chjj/compton: Patch to use libevent for the main loop

compton-libevent.patch

diff --git a/Makefile b/Makefile
index 10e6f17..bc0dcd2 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,6 @@
+# Use tab to indent recipe lines, spaces to indent other lines, otherwise
+# GNU make may get unhappy.
+
 CC ?= gcc
 
 PREFIX ?= /usr
@@ -8,44 +11,72 @@ PACKAGES = x11 xcomposite xfixes xdamage xrender xext xrandr
 LIBS = -lm -lrt
 INCS =
 
-# Parse configuration flags
+# Configuration flags
 CFG =
 
+# Seemingly, libevent1 has no pkg-config file!
+# FreeBSD may have issues handling the version in pkg-config.
+ifeq "$(shell pkg-config --modversion --print-errors libevent)" ""
+  $(warning libevent-2.0 not found, assuming libevent-1.4.x.)
+  CFG += -DCONFIG_LIBEVENT_LEGACY
+  LIBS += -levent
+else
+  # Using pkg-config for linking with libevent will result in linking with
+  # libevent.so instead of the smaller libevent_core.so. But FreeBSD keeps
+  # libevent2 .so files at a separate place, and we must learn it from
+  # pkg-config.
+  LIBS += $(shell pkg-config --libs libevent)
+  INCS += $(shell pkg-config --cflags libevent)
+endif
+
 ifeq "$(NO_LIBCONFIG)" ""
-  CFG += -DCONFIG_LIBCONFIG
-	PACKAGES += libconfig
+  CFG += -DCONFIG_LIBCONFIG
+  PACKAGES += libconfig
 
-	# libconfig-1.3* does not define LIBCONFIG_VER* macros, so we use
-	# pkg-config to determine its version here
-	CFG += $(shell pkg-config --atleast-version=1.4 libconfig || echo '-DCONFIG_LIBCONFIG_LEGACY')
+  # libconfig-1.3* does not define LIBCONFIG_VER* macros, so we use
+  # pkg-config to determine its version here
+  CFG += $(shell pkg-config --atleast-version=1.4 libconfig || echo '-DCONFIG_LIBCONFIG_LEGACY')
 endif
 
 ifeq "$(NO_REGEX_PCRE)" ""
-	CFG += -DCONFIG_REGEX_PCRE
-	LIBS += $(shell pcre-config --libs)
-	INCS += $(shell pcre-config --cflags)
-	ifeq "$(NO_REGEX_PCRE_JIT)" ""
-		CFG += -DCONFIG_REGEX_PCRE_JIT
-	endif
+  CFG += -DCONFIG_REGEX_PCRE
+  LIBS += $(shell pcre-config --libs)
+  INCS += $(shell pcre-config --cflags)
+  ifeq "$(NO_REGEX_PCRE_JIT)" ""
+    CFG += -DCONFIG_REGEX_PCRE_JIT
+  endif
 endif
 
 ifeq "$(NO_VSYNC_DRM)" ""
-	CFG += -DCONFIG_VSYNC_DRM
+  CFG += -DCONFIG_VSYNC_DRM
 endif
 
 ifeq "$(NO_VSYNC_OPENGL)" ""
-	CFG += -DCONFIG_VSYNC_OPENGL
-	LIBS += -lGL
+  CFG += -DCONFIG_VSYNC_OPENGL
+  LIBS += -lGL
 endif
 
-CFLAGS ?= -DNDEBUG -O2 -D_FORTIFY_SOURCE=2
+# ifeq "$(NO_DBUS)" ""
+#   CFG += -DCONFIG_DBUS
+#   PACKAGES += dbus-1
+# endif
+
+# Version string
+COMPTON_VERSION ?= git-$(shell git describe --always)
+CFG += -DCOMPTON_VERSION="\"$(COMPTON_VERSION)\""
+
+LDFLAGS ?= -Wl,-O1 -Wl,--as-needed
+CFLAGS ?= -DNDEBUG -O2 -D_FORTIFY_SOURCE=2 $(LDFLAGS)
 CFLAGS += $(CFG)
 
 LIBS += $(shell pkg-config --libs $(PACKAGES))
 INCS += $(shell pkg-config --cflags $(PACKAGES))
+
 CFLAGS += -Wall -std=c99
 OBJS = compton.o
 
+.DEFAULT_GOAL := compton
+
 %.o: src/%.c src/%.h
 	$(CC) $(CFLAGS) $(INCS) -c src/$*.c
 
@@ -75,4 +106,4 @@ uninstall:
 clean:
 	@rm -f $(OBJS) compton
 
-.PHONY: uninstall clean
+.PHONY: uninstall clean docs
diff --git a/README.md b/README.md
index 5d77134..f2d3a8a 100644
--- a/README.md
+++ b/README.md
@@ -56,6 +56,7 @@ __R__ for runtime
 * libdrm (B) (Will probably be made optional soon)
 * libGL (B,R) (Will probably be made optional soon)
 * asciidoc (B) (if you wish to run `make docs`)
+* libevent (B,R)
 
 ### How to build
 
diff --git a/src/compton.c b/src/compton.c
index eff195f..04a264e 100644
--- a/src/compton.c
+++ b/src/compton.c
@@ -1196,8 +1196,12 @@ paint_preprocess(session_t *ps, win *list) {
   bool is_highest = true;
 
