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