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nuttx/sched/sched_waitpid.c
patacongo 3736ae6ba9 Add logic to retain child task exit status if so configured 
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5553 42af7a65-404d-4744-a932-0658087f49c3
2013-01-23 22:23:46 +00:00

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/*****************************************************************************
* sched/sched_waitpid.c
*
* Copyright (C) 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 <nuttx/config.h>
#include <sys/wait.h>
#include <semaphore.h>
#include <signal.h>
#include <errno.h>
#include <nuttx/sched.h>
#include "os_internal.h"
#ifdef CONFIG_SCHED_WAITPID
/*****************************************************************************
* Private Functions
*****************************************************************************/
/*****************************************************************************
* Public Functions
*****************************************************************************/
/*****************************************************************************
* Name: waitpid
*
* Description:
*
* The waitpid() functions will obtain status information pertaining to one
* of the caller's child processes. The waitpid() function will suspend
* execution of the calling thread until status information for one of the
* terminated child processes of the calling process is available, or until
* delivery of a signal whose action is either to execute a signal-catching
* function or to terminate the process. If more than one thread is suspended
* in waitpid() awaiting termination of the same process, exactly one thread
* will return the process status at the time of the target process
* termination. If status information is available prior to the call to
* waitpid(), return will be immediate.
*
* The pid argument specifies a set of child processes for which status is
* requested. The waitpid() function will only return the status of a child
* process from this set:
*
* - If pid is equal to (pid_t)-1, status is requested for any child process.
* In this respect, waitpid() is then equivalent to wait().
* - If pid is greater than 0, it specifies the process ID of a single child
* process for which status is requested.
* - If pid is 0, status is requested for any child process whose process
* group ID is equal to that of the calling process.
* - If pid is less than (pid_t)-1, status is requested for any child process
* whose process group ID is equal to the absolute value of pid.
*
* The options argument is constructed from the bitwise-inclusive OR of zero
* or more of the following flags, defined in the <sys/wait.h> header:
*
* WCONTINUED - The waitpid() function will report the status of any
* continued child process specified by pid whose status has not been
* reported since it continued from a job control stop.
* WNOHANG - The waitpid() function will not suspend execution of the
* calling thread if status is not immediately available for one of the
* child processes specified by pid.
* WUNTRACED - The status of any child processes specified by pid that are
* stopped, and whose status has not yet been reported since they stopped,
* will also be reported to the requesting process.
*
* If the calling process has SA_NOCLDWAIT set or has SIGCHLD set to
* SIG_IGN, and the process has no unwaited-for children that were
* transformed into zombie processes, the calling thread will block until all
* of the children of the process containing the calling thread terminate, and
* waitpid() will fail and set errno to ECHILD.
*
* If waitpid() returns because the status of a child process is available,
* these functions will return a value equal to the process ID of the child
* process. In this case, if the value of the argument stat_loc is not a
* null pointer, information will be stored in the location pointed to by
* stat_loc. The value stored at the location pointed to by stat_loc will be
* 0 if and only if the status returned is from a terminated child process
* that terminated by one of the following means:
*
* 1. The process returned 0 from main().
* 2. The process called _exit() or exit() with a status argument of 0.
* 3. The process was terminated because the last thread in the process terminated.
*
* Regardless of its value, this information may be interpreted using the
* following macros, which are defined in <sys/wait.h> and evaluate to
* integral expressions; the stat_val argument is the integer value pointed
* to by stat_loc.
*
* WIFEXITED(stat_val) - Evaluates to a non-zero value if status was
* returned for a child process that terminated normally.
* WEXITSTATUS(stat_val) - If the value of WIFEXITED(stat_val) is non-zero,
* this macro evaluates to the low-order 8 bits of the status argument
* that the child process passed to _exit() or exit(), or the value the
* child process returned from main().
* WIFSIGNALED(stat_val) - Evaluates to a non-zero value if status was
* returned for a child process that terminated due to the receipt of a
* signal that was not caught (see <signal.h>).
* WTERMSIG(stat_val) - If the value of WIFSIGNALED(stat_val) is non-zero,
* this macro evaluates to the number of the signal that caused the
* termination of the child process.
