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/**
* xrdp: A Remote Desktop Protocol server.
*
* Copyright (C) Jay Sorg 2004-2012
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* session manager
* linux only
*/
#if defined(HAVE_CONFIG_H)
#include <config_ac.h>
#endif
#include "libscp_lock.h"
#include "thread_calls.h"
#include <pthread.h>
pthread_mutex_t lock_fork; /* this lock protects the counters */
pthread_mutexattr_t lock_fork_attr; /* mutex attributes */
tbus lock_fork_req; /* semaphore on which the process that are going to fork suspend on */
tbus 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 that are blocking fork */
int lock_fork_waiting_count; /* threads suspended until the fork finishes */
void
scp_lock_init(void)
{
/* initializing fork lock */
pthread_mutexattr_init(&lock_fork_attr);
pthread_mutex_init(&lock_fork, &lock_fork_attr);
lock_fork_req = tc_sem_create(0);
lock_fork_wait = tc_sem_create(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
scp_lock_fork_request(void)
{
/* lock mutex */
pthread_mutex_lock(&lock_fork);
if (lock_fork_blockers_count == 0)
{
/* if no one is blocking fork(), then we're allowed to fork */
tc_sem_inc(lock_fork_req);
}
lock_fork_forkers_count++;
pthread_mutex_unlock(&lock_fork);
/* we wait to be allowed to fork() */
tc_sem_dec(lock_fork_req);
}
/******************************************************************************/
void
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)
{
tc_sem_inc(lock_fork_req);
}
for (; lock_fork_waiting_count > 0; lock_fork_waiting_count--)
{
/* waking up the other processes */
tc_sem_inc(lock_fork_wait);
}
pthread_mutex_unlock(&lock_fork);
}
/******************************************************************************/
void
scp_lock_fork_critical_section_end(int blocking)
{
//LOG_DBG("lock_fork_critical_section_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))
{
tc_sem_inc(lock_fork_req);
}
pthread_mutex_unlock(&lock_fork);
}
/******************************************************************************/
int
scp_lock_fork_critical_section_start(void)
{
//LOG_DBG("lock_fork_critical_section_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 */
tc_sem_dec(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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