Use SIGCHLD with waitpid(); implemented wait() and waitid()

git-svn-id: http://svn.code.sf.net/p/nuttx/code/trunk@5515 42af7a65-404d-4744-a932-0658087f49c3

8 files changed, 561 insertions, 29 deletions

diff --git a/nuttx/sched/Kconfig b/nuttx/sched/Kconfig
index 69621a1fa..6d53a03aa 100644
--- a/nuttx/sched/Kconfig
+++ b/nuttx/sched/Kconfig
@@ -43,9 +43,10 @@ config SCHED_HAVE_PARENT
 	default n
 	---help---
 		Remember the ID of the parent thread when a new child thread is
-		created.  This support enables a few minor features (such as
-		SIGCHLD) and slightly increases the size of the Task Control Block
-		(TCB) of every task to hold the ID of the parent thread.  Default:
+		created.  This support enables some additional features (such as
+		SIGCHLD) and modifies the behavior of other interfaces.  For
+		example, it makes waitpid() more standards complete by restricting
+		the waited-for tasks to the children of the caller. Default:
 		disabled.
 
 config JULIAN_TIME
@@ -206,7 +207,12 @@ config SCHED_WAITPID
 	bool "Enable waitpid() API"
 	default n
 	---help---
-		Enables the waitpid() API
+		Enables the waitpid() interface in a default, non-standard mode
+		(non-standard in the sense that the waited for PID need not be child
+		of the caller).  If SCHED_HAVE_PARENT is also defined, then this
+		setting will modify the behavior or waitpid() (making more spec
+		compliant) and will enable the waitid() and wait() interfaces as
+		well.
 
 config SCHED_ATEXIT
 	bool "Enable atexit() API"
diff --git a/nuttx/sched/Makefile b/nuttx/sched/Makefile
index 23d1e9938..3d6b58bac 100644
--- a/nuttx/sched/Makefile
+++ b/nuttx/sched/Makefile
@@ -1,7 +1,7 @@
 ############################################################################
 # sched/Makefile
 #
-#   Copyright (C) 2007-2012 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2007-2013 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -69,6 +69,9 @@ endif
 
 ifeq ($(CONFIG_SCHED_WAITPID),y)
 SCHED_SRCS	+= sched_waitpid.c
+ifeq ($(CONFIG_SCHED_HAVE_PARENT),y)
+SCHED_SRCS	+= sched_waitid.c sched_wait.c
+endif
 endif
 
 ENV_SRCS	= env_getenvironptr.c env_dup.c env_share.c env_release.c \
diff --git a/nuttx/sched/os_internal.h b/nuttx/sched/os_internal.h
index 13b8083cf..32d9fb4ac 100644
--- a/nuttx/sched/os_internal.h
+++ b/nuttx/sched/os_internal.h
@@ -83,10 +83,10 @@ enum os_crash_codes_e
   OSERR_BADREPRIORITIZESTATE  /* Attempt to reprioritize in bad state or priority */
 };
 
-/* Special task IDS */
+/* Special task IDS.  Any negative PID is invalid. */
 
-#define NULL_TASK_PROCESS_ID 0
-#define INVALID_PROCESS_ID   0
+#define NULL_TASK_PROCESS_ID (pid_t)0
+#define INVALID_PROCESS_ID   (pid_t)-1
 
