diff --git a/common.h b/common.h
index f8531bcbd..469f8f1ae 100644
--- a/common.h
+++ b/common.h
@@ -60,6 +60,10 @@
 #error Cannot enable c2 debugging without c2 support.
 #endif
 
+#ifndef COMPTON_VERSION
+#define COMPTON_VERSION "unknown"
+#endif
+
 // === Includes ===
 
 // For some special functions
@@ -132,6 +136,12 @@
 #define MSTR_(s)        #s
 #define MSTR(s)         MSTR_(s)
 
+/// @brief Wrapper for gcc branch prediction builtin, for likely branch.
+#define likely(x)    __builtin_expect(!!(x), 1)
+
+/// @brief Wrapper for gcc branch prediction builtin, for unlikely branch.
+#define unlikely(x)  __builtin_expect(!!(x), 0)
+
 /// Print out an error message.
 #define printf_err(format, ...) \
   fprintf(stderr, format "\n", ## __VA_ARGS__)
@@ -431,9 +441,13 @@ typedef struct {
   // === General ===
   /// The configuration file we used.
   char *config_file;
+  /// Path to write PID to.
+  char *write_pid_path;
   /// The display name we used. NULL means we are using the value of the
   /// <code>DISPLAY</code> environment variable.
   char *display;
+  /// Safe representation of display name.
+  char *display_repr;
   /// The backend in use.
   enum backend backend;
   /// Whether to avoid using stencil buffer under GLX backend. Might be
@@ -986,7 +1000,7 @@ typedef struct _win {
   /// _NET_WM_OPACITY value
   opacity_t opacity_prop_client;
   /// Last window opacity value we set.
-  long opacity_set;
+  opacity_t opacity_set;
 
   // Fading-related members
   /// Do not fade if it's false. Change on window type change.
@@ -1150,6 +1164,15 @@ allocchk_(const char *func_name, void *ptr) {
 /// @brief Wrapper of allocchk_().
 #define allocchk(ptr) allocchk_(__func__, ptr)
 
+/// @brief Wrapper of malloc().
+#define cmalloc(nmemb, type) ((type *) allocchk(malloc((nmemb) * sizeof(type))))
+
+/// @brief Wrapper of calloc().
+#define ccalloc(nmemb, type) ((type *) allocchk(calloc((nmemb), sizeof(type))))
+
+/// @brief Wrapper of ealloc().
+#define crealloc(ptr, nmemb, type) ((type *) allocchk(realloc((ptr), (nmemb) * sizeof(type))))
+
 /**
  * Return whether a struct timeval value is empty.
  */
@@ -1310,10 +1333,7 @@ print_timestamp(session_t *ps) {
  */
 static inline char *
 mstrcpy(const char *src) {
-  char *str = malloc(sizeof(char) * (strlen(src) + 1));
-
-  if (!str)
-    printf_errfq(1, "(): Failed to allocate memory.");
+  char *str = cmalloc(strlen(src) + 1, char);
 
   strcpy(str, src);
 
@@ -1325,10 +1345,7 @@ mstrcpy(const char *src) {
  */
 static inline char *
 mstrncpy(const char *src, unsigned len) {
-  char *str = malloc(sizeof(char) * (len + 1));
-
-  if (!str)
-    printf_errfq(1, "(): Failed to allocate memory.");
+  char *str = cmalloc(len + 1, char);
 
   strncpy(str, src, len);
   str[len] = '\0';
@@ -1341,7 +1358,7 @@ mstrncpy(const char *src, unsigned len) {
  */
 static inline char *
 mstrjoin(const char *src1, const char *src2) {
-  char *str = malloc(sizeof(char) * (strlen(src1) + strlen(src2) + 1));
+  char *str = cmalloc(strlen(src1) + strlen(src2) + 1, char);
 
   strcpy(str, src1);
   strcat(str, src2);
@@ -1354,8 +1371,8 @@ mstrjoin(const char *src1, const char *src2) {
  */
 static inline char *
 mstrjoin3(const char *src1, const char *src2, const char *src3) {
-  char *str = malloc(sizeof(char) * (strlen(src1) + strlen(src2)
-        + strlen(src3) + 1));
+  char *str = cmalloc(strlen(src1) + strlen(src2)
+        + strlen(src3) + 1, char);
 