* WIFSTOPPED(stat_val) - Evaluates to a non-zero value if status was
* returned for a child process that is currently stopped.
* WSTOPSIG(stat_val) - If the value of WIFSTOPPED(stat_val) is non-zero,
* this macro evaluates to the number of the signal that caused the child
* process to stop.
* WIFCONTINUED(stat_val) - Evaluates to a non-zero value if status was
* returned for a child process that has continued from a job control stop.
*
* Parameters:
* pid - The task ID of the thread to waid for
* stat_loc - The location to return the exit status
* options - ignored
*
* Return Value:
* If waitpid() returns because the status of a child process is available,
* it will return a value equal to the process ID of the child process for
* which status is reported.
*
* If waitpid() returns due to the delivery of a signal to the calling
* process, -1 will be returned and errno set to EINTR.
*
* If waitpid() was invoked with WNOHANG set in options, it has at least
* one child process specified by pid for which status is not available, and
* status is not available for any process specified by pid, 0 is returned.
*
* Otherwise, (pid_t)-1 will be returned, and errno set to indicate the error:
*
* ECHILD - The process specified by pid does not exist or is not a child of
* the calling process, or the process group specified by pid does not exist
* or does not have any member process that is a child of the calling process.
* EINTR - The function was interrupted by a signal. The value of the location
* pointed to by stat_loc is undefined.
* EINVAL - The options argument is not valid.
*
* Assumptions:
*
*****************************************************************************/
/***************************************************************************
* NOTE: This is a partially functional, experimental version of waitpid()
*
* If there is no SIGCHLD signal supported (CONFIG_SCHED_HAVE_PARENT not
* defined), then waitpid() is still available, but does not obey the
* restriction that the pid be a child of the caller.
*
***************************************************************************/
#ifndef CONFIG_SCHED_HAVE_PARENT
pid_t waitpid(pid_t pid, int *stat_loc, int options)
{
_TCB *tcb;
bool mystat;
int err;
int ret;
DEBUGASSERT(stat_loc);
/* None of the options are supported */
#ifdef CONFIG_DEBUG
if (options != 0)
{
set_errno(ENOSYS);
return ERROR;
}
#endif
/* Disable pre-emption so that nothing changes in the following tests */
sched_lock();
/* Get the TCB corresponding to this PID */
tcb = sched_gettcb(pid);
if (!tcb)
{
err = ECHILD;
goto errout_with_errno;
}
/* "If more than one thread is suspended in waitpid() awaiting termination of
* the same process, exactly one thread will return the process status at the
* time of the target process termination." Hmmm.. what do we return to the
* others?
*/
if (stat_loc != NULL && tcb->stat_loc == NULL)
{
tcb->stat_loc = stat_loc;
mystat = true;
}
/* Then wait for the task to exit */
ret = sem_wait(&tcb->exitsem);
if (ret < 0)
{
/* Unlock pre-emption and return the ERROR (sem_wait has already set
* the errno). Handle the awkward case of whether or not we need to
* nullify the stat_loc value.
*/
if (mystat)
{
tcb->stat_loc = NULL;
}
goto errout;
}
/* On success, return the PID */
sched_unlock();
return pid;
errout_with_errno:
set_errno(err);
errout:
sched_unlock();
return ERROR;
}
/***************************************************************************
*
* If CONFIG_SCHED_HAVE_PARENT is defined, then waitpid will use the SIGHCLD
* signal. It can also handle the pid == (pid_t)-1 arguement. This is
* slightly more spec-compliant.
*
* But then I have to be concerned about the fact that NuttX does not queue
* signals. This means that a flurry of signals can cause signals to be
* lost (or to have the data in the struct siginfo to be overwritten by
* the next signal).
