Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/007.lha/runback.doc

Text File | 1986-11-09 | 17KB | 496 lines

From: [e-mail]
Followup-To: Questions about running background tasks.
Organization: Commodore-Amiga Inc., 983 University Ave #D, Los Gatos CA 95030
Keywords: RUNBACKGROUND background-tasks dump-initial-CLI
Summary: You CAN kill the initial CLI, and run functions as BACKGROUND tasks.

SYNOPSIS:

This tutorial note deals with the AmigaDOS Execute function, showing in
detail how its various FileHandle combinations affect the way the function
executes.  It also provides the source for a RUNBACKGROUND command that
you can add to your workbench to start one or more processes from the
s/startup-sequence and still allow the initial CLI to end with the
command line "endcli > NIL:".


SPECIAL NOTES ABOUT EXECUTE REDIRECTION

The Execute function can accept file handles as part of the command,
where the file handle is used to redirect the stdin and/or stdout.
There are special rules that Execute uses for this redirection.  The
following specifies the various forms that the Execute function call
can take and their effects.


Execute("something",0,0)

    means use "*" (that is, the current CLI window) for output.
    There is NO input expected for stdin.  This form crashes if
    used under Workbench because there is NO WINDOW to which the
    output can be directed!  The "something" string can include
    the redirection commands (< and >).  If you specify no
    redirection commands, the string will literally be interpreted
    as though you asked for the function:

        Execute("something > * ",0,0);

    which says "use the current window for output".  Since workbench
    itself has no current window of its own (its process simply has
    no window assigned), the function cannot terminate correctly.

    When you perform the Execute function with this calling sequence,
    it calls the RUN command, which, in turn, uses CreateProc()
    to load the code for the something you wish to run.   This
    code runs as a child of the CLI and the CLI must hang around
    until the child finishes.  Likewise it also means that the
    Execute command will not finish until the child exits.

    If you call Execute as:

        Execute("RUN something",0,0);

    you are asking the system to spawn a new CLI process that can
    handle the child process on its own, thereby seeming to free
    the originating CLI from handling the process, and control
    returns to the originating CLI immediately after RUN begins
    to operate.  HOWEVER, even though you've called RUN, the
    originating CLI still may not be able to "endcli > NIL:" itself,
    because  "something" inherits the stdout (*) from the calling process.

    This effectively prevents the originating CLI from going away until
    the user-count of its stdout output handle has gone to zero,  since
    that process has become a user of the stdout (*).  If EITHER ONE of
    the file- handles is a 0, the user-count for * is incremented,
    regardless of whether the program uses stdin or stdout at all.
    This happens since Execute cannot tell what will be in the
    execute-string.

    Thus, the originating CLI must hang around if either of the handles
    is zero, just to be sure the input and output paths are available
    if needed.  See Execute("something", nilfh, nilfh) for a way
    around this.


Execute("something",0,fout)

    means use fout (a valid file handle) for output.  There is NO input
    expected from stdin, although the current CLI window (*) is still
    marked as having one more user.

    The FileHandle fout is not closed for you once Execute has finished.
    You must close fout yourself.

    This form of the function works either under Workbench or CLI,
    as long as fout is valid.  The "something" can ALWAYS be a command that
    includes both < or > redirection.  The output redirection will be
    utilized for error messages from the CLI if the comand-string
    encounters an error.


Execute("something",fin,fout)

    Means do "something", then continue to read commands from "fin".
    The "something" can just as easily be specified as "" (the null
    string), which means do nothing, then continue to read commands from
    the file whose handle is "fin".  Again, you'll have to close fin
    yourself.

    Control returns when the CLI finishes "something".   Anything
    specified in fin will be done simultaneously with your own
    task that now is free to run.  (The CLI has done "something",
    and is now free to go on to do something else, while the execute
    process continues to read fin.)

    When fin is an interactive input stream (See IsInteractive()),
    the fin handle becomes the handle that you would get
    if you opened "*".   This means that you have asked the
    system to create a new interactive CLI process, with
    prompts and so on.   Since a CLI process is now a user of
    "*", the window cannot be made to go away until you issue an
    explicit ENDCLI command.

