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  1. Go Driver
  2. GODRIVER-1301

Data race around topology subscription

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 1.1.0
    • 1.1.2
    • Core API
    • None

    Description

      We have a simple goroutine that subscribes to the topology and then prints some log messages each time it receives an update. One of our tests caught a data race:

      03:48:08 Read at 0x00c00153a000 by goroutine 301:
      Our code that does "for toplogy := range subscription.C { ... }" and logs details of topology.
       
      03:48:08 Previous write at 0x00c00153a000 by goroutine 130:
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/description.(*serverSorter).Swap()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/description/topology.go:133 +0x149
      03:48:08   sort.medianOfThree()
      03:48:08       GOROOT/src/sort/sort.go:77 +0x14b
      03:48:08   sort.doPivot()
      03:48:08       GOROOT/src/sort/sort.go:105 +0x9b
      03:48:08   sort.quickSort()
      03:48:08       GOROOT/src/sort/sort.go:190 +0xa7
      03:48:08   sort.Sort()
      03:48:08       GOROOT/src/sort/sort.go:218 +0x8a
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/description.DiffTopology()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/description/topology.go:48 +0xba
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Topology).apply()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/topology.go:540 +0x365
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Topology).addServer.func1()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/topology.go:578 +0xf8
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Server).updateDescription()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/server.go:431 +0x345
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Server).update()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/server.go:381 +0x2cc
       
      03:48:08 Goroutine 130 (running) created at:
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Server).Connect()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/server.go:170 +0x160
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.ConnectServer()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/server.go:113 +0x9d
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Topology).addServer()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/topology.go:580 +0x181
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Topology).apply()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/topology.go:554 +0x5e9
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Topology).addServer.func1()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/topology.go:578 +0xf8
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Server).updateDescription()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/server.go:431 +0x345
      03:48:08   go.mongodb.org/mongo-driver/x/mongo/driver/topology.(*Server).update()
      03:48:08       external/org_mongodb_go_mongo_driver/x/mongo/driver/topology/server.go:381 +0x2cc
      

      I think what's happening is that Topology.apply is calling description.DiffTopology, which sorts in-place, on t.fsm.Topology, but it's still the case that a previous topology subscriber (i.e. our code) is running, presumably in response to a previous topology update. It feels like a bug that description.DiffTopology sorts in-place, though I don't think changing that would be sufficient, since fsm.go itself mutates Servers as well.

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            isabella.siu@mongodb.com Isabella Siu (Inactive)
            bartle David Bartley
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              Updated:
              Resolved: