/**************************************************************************** * 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 #include #include #include #include #include #include #include #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 == nxsched_gettid()) { 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. */ nxmutex_lock(&group->tg_joinlock); /* 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. */ ret = pthread_findjoininfo(group, (pid_t)thread, &pjoin); if (ret == OK) { if (pjoin->detached) { nxmutex_unlock(&group->tg_joinlock); leave_cancellation_point(); return EINVAL; } /* 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=%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. */ nxmutex_unlock(&group->tg_joinlock); /* 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. */ nxsem_wait_uninterruptible(&pjoin->exit_sem); /* The thread has exited! Get the thread exit value */ if (pexit_value) { *pexit_value = pjoin->exit_value; sinfo("exit_value=%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. */ nxmutex_lock(&group->tg_joinlock); } /* 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); } ret = OK; } nxmutex_unlock(&group->tg_joinlock); leave_cancellation_point(); sinfo("Returning %d\n", ret); return ret; }