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Source file test/chanlinear.go

Documentation: test

  // +build darwin linux
  // run
  
  // Copyright 2014 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 dequeueing from a pending channel doesn't
  // take linear time.
  
  package main
  
  import (
  	"fmt"
  	"runtime"
  	"time"
  )
  
  // checkLinear asserts that the running time of f(n) is in O(n).
  // tries is the initial number of iterations.
  func checkLinear(typ string, tries int, f func(n int)) {
  	// Depending on the machine and OS, this test might be too fast
  	// to measure with accurate enough granularity. On failure,
  	// make it run longer, hoping that the timing granularity
  	// is eventually sufficient.
  
  	timeF := func(n int) time.Duration {
  		t1 := time.Now()
  		f(n)
  		return time.Since(t1)
  	}
  
  	t0 := time.Now()
  
  	n := tries
  	fails := 0
  	for {
  		runtime.GC()
  		t1 := timeF(n)
  		runtime.GC()
  		t2 := timeF(2 * n)
  
  		// should be 2x (linear); allow up to 3x
  		if t2 < 3*t1 {
  			if false {
  				fmt.Println(typ, "\t", time.Since(t0))
  			}
  			return
  		}
  		// If n ops run in under a second and the ratio
  		// doesn't work out, make n bigger, trying to reduce
  		// the effect that a constant amount of overhead has
  		// on the computed ratio.
  		if t1 < 1*time.Second {
  			n *= 2
  			continue
  		}
  		// Once the test runs long enough for n ops,
  		// try to get the right ratio at least once.
  		// If five in a row all fail, give up.
  		if fails++; fails >= 5 {
  			panic(fmt.Sprintf("%s: too slow: %d channels: %v; %d channels: %v\n",
  				typ, n, t1, 2*n, t2))
  		}
  	}
  }
  
  func main() {
  	checkLinear("chanSelect", 1000, func(n int) {
  		const messages = 10
  		c := make(chan bool) // global channel
  		var a []chan bool    // local channels for each goroutine
  		for i := 0; i < n; i++ {
  			d := make(chan bool)
  			a = append(a, d)
  			go func() {
  				for j := 0; j < messages; j++ {
  					// queue ourselves on the global channel
  					select {
  					case <-c:
  					case <-d:
  					}
  				}
  			}()
  		}
  		for i := 0; i < messages; i++ {
  			// wake each goroutine up, forcing it to dequeue and then enqueue
  			// on the global channel.
  			for _, d := range a {
  				d <- true
  			}
  		}
  	})
  }
  

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