sched/group/group_foreachchild.c: group_foreachchild iterate by reverse order since the callback(e.g. group_killchildren) may remove the tcb from list

sched Kconfig and sched/task/exit.c:  Add SCHED_EXIT_KILL_CHILDREN option to kill all child threads when the main thread of a task exits.

TODO

@@ -44,7 +44,17 @@ o Task/Scheduler (sched/)
   Title:       CHILD PTHREAD TERMINATION
   Description: When a tasks exits, shouldn't all of its child pthreads also be
                terminated?
-  Status:      Closed.  No, this behavior will not be implemented.
+
+               This behavior was implemented as an options controlled by the
+               configuration setting CONFIG_SCHED_EXIT_KILL_CHILDREN.  This
+               option must be used with caution, however.  It  should not be
+               used unless you are certain of what you are doing.  Uninformed
+               of this option can often lead to memory leaks since, for
+               example, memory allocations held by threads are not
+               automatically freed!
+
+  Status:      Closed.  No, this behavior will not be implemented unless
+               specifically selected.
   Priority:    Medium, required for good emulation of process/pthread model.
                The current behavior allows for the main thread of a task to
                exit() and any child pthreads will persist.  That does raise

sched/Kconfig

@@ -582,6 +582,18 @@ config SCHED_WAITPID
 		compliant) and will enable the waitid() and wait() interfaces as
 		well.
 
+config SCHED_EXIT_KILL_CHILDREN
+	bool "Enable kill all children when exit"
+	default n
+	depends on SCHED_HAVE_PARENT && SCHED_CHILD_STATUS
+	---help---
+		When a task exits, all of its child threads will be killed.
+
+		Caution:  This selection should not be used unless you are certain
+		of what you are doing.  Uninformed of this option can often lead to
+		memory leaks since, for example, memory allocations held by threads
+		are not automatically freed!
+
 endmenu # Tasks and Scheduling
 
 menu "Pthread Options"

sched/group/group_foreachchild.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  *  sched/group/group_foreachchild.c
  *
- *   Copyright (C) 2013 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2013, 2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -77,7 +77,9 @@ int group_foreachchild(FAR struct task_group_s *group,
 
   DEBUGASSERT(group);
 
-  for (i = 0; i < group->tg_nmembers; i++)
+  /* Visit the main thread last (if present) */
+
+  for (i = group->tg_nmembers - 1; i >= 0; i--)
     {
       ret = handler(group->tg_members[i], arg);
       if (ret != 0)

sched/task/exit.c

@@ -1,7 +1,8 @@
 /****************************************************************************
  * sched/exit.c
  *
- *   Copyright (C) 2007-2008, 2011-2012 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2008, 2011-2012, 2018 Gregory Nutt. All rights
+ *     reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -47,6 +48,7 @@
 #include <nuttx/fs/fs.h>
 
 #include "task/task.h"
+#include "group/group.h"
 #include "sched/sched.h"
 
 /****************************************************************************
@@ -75,6 +77,15 @@ void exit(int status)
 
   status &= 0xff;
 
+#ifdef CONFIG_SCHED_EXIT_KILL_CHILDREN
+  /* Kill all of the children of the group, preserving only this thread.
+   * exit() is normally called from the main thread of the task.  pthreads
+   * exit through a different mechanism.
+   */
+
+  group_killchildren((FAR struct task_tcb_s *)tcb);
+#endif
+
   /* Perform common task termination logic.  This will get called again later
    * through logic kicked off by _exit().  However, we need to call it before
    * calling _exit() in order to handle atexit() and on_exit() callbacks and

sched/task/task_exit.c

@@ -76,7 +76,7 @@
  * Returned Value:
  *   OK on success; or ERROR on failure
  *
- * Assumeptions:
+ * Assumptions:
  *   Executing within a critical section established by the caller.
  *
  ****************************************************************************/