CONTEXT(3PVM)							  PVM Version 3.4						     CONTEXT(3PVM)

NAME

       pvm_newcontext - Request new context.
       pvm_setcontext - Change context.
       pvm_freecontext - Free existing context.
       pvm_getcontext - Get current context.

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)