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nuttx/sched/sched/sched_waitpid.c
yangyalei fd776e8cee fix wait after vfork return error 
vfork use waitpid hang father process,
but waitpid release child processs information by default.
So when user call wait, it return errno 10.

Signed-off-by: yangyalei <yangyalei@xiaomi.com>
2023-09-08 00:53:56 +03:00

654 lines
21 KiB
C
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/****************************************************************************
* sched/sched/sched_waitpid.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/wait.h>
#include <signal.h>
#include <assert.h>
#include <errno.h>
#include <nuttx/sched.h>
#include <nuttx/signal.h>
#include <nuttx/cancelpt.h>
#include <nuttx/semaphore.h>
#include "sched/sched.h"
#include "group/group.h"
#ifdef CONFIG_SCHED_WAITPID
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxsched_waitpid
*
* Description:
* This functions will obtain status information pertaining to one
* of the caller's child processes. This 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 nxsched_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 nxsched_waitpid(), return will be immediate.
*
* Input Parameters:
* pid - The task ID of the thread to waid for
* stat_loc - The location to return the exit status
* options - Modifiable behavior, see sys/wait.h.
*
* Returned Value:
* If nxsched_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 nxsched_waitpid() returns due to the delivery of a signal to the
* calling process, -1 will be returned and errno set to EINTR.
*
* If nxsched_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 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.
*
****************************************************************************/
#ifndef CONFIG_SCHED_HAVE_PARENT
pid_t nxsched_waitpid(pid_t pid, int *stat_loc, int options)
{
FAR struct tcb_s *ctcb;
FAR struct task_group_s *group;
bool mystat = false;
int ret;
/* NOTE: sched_lock() is not enough for SMP
* because the child task is running on another CPU
*/
#ifdef CONFIG_SMP
irqstate_t flags = enter_critical_section();
#else
/* Disable pre-emption so that nothing changes in the following tests */
sched_lock();
#endif
/* Get the TCB corresponding to this PID */
ctcb = nxsched_get_tcb(pid);
if (ctcb == NULL)
{
ret = -ECHILD;
goto errout;
}
/* Then the task group corresponding to this PID */
group = ctcb->group;
if (group == NULL)
{
ret = -ECHILD;
goto errout;
}
/* Lock this group so that it cannot be deleted until the wait completes */
group_add_waiter(group);
/* "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 (group->tg_waitflags == 0)
{
/* Save the waitpid() options, setting the non-standard WCLAIMED bit to
* assure that tg_waitflags is non-zero.
*/
group->tg_waitflags = (uint8_t)options | WCLAIMED;
/* Save the return status location (which may be NULL) */
group->tg_statloc = stat_loc;
/* We are the waipid() instance that gets the return status */
mystat = true;
}
/* Then wait for the task to exit */
if ((options & WNOHANG) != 0)
{
/* Don't wait if status is not available */
ret = nxsem_trywait(&group->tg_exitsem);
}
else
{
/* Wait if necessary for status to become available */
ret = nxsem_wait(&group->tg_exitsem);
}
group_del_waiter(group);
if (ret < 0)
{
/* Handle the awkward case of whether or not we
* need to nullify the stat_loc value.
*/
if (mystat)
{
group->tg_statloc = NULL;
group->tg_waitflags = 0;
}
if ((options & WNOHANG) != 0)
{
pid = 0;
}
else
{
goto errout;
}
}
/* On success, return the PID */
ret = pid;
errout:
#ifdef CONFIG_SMP
leave_critical_section(flags);
#else
sched_unlock();
#endif
return ret;
}
/****************************************************************************
*
* If CONFIG_SCHED_HAVE_PARENT is defined, then waitpid will use the SIGCHLD
* signal. It can also handle the pid == INVALID_PROCESS_ID argument. 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 nxsched_waitpid(pid_t pid, int *stat_loc, int options)
{
FAR struct tcb_s *rtcb = this_task();
FAR struct tcb_s *ctcb;
#ifdef CONFIG_SCHED_CHILD_STATUS
FAR struct child_status_s *child = NULL;
bool retains;
#endif
FAR struct siginfo info;
sigset_t set;
int ret;
/* Create a signal set that contains only SIGCHLD */
sigemptyset(&set);
nxsig_addset(&set, SIGCHLD);
/* NOTE: sched_lock() is not enough for SMP
* because the child task is running on another CPU
*/
#ifdef CONFIG_SMP
irqstate_t flags = enter_critical_section();
#else
/* Disable pre-emption so that nothing changes while the loop executes */
sched_lock();
#endif
/* Verify that this task actually has children and that the requested PID
* is actually a child of this task.
*/
#ifdef CONFIG_SCHED_CHILD_STATUS
/* Does this task retain child status? */
retains = ((rtcb->group->tg_flags & GROUP_FLAG_NOCLDWAIT) == 0);
if (rtcb->group->tg_children == NULL && retains)
{
ret = -ECHILD;
goto errout;
}
else if (pid != INVALID_PROCESS_ID)
{
/* Get the TCB corresponding to this PID. NOTE: If the child has
* already exited, then the PID will not map to a valid TCB.
