Dynamically launching more kernels *during* a parallel calculation -- is it safe?

*To*: mathgroup at smc.vnet.net*Subject*: [mg124727] Dynamically launching more kernels *during* a parallel calculation -- is it safe?*From*: Szabolcs HorvÃt <szhorvat at gmail.com>*Date*: Thu, 2 Feb 2012 04:58:42 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

It appears that it is possible to launch more kernels *during* a parallel calculation, and they will be utilized for the rest of the calculation. Here's a simple way to test and illustrate (in a fresh kernel): LaunchKernels[2] Parallelize[ Table[Pause@RandomInteger[20]; $KernelID, {i, 8}], Method -> "FinestGrained" ] Now use Evaluation -> Interrupt Evaluation... to interrupt the evaluation and go into a subsession. In the subsession evaluate $KernelCount (* check that we only have 2 kernels *) LaunchKernels[4] (* launch 4 more *) Return (* return from the dialog *) Notice that when the Table[] finally finishes, we get results between 1 and 6. This means that all 6 kernels have been used for the rest of the evaluation, even though some kernels were only launched in the middle of the calculation. Question: Is it safe to do this? Can this break anything? Consider some code like this: manageKernels[] :=(* uses LaunchKernels[] to launch more is compute resources become available *) SetSharedFunction[manageKernels] (* ensure that manageKernels[] is always evaluated on the master kernel *) Parallelize[ Table[manageKernels[]; compute[i], {i, 100}], Method -> "FinestGrained" ] Is this going to be safe? What if manageKernels[] uses CloseKernels[] as well?