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

1 files changed, 77 insertions, 2 deletions

diff --git a/nuttx/sched/Kconfig b/nuttx/sched/Kconfig
index 11d74b583..fe9a88085 100644
--- a/nuttx/sched/Kconfig
+++ b/nuttx/sched/Kconfig
@@ -42,13 +42,88 @@ config SCHED_HAVE_PARENT
 	bool "Support parent/child task relationships"
 	default n
 	---help---
-		Remember the ID of the parent thread when a new child thread is
+		Remember the ID of the parent task when a new child task is
 		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 SCHED_CHILD_STATUS
+	bool "Retain child exit status"
+	default n
+	depends on SCHED_HAVE_PARENT
+	---help---
+		If this option is selected, then the exit status of the child task
+		will be retained after the child task exits.  This option should be
+		selected if you require knowledge of a child process' exit status.
+		Without this setting, wait(), waitpid() or waitid() may fail.  For
+		example, if you do:
+
+			1) Start child task
+			2) Wait for exit status (using wait(), waitpid(), or waitid()).
+
+		This can fail because the child task may run to completion before
+		the wait begins.  There is a non-standard work-around in this case:
+		The above sequence will work if you disable pre-emption using
+		sched_lock() prior to starting the child task, then re-enable pre-
+		emption with sched_unlock() after the wait completes.  This works
+		because the child task is not permitted to run until the wait is in
+		place.
+
+		The standard solution would be to enable SCHED_CHILD_STATUS.  In
+		this case the exit status of the child task is retained after the
+		child exits and the wait will successful obtain the child task's
+		exit status whether it is called before the child task exits or not.
+
+		Warning:  If you enable this feature, then your application must
+		either (1) take responsibility for reaping the child status with wait(),
+		waitpid(), or waitid(), or (2) suppress retention of child status.
+		If you do not reap the child status, then you have a memory leak and
+		your system will eventually fail.
+
+		Retention of child status can be suppressed on the parent using logic like:
+
+			struct sigaction sa;
+
+			sa.sa_handler = SIG_IGN;
+			sa.sa_flags = SA_NOCLDWAIT;
+			int ret = sigaction(SIGCHLD, &sa, NULL);
+
+config PREALLOC_CHILDSTATUS
+	int "Number of pre-allocated child status"
+	default 0
+	depends on SCHED_CHILD_STATUS
+	---help---
+		To prevent runaway child status allocations and to improve
+		allocation performance, child task exit status structures are pre-
+		allocated when the system boots.  This setting determines the number
+		of child status structures that will be pre-allocated.  If this
+		setting is not defined or if it is defined to be zero then a value
+		of 2*MAX_TASKS is used.
+
+		Note that there cannot be more that CONFIG_MAX_TASKS tasks in total.
+		However, the number of child status structures may need to be
+		significantly larger because this number includes the maximum number
+		of tasks that are running PLUS the number of tasks that have exit'ed
+		without having their exit status reaped (via wait(), waitid(), or
+		waitpid()).
+
+		Obviously, if tasks spawn children indefinitely and never have the
+		exit status reaped, then you may have a memory leak!  If you enable
+		the SCHED_CHILD_STATUS feature, then your application must take
+		responsibility for either (1) reaping the child status with wait(),
+		waitpid(), or waitid() or it must (2) suppress retention of child
+		status.  Otherwise, your system will eventually fail.
+
+		Retention of child status can be suppressed on the parent using logic like:
+
+			struct sigaction sa;
+
+			sa.sa_handler = SIG_IGN;
+			sa.sa_flags = SA_NOCLDWAIT;
+			int ret = sigaction(SIGCHLD, &sa, NULL);
+
 config JULIAN_TIME
 	bool "Enables Julian time conversions"
 	default n
@@ -88,7 +163,7 @@ config PRIORITY_INHERITANCE
 		Set to enable support for priority inheritance on mutexes and semaphores. 
 
 config SEM_PREALLOCHOLDERS 
-	int "Pre-allocated holders"
+	int "Number of pre-allocated holders"
 	default 16
 	depends on PRIORITY_INHERITANCE
 	---help---