Ensure Process.ProcessName doesn't change when setting Thread.Name on Linux

src/coreclr/src/pal/src/thread/thread.cpp

@@ -1641,6 +1641,13 @@ CorUnix::InternalSetThreadDescription(
 
     pTargetThread->Lock(pThread);
 
+    // Ignore requests to set the main thread name because
+    // it causes the value returned by Process.ProcessName to change.
+    if ((pid_t)pTargetThread->GetThreadId() == getpid())
+    {
+        goto InternalSetThreadDescriptionExit;
+    }
+
     /* translate the wide char lpThreadDescription string to multibyte string */
     nameSize = WideCharToMultiByte(CP_ACP, 0, lpThreadDescription, -1, NULL, 0, NULL, NULL);
 

src/libraries/System.Threading.Thread/tests/ThreadTests.cs

@@ -647,6 +647,20 @@ public static void NameTest()
             });
         }
 
+        [Fact]
+        public static void ThreadNameDoesNotAffectProcessName()
+        {
+            // On Linux, changing the main thread name affects ProcessName.
+            // To avoid that, .NET ignores requests to change the main thread name.
+            RemoteExecutor.Invoke(() =>
+            {
+                const string ThreadName = "my-thread";
+                Thread.CurrentThread.Name = ThreadName;
+                Assert.Equal(ThreadName, Thread.CurrentThread.Name);
+                Assert.NotEqual(ThreadName, Process.GetCurrentProcess().ProcessName);
+            }).Dispose();
+        }
+
         [Fact]
         public static void PriorityTest()
         {

src/mono/mono/utils/mono-threads-posix.c

@@ -282,6 +282,15 @@ mono_native_thread_set_name (MonoNativeThreadId tid, const char *name)
 	if (tid != mono_native_thread_id_get ())
 		return;
 
+#if defined(__linux__)
+	/*
+	 * Ignore requests to set the main thread name because
+	 * it causes the value returned by Process.ProcessName to change.
+	 */
+	if (tid == (guint64)getpid ())
+		return;
+#endif
+
 	if (!name) {
 		pthread_setname_np ("");
 	} else {