Thank you for the investigating.
I believe I understand what happens in the runtime.
I found that a similar problem has been reported to UCRT runtime, and the
reporter says that Darwin libc and glibc does unlock the mutex while
calling atexit-ed functions.
The report:
https://developercommunity.visualstudio.com/t/atexit-deadlock-with-thread-safe-static-/1654756
glibc:
https://sourceware.org/git/?p=glibc.git;a=blob;f=stdlib/cxa_finalize.c;hb=2642002380aafb71a1d3b569b6d7ebeab3284816#l96
Darwin:
https://github.com/apple-open-source-mirror/Libc/blob/5e566be7a7047360adfb35ffc44c6a019a854bea/stdlib/FreeBSD/atexit.c#L274-L292
I'm also feel scared to do that, but it might be practically safe.
> Thanks for the report. I looked into the issue and found the
> cause is in newlib. I have confirmed that the following patch
> fixes the issue, but I am not very sure unlocking mutex here
> is safe. Let me consider a bit more.
>
>
> diff --git a/newlib/libc/stdlib/__call_atexit.c
b/newlib/libc/stdlib/__call_atexit.c
> index 710440389..44f1f6acc 100644
> --- a/newlib/libc/stdlib/__call_atexit.c
> +++ b/newlib/libc/stdlib/__call_atexit.c
> @@ -114,6 +114,11 @@ __call_exitprocs (int code, void *d)
>
> ind = p->_ind;
>
> +#ifndef __SINGLE_THREAD__
> + /* Unlock __atexit_recursive_mutex; otherwise, the function
fn() may
> + deadlock if it waits for another thread which calls
atexit(). */
> + __lock_release_recursive(__atexit_recursive_mutex);
> +#endif
> /* Call the function. */
> if (!args || (args->_fntypes & i) == 0)
> fn ();
> @@ -121,6 +126,9 @@ __call_exitprocs (int code, void *d)
> (*((void (*)(int, void *)) fn))(code, args->_fnargs[n]);
> else
> (*((void (*)(void *)) fn))(args->_fnargs[n]);
> +#ifndef __SINGLE_THREAD__
> + __lock_acquire_recursive(__atexit_recursive_mutex);
> +#endif
>
> /* The function we called call atexit and registered another
> function (or functions). Call these new functions before
--
Tomohiro Kashiwada (@kikairoya)
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