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 // \$G \$D/\$F.go && \$L \$F.\$A && ./\$A.out // 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. // This test is designed to flush out the case where 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) 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 simplier 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) { for { v := <-in if closed(in) { close(out) break } out <- v } } // 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 := <-in if closed(in) { break } if _, ok := seen[v]; ok { panic("got duplicate value: ", v) } seen[v] = true } } func main() { runtime.GOMAXPROCS(2) c1 := make(chan int) c2 := make(chan int) c3 := make(chan int) c4 := make(chan int) cmux := make(chan int) go sender(*iterations, c1, c2, c3, c4) go mux(cmux, c1) go mux(cmux, c2) go mux(cmux, c3) go mux(cmux, c4) // 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 panicing with: "throw: bad g->status in ready". recver(cmux) print("PASS\n") }