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nuttx/sched/pthread_join.c
Gregory Nutt 1909c44f87 Minor updates to READMEs and comments
2014-04-27 11:38:24 -06:00

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/****************************************************************************
* pthread_join.c
*
* Copyright (C) 2007, 2008, 2011, 2013 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <debug.h>
#include "os_internal.h"
#include "group_internal.h"
#include "pthread_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Type Declarations
****************************************************************************/
/****************************************************************************
* Global Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pthread_join
*
* Description:
* A thread can await termination of another thread and retrieve the
* return value of the thread.
*
* The caller's task/thread must belong to the same "task group" as the
* pthread is (or was) a member of. The thread may or may not still
* be running.
*
* Parameters:
* thread
* pexit_value
*
* Return Value:
* 0 if successful. Otherwise, one of the following error codes:
*
* EINVAL The value specified by thread does not refer to joinable
* thread.
* ESRCH No thread could be found corresponding to that specified by the
* given thread ID.
* EDEADLK A deadlock was detected or the value of thread specifies the
* calling thread.
*
* Assumptions:
*
****************************************************************************/
int pthread_join(pthread_t thread, FAR pthread_addr_t *pexit_value)
{
FAR struct tcb_s *rtcb = (FAR struct tcb_s *)g_readytorun.head;
FAR struct task_group_s *group = rtcb->group;
FAR struct join_s *pjoin;
int ret;
sdbg("thread=%d group=%p\n", thread, group);
DEBUGASSERT(group);
/* First make sure that this is not an attempt to join to
* ourself.
*/
if ((pid_t)thread == getpid())
{
return EDEADLK;
}
/* Make sure no other task is mucking with the data structures
* while we are performing the following operations. NOTE:
* we can be also sure that pthread_exit() will not execute
* because it will also attempt to get this semaphore.
*/
(void)pthread_takesemaphore(&group->tg_joinsem);
/* Find the join information associated with this thread.
* This can fail for one of three reasons: (1) There is no
* thread associated with 'thread,' (2) the thread is a task
* and does not have join information, or (3) the thread
* was detached and has exited.
*/
pjoin = pthread_findjoininfo(group, (pid_t)thread);
if (!pjoin)
{
/* Determine what kind of error to return */
FAR struct tcb_s *tcb = sched_gettcb((pthread_t)thread);
sdbg("Could not find thread data\n");
/* Case (1) or (3) -- we can't tell which. Assume (3) */
if (!tcb)
{
ret = ESRCH;
}
/* The thread is still active but has no join info. In that
* case, it must be a task and not a pthread.
*/
else
{
ret = EINVAL;
}
(void)pthread_givesemaphore(&group->tg_joinsem);
}
else
{
/* We found the join info structure. Increment for the reference
* to the join structure that we have. This will keep things
* stable for we have to do
*/
sched_lock();
pjoin->crefs++;
/* Check if the thread is still running. If not, then things are
* simpler. There are still race conditions to be concerned with.
* For example, there could be multiple threads executing in the
* 'else' block below when we enter!
*/
if (pjoin->terminated)
{
sdbg("Thread has terminated\n");
/* Get the thread exit value from the terminated thread. */
if (pexit_value)
{
sdbg("exit_value=0x%p\n", pjoin->exit_value);
*pexit_value = pjoin->exit_value;
}
}
else
{
sdbg("Thread is still running\n");
/* Relinquish the data set semaphore. Since pre-emption is
* disabled, we can be certain that no task has the
* opportunity to run between the time we relinquish the
* join semaphore and the time that we wait on the thread exit
* semaphore.
*/
(void)pthread_givesemaphore(&group->tg_joinsem);
/* Take the thread's thread exit semaphore. We will sleep here
* until the thread exits. We need to exercise caution because
* there could be multiple threads waiting here for the same
* pthread to exit.
*/
(void)pthread_takesemaphore(&pjoin->exit_sem);
/* The thread has exited! Get the thread exit value */
if (pexit_value)
{
*pexit_value = pjoin->exit_value;
sdbg("exit_value=0x%p\n", pjoin->exit_value);
}
/* Post the thread's data semaphore so that the exiting thread
* will know that we have received the data.
*/
(void)pthread_givesemaphore(&pjoin->data_sem);
/* Retake the join semaphore, we need to hold this when
* pthread_destroyjoin is called.
*/
(void)pthread_takesemaphore(&group->tg_joinsem);
}
/* Pre-emption is okay now. The logic still cannot be re-entered
* because we hold the join semaphore
*/
sched_unlock();
/* Release our reference to the join structure and, if the reference
* count decrements to zero, deallocate the join structure.
*/
if (--pjoin->crefs <= 0)
{
(void)pthread_destroyjoin(group, pjoin);
}
(void)pthread_givesemaphore(&group->tg_joinsem);
ret = OK;
}
sdbg("Returning %d\n", ret);
return ret;
}
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