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Fix send on closed channel panic #140

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Fix send on closed channel panic #140

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echistyakov
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Fix send-on-closed-channel panic in blockSubscriber

Motivation:

I caught this bug while stress-testing RSocket-based Client/Server implementation in Facebook Thrift: https://github.com/facebook/fbthrift/blob/main/thrift/lib/go/thrift/stress/server_test.go

==================
WARNING: DATA RACE
Read at 0x00c0042aa1d0 by goroutine 3166913:
  runtime.chansend()
      third-party/go/1.23.4/linux_amd64/src/runtime/chan.go:171 +0x0
  github.com/rsocket/rsocket-go/rx/mono.blockSubscriber.OnError()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/block_subscriber.go:42 +0xc9
  github.com/rsocket/rsocket-go/rx/mono.(*blockSubscriber).OnError()
      <autogenerated>:1 +0x66
  github.com/jjeffcaii/reactor-go/mono.(*processorSubscriber).OnError()
      fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:195 +0x6b
  github.com/jjeffcaii/reactor-go/mono.(*processorSubscriber).OnSubscribe()
      fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:227 +0xdd
  github.com/jjeffcaii/reactor-go/mono.(*processor).SubscribeWith.func1()
      fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:119 +0x64
  github.com/panjf2000/ants/v2.(*goWorker).run.func1()
      fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/worker.go:67 +0x130

Previous write at 0x00c0042aa1d0 by goroutine 3166370:
  runtime.closechan()
      third-party/go/1.23.4/linux_amd64/src/runtime/chan.go:397 +0x0
  github.com/rsocket/rsocket-go/rx/mono.toBlock.deferwrap2()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/utils.go:173 +0x33
  runtime.deferreturn()
      third-party/go/1.23.4/linux_amd64/src/runtime/panic.go:605 +0x5d
  github.com/rsocket/rsocket-go/rx/mono.(*oneshotProxy).BlockUnsafe()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/proxy_oneshot.go:114 +0x5a
  github.com/rsocket/rsocket-go/rx/mono.(*oneshotProxy).Block()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/proxy_oneshot.go:126 +0x78
  thrift/lib/go/thrift.(*rsocketClient).RequestResponse()
      fbcode/thrift/lib/go/thrift/rocket_rsocket_client.go:148 +0x15d
  thrift/lib/go/thrift.(*rocketClient).Flush()
      fbcode/thrift/lib/go/thrift/rocket_client.go:123 +0x436
  github.com/facebook/fbthrift/thrift/lib/go/thrift/types.(*SerialChannel).sendMsg()
      fbcode/thrift/lib/go/thrift/types/serial_channel.go:61 +0x2f0
  github.com/facebook/fbthrift/thrift/lib/go/thrift/types.(*SerialChannel).Call()
      fbcode/thrift/lib/go/thrift/types/serial_channel.go:118 +0x14f
  github.com/facebook/fbthrift/thrift/lib/go/thrift/dummy.(*DummyChannelClient).Echo()
      fbcode/thrift/lib/go/thrift/dummy/svcs.go:87 +0x114
  github.com/facebook/fbthrift/thrift/lib/go/thrift/dummy.(*DummyClient).Echo()
      fbcode/thrift/lib/go/thrift/dummy/svcs.go:95 +0x6c
  thrift/lib/go/thrift/stress.runStressTest.func4()
      fbcode/thrift/lib/go/thrift/stress/server_test.go:127 +0x2cd
  golang.org/x/sync/errgroup.(*Group).Go.func1()
      fbcode/third-party-go/vendor/golang.org/x/sync/errgroup/errgroup.go:78 +0xa1

Goroutine 3166913 (running) created at:
  github.com/panjf2000/ants/v2.(*goWorker).run()
      fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/worker.go:48 +0xc4
  github.com/panjf2000/ants/v2.(*Pool).retrieveWorker()
      fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/pool.go:348 +0x384
  github.com/panjf2000/ants/v2.(*Pool).Submit()
      fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/pool.go:222 +0x67
  github.com/jjeffcaii/reactor-go/scheduler.(*elasticScheduler).Do()
      fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/scheduler/elastic.go:34 +0x56
  github.com/jjeffcaii/reactor-go/mono.(*processor).SubscribeWith()
      fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:118 +0x232
  github.com/jjeffcaii/reactor-go/mono.(*wrapper).SubscribeWith()
      <autogenerated>:1 +0x72
  github.com/rsocket/rsocket-go/rx/mono.toBlock()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/utils.go:169 +0x141
  github.com/rsocket/rsocket-go/rx/mono.(*oneshotProxy).BlockUnsafe()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/proxy_oneshot.go:114 +0x5a
  github.com/rsocket/rsocket-go/rx/mono.(*oneshotProxy).Block()
      fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/proxy_oneshot.go:126 +0x78
  thrift/lib/go/thrift.(*rsocketClient).RequestResponse()
      fbcode/thrift/lib/go/thrift/rocket_rsocket_client.go:148 +0x15d
  thrift/lib/go/thrift.(*rocketClient).Flush()
      fbcode/thrift/lib/go/thrift/rocket_client.go:123 +0x436
  github.com/facebook/fbthrift/thrift/lib/go/thrift/types.(*SerialChannel).sendMsg()
      fbcode/thrift/lib/go/thrift/types/serial_channel.go:61 +0x2f0
  github.com/facebook/fbthrift/thrift/lib/go/thrift/types.(*SerialChannel).Call()
      fbcode/thrift/lib/go/thrift/types/serial_channel.go:118 +0x14f
  github.com/facebook/fbthrift/thrift/lib/go/thrift/dummy.(*DummyChannelClient).Echo()
      fbcode/thrift/lib/go/thrift/dummy/svcs.go:87 +0x114
  github.com/facebook/fbthrift/thrift/lib/go/thrift/dummy.(*DummyClient).Echo()
      fbcode/thrift/lib/go/thrift/dummy/svcs.go:95 +0x6c
  thrift/lib/go/thrift/stress.runStressTest.func4()
      fbcode/thrift/lib/go/thrift/stress/server_test.go:127 +0x2cd
  golang.org/x/sync/errgroup.(*Group).Go.func1()
      fbcode/third-party-go/vendor/golang.org/x/sync/errgroup/errgroup.go:78 +0xa1

