.\" $Id: pvm_newcontext.3,v 1.3 2004/11/29 18:57:08 pvmsrc Exp $
.TH CONTEXT 3PVM "8 April, 1997" "" "PVM Version 3.4"
.SH NAME
pvm_newcontext, pvm_setcontext, pvm_freecontext, pvm_getcontext
\- Request new context, change context, free existing context,
and get current context, respectively.

.SH SYNOPSIS
.nf
.ft B
C	int ctx = pvm_newcontext( void )
.br
	int old_ctx = pvm_setcontext( int new_ctx )
.br
	int info = pvm_freecontext( ctx )
.br
	int ctx = pvm_getcontext( void )
.br

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

.SH PARAMETERS
.IP ctx
.br
Context value.
.IP new_ctx
.br
New context value.
.IP old_ctx
.br
Prior context value.
.IP info
.br
Result code.

.SH 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 
\fIold_ctx\fR to \fInew_ctx\fR.

pvm_freecontext frees \fIctx\fR 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.


.SH EXAMPLES
.nf
/* 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);


.fi

.SH ERRORS
Only system resource errors will be returned as the context
programs themselves do not generate errors.
.PP
.SH SEE ALSO