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From: LK-KARI@FINTUVM.BITNET (Kari Sutela)
Newsgroups: comp.sys.amiga.tech
Subject: CreateTask() problems...
Message-ID: <740LK-KARI@FINTUVM>
Date: 12 Apr 89 14:35:17 GMT
Organization: University of Turku, Finland
Lines: 119

Sorry, this is a bit long.

For most part of the week now, I have been seriously confused about creating
a new task. I have looked on other peoples' source and I can understand them
just fine but they are not quite what I need to do. I have managed to locate
source code for tasks that end before their parent, only.

BUT I need to create a task that *outlives* its parent and I haven't managed
to do this in a reliable manner. What I need to do is start a task which
will initialize a public message port and waits for messages to arrive there.
The task should remove itself when a special 'kill yourself' message appears
in its message port.

The code goes something like this: (Please note, due to EBCDIC-ASCII
translation, square and curly brackets might appear as some other characters,
so the code might look a bit strange)

/* GLOBALS */

struct RxsLib *RexxSysBase;
struct IntuitionBase *IntuitionBase;   /* The task needs these libraries */

char PORTNAME#$ "MyPublicPort";

extern void the_task();

void main()
{
    struct Task *MyTask;

    OpenLibraries();    /* And other initializations */

    MyTask = CreateTask( "MyTask", 0L, the_task, 4000L );
    /* Hope I got the parameters right */
    if( mytask == NULL )
         error( "Couldn't create the task" );
         /* error() will release resources, too */

    return;

}

void the_task()
{
    struct MsgPort *MyPort;
    struct Message *mymsg;
    BOOL quit;

    geta4(); /* For Manx small code memory model */

    MyPort = CreatePort( PORTNAME ); /* Perhaps some other parameters as well*/
    if( MyPort == NULL )
         cleanup();
    /* Perhaps I remember the semantics of CreatePort() incorrectly, did it
     * return the signal bit? Any way, I'm typing this from memory
     */


    /* Make it public */
    AddPort( MyPort );

    /* Now wait */
    for(;;) {
         WaitPort( MyPort );
         mymsg = GetMsg( MyPort );
         if( quit = handle_msg( mymsg ) ) {
              ExhaustPort( MyPort );
              RemPort( MyPort );  /* Not public anymore */
              DeletePort( MyPort );  /* delete it entirely */
              cleanup();
         }
    }

}

BOOL handle_msg( msg )
struct Message *msg;
{
    /* Handles the message - returns true if it was 'kill yourself' */
}

void ExhaustPort( port )
struct MsgPort *port;
{
    /* replies to all pending messages */
}

void cleanup()
{
    CloseLibs();
    RemTask( 0L );
}

/* End of example */

I am using Aztec C, if it makes any difference. I seem to be able to launch
the new task allright, but the message port won't open properly most of the
time. What especially confuses me is that, if I run the program through SDB,
I'll get a proper message port with the name I wanted. And most of the time
my tests indicate that the messages are correctly handled.

But if I invoke the command straight from the command line, a message port
will open but its name is garbage. This is really confusing, why should a
program behave differently if it's being debugged (have I created a monster
program that's aware of monitoring :-)???

BTW, has anyone found a way to use SDB on tasks?

BTW, if I leave out the task creation and just 'run' the program (or use Manx's
detach.o) everything works absolutely fine. But these methods create a process
and this program doesn't actually need it - I'd really like to make it a task.

Any hints on this? Have I completely misunderstood the semantics of CreateTask
and task behaviour in general? Am I mistaken in assuming that a task can use
resources opened by its parent (even after the parent has died) and close the
resources when it exits? The Exec manual isn't too clear on this.

-   Kari Sutela
-   lk-kari@fintuvm.utu.fi (internet) OR lk-kari@fintuvm.bitnet (bitnet)