vweb: implement worker pool (#17298)

examples/vweb/vweb_example.v

@@ -3,9 +3,12 @@ module main
 import vweb
 import rand
 
-const (
-	port = 8082
-)
+const port = 8082
+
+struct State {
+mut:
+	cnt int
+}
 
 struct App {
 	vweb.Context
@@ -13,18 +16,10 @@ mut:
 	state shared State
 }
 
-struct State {
-mut:
-	cnt int
-}
-
-pub fn (app App) before_request() {
-	println('[vweb] before_request: ${app.req.method} ${app.req.url}')
-}
-
-fn main() {
-	println('vweb example')
-	vweb.run(&App{}, port)
+pub fn (app &App) before_request() {
+	$if trace_before_request ? {
+		eprintln('[vweb] before_request: ${app.req.method} ${app.req.url}')
+	}
 }
 
 ['/users/:user']
@@ -36,11 +31,17 @@ pub fn (mut app App) user_endpoint(user string) vweb.Result {
 }
 
 pub fn (mut app App) index() vweb.Result {
+	mut c := 0
 	lock app.state {
 		app.state.cnt++
+		c = app.state.cnt
+		//
+		$if trace_address_of_app_state_cnt ? {
+			dump(ptr_str(app.state.cnt))
+		}
 	}
 	show := true
-	hello := 'Hello world from vweb'
+	hello := 'Hello world from vweb, request number: ${c}'
 	numbers := [1, 2, 3]
 	return $vweb.html()
 }
@@ -58,3 +59,8 @@ pub fn (mut app App) cookie() vweb.Result {
 pub fn (mut app App) post() vweb.Result {
 	return app.text('Post body: ${app.req.data}')
 }
+
+fn main() {
+	println('vweb example')
+	vweb.run(&App{}, port)
+}