Use a different lock to manage breakpointStore

Fixes VSTS 1026591
SigTerm signal in Mono.Debugging.dll!Mono.Debugging.Client.DebuggerSession::get_Breakpoints+9

`slock` is used throughout DebuggerSession, however in this case we only need to guard against
multiple threads assigning an instance of BreakpointStore. Also, since BreakpointStore is thread-safe
we can remove the additional locks around it where we lock on enumeration of `breakpointStore`.

This fixes the case where one thread dispatches an OnExit (for example) which tries communicate
with the debuggee and waits on data from the socket and another thread attempts to clean up breakpoints.

1 files changed, 190 insertions, 0 deletions

diff --git a/UnitTests/Mono.Debugging.Tests/Shared/DebuggerSessionTests.cs b/UnitTests/Mono.Debugging.Tests/Shared/DebuggerSessionTests.cs
new file mode 100644
index 0000000..ac8d1c7
--- /dev/null
+++ b/UnitTests/Mono.Debugging.Tests/Shared/DebuggerSessionTests.cs
@@ -0,0 +1,190 @@
+// 
+// DebuggerSessionTests.cs
+//  
+// Author:
+//       Greg Munn <gregm@microsoft.com>
+// 
+// Copyright (c) 2019 Microsoft
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Mono.Debugging.Client;
+
+using NUnit.Framework;
+
+namespace Mono.Debugging.Tests
+{
+	[TestFixture]
+	public class DebuggerSessionTests
+	{
+		TestDebuggerSession session;
+
+		[TestFixtureSetUp]
+		public virtual void SetUp ()
+		{
+			session = new TestDebuggerSession ();
+		}
+
+		[TestFixtureTearDown]
+		public virtual void TearDown ()
+		{
+			session.Dispose ();
+		}
+
+		[Test]
+#pragma warning disable VSTHRD200 // Use "Async" suffix for async methods
+		public async Task WhenQueryigBreakpoints_ThenDoNotDeadlockDispatchedMethods()
+#pragma warning restore VSTHRD200 // Use "Async" suffix for async methods
+		{
+			// thread 1 cancels debugging, which triggers hot reload to clear breakpoints 
+			// thread 2 dispatches the OnExit method which is call via Dispatch and uses the same lock
+
+			var thread1 = new TaskCompletionSource<bool> ();
+			Task thread2 = null;
+
+			session.HandleOnExit = () => {
+				// we are on a background thread via session.Dispatch
+				thread2 = Task.Run (() => {
+					var bk = session.Breakpoints;
+					thread1.TrySetResult (true);
+				});
+
+				// mimic the cause of the deadlock by waiting here for a while
+				// we don't really want to deadlock, just long enough that we should have
+				// completed the call to breakpoints first.
+				Thread.Sleep (1000);
+
+				thread1.TrySetResult (false);
+			};
+
+			session.Exit ();
+
+			var result= await thread1.Task;
+			await thread2;
+
+			Assert.IsTrue (result, "the call to get breakpoints should have completed first");
+		}
+
+		class TestDebuggerSession : DebuggerSession
+		{
+			public Action HandleOnExit;
+
+			protected override void OnAttachToProcess (long processId)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnContinue ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnDetach ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnEnableBreakEvent (BreakEventInfo eventInfo, bool enable)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnExit ()
+			{
+				// this is called in dispatch
+				HandleOnExit?.Invoke ();
+				//throw new NotImplementedException ();
+			}
+
+			protected override void OnFinish ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override ProcessInfo [] OnGetProcesses ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override Backtrace OnGetThreadBacktrace (long processId, long threadId)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override ThreadInfo [] OnGetThreads (long processId)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override BreakEventInfo OnInsertBreakEvent (BreakEvent breakEvent)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnNextInstruction ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnNextLine ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnRemoveBreakEvent (BreakEventInfo eventInfo)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnRun (DebuggerStartInfo startInfo)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnSetActiveThread (long processId, long threadId)
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnStepInstruction ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnStepLine ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnStop ()
+			{
+				throw new NotImplementedException ();
+			}
+
+			protected override void OnUpdateBreakEvent (BreakEventInfo eventInfo)
+			{
+				throw new NotImplementedException ();
+			}
+		}
+	}
+}