ParallelSubmit & WaitAll: Non‑Blocking Parallelism in Wolfram Language

Why ParallelSubmit?

\n

Standard parallel functions block the main kernel until all subkernels finish. For long or independent tasks you want the main kernel to remain responsive. ParallelSubmit returns a placeholder instead of the result, letting you dispatch work and continue execution.

\n

Basic usage

\n

\n(* Verify kernels *)\nParallelKernelCount[];\n\n(* Submit a long task *)\ntask = ParallelSubmit[Pause[5]; 42];\nPrint[\"Task submitted, main kernel continues\"];\n\n(* Do something else *)\nPause[1];\nPrint[\"Doing other work while task runs\"];\n\n(* Collect result *)\nresult = WaitAll[{task}];\nPrint[\"Result: \", result];\n

\n

Managing resources

\n

Too many pending submissions can exhaust memory. A simple semaphore pattern limits active tasks:

\n

\nmaxActive = 4;\ntasks = {};\nDo[\n  While[Length[tasks] >= maxActive,\n    Pause[0.1];\n    tasks = DeleteCases[tasks, _?(!BusyQ[#]&)]\n  ];\n  AppendTo[tasks, ParallelSubmit[HeavyComputation[i]]]\n, {i, 1, 20}];\nresults = WaitAll[tasks];\n

\n

Diagnostics

\n

\n
• Check active kernels: ParallelKernelCount[]
\n
• Monitor status: $KernelStatus shows “Busy” for running subkernels.
\n
• When a task is stuck, terminate all subkernels with ParallelStop[].
\n