mirror of
https://github.com/golang/go
synced 2024-11-24 22:10:02 -07:00
50d6c81d4a
(Thanks to ken and rsc for pointing this out)
rsc:
ken pointed out that there's a race in the new
one-lock-per-channel code. the issue is that
if one goroutine has gone to sleep doing
select {
case <-c1:
case <-c2:
}
and then two more goroutines try to send
on c1 and c2 simultaneously, the way that
the code makes sure only one wins is the
selgen field manipulation in dequeue:
// if sgp is stale, ignore it
if(sgp->selgen != sgp->g->selgen) {
//prints("INVALID PSEUDOG POINTER\n");
freesg(c, sgp);
goto loop;
}
// invalidate any others
sgp->g->selgen++;
but because the global lock is gone both
goroutines will be fiddling with sgp->g->selgen
at the same time.
This results in a 7% slowdown in the single threaded case for a
ping-pong microbenchmark.
Since the cas predominantly succeeds, adding a simple check first
didn't make any difference.
R=rsc
CC=golang-dev
https://golang.org/cl/180068
84 lines
1.9 KiB
Go
84 lines
1.9 KiB
Go
// $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")
|
|
}
|