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/*
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
xrdp: A Remote Desktop Protocol server.
Copyright (C) Jay Sorg 2005-2010
session manager
linux only
*/
#include "libscp_lock.h"
#include <semaphore.h>
#include <pthread.h>
pthread_mutex_t lock_fork; /* this lock protects the counters */
pthread_mutexattr_t lock_fork_attr; /* mutex attributes */
sem_t lock_fork_req; /* semaphore on which the process that are going to fork suspend on */
sem_t lock_fork_wait; /* semaphore on which the suspended process wait on */
int lock_fork_forkers_count; /* threads that want to fork */
int lock_fork_blockers_count; /* threads thar are blocking fork */
int lock_fork_waiting_count; /* threads suspended until the fork finishes */
void DEFAULT_CC
scp_lock_init(void)
{
/* initializing fork lock */
pthread_mutexattr_init(&lock_fork_attr);
pthread_mutex_init(&lock_fork, &lock_fork_attr);
sem_init(&lock_fork_req, 0, 0);
sem_init(&lock_fork_wait, 0, 0);
/* here we don't use locking because lock_init() should be called BEFORE */
/* any thread is created */
lock_fork_blockers_count=0;
lock_fork_waiting_count=0;
lock_fork_forkers_count=0;
}
/******************************************************************************/
void DEFAULT_CC
scp_lock_fork_request(void)
{
/* lock mutex */
pthread_mutex_lock(&lock_fork);
if (lock_fork_blockers_count == 0)
{
/* if noone is blocking fork(), then we're allowed to fork */
sem_post(&lock_fork_req);
}
lock_fork_forkers_count++;
pthread_mutex_unlock(&lock_fork);
/* we wait to be allowed to fork() */
sem_wait(&lock_fork_req);
}
/******************************************************************************/
void DEFAULT_CC
scp_lock_fork_release(void)
{
pthread_mutex_lock(&lock_fork);
lock_fork_forkers_count--;
/* if there's someone else that want to fork, we let him fork() */
if (lock_fork_forkers_count > 0)
{
sem_post(&lock_fork_req);
}
for (;lock_fork_waiting_count > 0; lock_fork_waiting_count--)
{
/* waking up the other processes */
sem_post(&lock_fork_wait);
}
pthread_mutex_unlock(&lock_fork);
}
/******************************************************************************/
void DEFAULT_CC
scp_lock_fork_critical_section_end(int blocking)
{
//LOG_DBG("lock_fork_critical_secection_end()",0);
/* lock mutex */
pthread_mutex_lock(&lock_fork);
if (blocking == LIBSCP_LOCK_FORK_BLOCKER)
{
lock_fork_blockers_count--;
}
/* if there's someone who wants to fork and we're the last blocking */
/* then we let him go */
if ((lock_fork_blockers_count == 0) && (lock_fork_forkers_count>0))
{
sem_post(&lock_fork_req);
}
pthread_mutex_unlock(&lock_fork);
}
/******************************************************************************/
int DEFAULT_CC
scp_lock_fork_critical_section_start(void)
{
//LOG_DBG("lock_fork_critical_secection_start()",0);
do
{
pthread_mutex_lock(&lock_fork);
/* someone requested to fork */
if (lock_fork_forkers_count > 0)
{
lock_fork_waiting_count++;
pthread_mutex_unlock(&lock_fork);
/* we wait until the fork finishes */
sem_wait(&lock_fork_wait);
}
else
{
/* no fork, so we can go on... */
lock_fork_blockers_count++;
pthread_mutex_unlock(&lock_fork);
return LIBSCP_LOCK_FORK_BLOCKER;
}
} while (1);
/* we'll never get here */
return LIBSCP_LOCK_FORK_WAITING;
}
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