   // Fading step calculation
-  unsigned steps = (sub_unslong(get_time_ms(), ps->fade_time)
-      + FADE_DELTA_TOLERANCE * ps->o.fade_delta) / ps->o.fade_delta;
+  time_ms_t steps = ((get_time_ms() - ps->fade_time) + FADE_DELTA_TOLERANCE * ps->o.fade_delta) / ps->o.fade_delta;
+  if (steps < 0L) {
+    // Time disorder
+    ps->fade_time = get_time_ms();
+    steps = 0;
+  }
   ps->fade_time += steps * ps->o.fade_delta;
 
   XserverRegion last_reg_ignore = None;
@@ -2189,11 +2193,13 @@ static void
 determine_shadow(session_t *ps, win *w) {
   bool shadow_old = w->shadow;
 
-  w->shadow = (ps->o.wintype_shadow[w->window_type]
-      && !win_match(w, ps->o.shadow_blacklist, &w->cache_sblst)
-      && !(ps->o.shadow_ignore_shaped && w->bounding_shaped
-        && !w->rounded_corners)
-      && !(ps->o.respect_prop_shadow && 0 == w->attr_shadow));
+  w->shadow = (UNSET == w->shadow_force ?
+      (ps->o.wintype_shadow[w->window_type]
+       && !win_match(w, ps->o.shadow_blacklist, &w->cache_sblst)
+       && !(ps->o.shadow_ignore_shaped && w->bounding_shaped
+         && !w->rounded_corners)
+       && !(ps->o.respect_prop_shadow && 0 == w->attr_shadow))
+       : w->shadow_force);
 
   // Window extents need update on shadow state change
   if (w->shadow != shadow_old) {
@@ -2340,18 +2346,35 @@ win_recheck_client(session_t *ps, win *w) {
   win_mark_client(ps, w, cw);
 }
 
-static void
+static bool
 add_win(session_t *ps, Window id, Window prev) {
+  const static win win_def = {
+    .next = NULL,
+    .prev_trans = NULL,
+
+    .id = None,
+    .client_win = None,
+
+    .shadow_force = UNSET,
+    .focused_force = UNSET,
+  };
+
   // Reject overlay window and already added windows
   if (id == ps->overlay || find_win(ps, id)) {
-    return;
+    return false;
   }
 
+  // Allocate and initialize the new win structure
   win *new = malloc(sizeof(win));
-  win **p;
 
-  if (!new) return;
+  if (!new) {
+    printf_errf("(%#010lx): Failed to allocate memory for the new window.", id);
+    return false;
+  }
+
+  memcpy(new, &win_def, sizeof(win));
 
+  win **p;
   if (prev) {
     for (p = &ps->list; *p; p = &(*p)->next) {
       if ((*p)->id == prev && !(*p)->destroyed)
@@ -2365,8 +2388,10 @@ add_win(session_t *ps, Window id, Window prev) {
   set_ignore_next(ps);
 
   if (!XGetWindowAttributes(ps->dpy, id, &new->a)) {
+    // Failed to get window attributes. Which probably means, the window
+    // is gone already.
     free(new);
-    return;
+    return false;
   }
 
   // Delay window mapping
@@ -2439,7 +2464,6 @@ add_win(session_t *ps, Window id, Window prev) {
   new->top_width = 0;
   new->bottom_width = 0;
 
-  new->client_win = 0;
   new->wmwin = false;
 
   new->flags = 0;
@@ -2452,6 +2476,8 @@ add_win(session_t *ps, Window id, Window prev) {
   if (map_state == IsViewable) {
     map_win(ps, id);
   }
+
+  return true;
 }
 
 static void
@@ -2790,22 +2816,27 @@ static void
 win_update_focused(session_t *ps, win *w) {
   bool focused_old = w->focused;
 
-  w->focused = w->focused_real;
-
-  // Use wintype_focus, and treat WM windows and override-redirected
-  // windows specially
-  if (ps->o.wintype_focus[w->window_type]
-      || (ps->o.mark_wmwin_focused && w->wmwin)
-      || (ps->o.mark_ovredir_focused
-        && w->id == w->client_win && !w->wmwin)
-      || win_match(w, ps->o.focus_blacklist, &w->cache_fcblst))
-    w->focused = true;
-
-  // If window grouping detection is enabled, mark the window active if
-  // its group is
-  if (ps->o.track_leader && ps->active_leader
-      && win_get_leader(ps, w) == ps->active_leader) {
-    w->focused = true;
+  if (UNSET != w->focused_force) {
+    w->focused = w->focused_force;
+  }
+  else {
+    w->focused = w->focused_real;
+
+    // Use wintype_focus, and treat WM windows and override-redirected
+    // windows specially
+    if (ps->o.wintype_focus[w->window_type]
+        || (ps->o.mark_wmwin_focused && w->wmwin)
+        || (ps->o.mark_ovredir_focused
+          && w->id == w->client_win && !w->wmwin)
+        || win_match(w, ps->o.focus_blacklist, &w->cache_fcblst))
+      w->focused = true;
+
+    // If window grouping detection is enabled, mark the window active if
+    // its group is
+    if (ps->o.track_leader && ps->active_leader
+        && win_get_leader(ps, w) == ps->active_leader) {
+      w->focused = true;
+    }
   }
 
