(zilch statusbar): Fix resilience during shutdown

When the (current-error-port) is closed, other threads in the middle
of using the port are likely to error out with a "port is closed"
error. When this occurs, the Chicken Scheme runtime will either
deadlock (when this happens on the output port), or worse, _hang_.
As the barf procedure usess the current error port, it itself hits this
same issue.

We can't perfectly protect against this, as there's no mutex on the current
output/error port; but we can improve the chances of hitting it massively,
to the point where a simple program won't hit the deadlock.

Change-Id: I3ccec0073b375ca21e8b46861c2f8c146a6a6964

core/src/statusbar.sld

@@ -53,16 +53,19 @@
       (define-values (rows cols) (terminal-size err-port))
       (when (> cols 0) (set! terminal-width cols))
 
+      (define shutdown #f)
+
       (define (terminal-width-thread-thunk handler)
         ; Lock the output mutex whilst setting the terminal size.
         (define-values (rows cols) (terminal-size err-port))
         (mutex-lock! out-mutex)
         (when (> cols 0) (set! terminal-width cols))
+        (define is-shutdown shutdown)
         (mutex-unlock! out-mutex)
 
         ; Wait until the next SIGWINCH, then loop
         (handler #t)
-        (terminal-width-thread-thunk handler))
+        (unless is-shutdown (terminal-width-thread-thunk handler)))
 
       (define terminal-width-thread (make-thread (lambda () (terminal-width-thread-thunk (make-signal-handler signal/winch)))))
 
@@ -83,9 +86,11 @@
         (rerender-status-bar)
         (mutex-lock! out-mutex)
         (draw-status-bar)
+        (define is-shutdown shutdown)
         (mutex-unlock! out-mutex)
+        (unless is-shutdown
          (thread-sleep! 0.1)
-        (redraw-thread-thunk))
+         (redraw-thread-thunk)))
       (define redraw-thread (make-thread redraw-thread-thunk "redraw thread"))
 
       (define last-builds-activity-id #f)
@@ -123,12 +128,19 @@
        
       (define (close-this-port)
          (mutex-lock! out-mutex)
-         (thread-terminate! redraw-thread)
+         (when (eq? new-err-port (current-error-port))
+          (current-error-port err-port))
+         (when (eq? new-out-port (current-output-port))
+          (current-output-port out-port))
+         (define was-shutdown shutdown)
+         (set! shutdown #t)
+         (mutex-unlock! out-mutex)
+         (unless was-shutdown
+          (thread-join! redraw-thread)
+          (mutex-lock! out-mutex)
           (thread-terminate! terminal-width-thread)
           (mutex-unlock! out-mutex)
-         (fprintf err-port "\r\x1B[2K\n")
-         (close-output-port err-port)
-         (close-output-port out-port))
+          (fprintf err-port "\r\x1B[2K\n")))
 
       (define new-err-port (buffered-port out-mutex write-err-line draw-status-bar close-this-port))
       (define new-out-port (buffered-port out-mutex write-out-line draw-status-bar close-this-port))