trace2: write exit event

Add TRACE2 exit event, following the pattern established with the version
and start events.

src/shared/Core/Trace2.cs

@@ -22,6 +22,8 @@ public enum Trace2Event
     Version = 0,
     [EnumMember(Value = "start")]
     Start = 1,
+    [EnumMember(Value = "exit")]
+    Exit = 2
 }
 
 public class Trace2Settings
@@ -49,6 +51,16 @@ public interface ITrace2 : IDisposable
         string appPath,
         [System.Runtime.CompilerServices.CallerFilePath] string filePath = "",
         [System.Runtime.CompilerServices.CallerLineNumber] int lineNumber = 0);
+
+    /// <summary>
+    /// Shut down TRACE2 tracing by writing Exit event and disposing of writers.
+    /// </summary>
+    /// <param name="exitCode">The exit code of the GCM application.</param>
+    /// <param name="filePath">Path of the file this method is called from.</param>
+    /// <param name="lineNumber">Line number of file this method is called from.</param>
+    void Stop(int exitCode,
+        [System.Runtime.CompilerServices.CallerFilePath] string filePath = "",
+        [System.Runtime.CompilerServices.CallerLineNumber] int lineNumber = 0);
 }
 
 public class Trace2 : DisposableObject, ITrace2
@@ -93,6 +105,12 @@ public Trace2(IEnvironment environment, Trace2Settings settings, string[] argv,
         WriteStart(appPath, filePath, lineNumber);
     }
 
+    public void Stop(int exitCode, string filePath, int lineNumber)
+    {
+        WriteExit(exitCode, filePath, lineNumber);
+        ReleaseManagedResources();
+    }
+
     protected override void ReleaseManagedResources()
     {
         lock (_writersLock)
@@ -233,6 +251,22 @@ private void TryParseSettings(TextWriter error, IFileSystem fileSystem)
         });
     }
 
+    private void WriteExit(int code, string filePath = "", int lineNumber = 0)
+    {
+        EnsureArgument.NotNull(code, nameof(code));
+
+        WriteMessage(new ExitMessage()
+        {
+            Event = Trace2Event.Exit,
+            Sid = _sid,
+            Time = DateTimeOffset.Now,
+            File = Path.GetFileName(filePath).ToLower(),
+            Line = lineNumber,
+            Code = code,
+            ElapsedTime = (DateTimeOffset.UtcNow - _applicationStartTime).TotalSeconds
+        });
+    }
+
     private void AddWriter(ITrace2Writer writer)
     {
         ThrowIfDisposed();
@@ -362,3 +396,27 @@ public override string ToNormalString()
         return BuildNormalString(string.Join(" ", Argv));
     }
 }
+
+public class ExitMessage : Trace2Message
+{
+    [JsonProperty("t_abs", Order = 7)]
+    public double ElapsedTime { get; set; }
+
+    [JsonProperty("code", Order = 8)]
+    public int Code { get; set; }
+
+    public override string ToJson()
+    {
+        return JsonConvert.SerializeObject(this,
+            new StringEnumConverter(),
+            new IsoDateTimeConverter()
+            {
+                DateTimeFormat = TimeFormat
+            });
+    }
+
+    public override string ToNormalString()
+    {
+        return BuildNormalString($"elapsed:{ElapsedTime} code:{Code}");
+    }
+}

src/shared/Git-Credential-Manager/Program.cs

@@ -75,6 +75,7 @@ public static void Main(string[] args)
                                   .GetAwaiter()
                                   .GetResult();
 
+                context.Trace2.Stop(exitCode);
                 Environment.Exit(exitCode);
             }
         }

src/shared/TestInfrastructure/Objects/NullTrace.cs

@@ -59,6 +59,8 @@ public class NullTrace2 : ITrace2
             string filePath = "",
             int lineNumber = 0) { }
 
+        public void Stop(int exitCode, string fileName, int lineNumber) { }
+
         #endregion
 
         #region IDisposable