 /* Although task IDs can take the (positive, non-zero)
  * range of pid_t, the number of tasks that will be supported
diff --git a/nuttx/sched/sched_wait.c b/nuttx/sched/sched_wait.c
new file mode 100644
index 000000000..813d4f842
--- /dev/null
+++ b/nuttx/sched/sched_wait.c
@@ -0,0 +1,90 @@
+/*****************************************************************************
+ * sched/sched_wait.c
+ *
+ *   Copyright (C) 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 <signal.h>
+#include <errno.h>
+
+#include <nuttx/sched.h>
+
+#include "os_internal.h"
+
+#if defined(CONFIG_SCHED_WAITPID) && defined(CONFIG_SCHED_HAVE_PARENT)
+
+/*****************************************************************************
+ * Private Functions
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Public Functions
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Name: wait
+ *
+ * Description:
+ *   The wait() function will suspend execution of the calling thread until
+ *   status information for one of its terminated child processes 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 wait() or 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 wait(), return will be immediate.
+ *
+ *   The waitpid() function will behave identically to wait(), if the pid
+ *   argument is (pid_t)-1 and the options argument is 0. Otherwise, its
+ *   behaviour will be modified by the values of the pid and options arguments.
+ *
+ * Input Parameters:
+ *   stat_loc - The location to return the exit status
+ *
+ * Returned Value:
+ *   See waitpid();
+ *
+ *****************************************************************************/
+
+pid_t wait(FAR int *stat_loc)
+{
+  return waitpid((pid_t)-1, stat_loc, 0);
+}
+
+#endif /* CONFIG_SCHED_WAITPID && CONFIG_SCHED_HAVE_PARENT*/
diff --git a/nuttx/sched/sched_waitid.c b/nuttx/sched/sched_waitid.c
new file mode 100644
index 000000000..eabc69afe
--- /dev/null
+++ b/nuttx/sched/sched_waitid.c
@@ -0,0 +1,256 @@
+/*****************************************************************************
+ * sched/sched_waitid.c
+ *
+ *   Copyright (C) 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 <signal.h>
+#include <errno.h>
+
+#include <nuttx/sched.h>
+
+#include "os_internal.h"
+
+#if defined(CONFIG_SCHED_WAITPID) && defined(CONFIG_SCHED_HAVE_PARENT)
+
+/*****************************************************************************
+ * Private Functions
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Public Functions
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Name: waitid
+ *
+ * Description:
+ *   The waitid() function suspends the calling thread until one child of
+ *   the process containing the calling thread changes state. It records the
+ *   current state of a child in the structure pointed to by 'info'. If a
+ *   child process changed state prior to the call to waitid(), waitid()
+ *   returns immediately. If more than one thread is suspended in wait() or
+ *   waitpid() waiting termination of the same process, exactly one thread
+ *   will return the process status at the time of the target process
+ *   termination
+ *
+ *   The idtype and id arguments are used to specify which children waitid()
+ *   will wait for.
+ *
+ *     If idtype is P_PID, waitid() will wait for the child with a process
+ *     ID equal to (pid_t)id.
+ *
+ *     If idtype is P_PGID, waitid() will wait for any child with a process
+ *     group ID equal to (pid_t)id.
+ *
+ *     If idtype is P_ALL, waitid() will wait for any children and id is
+ *     ignored.
+ *
+ *   The options argument is used to specify which state changes waitid()
+ *   will will wait for. It is formed by OR-ing together one or more of the
+ *   following flags:
+ *
+ *     WEXITED - Wait for processes that have exited. 
+ *     WSTOPPED - Status will be returned for any child that has stopped
+ *       upon receipt of a signal. 
+ *     WCONTINUED - Status will be returned for any child that was stopped
+ *       and has been continued. 
+ *     WNOHANG - Return immediately if there are no children to wait for. 
+ *     WNOWAIT - Keep the process whose status is returned in 'info' in a
+ *       waitable state. This will not affect the state of the process; the
+ *       process may be waited for again after this call completes. 
+ *
+ *   The 'info' argument must point to a siginfo_t structure. If waitid()
