linux: Use VT_WAITEVENT if available to avoid spawn too many threads

Starting from linux kernel 2.6.32 there is a new ioctl VT_WAITEVENT
which can monitor vt switches and return new vt number.

https://bugs.freedesktop.org/show_bug.cgi?id=17720

4 files changed, 87 insertions, 8 deletions

diff --git a/NEWS b/NEWS
index 101cb1c..807e9c4 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,7 @@ Version 0.4.2
  * Don't take bus name until ready (Ray Strode)
  * systemd hookup (Lennart Poettering)
  * add --since option to ck-history (William Jon McCann)
+ * Reduce number of threads on Linux (Kan-Ru Chen)
  * Other fixes (Anders Kaseor, Frederic Crozat, Matthias Clasen, Michael Biebl, William Jon McCann)
 
 ==============
diff --git a/src/ck-sysdeps-unix.c b/src/ck-sysdeps-unix.c
index e4ab16b..6a8b5f8 100644
--- a/src/ck-sysdeps-unix.c
+++ b/src/ck-sysdeps-unix.c
@@ -296,6 +296,50 @@ ck_wait_for_active_console_num (int   console_fd,
         return ret;
 }
 
+#ifdef VT_WAITEVENT
+gboolean
+ck_wait_for_console_switch (int   console_fd,
+                            guint *num)
+{
+        gboolean ret;
+        int      res;
+        struct vt_event vt;
+
+        g_assert (console_fd != -1);
+
+ again:
+        ret = FALSE;
+        errno = 0;
+        vt.event = VT_EVENT_SWITCH;
+        vt.oldev = *num;
+        res = ioctl (console_fd, VT_WAITEVENT, &vt);
+
+        if (res == ERROR) {
+                const char *errmsg;
+
+                errmsg = g_strerror (errno);
+
+                if (errno == EINTR) {
+                        g_debug ("Interrupted waiting for native console event: %s",
+                                  errmsg);
+                       goto again;
+                } else if (errno == ENOTSUP) {
+                        g_debug ("Console event not supported on this system");
+                } else {
+                        g_warning ("Error waiting for native console event: %s",
+                                   errmsg);
+                }
+                goto out;
+        }
+
+        ret = TRUE;
+        *num = vt.newev;
+
+ out:
+        return ret;
+}
+#endif
+
 gboolean
 ck_activate_console_num (int   console_fd,
                          guint num)
diff --git a/src/ck-sysdeps.h b/src/ck-sysdeps.h
index 8f22d52..5dd573f 100644
--- a/src/ck-sysdeps.h
+++ b/src/ck-sysdeps.h
@@ -72,6 +72,8 @@ gboolean     ck_activate_console_num          (int             console_fd,
                                                guint           num);
 gboolean     ck_wait_for_active_console_num   (int             console_fd,
                                                guint           num);
+gboolean     ck_wait_for_console_switch       (int             console_fd,
+                                               guint          *num);
 
 G_END_DECLS
 
diff --git a/src/ck-vt-monitor.c b/src/ck-vt-monitor.c
index 67a1f49..369c63e 100644
--- a/src/ck-vt-monitor.c
+++ b/src/ck-vt-monitor.c
@@ -26,6 +26,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
+#include <signal.h>
 
 #include <glib.h>
 #include <glib/gi18n.h>
@@ -40,9 +41,11 @@
 #include "ck-sysdeps.h"
 #include "ck-marshal.h"
 
-#if defined (__sun) && defined (HAVE_SYS_VT_H)
+#ifdef HAVE_SYS_VT_H
 #include <sys/vt.h>
-#include <signal.h>
+#endif
+
+#ifdef __sun
 #include <stropts.h>
 #endif
 
@@ -163,7 +166,7 @@ ck_vt_monitor_get_active (CkVtMonitor    *vt_monitor,
         return TRUE;
 }
 
-#if defined (__sun) && defined (HAVE_SYS_VT_H)
+#if defined(HAVE_SYS_VT_H) && defined(__sun)
 static void
 handle_vt_active (void)
 {
@@ -313,11 +316,31 @@ vt_thread_start (ThreadData *data)
 {
         CkVtMonitor *vt_monitor;
         gboolean     res;
-        gint32       num;
+        guint        num;
 
         vt_monitor = data->vt_monitor;
         num = data->num;
 
+#ifdef VT_WAITEVENT
+        for (;;) {
+                res = ck_wait_for_console_switch (vt_monitor->priv->vfd, &num);
+                if (! res) {
+                        break;
+                } else {
+                        EventData *event;
+
+                        /* add event to queue */
+                        event = g_new0 (EventData, 1);
+                        event->num = num;
+                        g_debug ("Pushing activation event for VT %d onto queue", num);
+
+                        g_async_queue_push (vt_monitor->priv->event_queue, event);
+
+                        /* schedule processing of queue */
+                        schedule_process_queue (vt_monitor);
+                }
+        }
+#else
         res = ck_wait_for_active_console_num (vt_monitor->priv->vfd, num);
         if (! res) {
                 /* FIXME: what do we do if it fails? */
@@ -334,6 +357,7 @@ vt_thread_start (ThreadData *data)
                 /* schedule processing of queue */
                 schedule_process_queue (vt_monitor);
         }
+#endif
 
         G_LOCK (hash_lock);
         if (vt_monitor->priv->vt_thread_hash != NULL) {
@@ -377,10 +401,6 @@ vt_add_watch_unlocked (CkVtMonitor *vt_monitor,
 static void
 vt_add_watches (CkVtMonitor *vt_monitor)
 {
-        guint  max_consoles;
-        int    i;
-        gint32 current_num;
-
 #if defined (__sun) && !defined (HAVE_SYS_VT_H)
         /* Best to do nothing if VT is not supported */
 #elif defined (__sun) && defined (HAVE_SYS_VT_H)
@@ -398,7 +418,19 @@ vt_add_watches (CkVtMonitor *vt_monitor)
         sigaction (SIGPOLL, &act, NULL);
 
         ioctl (vt_monitor->priv->vfd, I_SETSIG, S_MSG);
+#elif defined (VT_WAITEVENT)
+        gpointer id;
+
+        G_LOCK (hash_lock);
+        id = GINT_TO_POINTER (1);
+        if (g_hash_table_lookup (vt_monitor->priv->vt_thread_hash, id) == NULL)
+                vt_add_watch_unlocked (vt_monitor, 1);
+        G_UNLOCK (hash_lock);
 #else
+        guint  max_consoles;
+        int    i;
+        gint32 current_num;
+
         G_LOCK (hash_lock);
 
         current_num = vt_monitor->priv->active_num;