mpi.bcast.cmd is an extension of mpi.bcast.
It is mainly used to transmit a command from master to all R slaves
spawned by using slavedaemon.R script.
mpi.bcast.cmd(cmd=NULL, ..., rank = 0, comm = 1, nonblock=FALSE, sleep=0.1)a command to be sent from master.
used as arguments to cmd (function command) for passing their (master) values to R slaves, i.e., if `myfun(x)' will be executed on R slaves with `x' as master variable, use mpi.bcast.cmd(cmd=myfun, x=x).
the sender
a communicator number
logical. If TRUE, a nonblock procedure is used on all receivers so that they will consume none or little CPUs while waiting.
a sleep interval, used when nonblock=TRUE. Smaller sleep is, more response receivers are, more CPUs consume
mpi.bcast.cmd returns no value for the sender and an expression of the transmitted command for others.
Be caution to use mpi.bcast.cmd alone by master in the middle of comptuation. Only all slaves in idle
states (waiting instructions from master) can it be used. Othewise it may result miscommunication
with other MPI calls.
mpi.bcast.cmd is a collective call. This means all members in a communicator must
execute it at the same time. If slaves are spawned (created) by using slavedaemon.R (Rprofile script),
then they are running mpi.bcast.cmd in infinite loop (idle state). Hence master can execute
mpi.bcast.cmd alone to start computation. On the master, cmd and ... are put together
as a list which is then broadcasted (after serialization) to all slaves (using for loop with mpi.send
and mpi.recv pair). All slaves will return an expression which will be evaluated by either slavedaemon.R,
or by whatever an R script based on slavedaemon.R.
If nonblock=TRUE, then on receiving side, a nonblock procedure is used to check if there is a message. If not, it will sleep for the specied amount and repeat itself.
Please use mpi.remote.exec if you want the executed results returned from R
slaves.