rom/exec/childwait.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     ChildWait() - Wait for a task to finish it processing.
   6 */
   7 #include "exec_intern.h"
   8 #include <proto/exec.h>
   9
  10 /*****************************************************************************
  11
  12     NAME */
  13
  14         AROS_LH1(IPTR, ChildWait,
  15
  16 /*  SYNOPSIS */
  17         AROS_LHA(ULONG, tid, D0),
  18
  19 /*  LOCATION */
  20         struct ExecBase *, SysBase, 126, Exec)
  21
  22 /*  FUNCTION
  23         Wait for either a specific child task, or any child task to finish.
  24         If you specify tid = 0, then this call will return when any child
  25         task exits, otherwise it will not return until the requested task
  26         finishes.
  27
  28         Note that the tid is NOT the task control block (ie struct Task *),
  29         rather it is the value of the ETask et_UniqueID field. Passing in a
  30         Task pointer will cause your Task to deadlock.
  31
  32         You must call ChildFree() on the returned task before calling
  33         ChildWait() again. Ie.
  34
  35             struct ETask *et;
  36
  37             et = ChildWait(0);
  38             ChildFree(et->et_UniqueID);
  39
  40     INPUTS
  41         tid -   The UniqueID of a task.
  42
  43     RESULT
  44         Returns either the ETask structure of the child, or one of the
  45         CHILD_* values on error.
  46
  47         This allows you to work out which of the children has exited.
  48
  49     NOTES
  50         This function will work correctly only for child tasks that are
  51         processes created with NP_NotifyOnDeath set to TRUE.
  52
  53         Calling ChildWait() on a task that isn't your child will result in
  54         a deadlock.
  55
  56     EXAMPLE
  57
  58     BUGS
  59         Be careful with the return result of this function.
  60
  61     SEE ALSO
  62
  63     INTERNALS
  64
  65 *****************************************************************************/
  66 {
  67     AROS_LIBFUNC_INIT
  68
  69     struct Task *this = FindTask(NULL);
  70     struct ETask *et;
  71     struct ETask *child;
  72
  73     /*
  74         ChildWait() will wait for either a specific or any child task to
  75         finish. We we get it we return the task unique id to the caller.
  76
  77         Firstly, are we a new-style Task?
  78     */
  79     if ((this->tc_Flags & TF_ETASK) == 0)
  80         return CHILD_NOTNEW;
  81
  82     et = this->tc_UnionETask.tc_ETask;
  83
  84     /*
  85         Scanning this list is unsafe, I need to Forbid(). Note that the
  86         Wait() below will break the Forbid() condition. This is how I need
  87         it to be.
  88     */
  89     Forbid();
  90
  91     /* We do not return until the condition is met */
  92     for (;;)
  93     {
  94         /* Check if it has returned already. This will also take the first. */
  95         ForeachNode(&et->et_TaskMsgPort.mp_MsgList, child)
  96         {
  97             if (tid == 0 || child->et_UniqueID == tid)
  98                 goto child_exited;
  99         }
 100
 101         /* No matching children, we have to wait */
 102         SetSignal(0, SIGF_CHILD);
 103         Wait(SIGF_CHILD);
 104     }
 105
 106 child_exited:
 107     Permit();
 108     return (IPTR)child;
 109
 110     AROS_LIBFUNC_EXIT
 111 } /* ChildWait */