[Review, 2nd] SF-0007: Subprocess

[ksluder (Kyle Sluder)]

@icharleshu

we do want to allow for "escape hatches" such that if you want to achieve some platform-specific behavior, you won't have to revert back to calling fork/exec yourself.

I think this is a subtle point that only becomes evident after spending a lot of time working with or trying to build a cross-platform framework. If you commit to zero platform-specific API, clients wind up reverse-engineering your abstractions in order to integrate with their target platform(s), which makes it much harder to evolve your framework.

@icharleshu

ProcessIdentifier here is a great example. Windows provides a main thread ID in addition to a process ID.

Where is this thread ID coming from? As far as I’m aware, Win32 processes do not have a “main” thread. Just like POSIX platforms, a Win32 process can exit the thread that WinMain() was called on. Is this a Swift- or Foundation-provided construct?

Edit: I see this is coming from the PROCESS_INFORMATION returned by CreateProcess. Since you are required to close the thread handle, that means the handle will still be valid even if the process exits the thread. You just won’t be able to do much with it if it does. Is Foundation taking care to call CloseHandle() on the thread?