   if (w->focused != focused_old)
@@ -3649,7 +3680,7 @@ ev_handle(session_t *ps, XEvent *ev) {
 static void
 usage(void) {
   const static char *usage_text =
-    "compton (development version)\n"
+    "compton (" COMPTON_VERSION ")\n"
     "usage: compton [options]\n"
     "Options:\n"
     "\n"
@@ -3888,15 +3919,16 @@ register_cm(session_t *ps, bool want_glxct) {
 /**
  * Fork program to background and disable all I/O streams.
  */
-static void
+static bool
 fork_after(void) {
-  if (getppid() == 1) return;
+  if (getppid() == 1)
+    return true;
 
   int pid = fork();
 
-  if (pid == -1) {
-    fprintf(stderr, "Fork failed\n");
-    return;
+  if (-1 == pid) {
+    printf_errf("(): fork() failed.");
+    return false;
   }
 
   if (pid > 0) _exit(0);
@@ -3906,11 +3938,17 @@ fork_after(void) {
   // Mainly to suppress the _FORTIFY_SOURCE warning
   bool success = freopen("/dev/null", "r", stdin);
   success = freopen("/dev/null", "w", stdout) && success;
-  if (!success)
-    fprintf(stderr, "fork_after(): freopen() failed.");
+  if (!success) {
+    printf_errf("(): freopen() failed.");
+    return false;
+  }
   success = freopen("/dev/null", "w", stderr);
-  if (!success)
-    fprintf(stderr, "fork_after(): freopen() failed.");
+  if (!success) {
+    printf_errf("(): freopen() failed.");
+    return false;
+  }
+
+  return true;
 }
 
 #ifdef CONFIG_LIBCONFIG
@@ -4058,8 +4096,10 @@ parse_config(session_t *ps, char *cpath, struct options_tmp *pcfgtmp) {
 
   f = open_config_file(cpath, &path);
   if (!f) {
-    if (cpath)
-      printf("Failed to read the specified configuration file.\n");
+    if (cpath) {
+      printf_err("Failed to read the specified configuration file \"%s\".", cpath);
+      exit(1);
+    }
     return;
   }
 
@@ -4223,8 +4263,9 @@ parse_config(session_t *ps, char *cpath, struct options_tmp *pcfgtmp) {
  */
 static void
 get_cfg(session_t *ps, int argc, char *const *argv) {
-  const static char *shortopts = "D:I:O:d:r:o:m:l:t:i:e:scnfFCaSzGb";
+  const static char *shortopts = "D:I:O:d:r:o:m:l:t:i:e:hscnfFCaSzGb";
   const static struct option longopts[] = {
+    { "help", no_argument, NULL, 'h' },
     { "config", required_argument, NULL, 256 },
     { "shadow-red", required_argument, NULL, 257 },
     { "shadow-green", required_argument, NULL, 258 },
@@ -4255,6 +4296,7 @@ get_cfg(session_t *ps, int argc, char *const *argv) {
     { "blur-background", no_argument, NULL, 283 },
     { "blur-background-frame", no_argument, NULL, 284 },
     { "blur-background-fixed", no_argument, NULL, 285 },
+    { "dbus", no_argument, NULL, 286 },
     // Must terminate with a NULL entry
     { NULL, 0, NULL, 0 },
   };
@@ -4303,6 +4345,9 @@ get_cfg(session_t *ps, int argc, char *const *argv) {
       (o = getopt_long(argc, argv, shortopts, longopts, &longopt_idx))) {
     switch (o) {
       // Short options
+      case 'h':
+        usage();
+        break;
       case 'd':
         ps->o.display = mstrcpy(optarg);
         break;
@@ -4484,6 +4529,10 @@ get_cfg(session_t *ps, int argc, char *const *argv) {
         // --blur-background-fixed
         ps->o.blur_background_fixed = true;
         break;
+      case 286:
+        // --dbus
+        ps->o.dbus = true;
+        break;
       default:
         usage();
     }
@@ -4609,7 +4658,7 @@ update_refresh_rate(session_t *ps) {
   XRRFreeScreenConfigInfo(randr_info);
 
   if (ps->refresh_rate)
-    ps->refresh_intv = NS_PER_SEC / ps->refresh_rate;
+    ps->refresh_intv = US_PER_SEC / ps->refresh_rate;
   else
     ps->refresh_intv = 0;
 }
@@ -4625,7 +4674,7 @@ sw_opti_init(session_t *ps) {
   // Check if user provides one
   ps->refresh_rate = ps->o.refresh_rate;
   if (ps->refresh_rate)
-    ps->refresh_intv = NS_PER_SEC / ps->refresh_rate;
+    ps->refresh_intv = US_PER_SEC / ps->refresh_rate;
 
