Move waitpid() data structures to task group; The caller of waitpid() is now only awakened when the final thread of the task group exits

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5608 42af7a65-404d-4744-a932-0658087f49c3

ChangeLog

@@ -4109,7 +4109,11 @@
 	* sched/pthread* and include/nuttx/sched: Move pthread join data
 	  and pthread key calculation data into the "task group" structure.
 	* sched/atexit.c, on_exit.c, task_exithook.c and include/nuttx/sched.h:
-	  Move atexit and on_exit data structure to task group.  These
+	  Move atexit and on_exit data structures to task group.  These
 	  callbacks are only issued now when the final member of the task
 	  group exits.
+	* sched/waitpid.c, task_exithook.c and include/nuttx/sched.h:
+	  Move waitpid data data structures to task group.  Callers of
+	  of waitpid() are now only awakened whent he final thread of the
+	  task group exits.
 

include/nuttx/sched.h

@@ -83,6 +83,8 @@
 #    define HAVE_TASK_GROUP   1
 #  elif defined(CONFIG_SCHED_ONEXIT)     /* Group on_exit() function */
 #    define HAVE_TASK_GROUP   1
+#  elif defined(CONFIG_SCHED_WAITPID)    /* Group waitpid() function */
+#    define HAVE_TASK_GROUP   1
 #  elif CONFIG_NFILE_DESCRIPTORS > 0     /* File descriptors */
 #    define HAVE_TASK_GROUP   1
 #  elif CONFIG_NFILE_STREAMS > 0         /* Standard C buffered I/O */
@@ -326,6 +328,14 @@ struct task_group_s
   FAR struct child_status_s *tg_children; /* Head of a list of child status     */
 #endif
 
+  /* waitpid support ************************************************************/
+  /* Simple mechanism used only when there is no support for SIGCHLD            */
+
+#if defined(CONFIG_SCHED_WAITPID) && !defined(CONFIG_SCHED_HAVE_PARENT)
+  sem_t tg_exitsem;                 /* Support for waitpid                      */
+  int *tg_statloc;                  /* Location to return exit status           */
+#endif
+
   /* Pthreads *******************************************************************/
 
 #ifndef CONFIG_DISABLE_PTHREAD
@@ -408,11 +418,6 @@ struct _TCB
   FAR void *starthookarg;                /* The argument passed to the function */
 #endif
 
-#if defined(CONFIG_SCHED_WAITPID) && !defined(CONFIG_SCHED_HAVE_PARENT)
-  sem_t    exitsem;                      /* Support for waitpid                 */
-  int     *stat_loc;                     /* Location to return exit status      */
-#endif
-
   uint8_t  sched_priority;               /* Current priority of the thread      */
 
 #ifdef CONFIG_PRIORITY_INHERITANCE

sched/sched_waitpid.c

@@ -182,7 +182,8 @@
 #ifndef CONFIG_SCHED_HAVE_PARENT
 pid_t waitpid(pid_t pid, int *stat_loc, int options)
 {
-  _TCB *ctcb;
+  FAR _TCB *ctcb;
+  FAR struct task_group_s *group;
   bool mystat;
   int err;
   int ret;
@@ -212,21 +213,26 @@ pid_t waitpid(pid_t pid, int *stat_loc, int options)
       goto errout_with_errno;
     }
 
+  /* The the task group corresponding to this PID */
+
+  group = ctcb->group;
+  DEBUGASSERT(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 (stat_loc != NULL && ctcb->stat_loc == NULL)
+  if (stat_loc != NULL && group->tg_statloc == NULL)
     {
-      ctcb->stat_loc = stat_loc;
+      group->tg_statloc = stat_loc;
-      mystat         = true;
+      mystat = true;
     }
 
   /* Then wait for the task to exit */
  
-  ret = sem_wait(&ctcb->exitsem);
+  ret = sem_wait(&group->tg_exitsem);
   if (ret < 0)
     {
       /* Unlock pre-emption and return the ERROR (sem_wait has already set
@@ -236,7 +242,7 @@ pid_t waitpid(pid_t pid, int *stat_loc, int options)
 
       if (mystat)
         {
-          ctcb->stat_loc = NULL;
+          group->tg_statloc = NULL;
         }
 
       goto errout;

sched/task_exithook.c

@@ -474,25 +474,52 @@ static inline void task_leavegroup(FAR _TCB *ctcb, int status)
 #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 */
+  FAR struct task_group_s *group = tcb->group;
 
-  while (tcb->exitsem.semcount < 0)
+  /* Have we already left the group? */
+
+  if (group)
     {
-      /* "If more than one thread is suspended in waitpid() awaiting
+      /* Only tasks return valid status.  Record the exit status when the
-       *  termination of the same process, exactly one thread will return
+       * task exists.  The group, however, may still be executing.
-       *  the process status at the time of the target process termination." 
-       *  Hmmm.. what do we return to the others?
        */
 
-      if (tcb->stat_loc)
+      if ((tcb->flags & TCB_FLAG_TTYPE_MASK) == TCB_FLAG_TTYPE_TASK)
         {
-          *tcb->stat_loc = status << 8;
+          /* Report the exit status.  We do not nullify tg_statloc here
-           tcb->stat_loc = NULL;
+           * because we want to prent other tasks from registering for
+           * the return status.  There is only one task per task group,
+           * there for, this logic should execute exactly once in the
+           * lifetime of the task 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_statloc)
+            {
+              *group->tg_statloc = status << 8;
+            }
         }
 
-      /* Wake up the thread */
+      /* Is this the last thread in the group? */
 
-      sem_post(&tcb->exitsem);
+      if (group->tg_nmembers == 1)
+        {
+          /* Yes.. Wakeup any tasks waiting for this task to exit */
+
+         group->tg_statloc = NULL;
+         while (group->tg_exitsem.semcount < 0)
+            { 
+              /* Wake up the thread */
+
+              sem_post(&group->tg_exitsem);
+            }
+        }
     }
 }
 #else
@@ -530,7 +557,7 @@ void task_exithook(FAR _TCB *tcb, int status)
 {
   /* Under certain conditions, task_exithook() can be called multiple times.
    * A bit in the TCB was set the first time this function was called.  If
-   * that bit is set, then just ext doing nothing more..
+   * that bit is set, then just exit doing nothing more..
    */
 
   if ((tcb->flags & TCB_FLAG_EXIT_PROCESSING) != 0)