Initial commit: Go 1.23 release state

test/chan/doubleselect.go

@@ -0,0 +1,87 @@
+// run
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test the situation in which two cases of a select can
+// both end up running. See http://codereview.appspot.com/180068.
+
+package main
+
+import (
+	"flag"
+	"runtime"
+)
+
+var iterations *int = flag.Int("n", 100000, "number of iterations")
+
+// sender sends a counter to one of four different channels. If two
+// cases both end up running in the same iteration, the same value will be sent
+// to two different channels.
+func sender(n int, c1, c2, c3, c4 chan<- int) {
+	defer close(c1)
+	defer close(c2)
+	defer close(c3)
+	defer close(c4)
+
+	for i := 0; i < n; i++ {
+		select {
+		case c1 <- i:
+		case c2 <- i:
+		case c3 <- i:
+		case c4 <- i:
+		}
+	}
+}
+
+// mux receives the values from sender and forwards them onto another channel.
+// It would be simpler to just have sender's four cases all be the same
+// channel, but this doesn't actually trigger the bug.
+func mux(out chan<- int, in <-chan int, done chan<- bool) {
+	for v := range in {
+		out <- v
+	}
+	done <- true
+}
+
+// recver gets a steam of values from the four mux's and checks for duplicates.
+func recver(in <-chan int) {
+	seen := make(map[int]bool)
+
+	for v := range in {
+		if _, ok := seen[v]; ok {
+			println("got duplicate value: ", v)
+			panic("fail")
+		}
+		seen[v] = true
+	}
+}
+
+func main() {
+	runtime.GOMAXPROCS(2)
+
+	flag.Parse()
+	c1 := make(chan int)
+	c2 := make(chan int)
+	c3 := make(chan int)
+	c4 := make(chan int)
+	done := make(chan bool)
+	cmux := make(chan int)
+	go sender(*iterations, c1, c2, c3, c4)
+	go mux(cmux, c1, done)
+	go mux(cmux, c2, done)
+	go mux(cmux, c3, done)
+	go mux(cmux, c4, done)
+	go func() {
+		<-done
+		<-done
+		<-done
+		<-done
+		close(cmux)
+	}()
+	// We keep the recver because it might catch more bugs in the future.
+	// However, the result of the bug linked to at the top is that we'll
+	// end up panicking with: "throw: bad g->status in ready".
+	recver(cmux)
+}