    It also means that the caller of this form of Execute will NOT
    regain control until the CLI completes its task.  Because fin
    it is an interactive process, it always has some input pending;
    thus it cannot be finished with its job until the input actually
    ends the CLI.  So the caller will go to sleep waiting for the
    interactive CLI to end.


Execute("something", fin, (fout = 0))

    FileHandle fout should normally be a file handle specifying some output
    such as a con: window or a file.  There is, however, one very special
    case, which is when fout is 0.  This means, as described earlier,
    use "*" as the output.

    Note that in this special case,  fin MUST be a console handler
    stream (CON:, RAW:, or "*").  Additionally, if you want to
    recognize an end-of-file condition on the input, you'll have
    to use only CON: windows.  CON: windows translate CTRL-\ into
    an end-of-file;  RAW: windows, on the other hand, pass on the
    numeric value of this key combination without treating it as EOF.


Execute("something_with_no_stdin_or_stdout", nilfh, nilfh)

    Here, "nilfh" is a file handle resulting from a call to Open
    with a filename of NIL:, as:

        struct FileHandle *nilfh;

        nilfh = Open("NIL:",MODE_NEWFILE);

    Several developers and users have expressed an interest
    in being able to start background processes using the Workbench
    startup script (s/startup-sequence).  An example would be to start
    things such as the CLOCK or something else, then end up on the
    Workbench without the originating CLI having to hang around for
    the user to close down.

    If you want the originating CLI to go away, you must somehow
    prevent any process started by that CLI from opening "*"
    for either input or output as mentioned above.

    Within the "something..." string, you must spawn an independent
    CLI process.  Additionally the independent process must have its own
    I/O restricted so that it does not in any way depend on or
    attempt to communicate with the originating CLI.  Here, then,
    is PART of the something-string:

        RUN >NIL: <NIL: <rest_of_string>

    This starts an independent process.

    The rest_of_string can contain the command and its parameters.
    But be aware that if your command uses the standard startup sequence,
    it still needs to open its stdin and stdout file handles.  You'll
    need to assure that a proper file handle is actually provided for
    stdin and stdout, so the rest of the string should look like this:

    rest_of_string = "MyCommand >NIL: <NIL: Parm1 Parm2 Parm3 etc";


    Thus, the complete Execute command string appropriate to letting
    the originating CLI close down and leave the CLOCK open on the
    Workbench is to run a program such is listed below.  Note, however,
    that the file handle to NIL:, dynamically allocated by this program,
    must hang around "forever" until the next system reset.  It has to be
    dynamically allocated, since you want this program and its calling
    CLI to die and leave the CLOCK and Workbench active.


/* runclock.c */

/* Author:  Rob Peck.  5/9/86 */

#include "exec/types.h"
#include "exec/memory.h"
#include "libraries/dosextens.h"

extern struct FileHandle *Open();

main()
{
    LONG success;
    struct FileHandle *nilfh;
    nilfh = (struct FileHandle *)
        AllocMem(sizeof(struct FileHandle),MEMF_CLEAR | MEMF_PUBLIC);

    success = Execute("RUN >NIL: <NIL: CLOCK >NIL: <NIL:",nilfh,nilfh);
    if(success)
    {
        printf("Started CLOCK as a separate process\n");
    }
    else
    {
        FreeMem(nilfh, sizeof(struct FileHandle));
    }
    /* Notice that if the program succeeds, nobody ever frees this mem */
}


    To try this program, your startup-sequence should contain
    at least the following lines:

        LOADWB
        RUNCLOCK
        ENDCLI > NIL:

    Notice that this program does NOT close the "nilfh", that is,
    the file handle obtained by opening NIL:.   This will tie up
    a small block of memory somewhere in the system until the next
    boot, unless someone spawns a process that keeps track of when
    the CLOCK tool exits, then finally frees this file handle.  But
    this piece of memory is probably not too high a price to pay
    to obtain the functionality people have requested.


