bionic (3) pvm_newcontext.3PVM.gz

NAME

       pvm_newcontext,  pvm_setcontext,  pvm_freecontext,  pvm_getcontext - Request new context, change context,
       free existing context, and get current context, respectively.

SYNOPSIS

       C    int ctx = pvm_newcontext( void )
            int old_ctx = pvm_setcontext( int new_ctx )
            int info = pvm_freecontext( ctx )
            int ctx = pvm_getcontext( void )

       Fortran
            call pvmfnewcontext( ctx )
            call pvmfsetcontext( new_ctx, old_ctx )
            call pvmffreecontext( ctx, info )
            call pvmfgetcontext( ctx )

PARAMETERS

       ctx
              Context value.

       new_ctx
              New context value.

       old_ctx
              Prior context value.

       info
              Result code.

DESCRIPTION

       The context functions provide a system-wide unique context and the means to manipulate this context.

       Contexts provide the ability for communicating tasks  to  automatically  differentiate  messages  by  the
       context  in  which  they  were  sent.  Thus a message sent in context A by the sender must be received in
       context A by the recipient.  A sender may send in any context.  However, a recipient will  not  accept  a
       message sent in a context that differs from its own.

       One  such  use of contexts is with library routines.  Using contexts, library routine inter-communication
       may be logically seperated from  the  user's  application  inter-communication.  This  will  prevent  the
       inadvertent receipt of one another's messages.

       Spawned  tasks  inherit the spawn-time context of their parent.  Existing PVM applications work unchanged
       using the default context.

       pvm_newcontext returns a newly allocated context.  However, this new context is not yet active.

       pvm_setcontext changes the current context from old_ctx to new_ctx.

       pvm_freecontext frees ctx so that it may be  reused.   Contexts  are  a  system  resource  that  will  be
       exhausted if not recycled.

       pvm_getcontext returns the current context of the requesting task.

EXAMPLES

       /* parent task with context */
            int cc, context0, context1;
            char buf[25];

            context0 = pvm_getcontext();       /*  get my current context */
            context1 = pvm_newcontext();       /*  get a new context */
            pvm_setcontext(context1);          /*  set my context to new context */
            printf("My context is: %d", context1);
            pvm_spawn("child", (char**)0, PvmTaskDefault, "", 1, &tid);
            cc = pvm_recv(-1, -1);             /*  receive message from child - in context1 */
            pvm_upkstr(buf);
            printf("%s", buf);
            pvm_setcontext(context0);          /*  reset my context to my original context0 */

       /* child task with context - child inherits parent's context as default */
            int context;
            int ptid;
            char buf[25];

            ptid = pvm_parent();
            context = pvm_getcontext();        /*  get my current context */
            sprintf(buf, "Greetings from child who's context is: %d.", context);
            pvm_initsend(PvmDataDefault);
            pvm_pkstr(buf);
            pvm_send(ptid, 1);

ERRORS

       Only system resource errors will be returned as the context programs themselves do not generate errors.

SEE ALSO

                                                  8 April, 1997                                    CONTEXT(3PVM)