go/test/chan/select2.go

// run

// Copyright 2010 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 that selects do not consume undue memory.

package main

import "runtime"

func sender(c chan int, n int) {
	for i := 0; i < n; i++ {
		c <- 1
	}
}

func receiver(c, dummy chan int, n int) {
	for i := 0; i < n; i++ {
		select {
		case <-c:
			// nothing
		case <-dummy:
			panic("dummy")
		}
	}
}

func main() {
	runtime.MemProfileRate = 0

	c := make(chan int)
	dummy := make(chan int)

	// warm up
	go sender(c, 100000)
	receiver(c, dummy, 100000)
	runtime.GC()
	memstats := new(runtime.MemStats)
	runtime.ReadMemStats(memstats)
	alloc := memstats.Alloc

	// second time shouldn't increase footprint by much
	go sender(c, 100000)
	receiver(c, dummy, 100000)
	runtime.GC()
	runtime.ReadMemStats(memstats)

	// Be careful to avoid wraparound.
	if memstats.Alloc > alloc && memstats.Alloc-alloc > 1.1e5 {
		println("BUG: too much memory for 100,000 selects:", memstats.Alloc-alloc)
	}
}