   strcpy(str, src1);
   strcat(str, src2);
@@ -1369,7 +1386,8 @@ mstrjoin3(const char *src1, const char *src2, const char *src3) {
  */
 static inline void
 mstrextend(char **psrc1, const char *src2) {
-  *psrc1 = realloc(*psrc1, (*psrc1 ? strlen(*psrc1): 0) + strlen(src2) + 1);
+  *psrc1 = crealloc(*psrc1, (*psrc1 ? strlen(*psrc1): 0) + strlen(src2) + 1,
+      char);
 
   strcat(*psrc1, src2);
 }
diff --git a/compton.c b/compton.c
index 0c9855281..770721596 100644
--- a/compton.c
+++ b/compton.c
@@ -1571,7 +1571,7 @@ win_paint_win(session_t *ps, win *w, XserverRegion reg_paint,
     }
   }
 
-  double dopacity = get_opacity_percent(w);;
+  double dopacity = get_opacity_percent(w);
 
   if (!w->frame_opacity) {
     win_render(ps, w, 0, 0, wid, hei, dopacity, reg_paint, pcache_reg, pict);
@@ -4309,6 +4309,8 @@ usage(int ret) {
     "  Enable synchronous operation (for debugging).\n"
     "--config path\n"
     "  Look for configuration file at the path.\n"
+    "--write-pid-path path\n"
+    "  Write process ID to a file.\n"
     "--shadow-red value\n"
     "  Red color value of shadow (0.0 - 1.0, defaults to 0).\n"
     "--shadow-green value\n"
@@ -4584,7 +4586,7 @@ ostream_reopen(session_t *ps, const char *path) {
 /**
  * Fork program to background and disable all I/O streams.
  */
-static bool
+static inline bool
 fork_after(session_t *ps) {
   if (getppid() == 1)
     return true;
@@ -4627,6 +4629,26 @@ fork_after(session_t *ps) {
   return success;
 }
 
+/**
+ * Write PID to a file.
+ */
+static inline bool
+write_pid(session_t *ps) {
+  if (!ps->o.write_pid_path)
+    return true;
+
+  FILE *f = fopen(ps->o.write_pid_path, "w");
+  if (unlikely(!f)) {
+    printf_errf("(): Failed to write PID to \"%s\".", ps->o.write_pid_path);
+    return false;
+  }
+
+  fprintf(f, "%ld\n", (long) getpid());
+  fclose(f);
+
+  return true;
+}
+
 /**
  * Parse a long number.
  */
@@ -5360,6 +5382,7 @@ get_cfg(session_t *ps, int argc, char *const *argv, bool first_pass) {
     { "xinerama-shadow-crop", no_argument, NULL, 307 },
     { "unredir-if-possible-exclude", required_argument, NULL, 308 },
     { "unredir-if-possible-delay", required_argument, NULL, 309 },
+    { "write-pid-path", required_argument, NULL, 310 },
     // Must terminate with a NULL entry
     { NULL, 0, NULL, 0 },
   };
@@ -5603,6 +5626,10 @@ get_cfg(session_t *ps, int argc, char *const *argv, bool first_pass) {
         condlst_add(ps, &ps->o.unredir_if_possible_blacklist, optarg);
         break;
       P_CASELONG(309, unredir_if_possible_delay);
+      case 310:
+        // --write-pid-path
+        ps->o.write_pid_path = mstrcpy(optarg);
+        break;
       default:
         usage(1);
         break;
@@ -6800,6 +6827,27 @@ session_init(session_t *ps_old, int argc, char **argv) {
     ps->shape_exists = true;
   }
 
+  // Build a safe representation of display name
+  {
+    char *display_repr = DisplayString(ps->dpy);
+    if (!display_repr)
+      display_repr = "unknown";
+    display_repr = mstrcpy(display_repr);
+
+    // Convert all special characters in display_repr name to underscore
+    {
+      char *pdisp = display_repr;
+
+      while (*pdisp) {
+        if (!isalnum(*pdisp))
+          *pdisp = '_';
+        ++pdisp;
+      }
+    }
+
+    ps->o.display_repr = display_repr;
+  }
+
   // Second pass
   get_cfg(ps, argc, argv, false);
 
@@ -6974,6 +7022,8 @@ session_init(session_t *ps_old, int argc, char **argv) {
     }
   }
 
