CONTEXT(3PVM)

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