   // Auto-detect refresh rate otherwise
   if (!ps->refresh_rate && ps->randr_exists) {
@@ -4670,52 +4719,49 @@ lceil_ntimes(long dividend, long divisor) {
  * @return > 0 if we get some events, 0 if timeout is reached, < 0 on
  *     problems
  */
-static int
-evpoll(session_t *ps, int timeout) {
-  struct pollfd ufd = {
-    .fd = ConnectionNumber(ps->dpy),
-    .events = POLLIN
-  };
-
-  // Always wait infinitely if asked so, to minimize CPU usage
-  if (timeout < 0) {
-    int ret = poll(&ufd, 1, timeout);
-    // Reset ps->fade_time so the fading steps during idling are not counted
-    ps->fade_time = get_time_ms();
-    return ret;
-  }
-
-  // Just do a poll() if we are not using optimization
-  if (!ps->o.sw_opti)
-    return poll(&ufd, 1, timeout);
-
-  // Convert the old timeout to struct timespec
-  struct timespec next_paint_tmout = {
-    .tv_sec = timeout / MS_PER_SEC,
-    .tv_nsec = timeout % MS_PER_SEC * (NS_PER_SEC / MS_PER_SEC)
-  };
+static void
+swopti_handle_timeout(session_t *ps, struct timeval *ptv) {
+  if (!ptv)
+    return;
 
-  // Get the nanosecond offset of the time when the we reach the timeout
+  // Get the microsecond offset of the time when the we reach the timeout
   // I don't think a 32-bit long could overflow here.
-  long target_relative_offset = (next_paint_tmout.tv_nsec + get_time_timespec().tv_nsec - ps->paint_tm_offset) % NS_PER_SEC;
+  long target_relative_offset = (ptv->tv_usec + get_time_timeval().tv_usec - ps->paint_tm_offset) % US_PER_SEC;
   if (target_relative_offset < 0)
-    target_relative_offset += NS_PER_SEC;
+    target_relative_offset += US_PER_SEC;
 
   assert(target_relative_offset >= 0);
 
   // If the target time is sufficiently close to a refresh time, don't add
   // an offset, to avoid certain blocking conditions.
-  if ((target_relative_offset % NS_PER_SEC) < SW_OPTI_TOLERANCE)
-    return poll(&ufd, 1, timeout);
+  if ((target_relative_offset % US_PER_SEC) < SW_OPTI_TOLERANCE)
+    return;
 
   // Add an offset so we wait until the next refresh after timeout
-  next_paint_tmout.tv_nsec += lceil_ntimes(target_relative_offset, ps->refresh_intv) - target_relative_offset;
-  if (next_paint_tmout.tv_nsec > NS_PER_SEC) {
-    next_paint_tmout.tv_nsec -= NS_PER_SEC;
-    ++next_paint_tmout.tv_sec;
+  ptv->tv_usec += lceil_ntimes(target_relative_offset, ps->refresh_intv) - target_relative_offset;
+  if (ptv->tv_usec > US_PER_SEC) {
+    ptv->tv_usec -= US_PER_SEC;
+    ++ptv->tv_sec;
   }
+}
 
-  return ppoll(&ufd, 1, &next_paint_tmout, NULL);
+/**
+ * Libevent callback function to handle X events.
+ */
+static void
+evcallback_x(evutil_socket_t fd, short what, void *arg) {
+  session_t *ps = ps_g;
+
+  // Sometimes poll() returns 1 but no events are actually read,
+  // causing XNextEvent() to block, I have no idea what's wrong, so we
+  // check for the number of events here
+  if (XEventsQueued(ps->dpy, QueuedAfterReading)) {
+    XEvent ev = { };
+
+    XNextEvent(ps->dpy, &ev);
+    ev_handle(ps, &ev);
+    ps->ev_received = true;
+  }
 }
 
 /**
@@ -4982,6 +5028,42 @@ redir_stop(session_t *ps) {
 }
 
 /**
+ * Main loop.
+ */
+static bool
+mainloop(session_t *ps) {
+  bool infinite_wait = false;
+
+  // Process existing events
+  if (XEventsQueued(ps->dpy, QueuedAfterReading)) {
+    evcallback_x(ConnectionNumber(ps->dpy), 0, NULL);
+    return true;
+  }
+
+  // Add timeout
+  if (ps->ev_received || !ps->idling) {
+    struct timeval tv = ms_to_tv(ps->ev_received ? 0: fade_timeout(ps));
+    if (ps->o.sw_opti)
+      swopti_handle_timeout(ps, &tv);
+    if (timeval_isempty(tv))
+      return false;
+    evtimer_add(ps->ev_tmout, &tv);
+  }
+  else {
+    infinite_wait = true;
+  }
+
+  // Run libevent main loop
+  if (event_base_loop(ps->ev_base, EVLOOP_ONCE))
+    printf_errfq(1, "(): Unexpected error when running event loop.");
+
+  if (infinite_wait)
+    ps->fade_time = get_time_ms();
+
+  return true;
+}
+
+/**
  * Initialize a session.
  *
  * @param ps_old old session, from which the function will take the X
@@ -5097,11 +5179,15 @@ session_init(session_t *ps_old, int argc, char **argv) {
     .refresh_intv = 0UL,
     .paint_tm_offset = 0L,
 
