"build directory locked" should say which process is holding the lock

[jyn514]

Since #88310, we don't allow multiple processes of bootstrap to run in parallel. That's good to avoid issues like #76661, but means that people sometimes don't know why the build directory is locked (e.g. if they're running rust-analyzer in the background or running x in two terminals at once). We should make it easier to figure this out.

In the short-term, ps -u $USER | grep bootstrap/debug/bootstrap on Unix will show all the relevant processes. In the long-term, and to support windows, we might want to run the equivalent of that ourselves and directly print all relevant PIDs.

[zephaniahong]

@clubby789 Hi! I saw that you implemented the solution for Linux. May I know why your solution would not work for Mac/Windows?
Also, if I'm trying if implement it for mac/windows, is there anything I should be taking note of?
(I'm a bit new but I'm slowly trying to solve more complex tasks)

Thank you!

[albertlarsan68]

Windows enthousiast here, quite sarcastic:
The solution for Linux was in the most Linux-y way, eg read a file that only exists in the head of the kernel and extract the information from it.
End of Windows user part, start of Rustacean:
The best way to do this is to do it in a platform-specifix way. If the Linux way also works on MacOS, then the change is trivial, but for Windows the solution will almost certainly be to call Win32 APIs and extract the information from this C-centric API.

[zephaniahong]

Okay! Hope I'm not biting more than I can chew here but I'll give this a shot!
@rustbot claim

[jyn514]

There might be an existing crate that does this, I would prefer that to maintaining more platform specific code.

[zephaniahong]

Okay! Let me go source around. But if you chance upon the crate, do let me know(:
Thank you!

[jyn514]

@ChrisDenton suggests using Restart Manager on Windows (which I think is https://learn.microsoft.com/en-us/windows/win32/rstmgr/about-restart-manager ?)

[jyn514]

@thomcc suggests we can skip all the target specific stuff and just write the PID to the lockfile when we create it 😍