        Here is a general purpose implementation of the above technique,
    allowing you to run a named process "in the background".  It
    includes a delay parameter to minimize disk thrashing among
    sequentially loaded processes.  It is a bit more complicated
    in that we've installed the appropriate error handling.

    DISCLAIMER:

    This program is provided as a service to the programmer
        community to demonstrate one or more features of the Amiga
        personal computer.  These code samples may be freely used
        for commercial or noncommercial purposes.

        Commodore Electronics, Ltd ("Commodore") makes no
        warranties, either expressed or implied, with respect
        to the program described herein, its quality, performance,
        merchantability, or fitness for any particular purpose.
        This program is provided "as is" and the entire risk
        as to its quality and performance is with the user.

    (Other standard disclaimers apply)

/*

--------------
runbackground.c
---------------

SUMMARY:  A Workbench Disk can be used to autostart an application
      through the use of the startup script and close the startup CLI.


Users have commented that it is not possible to start a process going
from the startup script and then cause the initial CLI to go away.
Here is the solution to that problem, named appropriately:

    RUNBACKGROUND

which starts and runs a background task.  This does indeed allow you to
create a startup script that will set up your workbench running any
programs you might wish, removing the initial CLI in the process.

Your s/startup-sequence can contain lines such as the following:

    RUNBACKGROUND -3 clock
    RUNBACKGROUND utilities/calculator
    RUNBACKGROUND -5 utilities/notepad

where RUNBACKGROUND is the command and the second parameter is the filename
which may be preceded by a flag-variable that specifies an optional delay
time.  The delay can be from 0 to 9, for the number of seconds that
the startup script should sleep while allowing the background task to
load and start.  I've put that in to minimize thrashing of the disk as it
tries to load several projects at once.


LIMITATIONS:

    The program that you run cannot require any input from an interactive
    CLI that starts it.    Additionally, you cannot specify any file
    redirection in the command line since this program provides the
    redirection for you already.  If you need to use redirection for
    your command, you can modify the source code where shown, thus
    allowing the redirection to become one of the parameters passed
    through to your program.

    RUNBACKGROUND does pass your command line parameters to the program
    you wish to start, but limits the total length of your command
    string to 227 (255 minus the 28 characters for "RUN >NIL: <NIL: "
    preceding your own file pathname and ">NIL: < NIL: " following it.)


LINKING INFORMATION:

    (Amiga/Lattice C)    use -v option for pass 2   (lc2 -v filename.q)
            to disable stack checking code installation.
            (stack checking code sometimes is incorrect).

    FROM lib:Astartup.obj runbackground.o
    TO runbackground
    LIBRARY lib:amiga.lib, lib:lc.lib

    ****************************  NOTE:  ********************************
    If you use Lstartup.obj, it won't let the startup CLI go away. This is
    because the source code for Lstartup.asm either opens its own window
    or uses an existing CLI window (Open("*",....)), so that it has some
    guaranteed place to put the output.   Astartup.obj does not do this.
    *********************************************************************

Hope this helps.


robp.
*/

/* runbackground.c */
/* Author:  Rob Peck.  5/9/86 */


#include "exec/types.h"
#include "exec/memory.h"
#include "libraries/dosextens.h"

extern struct FileHandle *Open();
extern struct FileLock *Lock();

main(argc, argv)
int argc;
char *argv[];
{
    LONG success, delaywillbe;
    UBYTE commandstring[255];
    char *test, *filename;
    LONG fromparm;
    struct FileInfoBlock *fib;
    struct FileHandle *nilfh;    /* NOTE: will hang around until next reset */
    struct FileLock *lock;

    fib = NULL;            /* No file info block so far. */
    delaywillbe = 1;

    if(argc < 2 )
    {
usage:
    printf("Usage: RUNBACKGROUND [ -<loaddelay>] <name> [<parm(s)>]\n");
    printf("          where optional loaddelay is 0-9,\n");
    printf("          specified in seconds for the CLI\n");
    printf("          to sleep, waiting for task to load\n");
    printf("          (minimizes inter-task disk-thrashing)\n");
    if(fib) FreeMem(fib, sizeof(struct FileInfoBlock));
    exit(0);
    }