*/
ctcb = nxsched_get_tcb(pid);
if (ctcb && ctcb->group)
{
/* Make sure that the thread it is our child. */
if (ctcb->group->tg_ppid != rtcb->group->tg_pid)
{
ret = -ECHILD;
goto errout;
}
}
/* The child task is ours or it is no longer active. Does the parent
* task retain child status?
*/
if (retains)
{
/* Yes.. Check if this specific pid has allocated child status? */
if (group_find_child(rtcb->group, pid) == NULL)
{
ret = -ECHILD;
goto errout;
}
}
}
#else /* CONFIG_SCHED_CHILD_STATUS */
if (rtcb->group->tg_nchildren == 0)
{
/* There are no children */
ret = -ECHILD;
goto errout;
}
else if (pid != INVALID_PROCESS_ID)
{
/* Get the TCB corresponding to this PID and make sure that the
* thread it is our child.
*/
ctcb = nxsched_get_tcb(pid);
if (!ctcb || !ctcb->group || ctcb->group->tg_ppid != rtcb->pid)
{
ret = -ECHILD;
goto errout;
}
}
#endif /* CONFIG_SCHED_CHILD_STATUS */
/* Loop until the child that we are waiting for dies */
for (; ; )
{
#ifdef CONFIG_SCHED_CHILD_STATUS
/* 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 == INVALID_PROCESS_ID)
{
/* We are waiting for any child, check if there are still
* children.
*/
DEBUGASSERT(!retains || rtcb->group->tg_children);
if (retains && (child = group_exit_child(rtcb->group)) != NULL)
{
/* A child has exited. Apparently we missed the signal.
* Return the saved exit status.
*/
/* The child has exited. Return the saved exit status */
if (stat_loc != NULL)
{
*stat_loc = child->ch_status << 8;
}
pid = child->ch_pid;
/* Discard the child entry and break out of the loop */
group_remove_child(rtcb->group, child->ch_pid);
group_free_child(child);
break;
}
}
/* We are waiting for a specific PID. Does this task retain child
* status?
*/
else if (retains)
{
/* Get the current status of the child task. */
child = group_find_child(rtcb->group, pid);
DEBUGASSERT(child);
/* Did the child exit? */
if ((child->ch_flags & CHILD_FLAG_EXITED) != 0)
{
/* The child has exited. Return the saved exit status */
if (stat_loc != NULL)
{
*stat_loc = child->ch_status << 8;
}
/* Discard the child entry and break out of the loop */
if ((options & WNOWAIT) == 0)
{
group_remove_child(rtcb->group, pid);
group_free_child(child);
}
break;
}
}
else
{
/* We can use nxsig_kill() with signal number 0 to determine if
* that task is still alive.
*/
ret = nxsig_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 than bogus status.
*/
ret = -ECHILD;
goto errout;
}
}
#else /* CONFIG_SCHED_CHILD_STATUS */
/* 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 (rtcb->group->tg_nchildren == 0 ||
(pid != INVALID_PROCESS_ID && nxsig_kill(pid, 0) < 0))
{
/* We know that the child task was running okay when we started,
* so we must have lost the signal. What can we do?
* Let's return ECHILD.. that is at least informative.
*/
ret = -ECHILD;
goto errout;
}
#endif /* CONFIG_SCHED_CHILD_STATUS */
if ((options & WNOHANG) != 0)
{
pid = 0;
break;
}
/* Wait for any death-of-child signal */
ret = nxsig_waitinfo(&set, &info);
if (ret < 0)
{
goto errout;
}
/* Was this the death of the thread we were waiting for? In the of
* pid == INVALID_PROCESS_ID, we are waiting for any child thread.
*/
if (info.si_signo == SIGCHLD &&
(pid == INVALID_PROCESS_ID || info.si_pid == pid))
{
/* Yes... return the status and PID (in the event it was -1) */
if (stat_loc != NULL)
{
*stat_loc = info.si_status << 8;
}
pid = info.si_pid;
#ifdef CONFIG_SCHED_CHILD_STATUS
if (retains)
{
/* Recover the exiting child */
child = group_find_child(rtcb->group, info.si_pid);
/* Discard the child entry, if we have one */
if (child != NULL && (options & WNOWAIT) == 0)
{
group_remove_child(rtcb->group, child->ch_pid);
group_free_child(child);
}
}
#endif /* CONFIG_SCHED_CHILD_STATUS */
break;
}
}
/* On success, return the PID */
ret = pid;
errout:
#ifdef CONFIG_SMP
leave_critical_section(flags);
#else
sched_unlock();
#endif
return ret;
}
#endif /* CONFIG_SCHED_HAVE_PARENT */
/****************************************************************************
* 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.
*
* Input Parameters:
* pid - The task ID of the thread to waid for
* stat_loc - The location to return the exit status
* options - Modifiable behavior, see sys/wait.h.
*
* Returned 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 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:
*
* Compatibility
* 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.
*
****************************************************************************/
pid_t waitpid(pid_t pid, int *stat_loc, int options)
{
pid_t ret;
/* waitpid() is a cancellation point */
enter_cancellation_point();
/* Let nxsched_waitpid() do the work. */
ret = nxsched_waitpid(pid, stat_loc, options);
if (ret < 0)
{
set_errno(-ret);
ret = ERROR;
}
leave_cancellation_point();
return ret;
}
#endif /* CONFIG_SCHED_WAITPID */
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