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 recip‐
ient 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 inadver‐
tent 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)