    /* See if there is a delay parameter present */

    test = argv[1];

    if(*test++ == '-')
    {
    filename = argv[2];    /* argv[1] is delay so argv[2] is file  */
    fromparm = 3;        /* Copy parms from 3 to end          */

    if(*test >= '0' && *test <= '9')
    {
        delaywillbe = 1 + (50 * (*test - '0'));
    }
    if (argc < 3) goto usage; /* Only a delay, and no filename!! */

    argc--;        /* one less parm to copy */
    }
    else
    {
    filename = argv[1];
    fromparm = 2;        /* Copy parms from 2 to end         */
    }

    /* Now see if the file exists!  If not, it can crash the background
     * CLI and take the system along with it.
     */
    lock = Lock(filename,ACCESS_READ);
    if(!lock)
    {
    test = filename;
    if(*test == '?') goto usage;
    else
    {
        printf("%ls: Command not found\n",filename);
        goto usage;
    }
    }
    else
    {
    /* If file exists, it better be a file and not a directory */

    /* Unfortunately, it is difficult to tell if it is an executable
     * file.  If not executable, we'll still get blown out of the
     * water, but that is up to the user to do it right!
     */

    fib =  (struct FileInfoBlock *)
            AllocMem(sizeof(struct FileInfoBlock),MEMF_CLEAR);
    if(!fib)
    {
        UnLock(lock);
        printf("Ran out of memory!\n");
        exit(0);
    }
    else
    {
        success = Examine(lock,fib);
        if(fib->fib_DirEntryType > 0)     /* its a directory!! */
        {
        printf("%ls is a directory, not a file!\n",filename);
        goto usage;
        }
    }
       FreeMem(fib, sizeof(struct FileInfoBlock));
    UnLock(lock);
    }

    nilfh = Open("NIL:",MODE_NEWFILE); /* will always succeed */

    strcpy( &commandstring[0], "RUN >NIL: <NIL: " );
    strcat( &commandstring[0], filename);

    /* REMOVE THIS NEXT LINE IF YOU WANT TO INCLUDE REDIRECTION IN
     * THE COMMAND LINE FOR RUNBACKGROUND.   (The line was installed
     * to assure that something like "RUNBACKGROUND date ?" would
     * not crash the system.  "Date ?" is expecting to have an interactive
     * CLI, and unless it is specifically told to direct its output to nil:
     * it causes a crash.  If the next line is removed, and you are careful
     * about putting only NON-interactive commands in the command line,
     * everything should be ok.  Notice that if you do not specify a
     * non-interactive file handle (named_disk_file or NIL:) for your
     * program, it may still prevent the originating CLI from going away
     * until your program ends.  Also note that specifying two instances
     * of the same redirection (">somewhere" or "<somewhere") for a
     * background task crashes.
     */

    strcat( &commandstring[0], " >NIL: <NIL: ");  /* stop interactive crash */

    argc--;

    while(--argc > 0)    /* Rebuild parameter string for passing it on */
    {
    strcat( &commandstring[0], " ");    /* add a blank */
    strcat( &commandstring[0], argv[fromparm++]);
    }

    success = Execute( &commandstring[0] , nilfh, nilfh);

    /* The full command passed to Execute now looks like this:
     *
     *    "RUN >NIL: <NIL: FILENAME >NIL: <NIL: PARAMETER(s)"
     *
     */

    if(success)
    {
    printf("Started %ls as a background task\n",filename);

    /* Execute, in this case, returns IMMEDIATELY.  The process
     * that is loading the code that is to be run as a background
     * process is working to get everything in and started.
     */
    }
    /* Now, to minimize thrashing between tasks, lets put this task to
     * sleep so that the each task actually gets a chance to load.
     */
    Delay(delaywillbe);
}

strcpy( to, from )
register char *to, *from;
{
   do {
       *to++ = *from;
   } while( *from++ );
}
strcat( to, from )
register char *to, *from;
{
    while( *to ) to++;
    strcpy( to, from );
}