io/ioutil: data race on blackHole #3970
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How can you be sure what happens inside a blackhole? In more seriousness, do we care? The whole point of ioutil.Discard and its devNull type is to just throw away data. I don't care if multiple goroutines are throwing away data to the same place. What are you proposing? Changing the implementation or quieting this warning somehow? |
I agree that it's not particularly harmful. But it must be quieted somehow to not fail tests. I still do not have a suppression mechanism for Go, and I do not want to introduce it. So the only option for now is changing code. I do not know how to do it, though (I understand that memory allocation is not a good option performance-wise). Another point is that if several parallel goroutines write to the same memory it is slooooooow. |
Well, in C1x it would be an Undefined Behaviour, your box catches fire and launches nuclear missles. Go Memory Model is somwhat evasive on this. I also don't see a reasonable alternative for now. Can we leave this issue in some postponed state? It must be somehow solved for ThreadSanitizer - one way or another it must not produce reports here for user tests. To date I have no special means to "suppress" some reports, that would be good to preserve. One possible future solution would be - if/when runtime Processors are commited and we have support for per-Processor caching (there are exactly GOMAXPROCS Processors), the blackhole woule be a good candidate for such caching. |
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When running: $ go test -race net/http ThreadSanitizer says: WARNING: DATA RACE Write by goroutine 205: bufio.(*Reader).Read() src/pkg/bufio/bufio.go:152 +0x4b6 io.(*LimitedReader).Read() src/pkg/io/io.go:406 +0x181 net/http.(*body).Read() src/pkg/net/http/transfer.go:538 +0xd4 io/ioutil.devNull.ReadFrom() src/pkg/io/ioutil/ioutil.go:138 +0x6f io/ioutil.devNull.ReadFrom·i() src/pkg/io/ioutil/ioutil.go:0 +0x52 io.Copy() src/pkg/io/io.go:352 +0xc6 net/http.(*body).Close() src/pkg/net/http/transfer.go:628 +0x170 net/http.(*bodyEOFSignal).Close() src/pkg/net/http/transport.go:817 +0xb9 net/http_test.func·082() src/pkg/net/http/transport_test.go:428 +0xb7 Previous write by goroutine 111: bufio.(*Reader).Read() src/pkg/bufio/bufio.go:152 +0x4b6 io.(*LimitedReader).Read() src/pkg/io/io.go:406 +0x181 net/http.(*body).Read() src/pkg/net/http/transfer.go:538 +0xd4 io/ioutil.devNull.ReadFrom() src/pkg/io/ioutil/ioutil.go:138 +0x6f io/ioutil.devNull.ReadFrom·i() src/pkg/io/ioutil/ioutil.go:0 +0x52 io.Copy() src/pkg/io/io.go:352 +0xc6 net/http.(*body).Close() src/pkg/net/http/transfer.go:628 +0x170 net/http.(*bodyEOFSignal).Close() src/pkg/net/http/transport.go:817 +0xb9 net/http_test.func·082() src/pkg/net/http/transport_test.go:428 +0xb7 Goroutine 205 (running) created at: net/http_test.TestStressSurpriseServerCloses() src/pkg/net/http/transport_test.go:432 +0x369 testing.tRunner() src/pkg/testing/testing.go:297 +0xc9 Goroutine 111 (running) created at: net/http_test.TestStressSurpriseServerCloses() src/pkg/net/http/transport_test.go:432 +0x369 testing.tRunner() src/pkg/testing/testing.go:297 +0xc9 When devNull is used all goroutines write to the single blackHole slice. The race aside, it has performance implications when several parallel goroutines write the same memory.The text was updated successfully, but these errors were encountered: