The logic for this calculation is actually open-source, so you can see how it's done yourself.Įach simulator I load adds about 150 processes and 3000 file descriptors, and in practice we will start bumping up against these limits around 9-10 simulators. For processes, it also sets up a hard maximum, which on an M1 Mac Mini is 4000 processes. For an M1 Mac Mini, these default to 2666 processes, and 49,152 file descriptors. The system sets up some default maximums for the number of active processes and open file descriptors on the system, based on the specs of the machine. Sudo chown root:wheel /Library/LaunchDaemons/.plist.įinally, restart your machine for these changes to take effect.

Then update their ownership using the following command (once for each file): I'll start with the minimal solution I came up with (as of macOS 11.4), and then give more of an explanation below.Īdd the following two files to /Library/LaunchDaemons: The next two biggest issues are hitting the system limits for open file descriptors, and open processes. Multiple simulators attempting to access the clipboard can cause deadlocks that leave them frozen.

You will see serious animation and UI slowdown when this is not selected. Simulator Settingsįile > GPU Selection > Prefer Discrete GPU I upgraded my build machines to M1 Mac Minis recently, and despite clearly having the CPU and memory headroom to run more simulators, I was getting strange errors (XPC daemon crashes, hangs, etc.) once I tried to push beyond about 5 simulators in parallel.įortunately, with some help from the Simulators team in a WWDC lab, I was able to figure out the issue and get a reliable setup of 10+ simulators running in parallel. I have a large UI test suite I run for Nihongo, and the more simulators I can run in parallel, the faster it can complete.

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