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+/****************************************************************************
+ * pthread_join.c
+ *
+ * Copyright (C) 2007, 2008, 2011 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 "pthread_internal.h"
+
+/****************************************************************************
+ * 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.
+ *
+ * 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 ajoinable
+ * thread.
+ * ESRCH No thread could be found corresponding to thatspecified 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 join_t *pjoin;
+ int ret;
+
+ sdbg("thread=%d\n", thread);
+
+ /* 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(&g_join_semaphore);
+
+ /* 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 exitted.
+ */
+
+ pjoin = pthread_findjoininfo((pid_t)thread);
+ if (!pjoin)
+ {
+ /* Determine what kind of error to return */
+
+ FAR _TCB *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(&g_join_semaphore);
+ }
+ 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(&g_join_semaphore);
+
+ /* 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 exitting 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(&g_join_semaphore);
+ }
+
+ /* 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(pjoin);
+ }
+
+ (void)pthread_givesemaphore(&g_join_semaphore);
+ ret = OK;
+ }
+
+ sdbg("Returning %d\n", ret);
+ return ret;
+}
+
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