+#ifdef CONFIG_VSYNC_DRM
     .drm_fd = 0,
+#endif
 
+#ifdef CONFIG_VSYNC_OPENGL
     .glx_context = None,
     .glx_get_video_sync = NULL,
     .glx_wait_video_sync = NULL,
+#endif
 
     .xfixes_event = 0,
     .xfixes_error = 0,
@@ -5119,9 +5205,11 @@ session_init(session_t *ps_old, int argc, char **argv) {
     .randr_exists = 0,
     .randr_event = 0,
     .randr_error = 0,
+#ifdef CONFIG_VSYNC_OPENGL
     .glx_exists = false,
     .glx_event = 0,
     .glx_error = 0,
+#endif
     .dbe_exists = false,
     .xrfilter_convolution_exists = false,
 
@@ -5269,8 +5357,6 @@ session_init(session_t *ps_old, int argc, char **argv) {
   if (ps->o.dbe)
     init_dbe(ps);
 
-  if (ps->o.fork_after_register) fork_after();
-
   init_atoms(ps);
   init_alpha_picts(ps);
 
@@ -5313,6 +5399,24 @@ session_init(session_t *ps_old, int argc, char **argv) {
   }
 
   ps->all_damage = None;
+
+  // Build event base
+  if (!(ps->ev_base =
+#ifndef CONFIG_LIBEVENT_LEGACY
+        event_base_new()
+#else
+        event_init()
+#endif
+        ))
+    printf_errfq(1, "(): Failed to build event base.");
+  if (!(ps->ev_x = EVENT_NEW(ps->ev_base, ConnectionNumber(ps->dpy),
+          EV_READ | EV_PERSIST, evcallback_x, NULL)))
+    printf_errfq(1, "(): Failed to build event.");
+  if (event_add(ps->ev_x, NULL))
+    printf_errfq(1, "(): Failed to add event.");
+  if (!(ps->ev_tmout = evtimer_new(ps->ev_base, NULL, NULL)))
+    printf_errfq(1, "(): Failed to build event.");
+
   XGrabServer(ps->dpy);
 
   redir_start(ps);
@@ -5345,6 +5449,18 @@ session_init(session_t *ps_old, int argc, char **argv) {
 
   XUngrabServer(ps->dpy);
 
+  // Fork to background, if asked
+  if (ps->o.fork_after_register) {
+    if (!fork_after()) {
+      session_destroy(ps);
+      return NULL;
+    }
+
+    // Reinitialize event base
+    if (event_reinit(ps->ev_base) < 0)
+      printf_errfq(1, "Failed to reinitialize event base.");
+  }
+
   // Free the old session
   if (ps_old)
     free(ps_old);
@@ -5447,10 +5563,13 @@ session_destroy(session_t *ps) {
     XDestroyWindow(ps->dpy, ps->reg_win);
     ps->reg_win = None;
   }
+
+#ifdef CONFIG_VSYNC_OPENGL
   if (ps->glx_context) {
     glXDestroyContext(ps->dpy, ps->glx_context);
     ps->glx_context = None;
   }
+#endif
 
   // Free double buffer
   if (ps->root_dbe) {
@@ -5458,11 +5577,13 @@ session_destroy(session_t *ps) {
     ps->root_dbe = None;
   }
 
+#ifdef CONFIG_VSYNC_DRM
   // Close file opened for DRM VSync
   if (ps->drm_fd) {
     close(ps->drm_fd);
     ps->drm_fd = 0;
   }
+#endif
 
   // Release overlay window
   if (ps->overlay) {
@@ -5470,6 +5591,11 @@ session_destroy(session_t *ps) {
     ps->overlay = None;
   }
 
+  // Free libevent things
+  event_free(ps->ev_x);
+  event_free(ps->ev_tmout);
+  event_base_free(ps->ev_base);
+
   // Flush all events
   XSync(ps->dpy, True);
 
@@ -5487,7 +5613,7 @@ session_run(session_t *ps) {
   win *t;
 
   if (ps->o.sw_opti)
-    ps->paint_tm_offset = get_time_timespec().tv_nsec;
+    ps->paint_tm_offset = get_time_timeval().tv_usec;
 
   ps->reg_ignore_expire = true;
 
@@ -5503,22 +5629,10 @@ session_run(session_t *ps) {
 
   // Main loop
   while (!ps->reset) {
-    bool ev_received = false;
-
-    while (XEventsQueued(ps->dpy, QueuedAfterReading)
-        || (evpoll(ps,
-            (ev_received ? 0: (ps->idling ? -1: fade_timeout(ps)))) > 0)) {
-      // Sometimes poll() returns 1 but no events are actually read,
-      // causing XNextEvent() to block, I have no idea what's wrong, so we
-      // check for the number of events here
-      if (XEventsQueued(ps->dpy, QueuedAfterReading)) {
-        XEvent ev;
-
-        XNextEvent(ps->dpy, &ev);
-        ev_handle(ps, &ev);
-        ev_received = true;
-      }
-    }
+    ps->ev_received = false;
+
+    while (mainloop(ps))
+      continue;
 
