Avoid crashing if a new thread is signaled right away

* src/thread.c (post_acquire_global_lock): Don't raise the pending
signal if the thread's handlers were not yet set up, as that will
cause Emacs to exit with a fatal error.  This can happen if a
thread is signaled as soon as make-thread returns, before the new
thread had an opportunity to acquire the global lock, set up the
handlers, and call the thread function.

* test/src/thread-tests.el (thread-signal-early): New test.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/src/thread-tests.el b/test/src/thread-tests.el
index 7261cda9fbb..26c0b725ff8 100644
--- a/test/src/thread-tests.el
+++ b/test/src/thread-tests.el
@@ -235,4 +235,13 @@
     (sit-for 1)
     (should (= (point) 21))))
 
+(ert-deftest thread-signal-early ()
+  "Test signaling a thread as soon as it is started by the OS."
+  (let ((thread
+         (make-thread #'(lambda ()
+                          (while t (thread-yield))))))
+    (thread-signal thread 'error nil)
+    (sit-for 1)
+    (should-not (thread-alive-p thread))))
+
 ;;; threads.el ends here