Lack of thread safety in hashset causing odd exception

[borrrden]

Library Version

1.4.1

.NET Runtime

Probably all, but reported on Mono 5.8.1.0

Operating System / Device Details

macOS 10.9 (but probably all)

Log Output

During replication start, the following is output:

[Error] 2018-05-17 02:01:08.3885|SYNC (Replication): State machine error System.NullReferenceException Object reference not set to an instance of an object Boolean AddIfNotPresent(Couchbase.Lite.Auth.RemoteLogin) at System.Collections.Generic.HashSet1[T].AddIfNotPresent (T value) [0x000a3] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/external/corefx/src/System.Collections/src/System/Collections/Generic/HashSet.cs:1234 -- at System.Collections.Generic.HashSet1[T].Add (T item) [0x00000] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/external/corefx/src/System.Collections/src/System/Collections/Generic/HashSet.cs:456
at Couchbase.Lite.Auth.RemoteLogin.AttemptLogin () [0x00026] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0
at Couchbase.Lite.Replication.Login () [0x00028] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0
at Couchbase.Lite.Replication.StartInternal () [0x00248] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0
at Couchbase.Lite.Replication.m__6 (Stateless.StateMachine2+Transition[TState,TTrigger] transition) [0x00049] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0 at Stateless.StateMachine2+StateConfiguration+<>c__DisplayClass16_0[TState,TTrigger].b__0 (Stateless.StateMachine2+Transition[TState,TTrigger] t, System.Object[] args) [0x00000] in <a3b08423b2ad4653acb40d40eae11cb5>:0 at Stateless.StateMachine2+StateRepresentation[TState,TTrigger].ExecuteEntryActions (Stateless.StateMachine2+Transition[TState,TTrigger] transition, System.Object[] entryArgs) [0x00031] in <a3b08423b2ad4653acb40d40eae11cb5>:0 at Stateless.StateMachine2+StateRepresentation[TState,TTrigger].Enter (Stateless.StateMachine2+Transition[TState,TTrigger] transition, System.Object[] entryArgs) [0x00040] in <a3b08423b2ad4653acb40d40eae11cb5>:0 at Stateless.StateMachine2[TState,TTrigger].InternalFire (TTrigger trigger, System.Object[] args) [0x00092] in :0
at Stateless.StateMachine2[TState,TTrigger].Fire (TTrigger trigger) [0x00000] in <a3b08423b2ad4653acb40d40eae11cb5>:0 at Couchbase.Lite.Replication+<FireTrigger>c__AnonStorey0.<>m__0 () [0x00036] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0 at System.Threading.Tasks.Task.InnerInvoke () [0x0000f] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/Tasks/Task.cs:2879 at System.Threading.Tasks.Task.Execute () [0x00010] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/Tasks/Task.cs:2502 [Error] 2018-05-17 02:01:08.3885\|SYNC (Replication): State machine error System.NullReferenceException Object reference not set to an instance of an object Boolean AddIfNotPresent(Couchbase.Lite.Auth.RemoteLogin) at System.Collections.Generic.HashSet1[T].AddIfNotPresent (T value) [0x000a3] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/external/corefx/src/System.Collections/src/System/Collections/Generic/HashSet.cs:1234
at System.Collections.Generic.HashSet1[T].Add (T item) [0x00000] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/external/corefx/src/System.Collections/src/System/Collections/Generic/HashSet.cs:456 at Couchbase.Lite.Auth.RemoteLogin.AttemptLogin () [0x00026] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0 at Couchbase.Lite.Replication.Login () [0x00028] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0 at Couchbase.Lite.Replication.StartInternal () [0x00248] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0 at Couchbase.Lite.Replication.<InitializeStateMachine>m__6 (Stateless.StateMachine2+Transition[TState,TTrigger] transition) [0x00049] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0
at Stateless.StateMachine2+StateConfiguration+<>c__DisplayClass16_0[TState,TTrigger].<OnEntry>b__0 (Stateless.StateMachine2+Transition[TState,TTrigger] t, System.Object[] args) [0x00000] in :0
at Stateless.StateMachine2+StateRepresentation[TState,TTrigger].ExecuteEntryActions (Stateless.StateMachine2+Transition[TState,TTrigger] transition, System.Object[] entryArgs) [0x00031] in :0
at Stateless.StateMachine2+StateRepresentation[TState,TTrigger].Enter (Stateless.StateMachine2+Transition[TState,TTrigger] transition, System.Object[] entryArgs) [0x00040] in :0
at Stateless.StateMachine2[TState,TTrigger].InternalFire (TTrigger trigger, System.Object[] args) [0x00092] in <a3b08423b2ad4653acb40d40eae11cb5>:0 at Stateless.StateMachine2[TState,TTrigger].Fire (TTrigger trigger) [0x00000] in :0
at Couchbase.Lite.Replication+c__AnonStorey0.<>m__0 () [0x00036] in <8a7a2fbeb3164f1184a2d5f7a86f5163>:0
at System.Threading.Tasks.Task.InnerInvoke () [0x0000f] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/Tasks/Task.cs:2879
at System.Threading.Tasks.Task.Execute () [0x00010] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/Tasks/Task.cs:2502

Expected behavior

No exception

Actual behavior

The above exception

Steps To Reproduce

Still unclear, report from CBSE 5561

Reproduction Project