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

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);