Add variable main-thread, fix Bug#32169

* doc/lispref/threads.texi (Basic Thread Functions): Add example,
how to propagate signals to the main thread.  Describe variable
`main-thread'.  Document optional argument CLEANUP of
`thread-last-error'.

* src/thread.c (Fthread_last_error): Add optional argument
CLEANUP.  (Bug#32169)
(main-thread): New defvar.

* test/src/thread-tests.el (thread-last-error): Adapt declaration.
(main-thread): Declare.
(threads-main-thread): New test.
(threads-errors): Extend test.

1 files changed, 19 insertions, 4 deletions

diff --git a/src/thread.c b/src/thread.c
index 3eba25b7b43..754d286e9f8 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -973,11 +973,17 @@ DEFUN ("all-threads", Fall_threads, Sall_threads, 0, 0, 0,
   return result;
 }
 
-DEFUN ("thread-last-error", Fthread_last_error, Sthread_last_error, 0, 0, 0,
-       doc: /* Return the last error form recorded by a dying thread.  */)
-  (void)
+DEFUN ("thread-last-error", Fthread_last_error, Sthread_last_error, 0, 1, 0,
+       doc: /* Return the last error form recorded by a dying thread.
+If CLEANUP is non-nil, remove this error form from history.  */)
+     (Lisp_Object cleanup)
 {
-  return last_thread_error;
+  Lisp_Object result = last_thread_error;
+
+  if (!NILP (cleanup))
+    last_thread_error = Qnil;
+
+  return result;
 }
 
 
@@ -1083,4 +1089,13 @@ syms_of_threads (void)
   DEFSYM (Qthreadp, "threadp");
   DEFSYM (Qmutexp, "mutexp");
   DEFSYM (Qcondition_variable_p, "condition-variable-p");
+
+  DEFVAR_LISP ("main-thread",
+               Vmain_thread,
+    doc: /* The main thread of Emacs.  */);
+#ifdef THREADS_ENABLED
+  XSETTHREAD (Vmain_thread, &main_thread);
+#else
+  Vmain_thread = Qnil;
+#endif
 }