missed redraws due to concurrency error

[irssibot]

• • • Issue missed redraws due to concurrency error #827 opened by @yourealwaysbe

There's a concurrency error between sig_winch() and check_dirty() that results in the screen not being redrawn when it should be.

To be more precise, in src/fe-text/irssi.c we have

    void irssi_set_dirty(void)
    {
        dirty = TRUE;
    }

    static void dirty_check(void)
    {
        if (!dirty || dummy)
            return;

        // ... Do redraw stuff ...

        dirty = FALSE;
    }

and in src/fe-text/term.c we have

    static void sig_winch(int p)
    {
        irssi_set_dirty();
        resize_dirty = TRUE;
    }

The problem is that dirty_check() might be in the middle of a redraw when the winch signal comes in, at which point sig_winch sets dirty = TRUE. Then, after dirty_check() is done with its (now out of date) redraw, it sets dirty back to FALSE. Hence the required redraw never occurs.

I've fixed this for now (patch attached) by moving dirty = FALSE in dirty_check to before the redraw stuff takes place, reasoning that a redundant redraw is less worse than a missed redraw (which leaves the screen in a mess on my machines).

I guess really there should be some locking on the dirty variable, but maybe that's a bit heavy weight...

[irssibot]

• • • Attachment 270 by @yourealwaysbe

dirty_check.patch

diff -aur irssi-0.8.15/src/fe-text/irssi.c irssi-0.8.15-patched/src/fe-text/irssi.c
--- irssi-0.8.15/src/fe-text/irssi.c	2010-04-03 18:19:42.000000000 +0200
+++ irssi-0.8.15-patched/src/fe-text/irssi.c	2011-12-22 21:22:11.000000000 +0100
@@ -114,6 +114,8 @@
 	if (!dirty || dummy)
 		return;
 
+        dirty = FALSE;
+
         term_resize_dirty();
 
 	if (full_redraw) {
@@ -131,8 +133,6 @@
 	mainwindows_redraw_dirty();
         statusbar_redraw_dirty();
 	term_refresh(NULL);
-
-        dirty = FALSE;
 }
 
 static void textui_init(void)