From 7d1dec5b44a7dac8e05d86603b2ca89f967b8cc9 Mon Sep 17 00:00:00 2001
From: Taillook <jousoku@gmail.com>
Date: Mon, 6 Dec 2021 02:44:25 +0900
Subject: [PATCH] sync: add sync.ManyTimes (#12729)

---
 cmd/tools/vtest-self.v      |  1 +
 vlib/sync/many_times.v      | 36 +++++++++++++++++++++++++++
 vlib/sync/many_times_test.v | 49 +++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)
 create mode 100644 vlib/sync/many_times.v
 create mode 100644 vlib/sync/many_times_test.v

diff --git a/cmd/tools/vtest-self.v b/cmd/tools/vtest-self.v
index 7162ea53d..859029ef3 100644
--- a/cmd/tools/vtest-self.v
+++ b/cmd/tools/vtest-self.v
@@ -115,6 +115,7 @@ const (
 		'vlib/vweb/request_test.v',
 		'vlib/net/http/request_test.v',
 		'vlib/vweb/route_test.v',
+		'vlib/sync/many_times_test.v',
 		'vlib/sync/once_test.v',
 	]
 	skip_on_non_windows           = [
diff --git a/vlib/sync/many_times.v b/vlib/sync/many_times.v
new file mode 100644
index 000000000..286defc34
--- /dev/null
+++ b/vlib/sync/many_times.v
@@ -0,0 +1,36 @@
+module sync
+
+import sync.atomic2
+
+pub struct ManyTimes {
+mut:
+	m RwMutex
+pub:
+	times u64 = 1
+	count u64
+}
+
+// new_many_times return a new ManyTimes struct.
+pub fn new_many_times(times u64) &ManyTimes {
+	mut many_times := &ManyTimes{
+		times: times
+	}
+	many_times.m.init()
+	return many_times
+}
+
+// do execute the function only setting times.
+pub fn (mut m ManyTimes) do(f fn ()) {
+	if atomic2.load_u64(&m.count) < m.times {
+		m.do_slow(f)
+	}
+}
+
+fn (mut m ManyTimes) do_slow(f fn ()) {
+	m.m.@lock()
+	if m.count < m.times {
+		atomic2.store_u64(&m.count, m.count + 1)
+		f()
+	}
+	m.m.unlock()
+}
diff --git a/vlib/sync/many_times_test.v b/vlib/sync/many_times_test.v
new file mode 100644
index 000000000..e2ddca3ae
--- /dev/null
+++ b/vlib/sync/many_times_test.v
@@ -0,0 +1,49 @@
+import sync
+
+struct Counter {
+pub mut:
+	i int
+}
+
+fn (mut c Counter) add(i int) {
+	c.i = c.i + i
+}
+
+fn run(mut m sync.ManyTimes, mut co Counter, c chan bool) {
+	m.do(fn [mut co] () {
+		co.add(5)
+	})
+	c <- true
+}
+
+fn test_many_times_once() {
+	mut co := &Counter{}
+	mut m := sync.new_many_times(1)
+	c := chan bool{}
+	n := 10
+
+	// It is executed 10 times, but only once actually.
+	for i := 0; i < n; i++ {
+		go run(mut m, mut co, c)
+	}
+	for i := 0; i < n; i++ {
+		<-c
+	}
+	assert co.i == 5
+}
+
+fn test_many_times_fifth() {
+	mut co := &Counter{}
+	mut m := sync.new_many_times(5)
+	c := chan bool{}
+	n := 10
+
+	// It is executed 10 times, but only 5 times actually.
+	for i := 0; i < n; i++ {
+		go run(mut m, mut co, c)
+	}
+	for i := 0; i < n; i++ {
+		<-c
+	}
+	assert co.i == 25
+}
-- 
2.30.2