Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!olivea!oliveb!isc-br!hawk!rsami!rick
From: rick@rsami.UUCP (Rick Schaeffer)
Newsgroups: comp.sys.amiga.tech
Subject: Re: CreateNewProc
Message-ID: <rick.2092@rsami.UUCP>
Date: 5 Jan 91 12:27:28 GMT
References: <484@swrinde.nde.swri.edu>
Sender: ricks@hawk.isc-br.com (Rick Schaeffer)
Lines: 99


>If I were to start a thread from a function in my code segment using
>CreateNewProc(), can I access variables global to the parent process?
>Or would this thread be a full-blown process for which I would need to
>set up a shared mem arrangement? The reason for this thread is to
>handle gadget input events for a window created by the parent since the
>parent is too busy to deal with them in a timely manner. I see I can
>pass the window ptr in the CreateNewProc() call. Is this kosher?

Yes, you can access globals from the thread process...provided you either
compile with LARGE data model (ie non-relative data addresses) or get the
a4 register loaded as the first thing in the thread process.  Do this with
the function "geta4()" in either Manx or Lattice or use the "__saveds" 
keyword on the function declaration in Lattice.  Note that accessing
globals makes it impossible to make your program resident, though.  It's
probably better to pass pointers to everything you need access to from 
the thread in the startup message (see below).

>
>Also, I assume I need to set up a message port in the parent process to
>send a 'kill' message.  Since this thread will be used to handle all
>window input events for this window (created by the parent), the window
>message port should be adequate for receiving the 'kill' message, no?

CreateNewProc() returns a pointer to the process structure created.  This
includes a message port that you can use to kick off the thread.  All you
have to do is allocate a message port to be used as the reply port for the
child.  An example should suffice:

struct pomsg {
	struct Message POm;
	/* you can put whatever you want after this */
	int		rc;
	char	*cmd;
	int		*ptr1;
	int		*ptr2;
	} *childmsg;

	childmsg = malloc((size_t)sizeof(struct pomsg));
	childmsg->POm.mn_ReplyPort = CreateMsgPort();
	childmsg->POm.mn_Node.ln_Type = NT_MESSAGE;
	childmsg->POm.mn_Node.ln_Pri = 0;
	/* at this point you can load up the rest of the elements of childmsg */
	ptr1 = "A message for the child"

	/* nptags contains a pointer to the function "childprocess" */
	child = CreateNewProc(nptags);
	/* now pass the child the startup message */
	PutMsg(&child->pr_MsgPort,(struct Message *) childmsg);
	.
	.
	.
	/* somewhere you want to do a waitport on childmsg->POm.mn_ReplyPort
	   this can be used to detect the completion of the thread process
	   or whatever
	*/
	WaitPort(childmsg->POm.mn_ReplyPort);
	/* clean things up */
	DeleteMsgPort(childmsg->POm.mn_ReplyPort);
	free(childmsg->cmd);
	rc = childmsg->rc;
	free(childmsg);

/* Now the thread (or child) process */
int childprocess()
{
	struct Process	*me;
	struct pomsg	*startupmsg;
	int				i;
	struct Library  *DOSBase;

	DOSBase = OpenLibrary("dos.library",0L);
	/* find our process structure */
	me = (struct Process *) FindTask(NULL);

	/* Wait for the parent to kick us off */
	WaitPort(&me->pr_MsgPort);

	/* Get the command to execute */
	startupmsg = (struct pomsg *) GetMsg(&me->pr_MsgPort);
	/* Now you can do whatever you want with the stuff in the startupmsg */
	.
	.
	.
	/* pass the exit code back to the parent */
	startupmsg->rc = whatever;
	ReplyMsg((struct Message *) startupmsg);
	CloseLibrary(DOSBase);
	return(0);
}

Note that the return address put on this message by my Amiga UUCP system
is probably bogus.  Please reply to the address in my .signature.


-- 
Rick Schaeffer          UUCP:  uunet!isc-br.isc-br.com!ricks
E. 13611 26th Ave.             ricks@isc-br.isc-br.com
Spokane, Wa.  99216     Phone: (509)928-3533