+  write_pid(ps);
+
   // Free the old session
   if (ps_old)
     free(ps_old);
@@ -7099,9 +7149,12 @@ session_destroy(session_t *ps) {
   free(ps->shadow_corner);
   free(ps->shadow_top);
   free(ps->gaussian_map);
+
+  free(ps->o.config_file);
+  free(ps->o.write_pid_path);
   free(ps->o.display);
+  free(ps->o.display_repr);
   free(ps->o.logpath);
-  free(ps->o.config_file);
   for (int i = 0; i < MAX_BLUR_PASS; ++i) {
     free(ps->o.blur_kerns[i]);
     free(ps->blur_kerns_cache[i]);
diff --git a/dbus.c b/dbus.c
index 1d20a061a..8aec9ea82 100644
--- a/dbus.c
+++ b/dbus.c
@@ -39,30 +39,10 @@ cdbus_init(session_t *ps) {
 
   // Request service name
   {
-    // Get display name
-    char *display = DisplayString(ps->dpy);
-    if (!display)
-      display = "unknown";
-    display = mstrcpy(display);
-
-    // Convert all special characters in display name to underscore
-    {
-      char *pdisp = display;
-
-      while (*pdisp) {
-        if (!isalnum(*pdisp))
-          *pdisp = '_';
-        ++pdisp;
-      }
-    }
-
     // Build service name
-    char *service = mstrjoin3(CDBUS_SERVICE_NAME, ".", display);
+    char *service = mstrjoin3(CDBUS_SERVICE_NAME, ".", ps->o.display_repr);
     ps->dbus_service = service;
 
-    free(display);
-    display = NULL;
-
     // Request for the name
     int ret = dbus_bus_request_name(ps->dbus_conn, service,
         DBUS_NAME_FLAG_DO_NOT_QUEUE, &err);
@@ -735,7 +715,13 @@ cdbus_process_win_get(session_t *ps, DBusMessage *msg) {
   cdbus_m_win_get_do(class_instance, cdbus_reply_string);
   cdbus_m_win_get_do(class_general, cdbus_reply_string);
   cdbus_m_win_get_do(role, cdbus_reply_string);
+
   cdbus_m_win_get_do(opacity, cdbus_reply_uint32);
+  cdbus_m_win_get_do(opacity_tgt, cdbus_reply_uint32);
+  cdbus_m_win_get_do(opacity_prop, cdbus_reply_uint32);
+  cdbus_m_win_get_do(opacity_prop_client, cdbus_reply_uint32);
+  cdbus_m_win_get_do(opacity_set, cdbus_reply_uint32);
+
   cdbus_m_win_get_do(frame_opacity, cdbus_reply_double);
   cdbus_m_win_get_do(left_width, cdbus_reply_uint32);
   cdbus_m_win_get_do(right_width, cdbus_reply_uint32);
@@ -889,6 +875,18 @@ cdbus_process_opts_get(session_t *ps, DBusMessage *msg) {
     return true; \
   }
 
+  // version
+  if (!strcmp("version", target)) {
+    cdbus_reply_string(ps, msg, COMPTON_VERSION);
+    return true;
+  }
+
+  // pid
+  if (!strcmp("pid", target)) {
+    cdbus_reply_int32(ps, msg, getpid());
+    return true;
+  }
+
   // display
   if (!strcmp("display", target)) {
     cdbus_reply_string(ps, msg, DisplayString(ps->dpy));
@@ -896,6 +894,8 @@ cdbus_process_opts_get(session_t *ps, DBusMessage *msg) {
   }
 
   cdbus_m_opts_get_do(config_file, cdbus_reply_string);
+  cdbus_m_opts_get_do(display_repr, cdbus_reply_string);
+  cdbus_m_opts_get_do(write_pid_path, cdbus_reply_string);
   cdbus_m_opts_get_do(mark_wmwin_focused, cdbus_reply_bool);
   cdbus_m_opts_get_do(mark_ovredir_focused, cdbus_reply_bool);
   cdbus_m_opts_get_do(fork_after_register, cdbus_reply_bool);
diff --git a/dbus.h b/dbus.h
index 50770d63c..a806c2de9 100644
--- a/dbus.h
+++ b/dbus.h
@@ -10,6 +10,8 @@
 
 #include "common.h"
 #include <ctype.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #define CDBUS_SERVICE_NAME      "com.github.chjj.compton"
 #define CDBUS_INTERFACE_NAME    CDBUS_SERVICE_NAME