remove skynet.watch, move simplemonitor to examples

examples/simplemonitor.lua

@@ -0,0 +1,39 @@
+local skynet = require "skynet"
+
+-- It's a simple service exit monitor, you can do something more when a service exit.
+
+local service_map = {}
+
+skynet.register_protocol {
+	name = "client",
+	id = skynet.PTYPE_CLIENT,	-- PTYPE_CLIENT = 3
+	unpack = function() end,
+	dispatch = function(_, address)
+		local w = service_map[address]
+		if w then
+			for watcher in pairs(w) do
+				skynet.redirect(watcher, address, "error", "")
+			end
+			service_map[address] = false
+		end
+	end
+}
+
+local function monitor(session, watcher, command, service)
+	assert(command, "WATCH")
+	local w = service_map[service]
+	if not w then
+		if w == false then
+			skynet.ret(skynet.pack(false))
+			return
+		end
+		w = {}
+		service_map[service] = w
+	end
+	w[watcher] = true
+	skynet.ret(skynet.pack(true))
+end
+
+skynet.start(function()
+	skynet.dispatch("lua", monitor)
+end)