Debugger doesn't always show all threads in the call stack window

[gregg-miskelly]

Environment data

VS Code version: 1.9.0-insiders (Commit 80481edbdf1272a87ca54d4c48a829e0a134dffe)
C# Extension version: 1.6.0
OS: Windows 10
CoreCLR: 1.0.1

Steps to reproduce

1. Hit F5 on the following program
2. After it has been running for a few seconds, set a breakpoint on the sleep call in Main
3. After the breakpoint hits, look at the call stack Window

    static void Main(string[] args)
    {
        new Thread(SleepThread).Start();

        while (true)
        {
            Thread.Sleep(100);
        }
    }

    private static void SleepThread(object obj)
    {
        while (true)
        {
            Thread.Sleep(100);
        }
    }

Expected behavior

Both threads shown

Actual behavior

Only the main thread is show

Tracing

We do have the issue that we don't return the threads from run mode, but once we hit break mode we are returning the correct set of threads.

C threads: null
R: {"success":true,"message":null,"request_seq":15,"command":"threads","body":{"threads":[]},"running":false,"refs":null,"seq":0,"type":"response"}
E breakpoint: {"reason":"changed","breakpoint":{"id":2,"verified":true,"line":12,"message":null},"type":"breakpoint"}
E stopped: {"threadId":64072,"reason":"breakpoint","source":{"name":"Program.cs","path":"d:\proj\clicon\Program.cs","sourceReference":0},"line":12,"column":13,"text":null,"allThreadsStopped":true,"type":"stopped"}
C threads: null
R: {"success":true,"message":null,"request_seq":16,"command":"threads","body":{"threads":[{"id":64072,"name":"Main Thread"},{"id":41420,"name":""}]},"running":false,"refs":null,"seq":0,"type":"response"}
C stackTrace: {"threadId":64072,"startFrame":0,"levels":20}
R: {"success":true,"message":null,"request_seq":17,"command":"stackTrace","body":{"stackFrames":[{"id":1000,"source":{"name":"Program.cs","path":"d:\proj\clicon\Program.cs","sourceReference":0},"line":12,"column":13,"name":"Program.Main(string[] args)"},{"id":1001,"source":null,"line":0,"column":0,"name":"[External Code]"}],"totalFrames":2},"running":false,"refs":null,"seq":0,"type":"response"}
C scopes: {"frameId":1000}
E output: {"category":"telemetry","output":"VS/Diagnostics/Debugger/ExpressionEvaluator/Compile","data":{"VS.Diagnostics.Debugger.ExpressionEvaluator.Compile.CompilerError":"None","VS.Diagnostics.Debugger.ExpressionEvaluator.Language":"C#","VS.Diagnostics.Debugger.clrdbg.Version":"15.0.26013.0 built by: PREVIEW.DBG2","VS.Diagnostics.Debugger.clrdbg.OSFamily":"Windows","VS.Diagnostics.Debugger.clrdbg.WindowsVersion":"10.0.14393"},"type":"output"}
R: {"success":true,"message":null,"request_seq":18,"command":"scopes","body":{"scopes":[{"name":"Locals","variablesReference":1000,"expensive":false}]},"running":false,"refs":null,"seq":0,"type":"response"}
C variables: {"variablesReference":1000}
R: {"success":true,"message":null,"request_seq":19,"command":"variables","body":{"variables":[{"name":"args [string[]]","value":"{string[0]}","type":"string[]","variablesReference":0,"evaluateName":"args"}]},"running":false,"refs":null,"seq":0,"type":"response"}