+ *   returns because a child process was found that satisfied the conditions
+ *   indicated by the arguments idtype and options, then the structure pointed
+ *   to by 'info' will be filled in by the system with the status of the
+ *   process. The si_signo member will always be equal to SIGCHLD. 
+ *
+ * Input Parameters:
+ *   See description.
+ *
+ * Returned Value:
+ *   If waitid() returns due to the change of state of one of its children,
+ *   0 is returned. Otherwise, -1 is returned and errno is set to indicate
+ *   the error. 
+ *
+ *   The waitid() function will fail if:
+ *
+ *     ECHILD - The calling process has no existing unwaited-for child
+ *       processes. 
+ *     EINTR - The waitid() function was interrupted by a signal. 
+ *     EINVAL - An invalid value was specified for options, or idtype and id
+ *       specify an invalid set of processes. 
+ *
+ *****************************************************************************/
+
+int waitid(idtype_t idtype, id_t id, siginfo_t *info, int options)
+{
+  FAR _TCB *rtcb = (FAR _TCB *)g_readytorun.head;
+  sigset_t sigset;
+  int err;
+  int ret;
+
+  /* MISSING LOGIC:   If WNOHANG is provided in the options, then this function
+   * should returned immediately.  However, there is no mechanism available now
+   * know if the thread has child:  The children remember their parents (if
+   * CONFIG_SCHED_HAVE_PARENT) but the parents do not remember their children.
+   */
+
+  /* None of the options are supported except for WEXITED (which must be
+   * provided.  Currently SIGCHILD always reports CLD_EXITED so we cannot
+   * distinguish any other events.
+   */
+
+#ifdef CONFIG_DEBUG
+  if (options != WEXITED)
+    {
+      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 requeste
+   * TCB is actually a child of this task.
+   */
+
+  if (rtcb->nchildren == 0)
+    {
+      err = ECHILD;
+      goto errout_with_errno;
+    }
+  else if (idtype == P_PID)
+    {
+     /* Get the TCB corresponding to this PID and make sure it is our child. */
+
+      FAR _TCB *ctcb = sched_gettcb((pid_t)id);
+      if (!ctcb || ctcb->parent != rtcb->pid)
+        {
+          err = ECHILD;
+          goto errout_with_errno;
+        }
+    }
+
+  /* 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 (rtcb->nchildren == 0 ||
+          (idtype == P_PID && (ret = kill((pid_t)id, 0)) < 0))
+        {
+          /* We know that the child task was running okay we stared,
+           * so we must have lost the signal.  What can we do?
+           * Let's claim we were interrupted by a signal.
+           */
+
+          err = EINTR;
+          goto errout_with_errno;
+        }
+
+      /* Wait for any death-of-child signal */
+
+      ret = sigwaitinfo(&sigset, info);
+      if (ret < 0)
+        {
+          goto errout;
+        }
+
+      /* Make there this was SIGCHLD */
+
+      if (info->si_signo == SIGCHLD)
+        {
+          /* Yes.. Are we waiting for the death of a specific child? */
+
+          if (idtype == P_PID)
+            {
+              /* Was this the death of the thread we were waiting for? */
+
+              if (info->si_pid == (pid_t)id)
+                {
+                   /* Yes... return success */
+
+                   break;
+                }
+            }
+
+          /* Are we waiting for any child to change state? */
+
+          else if (idtype == P_ALL)
+            {
+              /* Return success */
+
+              break;
+            }
+
+          /* Other ID types are not supported */
+
+          else /* if (idtype == P_PGID) */
+            {
+              set_errno(ENOSYS);
+              goto errout;
+            }
+        }
+    }
+
+  sched_unlock();
+  return OK;
+
+errout_with_errno:
+  set_errno(err);
+errout:
+  sched_unlock();
+  return ERROR;
+}
+
+#endif /* CONFIG_SCHED_WAITPID && CONFIG_SCHED_HAVE_PARENT*/
diff --git a/nuttx/sched/sched_waitpid.c b/nuttx/sched/sched_waitpid.c
index 692ef6410..dc715b2e9 100644
--- a/nuttx/sched/sched_waitpid.c
+++ b/nuttx/sched/sched_waitpid.c
@@ -1,7 +1,7 @@
 /*****************************************************************************
  * sched/sched_waitpid.c
  *
- *   Copyright (C) 2011-2012 Gregory Nutt. All rights reserved.
+ *   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
@@ -41,13 +41,14 @@
 
