MAN page from Old RedHat 5.X pvm-3.4beta7-2.i386.rpm

CONTEXT

Section: PVM Version 3.4 (3PVM)
Updated: 8 April, 1997
Index

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 andthe means to manipulate this context.

Contexts provide the ability for communicating tasks to automaticallydifferentiate messages by the context in which they were sent.Thus a message sent in context A by the sender must be receivedin 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 inadvertentreceipt 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 contextprograms themselves do not generate errors.

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