thread-join returns the result of finished thread

* doc/lispref/threads.texi (Basic Thread Functions):
* etc/NEWS: Document return value of `thread-join'.

* src/thread.c (invoke_thread_function, Fmake_thread)
(init_main_thread): Set result.
(Fthread_join): Propagate signals, and return result.
(Vmain_thread): New defvar.

* src/thread.h (struct thread_state): Add `result' field.

* test/src/thread-tests.el (threads-join): Test also return value.
(threads-join-error): New test.
(threads-mutex-signal): Check for propagation of `quit' signal.

1 files changed, 2 insertions, 2 deletions

diff --git a/doc/lispref/threads.texi b/doc/lispref/threads.texi
index 4cef9c9c6e8..58a3a918efd 100644
--- a/doc/lispref/threads.texi
+++ b/doc/lispref/threads.texi
@@ -75,8 +75,8 @@ thread, @code{nil} otherwise.
 
 @defun thread-join thread
 Block until @var{thread} exits, or until the current thread is
-signaled.  If @var{thread} has already exited, this returns
-immediately.
+signaled.  It returns the result of the @var{thread} function.  If
+@var{thread} has already exited, this returns immediately.
 @end defun
 
 @defun thread-signal thread error-symbol data