     // idling will be turned off during paint_preprocess() if needed
     ps->idling = true;
@@ -5577,6 +5691,10 @@ main(int argc, char **argv) {
   session_t *ps_old = ps_g;
   while (1) {
     ps_g = session_init(ps_old, argc, argv);
+    if (!ps_g) {
+      printf_errf("Failed to create new session.");
+      return 1;
+    }
     session_run(ps_g);
     ps_old = ps_g;
     session_destroy(ps_g);
diff --git a/src/compton.h b/src/compton.h
index 66ed396..4db984a 100644
--- a/src/compton.h
+++ b/src/compton.h
@@ -54,6 +54,21 @@
 #include <fnmatch.h>
 #include <signal.h>
 
+// libevent
+#ifndef CONFIG_LIBEVENT_LEGACY
+#include <event2/event.h>
+#else
+#include <event.h>
+typedef int evutil_socket_t;
+typedef void(* event_callback_fn)(evutil_socket_t, short, void *);
+#define event_free(ev) (event_del(ev), free(ev))
+#endif
+
+#ifndef evtimer_new
+#define evtimer_new(b, cb, arg)   EVENT_NEW((b), -1, 0, (cb), (arg))
+#endif
+
+// libpcre
 #ifdef CONFIG_REGEX_PCRE
 #include <pcre.h>
 
@@ -72,6 +87,10 @@
 #include <libconfig.h>
 #endif
 
+#ifdef CONFIG_DBUS
+#include <dbus/dbus.h>
+#endif
+
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/Xatom.h>
@@ -112,6 +131,8 @@
 #define SW_OPTI_TOLERANCE 1000
 #define WIN_GET_LEADER_MAX_RECURSION 20
 
+#define SEC_WRAP (15L * 24L * 60L * 60L)
+
 #define NS_PER_SEC 1000000000L
 #define US_PER_SEC 1000000L
 #define MS_PER_SEC 1000
@@ -134,10 +155,27 @@
 // #define MSTR_(s)        #s
 // #define MSTR(s)         MSTR_(s)
 
+/// Print out an error message.
+#define printf_err(format, ...) \
+  fprintf(stderr, format "\n", ## __VA_ARGS__)
+
+/// Print out an error message with function name.
+#define printf_errf(format, ...) \
+  printf_err("%s" format,  __func__, ## __VA_ARGS__)
+
+/// Print out an error message with function name, and quit with a
+/// specific exit code.
+#define printf_errfq(code, format, ...) { \
+  printf_err("%s" format,  __func__, ## __VA_ARGS__); \
+  exit(code); \
+}
+
+/// Print out a debug message.
 #define printf_dbg(format, ...) \
   printf(format, ## __VA_ARGS__); \
   fflush(stdout)
 
+/// Print out a debug message with function name.
 #define printf_dbgf(format, ...) \
   printf_dbg("%s" format, __func__, ## __VA_ARGS__)
 
@@ -148,6 +186,7 @@
 // === Types ===
 
 typedef uint32_t opacity_t;
+typedef long time_ms_t;
 
 typedef enum {
   WINTYPE_UNKNOWN,
@@ -190,6 +229,8 @@ typedef struct {
     long *p32;
   } data;
   unsigned long nitems;
+  Atom type;
+  int format;
 } winprop_t;
 
 typedef struct _ignore {
@@ -263,6 +304,8 @@ typedef struct {
   /// Whether to unredirect all windows if a full-screen opaque window
   /// is detected.
   bool unredir_if_possible;
+  /// Whether to enable D-Bus support.
+  bool dbus;
   /// Whether to work under synchronized mode for debugging.
   bool synchronize;
 
@@ -301,7 +344,8 @@ typedef struct {
   opacity_t fade_in_step;
   /// How much to fade out in a single fading step.
   opacity_t fade_out_step;
-  unsigned long fade_delta;
+  /// Fading time delta. In milliseconds.
+  time_ms_t fade_delta;
   /// Whether to disable fading on window open/close.
   bool no_fading_openclose;
   /// Fading blacklist. A linked list of conditions.
@@ -401,6 +445,17 @@ typedef struct {
   // === Operation related ===
   /// Program options.
   options_t o;
+  /// Libevent event base.
+  struct event_base *ev_base;
+  /// Libevent event for X connection.
+  struct event *ev_x;
+  /// Libevent event for timeout.
+  struct event *ev_tmout;
+  /// Whether we have received an event in this cycle.
+  bool ev_received;
+  /// Whether the program is idling. I.e. no fading, no potential window
+  /// changes.
+  bool idling;
   /// Program start time.
   struct timeval time_start;
   /// The region needs to painted on next paint.
@@ -414,11 +469,8 @@ typedef struct {
   Picture *alpha_picts;
   /// Whether all reg_ignore of windows should expire in this paint.
   bool reg_ignore_expire;
-  /// Whether the program is idling. I.e. no fading, no potential window
-  /// changes.
-  bool idling;
   /// Time of last fading. In milliseconds.
-  unsigned long fade_time;
+  time_ms_t fade_time;
   /// Head pointer of the error ignore linked list.
   ignore_t *ignore_head;
   /// Pointer to the <code>next</code> member of tail element of the error
@@ -471,13 +523,13 @@ typedef struct {
   /// Nanosecond offset of the first painting.
   long paint_tm_offset;
 
