Avoid module resolution in 'call-with-new-thread'.

Fixes <https://bugs.gnu.org/62691>.
Reported by Михаил Бахтерев <mike.bakhterev@gmail.com>.

* module/ice-9/threads.scm (call-with-new-thread): Do not use 'set!'
to set object properties while the calling thread is waiting on the
new thread to initialize.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

NEWS

@@ -33,6 +33,8 @@ the compiler reports it as "possibly unused".
    (<https://bugs.gnu.org/63024>)
 ** Fix possible deadlock in 'sigaction' (aka. 'scm_sigaction_for_thread')
    (<https://bugs.gnu.org/64666>)
+** Avoid module resolution in 'call-with-new-thread', which could deadlock
+   (<https://bugs.gnu.org/62691>)
 ** Hashing of UTF-8 symbols with non-ASCII characters avoids corruption
    (<https://bugs.gnu.org/56413>)
 

module/ice-9/threads.scm

@@ -151,7 +151,15 @@ Once @var{thunk} or @var{handler} returns, the return value is made the
                  (lambda ()
                    (lock-mutex mutex)
                    (set! thread (current-thread))
-                   (set! (thread-join-data thread) (cons cv mutex))
+                   ;; Rather than use the 'set!' syntax here, we use the
+                   ;; underlying 'setter' generic function to set the
+                   ;; 'thread-join-data' property on 'thread'.  This is
+                   ;; because 'set!' will try to resolve 'setter' in the
+                   ;; '(guile)' module, which means acquiring the
+                   ;; 'autoload' mutex.  If the calling thread is
+                   ;; already holding that mutex, this will result in
+                   ;; deadlock.  See <https://bugs.gnu.org/62691>.
+                   ((setter thread-join-data) thread (cons cv mutex))
                    (signal-condition-variable cv)
                    (unlock-mutex mutex)
                    (call-with-unblocked-asyncs