RemoteTask provides partitioning of processing tasks at the level of cooperating OS processes. For problems that can be partitioned into independent tasks running under the supervision of a Squeak image, such that each task performs a significant amount of processing and returns a moderately sized result, RemoteTask can provide substantial improvements in processing run time versus the equivalent serial processing when running on multi-core hardware.
A task is scheduled in a working image with
RemoteTask do: taskBlock whenComplete: aOneArgumentBlock
where taskBlock is the task to be scheduled in a forked Squeak image, and aOneArgumentBlock handles the result object when the remote task makes data available. Result data is returned through a ReferenceStream on the stdout pipe from the remote Squeak image. The forked Squeak image is headless and is quite memory efficient due to Unix copy-on-write for forked processes.
RemoteTask may also be useful for evaluating a method that otherwise would block the VM, such as an FFI call to a long-running external function.
RemoteTask is part of the latest CommandShell package on SqueakSource (CommandShell 4.5.0), and requires OSProcess as well as a Unix or Mac VM with OSProcessPlugin (it is helpful if the VM also has AioPlugin for process completion notification, although polling will be used if this is not present). I have tested only on Linux with standard VM and Cog, although I am hopeful that this will work on Mac also (confirmation would be appreciated).
Following is an example of three processing tasks assigned to three Squeak worker images with results returned to the supervisory image on task completion.
threeParallelTasks "Find all primes in a range of large integers. Divide the problem into three tasks running the three child images, and return the results to the supervisory image. Answer a tasks array and a results array, where the results array will be populated on completion of the tasks."
"RemoteTask threeParallelTasks"
| p1 p2 p3 results task1 task2 task3 | results := Array new: 3. task1 := [(100000000000000000000000000000 to: 100000000000000000000000019999) select: [:f | f isPrime] thenCollect: [:s | s asString]]. task2 := [(100000000000000000000000020000 to: 100000000000000000000000039999) select: [:f | f isPrime] thenCollect: [:s | s asString]]. task3 := [(100000000000000000000000040000 to: 100000000000000000000000059999) select: [:f | f isPrime] thenCollect: [:s | s asString]]. "n.b. Assign task to a variable to prevent RemoteTask from being finalized" p1 := RemoteTask do: task1 whenComplete: [:result | results at: 1 put: result]. p2 := RemoteTask do: task2 whenComplete: [:result | results at: 2 put: result]. p3 := RemoteTask do: task3 whenComplete: [:result | results at: 3 put: result]. ^ { #tasks -> { p1 . p2 . p3 } . #results -> results }
Dave