[Lldb-commits] [lldb] [lldb][Windows] Suspend new threads when stopped (PR #201558)

[Charles Zablit via lldb-commits]

https://github.com/charles-zablit created https://github.com/llvm/llvm-project/pull/201558

`OnCreateThread` runs from the `DebuggerThread` loop after a `CREATE_THREAD_DEBUG_EVENT`. Each iteration of that loop ends with a `ContinueDebugEvent`, which on Windows resumes every thread in the debuggee that *isn't* individually suspended with `SuspendThread`.

If a thread is created while the debuggee is stopped, all the existing threads are suspended expect the new one. After the next ContinueDebugEvent it just runs, while lldb's StateType still reads eStateStopped.

This patch suspends the new thread when the debuggee is stopped.

This fixes `TestTwoHitsOneActual.py` and `TestBreakOnLambdaCapture.py` when running the test suite with `LLDB_USE_LLDB_SERVER=1`.

rdar://178718627

>From 49968e505cae6e376625790a0926277b943be98e Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Thu, 4 Jun 2026 13:06:20 +0100
Subject: [PATCH] [lldb][Windows] Suspend new threads when stopped

---
 .../Process/Windows/Common/NativeProcessWindows.cpp  | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
index 73989f18173c9..60cd4106d9db4 100644
--- a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
+++ b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
@@ -633,6 +633,18 @@ void NativeProcessWindows::OnCreateThread(const HostThread &new_thread) {
                           wp.m_hardware);
   }
 
+  if (StateType state = GetState();
+      state == eStateStopped || state == eStateCrashed) {
+    if (Status error = thread->DoStop(); error.Fail()) {
+      Log *log = GetLog(WindowsLog::Thread);
+      LLDB_LOG(log, "failed to suspend newly-created thread {0}: {1}",
+               thread->GetID(), error);
+    }
+    ThreadStopInfo stop_info;
+    stop_info.reason = lldb::eStopReasonNone;
+    thread->SetStopReason(stop_info, "");
+  }
+
   m_threads.push_back(std::move(thread));
 }