*
***************************************************************************/
#else
pid_t waitpid(pid_t pid, int *stat_loc, int options)
{
FAR _TCB *rtcb = (FAR _TCB *)g_readytorun.head;
#ifdef CONFIG_SCHED_CHILD_STATUS
FAR struct child_status_s *child;
#endif
FAR struct siginfo info;
sigset_t sigset;
int err;
int ret;
DEBUGASSERT(stat_loc);
/* None of the options are supported */
#ifdef CONFIG_DEBUG
if (options != 0)
{
set_errno(ENOSYS);
return ERROR;
}
#endif
/* Create a signal set that contains only SIGCHLD */
(void)sigemptyset(&sigset);
(void)sigaddset(&sigset, SIGCHLD);
/* Disable pre-emption so that nothing changes while the loop executes */
sched_lock();
/* Verify that this task actually has children and that the the request
* TCB is actually a child of this task.
*/
#ifdef CONFIG_SCHED_CHILD_STATUS
if (rtcb->children == NULL)
{
/* There are no children */
err = ECHILD;
goto errout_with_errno;
}
else if (pid != (pid_t)-1)
{
/* This specific pid is not a child */
if (task_findchild(rtcb, pid) == NULL)
{
err = ECHILD;
goto errout_with_errno;
}
}
#else
if (rtcb->nchildren == 0)
{
/* There are no children */
err = ECHILD;
goto errout_with_errno;
}
else if (pid != (pid_t)-1)
{
/* Get the TCB corresponding to this PID and make sure it is our child. */
FAR _TCB *ctcb = sched_gettcb(pid);
if (!ctcb || ctcb->parent != rtcb->pid)
{
err = ECHILD;
goto errout_with_errno;
}
}
#endif
/* Loop until the child that we are waiting for dies */
for (;;)
{
/* Check if the task has already died. Signals are not queued in
* NuttX. So a possibility is that the child has died and we
* missed the death of child signal (we got some other signal
* instead).
*/
if (pid == (pid_t)-1)
{
/* We are waiting for any child, check if there are still
* chilren.
*/
#ifdef CONFIG_SCHED_CHILD_STATUS
DEBUGASSERT(rtcb->children);
if (rtcb->children == NULL)
#else
if (rtcb->nchildren == 0)
#endif
{
/* There were one or more children when we started so they
* must have exit'ed. There are just no bread crumbs left
* behind to tell us the PID(s) of the existed children.
* Reporting ECHLD is about all we can do in this case.
*/
err = ECHILD;
goto errout_with_errno;
}
}
else
{
#ifdef CONFIG_SCHED_CHILD_STATUS
/* We are waiting for a specific PID. Get the current status
* of the child task.
*/
child = task_findchild(rtcb, pid);
DEBUGASSERT(child);
if (!child)
{
/* Yikes! The child status entry just disappeared! */
err = ECHILD;
goto errout_with_errno;
}
/* Did the child exit? */
if ((child->ch_flags & CHILD_FLAG_EXITED) != 0)
{
/* The child has exited. Return the saved exit status */
*stat_loc = child->ch_status;
/* Discard the child entry and break out of the loop */
(void)task_removechild(rtcb, pid);
task_freechild(child);
}
#else
/* We are waiting for a specific PID. We can use kill() with
* signal number 0 to determine if that task is still alive.
*/
ret = kill(pid, 0);
if (ret < 0)
{
/* It is no longer running. We know that the child task was
* running okay when we started, so we must have lost the
* signal. In this case, we know that the task exit'ed, but
* we do not know its exit status. It would be better to
* reported ECHILD that bogus status.
*/
err = ECHILD;
goto errout_with_errno;
}
#endif
}
/* Wait for any death-of-child signal */
ret = sigwaitinfo(&sigset, &info);
if (ret < 0)
{
goto errout_with_lock;
}
/* Was this the death of the thread we were waiting for? In the of
* pid == (pid_t)-1, we are waiting for any child thread.
*/
if (info.si_signo == SIGCHLD &&
(pid == (pid_t)-1 || info.si_pid == pid))
{
/* Yes... return the status and PID (in the event it was -1) */
*stat_loc = info.si_status;
pid = info.si_pid;
break;
}
}
sched_unlock();
return (int)pid;
errout_with_errno:
set_errno(err);
errout_with_lock:
sched_unlock();
return ERROR;
}
#endif /* CONFIG_SCHED_HAVE_PARENT */
#endif /* CONFIG_SCHED_WAITPID */
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