-  #ifdef CONFIG_VSYNC_DRM
+#ifdef CONFIG_VSYNC_DRM
   // === DRM VSync related ===
   /// File descriptor of DRI device file. Used for DRM VSync.
   int drm_fd;
-  #endif
+#endif
 
-  #ifdef CONFIG_VSYNC_OPENGL
+#ifdef CONFIG_VSYNC_OPENGL
   // === OpenGL VSync related ===
   /// GLX context.
   GLXContext glx_context;
@@ -485,7 +537,7 @@ typedef struct {
   f_GetVideoSync glx_get_video_sync;
   /// Pointer to glXWaitVideoSyncSGI function.
   f_WaitVideoSync glx_wait_video_sync;
-  #endif
+#endif
 
   // === X extension related ===
   /// Event base number for X Fixes extension.
@@ -521,14 +573,14 @@ typedef struct {
   int randr_event;
   /// Error base number for X RandR extension.
   int randr_error;
-  #ifdef CONFIG_VSYNC_OPENGL
+#ifdef CONFIG_VSYNC_OPENGL
   /// Whether X GLX extension exists.
   bool glx_exists;
   /// Event base number for X GLX extension.
   int glx_event;
   /// Error base number for X GLX extension.
   int glx_error;
-  #endif
+#endif
   /// Whether X DBE extension exists.
   bool dbe_exists;
   /// Whether X Render convolution filter exists.
@@ -565,9 +617,11 @@ typedef struct {
 } session_t;
 
 /// Structure representing a top-level window compton manages.
-typedef struct _win {
+typedef struct __attribute__((__packed__)) _win {
   // Next structure in the linked list.
   struct _win *next;
+  // Pointer to the next higher window to paint.
+  struct _win *prev_trans;
 
   // ID of the top-level frame window.
   Window id;
@@ -587,10 +641,15 @@ typedef struct _win {
   XserverRegion extents;
   // Type of the window.
   wintype_t window_type;
+
+  // Focus-related members
   /// Whether the window is to be considered focused.
   bool focused;
+  /// Override value of window focus state. Set by D-Bus method calls.
+  switch_t focused_force;
   /// Whether the window is actually focused.
   bool focused_real;
+
   /// Leader window ID of the window.
   Window leader;
   /// Cached topmost window ID of the window.
@@ -649,8 +708,10 @@ typedef struct _win {
   unsigned int left_width, right_width, top_width, bottom_width;
 
   // Shadow-related members
-  /// Whether a window has shadow. Affected by window type.
+  /// Whether a window has shadow. Calculated.
   bool shadow;
+  /// Override value of window shadow state. Set by D-Bus method calls.
+  switch_t shadow_force;
   /// Opacity of the shadow. Affected by window opacity and frame opacity.
   double shadow_opacity;
   /// X offset of shadow. Affected by commandline argument.
@@ -691,8 +752,6 @@ typedef struct _win {
   /// opacity state, window geometry, window mapped/unmapped state,
   /// window mode, of this and all higher windows.
   XserverRegion reg_ignore;
-
-  struct _win *prev_trans;
 } win;
 
 /// Temporary structure used for communication between
@@ -773,6 +832,22 @@ XFixesDestroyRegion_(Display *dpy, XserverRegion reg,
 
 // == Functions ==
 
+/**
+ * Wrapper of libevent event_new(), for compatibility with libevent-1\.x.
+ */
+static inline struct event *
+EVENT_NEW(struct event_base *base, evutil_socket_t fd,
+    short what, event_callback_fn cb, void *arg) {
+#ifndef CONFIG_LIBEVENT_LEGACY
+  return event_new(base, fd, what, cb, arg);
+#else
+  struct event *pev = malloc(sizeof(struct event));
+  if (pev)
+    event_set(pev, fd, what, cb, arg);
+  return pev;
+#endif
+}
+
 // inline functions must be made static to compile correctly under clang:
 // http://clang.llvm.org/compatibility.html#inline
 
@@ -784,6 +859,9 @@ discard_ignore(session_t *ps, unsigned long sequence);
 static void
 set_ignore(session_t *ps, unsigned long sequence);
 
+/**
+ * Ignore X errors caused by next X request.
+ */
 static inline void
 set_ignore_next(session_t *ps) {
   set_ignore(ps, NextRequest(ps->dpy));
@@ -793,6 +871,14 @@ static int
 should_ignore(session_t *ps, unsigned long sequence);
 
 /**
+ * Wrapper of XInternAtom() for convience.
+ */
+static inline Atom
+get_atom(session_t *ps, char *atom_name) {
+  return XInternAtom(ps->dpy, atom_name, False);
+}
+
+/**
  * Return the painting target window.
  */
 static inline Window
@@ -957,6 +1043,14 @@ array_wid_exists(const Window *arr, int count, Window wid) {
   return false;
 }
 
+/**
+ * Return whether a struct timeval value is empty.
+ */
+static inline bool
+timeval_isempty(struct timeval tv) {
+  return !(tv.tv_sec && tv.tv_usec);
+}
+
 /*
  * Subtracting two struct timeval values.
  *
@@ -1028,6 +1122,19 @@ timespec_subtract(struct timespec *result,
 