Goroutine 3166370 (running) created at:
  golang.org/x/sync/errgroup.(*Group).Go()
      fbcode/third-party-go/vendor/golang.org/x/sync/errgroup/errgroup.go:75 +0x15c
  thrift/lib/go/thrift/stress.runStressTest()
      fbcode/thrift/lib/go/thrift/stress/server_test.go:151 +0x77e
  thrift/lib/go/thrift/stress.TestServerStress.func1()
      fbcode/thrift/lib/go/thrift/stress/server_test.go:45 +0x2b
  testing.tRunner()
      third-party/go/1.23.4/linux_amd64/src/testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      third-party/go/1.23.4/linux_amd64/src/testing/testing.go:1743 +0x44
==================
2025/01/13 11:47:01.150080 [ants]: worker exits from panic: send on closed channel
goroutine 3161627 [running]:
runtime/debug.Stack()
        third-party/go/1.23.4/linux_amd64/src/runtime/debug/stack.go:26 +0x67
github.com/panjf2000/ants/v2.(*goWorker).run.func1.1()
        fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/worker.go:56 +0x15d
panic({0x2583a0?, 0x352ee0?})
        third-party/go/1.23.4/linux_amd64/src/runtime/panic.go:785 +0x132
github.com/rsocket/rsocket-go/rx/mono.blockSubscriber.OnError({0xc0034fe070?, 0xc0042aa150?, 0xc0042aa1c0?}, {0x3553e0, 0xc002786060})
        fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/block_subscriber.go:42 +0xca
github.com/jjeffcaii/reactor-go/mono.(*processorSubscriber).OnError(0xc002e5e040, {0x3553e0, 0xc002786060})
        fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:195 +0x6c
github.com/jjeffcaii/reactor-go/mono.(*processorSubscriber).OnSubscribe(0xc002e5e040, {0x357a68, 0xc004b00700}, {0x356f00, 0xc002e5e040})
        fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:227 +0xde
github.com/jjeffcaii/reactor-go/mono.(*processor).SubscribeWith.func1()
        fbcode/third-party-go/vendor/github.com/jjeffcaii/reactor-go/mono/processor.go:119 +0x65
github.com/panjf2000/ants/v2.(*goWorker).run.func1()
        fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/worker.go:67 +0x131
created by github.com/panjf2000/ants/v2.(*goWorker).run in goroutine 3166632
        fbcode/third-party-go/vendor/github.com/panjf2000/ants/v2/worker.go:48 +0xc5

panic: send on closed channel

goroutine 3166696 [running]:
github.com/rsocket/rsocket-go/rx/mono.blockSubscriber.OnError({0xc0019be230?, 0xc003f06070?, 0xc003f060e0?}, {0x354340, 0xad0570})
        fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/block_subscriber.go:42 +0xca
github.com/rsocket/rsocket-go/rx/mono.blockSubscriber.OnSubscribe.func1()
        fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/block_subscriber.go:64 +0x12d
created by github.com/rsocket/rsocket-go/rx/mono.blockSubscriber.OnSubscribe in goroutine 3165248
        fbcode/third-party-go/vendor/github.com/rsocket/rsocket-go/rx/mono/block_subscriber.go:61 +0x1cd

This bug is caused by a potential race condition on the following lines:

rsocket-go/rx/mono/block_subscriber.go

Lines 41 to 43 in 099cb5b

if common.SafeCloseDoneChan(b.done) {
b.echan <- err
}

  • On the above lines - done channel gets closed, and echan gets sent on.
  • The receiver will get awaken, by the done channel closing. However, it may run to completion before echan is sent on. If that happens - the receiver will close echan and the sender (blockSubscriber) will send on a closed channel - panic!

rsocket-go/rx/mono/utils.go

Lines 170 to 182 in 099cb5b

<-done
defer close(vchan)
defer close(echan)
select {
case value := <-vchan:
return value, nil
case err := <-echan:
return nil, err
default:
return nil, nil
}

Modifications:

  • Make blockSubscriber the explicit owner of all the channels (done/vchan/echan).
  • Ensure that done channel can be closed only once - by protecting it with an atomic.Bool that gets swapped to true after done is closed.
  • vchan/echan don't actually need to be closed (there is no such requirement in Go - the channels will just be garbage collected).

Result:

With this change - I was not able to reproduce this failure/panic anymore.

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@echistyakov