ndk-build: Return PID after launching the app

[Jasper-Bekkers]

Depends on #329 to apply cleanly.

Shows the process PID after launching. Requires -W as an am start arg to wait for process completion to prevent a race condition. Having the PID is useful in a lot of cases, such as filtering logs with adb logcat --pid=...

[MarijnS95]

That's neat, I was wondering how this was implemented by @dvc94ch in x, turns out to be a sleep-loop: https://github.com/cloudpeers/xbuild/blob/e0ebb50bfa78cfad61931bb30c70a624b85fdddd/xbuild/src/devices/adb.rs#L175-L186

[MarijnS95]

It's probably semi-smart to keep a loop so that duplicate PIDs for yet-to-exit app instances are not causing issues:

https://github.com/cloudpeers/xbuild/blob/e58cc09b4f2cb07c1fa0591f9d65cea435dd5646/xbuild/src/devices/adb.rs#L179

But IMO am start should be able to emit the pid instead of this hackery. Android Studio must also have a smart yet concise way of dealing with this, that isn't error-prone. Perhaps just outputting all the PIDs (--pid is probably a coma-separated list or can be stacked), and we can combine that with a last timestamp filter.

[MarijnS95]

Rebased now that #329 is in, and dropped #330 from it to be merged separately.

[MarijnS95]

I think the pid thing is good enough for now. Was seeing duplicate PIDs because one of my gdb sessions got stuck and the processes couldn't get killed and detached even under root.

If we ever observe problems with it we'll make it more fallible or change it altogether.