Build parallel.pool.Constant from data or function handle
C = parallel.pool.Constant(X)
C = parallel.pool.Constant(FH)
C = parallel.pool.Constant(FH,CLEANUP)
C = parallel.pool.Constant(COMP)
C = parallel.pool.Constant(X) copies the
value X to each worker and returns a parallel.pool.Constant
object, C, which allows each worker to access the
value X within a parallel language construct (parfor, spmd, parfeval)
using the property C.Value. This can improve performance
when you have multiple parfor-loops accessing the same constant set
of data, because X is transferred only once to
the workers.
C = parallel.pool.Constant(FH) evaluates
function handle FH on each worker and stores the
result in C.Value. This is also useful for creating
and using any handle-type resources on the workers, such as file handles
and database connections.
C = parallel.pool.Constant(FH,CLEANUP) evaluates
function handle FH on each worker and stores the
result in C.Value. When C is
cleared, the function handle CLEANUP is evaluated
with a single argument C.Value on each worker.
C = parallel.pool.Constant(COMP) uses the
values stored in the Composite COMP, and stores
them in C.Value on each worker. This is especially
useful when the data that you need to use inside a parfor-loop can
be constructed only on the workers, such as when the data is too large
to conveniently fit in the client, or when it is being loaded from
a file that only the workers can access. If COMP does
not have a defined value on every worker, an error results.
parallel.pool.Constant must be called in
the MATLAB client session.
parallel.pool.Constant automatically starts
a parallel pool, if possible. If no pool is running, and one cannot
be started automatically, parallel.pool.Constant generates
an error.
This example shows how to create a numeric parallel.pool.Constant,
and use it in multiple parfor-loops on the same
pool.
First, create some large data on the client, then build a parallel.pool.Constant, transferring the data to the pool only once.
data = rand(1000); c = parallel.pool.Constant(data); for ii = 1:10 % Run multiple PARFOR loops accessing the data. parfor jj = 1:10 x(ii,jj) = c.Value(ii,jj); end end
This example shows how to create a parallel.pool.Constant with a function handle and a cleanup function.
Create a temporary file on each worker. By passing @fclose as
the second argument, the file is automatically closed when c goes
out of scope.
c = parallel.pool.Constant(@() fopen(tempname(pwd),'wt'),@fclose); spmd disp(fopen(c.Value)); % Displays the temporary filenames. end parfor idx = 1:1000 fprintf(c.Value,'Iteration: %d\n',idx); end clear c; % Closes the temporary files.
This example shows how to build large data sets as a Composite
on pool workers inside an spmd block, and then
use that data as a parallel.pool.Constant inside a parfor-loop.
spmd if labindex == 1 x = labBroadcast(1,rand(5000)); else x = labBroadcast(1); end end xc = parallel.pool.Constant(x); parfor idx = 1:10 s(idx) = sum(xc.Value(:,idx)); end s
s =
1.0e+03 *
2.5108 2.5031 2.5123 2.4909 2.4957 2.5462 2.4859 2.5320 2.5076 2.5432parcluster | parfeval | parfor | parpool | spmd