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Full Discussion: C function to start process but to return right away
Top Forums Programming C function to start process but to return right away Post 302428059 by Corona688 on Tuesday 8th of June 2010 05:15:02 PM
Old 06-08-2010
Quote:
Originally Posted by JCR
You'r right. 100% right. I should call exit(1) instead of continue. At that point, right after this exit, isn't the child process killed? If the child process is killed why would I need a way to handle zombies?
The process terminates, but isn't removed from the process table until you wait() for it. Things like runtime statistics and return value can still be gleaned from it until you do, which is why they keep it. You don't need to wait() for it at the bottom of your loop there(and thereby block until it quits) but something in your program must do it sooner or later.

Fortunately it's not a big deal. There's nonblocking ways to check if a child has exited ( see waitpid's WNOHANG flag ), ways to handle child exits asynchronously with sigaction and SIGCHLD(not reccomended; if you get two SIGCHLD's too fast to handle you might miss one), or you can just do a wait() loop in an independent thread. The thread method's probably the most bulletproof and least resource-intensive, the thread will spend 99.9% of its time asleep and only run when needed. (or when you want it to.)

I think you misunderstood a little with the exit(1). It doesn't have to be exit(1). In the example I showed I used execv(), which replaces the process with something else, so the exit(1) would only happen if execv() failed to load /bin/echo. If you're just doing your own thing you could have an exit(0) for normal return and exit(1) on error and so forth, it's just the return value for main().

---------- Post updated at 03:15 PM ---------- Previous update was at 02:58 PM ----------

It occurs to me to ask, how many loops does this program run? I figured it was like a daemon that takes several requests, which could create zombies forever which would be bad. If the loop only runs once and it quits thereafter, it's probably safe not to wait() if the child is disowned first. It will be owned by init instead and waited for by it. Researching how to do this.
Last edited by Corona688; 06-08-2010 at 06:07 PM..
This User Gave Thanks to Corona688 For This Post:
JCR
 

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LEARN ABOUT REDHAT

xmdropsitequerystackingorder

XmDropSiteQueryStackingOrder(library call)								XmDropSiteQueryStackingOrder(library call)

NAME

       XmDropSiteQueryStackingOrder  --  A  Drag  and  Drop function that returns the parent, a list of children, and the number of children for a
       specified widget

SYNOPSIS

       #include <Xm/DragDrop.h>
       Status XmDropSiteQueryStackingOrder(
       Widget widget,
       Widget *parent_return,
       Widget **child_returns,
       Cardinal *num_child_returns);

DESCRIPTION

       XmDropSiteQueryStackingOrder obtains the parent, a list of children registered as drop sites, and the number of children registered as drop
       sites  for  a given widget. The children are listed in current stacking order, from bottom-most (first child) to the top-most (last child).
       This function allocates memory for the returned data that must be freed by calling XtFree.

       widget	 Specifies the widget ID. For this widget, you obtain the list of its children, its parent, and the number of children.

       parent_return
		 Returns the widget ID of the drop site parent of the specified widget.

       child_returns
		 Returns a pointer to the list of drop site children associated with the specified widget.  The function allocates memory to  hold
		 the  list.   The application is responsible for managing the allocated space.	The application can recover the allocated space by
		 calling XtFree.

       num_child_returns
		 Returns the number of drop site children for the specified widget.

       For a complete definition of DropSite and its associated resources, see XmDropSite(3).

RETURN

       Returns 0 (zero) if the routine fails; returns a nonzero value if it succeeds.

RELATED

       XmDropSite(3) and XmDropSiteConfigureStackingOrder(3).

													XmDropSiteQueryStackingOrder(library call)
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