 /**
  * Get current time in struct timespec.
+ */
+static inline struct timeval __attribute__((const))
+get_time_timeval(void) {
+  struct timeval tv = { 0, 0 };
+
+  gettimeofday(&tv, NULL);
+
+  // Return a time of all 0 if the call fails
+  return tv;
+}
+
+/**
+ * Get current time in struct timespec.
  *
  * Note its starting time is unspecified.
  */
@@ -1154,18 +1261,25 @@ free_win_res(session_t *ps, win *w) {
 
 /**
  * Get current system clock in milliseconds.
- *
- * The return type must be unsigned long because so many milliseconds have
- * passed since the epoch.
  */
-static unsigned long
+static time_ms_t
 get_time_ms(void) {
   struct timeval tv;
 
   gettimeofday(&tv, NULL);
 
-  return (unsigned long) tv.tv_sec * 1000
-    + (unsigned long) tv.tv_usec / 1000;
+  return tv.tv_sec % SEC_WRAP * 1000 + tv.tv_usec / 1000;
+}
+
+/**
+ * Convert time from milliseconds to struct timeval.
+ */
+static inline struct timeval
+ms_to_tv(int timeout) {
+  return (struct timeval) {
+    .tv_sec = timeout / MS_PER_SEC,
+    .tv_usec = timeout % MS_PER_SEC * (US_PER_SEC / MS_PER_SEC)
+  };
 }
 
 static int
@@ -1255,34 +1369,66 @@ wid_has_prop(const session_t *ps, Window w, Atom atom) {
  * @return a <code>winprop_t</code> structure containing the attribute
  *    and number of items. A blank one on failure.
  */
+// TODO: Move to compton.c
 static winprop_t
-wid_get_prop(const session_t *ps, Window w, Atom atom, long length,
-    Atom rtype, int rformat) {
+wid_get_prop_adv(const session_t *ps, Window w, Atom atom, long offset,
+    long length, Atom rtype, int rformat) {
   Atom type = None;
   int format = 0;
   unsigned long nitems = 0, after = 0;
   unsigned char *data = NULL;
 
-  // Use two if statements to deal with the sequence point issue.
-  if (Success == XGetWindowProperty(ps->dpy, w, atom, 0L, length, False,
-        rtype, &type, &format, &nitems, &after, &data)) {
-    if (type == rtype && format == rformat) {
+  if (Success == XGetWindowProperty(ps->dpy, w, atom, offset, length,
+        False, rtype, &type, &format, &nitems, &after, &data)
+      && nitems && (AnyPropertyType == type || type == rtype)
+      && (!format || format == rformat)
+      && (8 == format || 16 == format || 32 == format)) {
       return (winprop_t) {
         .data.p8 = data,
-        .nitems = nitems
+        .nitems = nitems,
+        .type = type,
+        .format = format,
       };
-    }
   }
 
   XFree(data);
 
   return (winprop_t) {
     .data.p8 = NULL,
-    .nitems = 0
+    .nitems = 0,
+    .type = type,
+    .format = format
   };
 }
 
 /**
+ * Wrapper of wid_get_prop_adv().
+ */
+static inline winprop_t
+wid_get_prop(const session_t *ps, Window wid, Atom atom, long length,
+    Atom rtype, int rformat) {
+  return wid_get_prop_adv(ps, wid, atom, 0L, length, rtype, rformat);
+}
+
+static inline
+long winprop_get_int(winprop_t prop) {
+  long tgt = 0;
+
+  if (!prop.nitems)
+    return 0;
+
+  switch (prop.format) {
+    case 8:   tgt = *(prop.data.p8);    break;
+    case 16:  tgt = *(prop.data.p16);   break;
+    case 32:  tgt = *(prop.data.p32);   break;
+    default:  assert(0);
+              break;
+  }
+
+  return tgt;
+}
+
+/**
  * Free a <code>winprop_t</code>.
  *
  * @param pprop pointer to the <code>winprop_t</code> to free.
@@ -1639,7 +1785,7 @@ win_unmark_client(session_t *ps, win *w);
 static void
 win_recheck_client(session_t *ps, win *w);
 
-static void
+static bool
 add_win(session_t *ps, Window id, Window prev);
 
 static void
@@ -1855,7 +2001,7 @@ ev_window_name(session_t *ps, Window wid, char **name);
 inline static void
 ev_handle(session_t *ps, XEvent *ev);
 
-static void
+static bool
 fork_after(void);
 
 #ifdef CONFIG_LIBCONFIG
@@ -1918,8 +2064,11 @@ update_refresh_rate(session_t *ps);
 static bool
 sw_opti_init(session_t *ps);
 
-static int
-evpoll(session_t *ps, int timeout);
+static void
+swopti_handle_timeout(session_t *ps, struct timeval *ptv);
+
+static void
+evcallback_x(evutil_socket_t fd, short what, void *arg);
 
 static bool
 vsync_drm_init(session_t *ps);
@@ -1955,6 +2104,9 @@ redir_start(session_t *ps);
 static void
 redir_stop(session_t *ps);
 
+static bool
+mainloop(session_t *ps);
+
 static session_t *
 session_init(session_t *ps_old, int argc, char **argv);