sd-bus: add new sd_bus_pending_method_calls() call

src/libsystemd/libsystemd.sym

@@ -843,3 +843,8 @@ global:
         sd_journal_stream_fd_with_namespace;
         sd_event_source_get_inotify_path;
 } LIBSYSTEMD_255;
+
+LIBSYSTEMD_257 {
+global:
+        sd_bus_pending_method_calls;
+} LIBSYSTEMD_256;

src/libsystemd/sd-bus/sd-bus.c

@@ -4471,3 +4471,21 @@ _public_ int sd_bus_enqueue_for_read(sd_bus *bus, sd_bus_message *m) {
         bus->rqueue[bus->rqueue_size++] = bus_message_ref_queued(m, bus);
         return 0;
 }
+
+_public_ int sd_bus_pending_method_calls(sd_bus *bus) {
+
+        /* Returns the number of currently pending asynchronous method calls. This is graceful, i.e. an
+         * unallocated (i.e. NULL) bus connection has no method calls pending. */
+
+        if (!bus)
+                return 0;
+
+        assert_return(bus = bus_resolve(bus), -ENOPKG);
+
+        if (!BUS_IS_OPEN(bus->state))
+                return 0;
+
+        size_t n = ordered_hashmap_size(bus->reply_callbacks);
+
+        return n > INT_MAX ? INT_MAX : (int) n; /* paranoid overflow check */
+}