake->p_nextwaiting;
th->p_nextwaiting = NULL;
restart(th);
}
}
#if defined PIC && DO_VERSIONING
symbol_version (__old_sem_init, sem_init, GLIBC_2.0);
symbol_version (__old_sem_wait, sem_wait, GLIBC_2.0);
symbol_version (__old_sem_trywait, sem_trywait, GLIBC_2.0);
symbol_version (__old_sem_post, sem_post, GLIBC_2.0);
symbol_version (__old_sem_getvalue, sem_getvalue, GLIBC_2.0);
symbol_version (__old_sem_destroy, sem_destroy, GLIBC_2.0);
#endif
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