/****************************************************************************
* sched/pthread/pthread_join.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you 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.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <debug.h>
#include <nuttx/cancelpt.h>
#include "sched/sched.h"
#include "group/group.h"
#include "pthread/pthread.h"
/****************************************************************************
* 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.
*
* Input Parameters:
* thread
* pexit_value
*
* Returned 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 = this_task();
FAR struct task_group_s *group = rtcb->group;
FAR struct join_s *pjoin;
int ret;
sinfo("thread=%d group=%p\n", thread, group);
DEBUGASSERT(group);
/* pthread_join() is a cancellation point */
enter_cancellation_point();
/* First make sure that this is not an attempt to join to
* ourself.
*/
if ((pid_t)thread == getpid())
{
leave_cancellation_point();
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.
*/
pthread_sem_take(&group->tg_joinsem, NULL, false);
/* 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 == NULL)
{
/* Determine what kind of error to return */
FAR struct tcb_s *tcb = nxsched_get_tcb((pthread_t)thread);
swarn("WARNING: Could not find thread data\n");
/* Case (1) or (3) -- we can't tell which. Assume (3) */
if (tcb == NULL)
{
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;
}
pthread_sem_give(&group->tg_joinsem);
}
else
{
/* NOTE: sched_lock() is not enough for SMP
* because another CPU would continue the pthread and exit
* sequences so need to protect it with a critical section
*/
#ifdef CONFIG_SMP
irqstate_t flags = enter_critical_section();
#endif
/* 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)
{
sinfo("Thread has terminated\n");
/* Get the thread exit value from the terminated thread. */
if (pexit_value)
{
sinfo("exit_value=0x%p\n", pjoin->exit_value);
*pexit_value = pjoin->exit_value;
}
}
else
{
sinfo("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.
*/
pthread_sem_give(&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.
*/
pthread_sem_take(&pjoin->exit_sem, NULL, false);
/* The thread has exited! Get the thread exit value */
if (pexit_value)
{
*pexit_value = pjoin->exit_value;
sinfo("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.
*/
pthread_sem_give(&pjoin->data_sem);
/* Retake the join semaphore, we need to hold this when
* pthread_destroyjoin is called.
*/
pthread_sem_take(&group->tg_joinsem, NULL, false);
}
/* Pre-emption is okay now. The logic still cannot be re-entered
* because we hold the join semaphore
*/
sched_unlock();
#ifdef CONFIG_SMP
leave_critical_section(flags);
#endif
/* Release our reference to the join structure and, if the reference
* count decrements to zero, deallocate the join structure.
*/
if (--pjoin->crefs <= 0)
{
pthread_destroyjoin(group, pjoin);
}
pthread_sem_give(&group->tg_joinsem);
ret = OK;
}
leave_cancellation_point();
sinfo("Returning %d\n", ret);
return ret;
}