Re: [PATCH v2 7/7] t/helper/simple-ipc: convert test-simple-ipc to use start_bg_command

> On 08/11/2021 23:59, Johannes Schindelin wrote:
> [snip]
> > I had a look at this and could reproduce... partially. I only managed to
> > make it fail every once in a while.
> >
> > Digging deeper, it turns out that the `lstat()` call in
> > `ipc_get_active_state()` does not receive an `st_mode` indicating a
> > socket, but rather a file (in my tests, it was usually 0100644, but
> > sometimes even 0100755).
> >
> > The reason is, of course, that Cygwin _emulates_ Unix sockets. What is in
> > the file system is just a special file, it is marked with the `system` bit
> > (which only exists on Windows), and its contents start with the tell-tale
> > `!<socket>`.
> >
> > And as you might have guessed, there is a race going on between Cygwin
> > writing that file _and_ flipping that `system` bit, and Git trying to
> > access the Unix socket and encountering an unexpected file.
> >
> > Now, why this only happens in your 32-bit setup, I have no idea.
> >
> > In my tests, the following patch works around the issue. Could I ask you
> > to test it in your environment?
>
> Just FYI, I just tried the patch below (on 64-bit cygwin) and this test
> now works fine for me. (well, run 5 times by hand - not with --stress).

> This is on windows 10 21H1 and cygwin:
>
>   $ uname -a
>   CYGWIN_NT-10.0 satellite 3.3.2(0.341/5/3) 2021-11-08 16:55 x86_64 Cygwin
>   $
>
> [Yes, I updated last night!]

>
> ATB,
> Ramsay Jones
>
> > -- snip --
> > diff --git a/compat/simple-ipc/ipc-unix-socket.c
> > b/compat/simple-ipc/ipc-unix-socket.c
> > index 4e28857a0a..1c591b2adf 100644
> > --- a/compat/simple-ipc/ipc-unix-socket.c
> > +++ b/compat/simple-ipc/ipc-unix-socket.c
> > @@ -36,6 +36,23 @@ enum ipc_active_state ipc_get_active_state(const char
> > *path)
> >  	}
> >
> >  	/* also complain if a plain file is in the way */
> > +#ifdef __CYGWIN__
> > +	{
> > +		static const int delay[] = { 1, 10, 20, 40, -1 };
> > +		int i;
> > +
> > +		for (i = 0; S_ISREG(st.st_mode) && delay[i] > 0; i++) {
> > +			/*
> > +			 * Cygwin might still be in the process of marking the
> > +			 * underlying file as a system file.
> > +			 */
> > +			sleep_millisec(delay[i]);
> > +			if (lstat(path, &st) == -1)
> > +				return IPC_STATE__INVALID_PATH;
> > +		}
> > +	}
> > +#endif
> > +
> >  	if ((st.st_mode & S_IFMT) != S_IFSOCK)
> >  		return IPC_STATE__INVALID_PATH;
> >
> > -- snap --
> >
> > FWIW it looks as if the loop might be a bit of an overkill, as I could not
> > get the code to need more than a single one-millisecond sleep, but it's
> > probably safer to just keep the delay loop in place as-is.
> >
> > Ciao,
> > Dscho
> >
>
>