244 lines
7.2 KiB
C
244 lines
7.2 KiB
C
/****************************************************************************
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* sched/pthread/pthread_join.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <pthread.h>
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#include <errno.h>
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#include <debug.h>
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#include <nuttx/cancelpt.h>
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#include "sched/sched.h"
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#include "group/group.h"
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#include "pthread/pthread.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: pthread_join
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*
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* Description:
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* A thread can await termination of another thread and retrieve the
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* return value of the thread.
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*
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* The caller's task/thread must belong to the same "task group" as the
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* pthread is (or was) a member of. The thread may or may not still
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* be running.
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*
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* Input Parameters:
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* thread
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* pexit_value
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*
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* Returned Value:
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* 0 if successful. Otherwise, one of the following error codes:
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*
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* EINVAL The value specified by thread does not refer to joinable
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* thread.
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* ESRCH No thread could be found corresponding to that specified by the
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* given thread ID.
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* EDEADLK A deadlock was detected or the value of thread specifies the
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* calling thread.
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*
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* Assumptions:
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*
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****************************************************************************/
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int pthread_join(pthread_t thread, FAR pthread_addr_t *pexit_value)
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{
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FAR struct tcb_s *rtcb = this_task();
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FAR struct task_group_s *group = rtcb->group;
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FAR struct join_s *pjoin;
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int ret;
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sinfo("thread=%d group=%p\n", thread, group);
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DEBUGASSERT(group);
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/* pthread_join() is a cancellation point */
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enter_cancellation_point();
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/* First make sure that this is not an attempt to join to
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* ourself.
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*/
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if ((pid_t)thread == getpid())
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{
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leave_cancellation_point();
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return EDEADLK;
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}
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/* Make sure no other task is mucking with the data structures
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* while we are performing the following operations. NOTE:
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* we can be also sure that pthread_exit() will not execute
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* because it will also attempt to get this semaphore.
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*/
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pthread_sem_take(&group->tg_joinsem, NULL, false);
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/* Find the join information associated with this thread.
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* This can fail for one of three reasons: (1) There is no
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* thread associated with 'thread,' (2) the thread is a task
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* and does not have join information, or (3) the thread
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* was detached and has exited.
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*/
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pjoin = pthread_findjoininfo(group, (pid_t)thread);
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if (pjoin == NULL)
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{
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/* Determine what kind of error to return */
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FAR struct tcb_s *tcb = nxsched_get_tcb((pthread_t)thread);
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swarn("WARNING: Could not find thread data\n");
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/* Case (1) or (3) -- we can't tell which. Assume (3) */
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if (tcb == NULL)
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{
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ret = ESRCH;
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}
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/* The thread is still active but has no join info. In that
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* case, it must be a task and not a pthread.
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*/
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else
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{
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ret = EINVAL;
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}
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pthread_sem_give(&group->tg_joinsem);
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}
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else
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{
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/* NOTE: sched_lock() is not enough for SMP
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* because another CPU would continue the pthread and exit
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* sequences so need to protect it with a critical section
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*/
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#ifdef CONFIG_SMP
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irqstate_t flags = enter_critical_section();
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#endif
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/* We found the join info structure. Increment for the reference
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* to the join structure that we have. This will keep things
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* stable for we have to do
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*/
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sched_lock();
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pjoin->crefs++;
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/* Check if the thread is still running. If not, then things are
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* simpler. There are still race conditions to be concerned with.
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* For example, there could be multiple threads executing in the
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* 'else' block below when we enter!
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*/
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if (pjoin->terminated)
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{
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sinfo("Thread has terminated\n");
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/* Get the thread exit value from the terminated thread. */
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if (pexit_value)
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{
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sinfo("exit_value=0x%p\n", pjoin->exit_value);
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*pexit_value = pjoin->exit_value;
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}
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}
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else
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{
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sinfo("Thread is still running\n");
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/* Relinquish the data set semaphore. Since pre-emption is
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* disabled, we can be certain that no task has the
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* opportunity to run between the time we relinquish the
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* join semaphore and the time that we wait on the thread exit
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* semaphore.
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*/
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pthread_sem_give(&group->tg_joinsem);
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/* Take the thread's thread exit semaphore. We will sleep here
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* until the thread exits. We need to exercise caution because
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* there could be multiple threads waiting here for the same
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* pthread to exit.
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*/
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pthread_sem_take(&pjoin->exit_sem, NULL, false);
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/* The thread has exited! Get the thread exit value */
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if (pexit_value)
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{
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*pexit_value = pjoin->exit_value;
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sinfo("exit_value=0x%p\n", pjoin->exit_value);
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}
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/* Post the thread's data semaphore so that the exiting thread
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* will know that we have received the data.
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*/
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pthread_sem_give(&pjoin->data_sem);
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/* Retake the join semaphore, we need to hold this when
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* pthread_destroyjoin is called.
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*/
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pthread_sem_take(&group->tg_joinsem, NULL, false);
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}
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/* Pre-emption is okay now. The logic still cannot be re-entered
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* because we hold the join semaphore
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*/
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sched_unlock();
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#ifdef CONFIG_SMP
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leave_critical_section(flags);
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#endif
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/* Release our reference to the join structure and, if the reference
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* count decrements to zero, deallocate the join structure.
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*/
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if (--pjoin->crefs <= 0)
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{
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pthread_destroyjoin(group, pjoin);
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}
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pthread_sem_give(&group->tg_joinsem);
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ret = OK;
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}
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leave_cancellation_point();
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sinfo("Returning %d\n", ret);
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return ret;
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}
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