parpool

The pool status indicator in the lower-left corner of the desktop shows the client session connection to the pool and the pool status. Click the icon for a menu of supported pool actions.

With a pool running: With no pool running:

If you set your parallel preferences to automatically create a parallel pool when necessary, you do not need to explicitly call the parpool command. You might explicitly create a pool to control when you incur the overhead time of setting it up, so the pool is ready for subsequent parallel language constructs.

delete(poolobj) shuts down the parallel pool. Without a parallel pool, spmd and parfor run as a single thread in the client, unless your parallel preferences are set to automatically start a parallel pool for them.

When you use the MATLAB editor to update files on the client that are attached to a parallel pool, those updates automatically propagate to the workers in the pool. (This automatic updating does not apply to Simulink^® model files. To propagate updated model files to the workers, use the updateAttachedFiles function.)

If possible, the working folder on the workers is initially set to match that of the MATLAB client session. Subsequently, the following commands entered in the client Command Window also execute on all the workers in the pool:

This behavior allows you to set the working folder and the command search path on all the workers, so that subsequent pool activities such as parfor-loops execute in the proper context.

When changing folders or adding a path with cd or addpath on clients with Windows^® operating systems, the value sent to the workers is the UNC path for the folder if possible. For clients with Linux^® operating systems, it is the absolute folder location.

If any of these commands does not work on the client, it is not executed on the workers either. For example, if addpath specifies a folder that the client cannot access, the addpath command is not executed on the workers. However, if the working folder can be set on the client, but cannot be set as specified on any of the workers, you do not get an error message returned to the client Command Window.

Be careful of this slight difference in behavior in a mixed-platform environment where the client is not the same platform as the workers, where folders local to or mapped from the client are not available in the same way to the workers, or where folders are in a nonshared file system. For example, if you have a MATLAB client running on a Microsoft^® Windows operating system while the MATLAB workers are all running on Linux operating systems, the same argument to addpath cannot work on both. In this situation, you can use the function pctRunOnAll to assure that a command runs on all the workers.

Another difference between client and workers is that any addpath arguments that are part of the matlabroot folder are not set on the workers. The assumption is that the MATLAB install base is already included in the workers' paths. The rules for addpath regarding workers in the pool are:

For example, suppose that matlabroot on the client is C:\Applications\matlab\. With an open parallel pool, execute the following to set the path on the client and all workers:

addpath("P1",
        "P2",
        "C:\Applications\matlab\T3",
        "C:\Applications\matlab\T4",
        "P5",
        "C:\Applications\matlab\T6",
        "P7",
        "P8");

Because T3, T4, and T6 are subfolders of matlabroot, they are not set on the workers' paths. So on the workers, the pertinent part of the path resulting from this command is:

P1
P2
<worker original matlabroot folders...>
P5
P7
P8

If you are using Macintosh or Linux, and see problems during large parallel pool creation, see Recommended System Limits for Macintosh and Linux.