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)