 #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 /* Experimental */
+#ifdef CONFIG_SCHED_WAITPID
 
 /*****************************************************************************
  * Private Functions
@@ -58,7 +59,7 @@
  *****************************************************************************/
 
 /*****************************************************************************
- * Name: sched_waitpid
+ * Name: waitpid
  *
  * Description:
  *
@@ -172,10 +173,16 @@
  *
  *****************************************************************************/
 
-/***************************************************************************/
-/* NOTE: This is a partially functional, experimental version of waitpid() */
-/***************************************************************************/
+/***************************************************************************
+ * 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;
@@ -183,9 +190,24 @@ pid_t waitpid(pid_t pid, int *stat_loc, int options)
   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)
     {
@@ -193,16 +215,6 @@ pid_t waitpid(pid_t pid, int *stat_loc, int options)
       goto errout_with_errno;
     }
 
-  /* None of the options are supported */
-
-#ifdef CONFIG_DEBUG
-  if (options != 0)
-    {
-      err = ENOSYS;
-      goto errout_with_errno;
-    }
-#endif
-
   /* "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
@@ -245,4 +257,152 @@ errout:
   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;
+  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 requeste
+   * TCB is actually a child of this task.
+   */
+
+  if (rtcb->nchildren == 0)
+    {
+      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;
+        }
+    }
+
+  /* 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.
+           */
+
+          if (rtcb->nchildren == 0)
+            {
+              /* 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
+        {
+          /* 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;
+            }
+        }
+
+      /* 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 */
diff --git a/nuttx/sched/task_exithook.c b/nuttx/sched/task_exithook.c
index 9ce2e5899..1106f2885 100644
--- a/nuttx/sched/task_exithook.c
+++ b/nuttx/sched/task_exithook.c
@@ -217,6 +217,20 @@ static inline void task_sigchild(FAR _TCB *tcb, int status)
       return;
     }
 
+  /* Decrement the number of children from this parent */
+
+  DEBUGASSERT(ptcb->nchildren > 0);
+  ptcb->nchildren--;
+
+  /* Set the parent to an impossible PID.  We do this because under certain
+   * conditions, task_exithook() can be called multiple times.  If this
+   * function is called again, sched_gettcb() will fail on the invalid
+   * parent PID above, nchildren will be decremented once and all will be
+   * well.
+   */
+
+  tcb->parent = INVALID_PROCESS_ID;
+
   /* Create the siginfo structure.  We don't actually know the cause.  That
    * is a bug. Let's just say that the child task just exit-ted for now.
    */
@@ -246,7 +260,7 @@ static inline void task_sigchild(FAR _TCB *tcb, int status)
  *
  ****************************************************************************/
 
-#ifdef CONFIG_SCHED_WAITPID
+#if defined(CONFIG_SCHED_WAITPID) && !defined(CONFIG_SCHED_HAVE_PARENT)
 static inline void task_exitwakeup(FAR _TCB *tcb, int status)
 {
   /* Wakeup any tasks waiting for this task to exit */
@@ -310,14 +324,14 @@ void task_exithook(FAR _TCB *tcb, int status)
 
   task_atexit(tcb);
 
-  /* Send SIGCHLD to the parent of the exiting task */
-
-  task_sigchild(tcb, status);
-
   /* Call any registered on_exit function(s) */
 
   task_onexit(tcb, status);
 
+  /* Send SIGCHLD to the parent of the exit-ing task */
+
+  task_sigchild(tcb, status);
+
   /* Wakeup any tasks waiting for this task to exit */
 
   task_exitwakeup(tcb, status);
diff --git a/nuttx/sched/task_setup.c b/nuttx/sched/task_setup.c
index c5dd8ca3a..92897f0ae 100644
--- a/nuttx/sched/task_setup.c
+++ b/nuttx/sched/task_setup.c
@@ -168,7 +168,10 @@ static int task_assignpid(FAR _TCB *tcb)
 static inline void task_saveparent(FAR _TCB *tcb)
 {
   FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
+
+  DEBUGASSERT(rtcb->nchildren < UINT16_MAX);
   tcb->parent = rtcb->pid;
+  rtcb->nchildren++;
 }
 #else
 #  define task_saveparent(tcb)