MCAST(3PVM)

NAME
pvm_mcast - Multicasts the data in the active message buffer to a set of tasks.

SYNOPSIS
C    int info = pvm_mcast( int *tids, int ntask, int msgtag )
Fortran    call pvmfmcast( ntask, tids, msgtag, info )

PARAMETERS

ntask
    Integer specifying the number of tasks to be sent to.

tids
    Integer array of length ntask containing the task IDs of the tasks to be sent to.

msgtag
    Integer message tag supplied by the user. msgtag should be >= 0. It allows the user's program to distinguish between different kinds of messages .

info
    Integer status code returned by the routine. Values less than zero indicate an error.

DISCUSSION
The routine pvm_mcast multicasts a message stored in the active send buffer to ntask tasks specified in the tids array. The message is not sent to the caller even if listed in the array of tids. The content of the message can be distinguished by msgtag. If pvm_mcast is successful, info will be 0. If some error occurs then info will be < 0.

The receiving processes can call either pvm_recv or pvm_nrecv to receive their copy of the multicast. pvm_mcast is asynchronous and based on a minimum spanning tree algorithm between the pvmds. Computation on the sending processor resumes as soon as the message is safely on its way to the receiving processors. This is in contrast to synchronous communication, during which computation on the sending processor halts until the matching receive is executed by the receiving processor.

pvm_mcast first determines which other pvmds contain the specified tasks. Then passes the message to these pvmds which in turn distribute the message to their local tasks without further network traffic.

Multicasting is not supported by most multiprocessor vendors. Typically their native calls only support broadcasting to {\m all the user's processes on a multiprocessor. Because of this omission, pvm_mcast may not be an efficient communication method on some multiprocessors except in the special case of broadcasting to all PVM processes.

EXAMPLES
C:
	info = pvm_initsend( PvmDataRaw );
	info = pvm_pkint( array, 10, 1 );
	msgtag = 5 ;
	info = pvm_mcast( tids, ntask, msgtag );

Fortran:
	CALL PVMFINITSEND(PVMDEFAULT)
	CALL PVMFPACK( REAL4, DATA, 100, 1, INFO )
	CALL PVMFMCAST( NPROC, TIDS, 5, INFO )

ERRORS
These error conditions can be returned by pvm_mcast
	PvmBadParam	giving a msgtag < 0.
	PvmSysErr	pvmd not responding.
	PvmNoBuf	no send buffer.