add skynet command MQLEN for debug

lualib/skynet.lua

@@ -526,6 +526,7 @@ function dbgcmd.STAT()
 	query_state(stat, "count")
 	query_state(stat, "time")
 	stat.boottime = debug.getregistry().skynet_boottime
+	stat.mqlen = skynet.mqlen()
 	skynet.ret(skynet.pack(stat))
 end
 
@@ -692,4 +693,8 @@ function skynet.monitor(service, query)
 	c.command("MONITOR", string.format(":%08x", monitor))
 end
 
+function skynet.mqlen()
+	return tonumber(c.command "MQLEN")
+end
+
 return skynet

skynet-src/skynet_mq.c

@@ -109,6 +109,19 @@ skynet_mq_handle(struct message_queue *q) {
 	return q->handle;
 }
 
+int
+skynet_mq_length(struct message_queue *q) {
+	int head, tail;
+	LOCK(q)
+	head = q->head;
+	tail = q->tail;
+	UNLOCK(q)
+	
+	if (head <= tail) {
+		return tail - head;
+	}
+	return tail + q->cap - head;
+}
 
 int
 skynet_mq_pop(struct message_queue *q, struct skynet_message *message) {

skynet-src/skynet_mq.h

@@ -26,6 +26,9 @@ void skynet_mq_push(struct message_queue *q, struct skynet_message *message);
 void skynet_mq_lock(struct message_queue *q, int session);
 void skynet_mq_unlock(struct message_queue *q);
 
+// return the length of message queue, for debug
+int skynet_mq_length(struct message_queue *q);
+
 void skynet_mq_force_push(struct message_queue *q);
 void skynet_mq_pushglobal(struct message_queue *q);
 

skynet-src/skynet_server.c

@@ -563,6 +563,12 @@ skynet_command(struct skynet_context * context, const char * cmd , const char *
 		return NULL;
 	}
 
+	if (strcmp(cmd, "MQLEN") == 0) {
+		int len = skynet_mq_length(context->queue);
+		sprintf(context->result, "%d", len);
+		return context->result;
+	}
+
 	return NULL;
 }