trace2: capture thread name

With the upcoming introduction of regions, we will need to capture thread
names. This change adds a new static BuildThreadName() method that defines
a thread name by:

1. Determining if it is the entry thread and, if so, calling it "main",
per Trace2 convention.
2. If it's not the main thread, determining whether it is a thread pool
thread and naming it with a static prefix and the thread pool thread id.
3. If it is not the entry thread or a thread pool thread, use the thread
name, if it has one.
4. Return an empty string if none of the above are true.

Author: ldennington

src/shared/Core/Trace2.cs

@@ -3,6 +3,7 @@
 using System.IO;
 using System.IO.Pipes;
 using System.Text;
+using System.Threading;
 
 namespace GitCredentialManager;
 
@@ -114,6 +115,7 @@ void WriteChildStart(DateTimeOffset startTime,
     /// <param name="pid">Id of exiting process.</param>
     /// <param name="code">Process exit code.</param>
     /// <param name="sid">The child process's session id.</param>
+    /// <param name="threadName">Name of the currently-executing thread.</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 WriteChildExit(
@@ -182,7 +184,7 @@ public void Initialize(DateTimeOffset startTime)
     public void Start(string appPath,
         string[] args,
         string filePath,
-        int lineNumber)
+        int lineNumber = 0)
     {
         if (!AssemblyUtils.TryGetAssemblyVersion(out string version))
         {
@@ -233,6 +235,7 @@ public void WriteChildStart(DateTimeOffset startTime,
             Event = Trace2Event.ChildStart,
             Sid = _sid,
             Time = startTime,
+            Thread = BuildThreadName(),
             File = Path.GetFileName(filePath),
             Line = lineNumber,
             Id = ++_childProcCounter,
@@ -265,6 +268,7 @@ public void WriteChildExit(
             Event = Trace2Event.ChildExit,
             Sid = _sid,
             Time = DateTimeOffset.UtcNow,
+            Thread = BuildThreadName(),
             File = Path.GetFileName(filePath),
             Line = lineNumber,
             Id = _childProcCounter,
@@ -296,6 +300,7 @@ public void WriteError(
             Event = Trace2Event.Error,
             Sid = _sid,
             Time = DateTimeOffset.UtcNow,
+            Thread = BuildThreadName(),
             File = Path.GetFileName(filePath),
             Line = lineNumber,
             Message = errorMessage,
@@ -389,6 +394,7 @@ private void WriteVersion(
             Event = Trace2Event.Version,
             Sid = _sid,
             Time = DateTimeOffset.UtcNow,
+            Thread = BuildThreadName(),
             File = Path.GetFileName(filePath),
             Line = lineNumber,
             Evt = eventFormatVersion,
@@ -418,6 +424,7 @@ private void WriteStart(
             Event = Trace2Event.Start,
             Sid = _sid,
             Time = DateTimeOffset.UtcNow,
+            Thread = BuildThreadName(),
             File = Path.GetFileName(filePath),
             Line = lineNumber,
             Argv = argv,
@@ -434,6 +441,7 @@ private void WriteExit(int code, string filePath = "", int lineNumber = 0)
             Event = Trace2Event.Exit,
             Sid = _sid,
             Time = DateTimeOffset.UtcNow,
+            Thread = BuildThreadName(),
             File = Path.GetFileName(filePath),
             Line = lineNumber,
             Code = code,
@@ -480,4 +488,28 @@ private void WriteMessage(Trace2Message message)
             }
         }
     }
+
+    private static string BuildThreadName()
+    {
+        // If this is the entry thread, call it "main", per Trace2 convention
+        if (Thread.CurrentThread.ManagedThreadId == 0)
+        {
+            return "main";
+        }
+
+        // If this is a thread pool thread, name it as such
+        if (Thread.CurrentThread.IsThreadPoolThread)
+        {
+            return $"thread_pool_{Environment.CurrentManagedThreadId}";
+        }
+
+        // Otherwise, if the thread is named, use it!
+        if (!string.IsNullOrEmpty(Thread.CurrentThread.Name))
+        {
+            return Thread.CurrentThread.Name;
+        }
+
+        // We don't know what this thread is!
+        return string.Empty;
+    }
 }

src/shared/Core/Trace2Message.cs

@@ -32,9 +32,8 @@ public abstract class Trace2Message : ITrace2Message
     [JsonProperty("sid")]
     public string Sid { get; set; }
 
-    // TODO: Remove this default value when TRACE2 regions are introduced.
     [JsonProperty("thread")]
-    public string Thread { get; set; } = "main";
+    public string Thread { get; set; }
 
     [JsonProperty("time")]
     public DateTimeOffset Time { get; set; }

src/shared/TestInfrastructure/Objects/NullTrace.cs

@@ -78,13 +78,11 @@ public void WriteChildExit(
             string filePath = "",
             int lineNumber = 0) { }
 
-        public void WriteError(string errorMessage,
+        public void WriteError(
+            string errorMessage,
             string parameterizedMessage = null,
             string filePath = "",
-            int lineNumber = 0)
-        { }
-
-        public string SetSid() { return ""; }
+            int lineNumber = 0) { }
 
         #endregion