Race condition in wait(::Process) with process end?

[NHDaly]

I'm not very familiar with the details of process spawning, but this part looks like it could potentially be a race to me? Inside wait(x::Process), here, we double-check process_exited after grabbing the io_lock:

julia/base/process.jl

Lines 655 to 668 in 329f92c

	iolock_begin()
	if !process_exited(x)
	preserve_handle(x)
	lock(x.exitnotify)
	iolock_end()
	try
	wait(x.exitnotify)
	finally
	unlock(x.exitnotify)
	unpreserve_handle(x)
	end
	else
	iolock_end()
	end

But then, when the process is killed, we don't lock the io_lock before we notify the .exitnotify condition...:

julia/base/process.jl

Lines 61 to 67 in 329f92c

	proc.handle = C_NULL
	lock(proc.exitnotify)
	try
	notify(proc.exitnotify)
	finally
	unlock(proc.exitnotify)
	end

Isn't it therefore possible that we could set the process's handle to NULL and signal the CV after the process_exited check, but before the lock(x.exitnotify), and thus the waiter would miss it?

That is, isn't there a possible race here?:

    iolock_begin()
    if !process_exited(x)  # x.handle != C_NULL
        # ------------
        # Right here, since `uv_return_spawn` hasn't locked the iolock, it could set x.handle = C_NULL,
        # and then notify exitnotify, before this task is waiting on it, so no one gets notified?
        # ------------
        preserve_handle(x)  # <-- this just preserves C_NULL :)
        lock(x.exitnotify)
        iolock_end()
        try
            wait(x.exitnotify)      # <-- then this waits forever?
        finally
            unlock(x.exitnotify)
            unpreserve_handle(x)
        end
    else
        iolock_end()
    end

Originally posted by @NHDaly in #54145 (comment)

[NHDaly]

Actually, even simpler, why is the iolock involved at all? Why doesn't the waiter lock the exitnotify before checking process_exited, and why doesn't uv_return_spawn lock the exitnotify before nulling the handle?

Isn't the monitor hygiene supposed to be: you should always be holding the monitor's lock before reading or writing the condition that the monitor is checking, right?