Have you run a test recently? Trivial mach IPC round-trip (same process) seems to be about ~8.5µs in my test, so around 4µs per call. I'm sure if you transferr

Have you run a test recently? Trivial mach IPC round-trip (same process) seems to be about ~8.5µs in my test, so around 4µs per call. I'm sure if you transferred port rights, memory, etc the cost would go up. edit: I would advise anyone to run your own tests. Anecdotes aren't data and some things like syscalls are not nearly as expensive on modern hardware as they once were. Sometimes things can get ridiculously faster than you remember. For example the original iPhone took nearly 200ns to do objc_msgSend() [1]. In 2016 modern hardware did the same thing in 2.6ns [2]. That's two orders of magnitude improvement. So saying "message passing is slow" is not a correct statement... it's almost as cheap as a C++ virtual method call. [1] https://www.mikeash.com/pyblog/friday-qa-2016-04-15-performance-comparisons-of-common-operations-2016-edition.html https://www.mikeash.com/pyblog/friday-qa-2016-04-15-performa... [2] https://www.mikeash.com/pyblog/friday-qa-2016-04-15-performance-comparisons-of-common-operations-2016-edition.html https://www.mikeash.com/pyblog/friday-qa-2016-04-15-performa...