[Lldb-commits] [lldb] [lldb][windows] fix a race condition in IO reader thread (PR #194422)

[Charles Zablit via lldb-commits]

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@@ -740,9 +740,39 @@ ProcessWindows::OnDebugException(bool first_chance,
     return ExceptionResult::SendToApplication;
   }
 
+  // Drain any in-flight process output before announcing the stop. The I/O
+  // reader thread and this debug-event thread run concurrently. Without
+  // synchronization the eBroadcastBitStateChanged(Stopped) event can reach
+  // the Debugger event thread before the preceding eBroadcastBitSTDOUT
+  // events.
+  auto drain_stdout = [this] {
+    if (!m_stdio_communication.ReadThreadIsRunning())
+      return;
+    m_stdio_communication.SynchronizeWithReadThread();
+    if (!m_pty || m_pty->GetMode() != PseudoConsole::Mode::ConPTY)
+      return;
+
+    HANDLE pipe = m_pty->GetSTDOUTHandle();
+    for (int consec_empty = 0; consec_empty < 3;) {
+      DWORD avail = 0;
+      if (!::PeekNamedPipe(pipe, nullptr, 0, nullptr, &avail, nullptr))
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charles-zablit wrote:

Not reading, only peeking the pipe, which is thread safe. I added a comment.

https://github.com/llvm/llvm-project/pull/194422