Execute code in parallel on workers of parallel pool
spmd, statements, end
spmd(n), statements, end
spmd(m,n), statements, end
The general form of an spmd (single program,
multiple data) statement is:
spmd
statements
endspmd, statements, end defines an spmd statement
on a single line. MATLAB® executes the spmd body
denoted by statements on several MATLAB workers
simultaneously. The spmd statement can be used
only if you have Parallel Computing Toolbox. To execute the statements
in parallel, you must first open a pool of MATLAB workers using parpool or have your parallel prefences
allow the automatic start of a pool.
Inside the body of the spmd statement, each MATLAB worker
has a unique value of labindex,
while numlabs denotes the
total number of workers executing the block in parallel. Within the
body of the spmd statement, communication functions
for communicating jobs (such as labSend and labReceive) can transfer data between
the workers.
Values returning from the body of an spmd statement
are converted to Composite objects
on the MATLAB client. A Composite object contains references
to the values stored on the remote MATLAB workers, and those
values can be retrieved using cell-array indexing. The actual data
on the workers remains available on the workers for subsequent spmd execution,
so long as the Composite exists on the client and the parallel pool
remains open.
By default, MATLAB uses all workers in the pool. When there
is no pool active, MATLAB will create a pool and use all the
workers from that pool. If your preferences do not allow automatic
pool creation, MATLAB executes the block body locally and creates
Composite objects as necessary. You cannot execute an spmd block
if any worker is busy executing a parfeval request,
unless you use spmd(0).
spmd(n), statements, end uses n to
specify the exact number of MATLAB workers to evaluate statements,
provided that n workers are available from the
parallel pool. If there are not enough workers available, an error
is thrown. If n is zero, MATLAB executes the
block body locally and creates Composite objects, the same as if there
is no pool available.
spmd(m,n), statements, end uses a minimum
of m and a maximum of n workers
to evaluate statements. If there are not enough
workers available, an error is thrown. m can be
zero, which allows the block to run locally if no workers are available.
For more information about spmd and Composite
objects, see Distribute Arrays and Run SPMD.
Use parfevalOnAll instead
of parfor or spmd if you
want to use clear.
This preserves workspace transparency. See Ensure Transparency in parfor-Loops.
Perform a simple calculation in parallel, and plot the results:
parpool(3) spmd % build magic squares in parallel q = magic(labindex + 2); end for ii=1:length(q) % plot each magic square figure, imagesc(q{ii}); end delete(gcp)
An spmd block runs on the workers
of the existing parallel pool. If no pool exists, spmd will
start a new parallel pool, unless the automatic starting of pools
is disabled in your parallel preferences. If there is no parallel
pool and spmd cannot start one, the code runs serially
in the client session.
If the AutoAttachFiles property
in the cluster profile for the parallel pool is set to true,
MATLAB performs an analysis on an spmd block
to determine what code files are necessary for its execution, then
automatically attaches those files to the parallel pool job so that
the code is available to the workers.
For information about restrictions and limitations
when using spmd, see Run Single Programs on Multiple Data Sets.