[Lldb-commits] [lldb] 158434a - [lldb][windows] use a marker to drain the ConPTY's init sequence (#191472)

[via lldb-commits]

Author: Charles Zablit
Date: 2026-04-15T17:57:28+01:00
New Revision: 158434ae5e2d6bece6db4a1447eee2df6380321b

URL: https://github.com/llvm/llvm-project/commit/158434ae5e2d6bece6db4a1447eee2df6380321b
DIFF: https://github.com/llvm/llvm-project/commit/158434ae5e2d6bece6db4a1447eee2df6380321b.diff

LOG: [lldb][windows] use a marker to drain the ConPTY's init sequence (#191472)

This patch improves the ConPTY method that drains the init sequence. It
uses a string marker to ensure that the init sequence has been received.
The previous implementation was prone to race condition, because the
method could return before all the init sequence was received.

This only seems to reproduce on windows-server-2019.

Added: 
    

Modified: 
    lldb/source/Host/windows/PseudoConsole.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Host/windows/PseudoConsole.cpp b/lldb/source/Host/windows/PseudoConsole.cpp
index bf11a08cc1b85..ef6f17771fc34 100644
--- a/lldb/source/Host/windows/PseudoConsole.cpp
+++ b/lldb/source/Host/windows/PseudoConsole.cpp
@@ -252,7 +252,10 @@ llvm::Error PseudoConsole::DrainInitSequences() {
         std::error_code(GetLastError(), std::system_category()),
         "Failed to get the 'COMSPEC' environment variable");
 
-  std::wstring cmdline_str = std::wstring(comspec) + L" /c cls";
+  static constexpr char s_drain_marker[] = "LLDB_CONPTY_DRAIN_DONE";
+  static constexpr wchar_t s_drain_marker_w[] = L"LLDB_CONPTY_DRAIN_DONE";
+  std::wstring cmdline_str =
+      std::wstring(comspec) + L" /c echo " + s_drain_marker_w;
   std::vector<wchar_t> cmdline(cmdline_str.begin(), cmdline_str.end());
   cmdline.push_back(L'\0');
 
@@ -272,12 +275,17 @@ llvm::Error PseudoConsole::DrainInitSequences() {
   OVERLAPPED ov = {};
   ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
 
-  DWORD read;
+  DWORD read = 0;
   ReadFile(m_conpty_output, buf, sizeof(buf), &read, &ov);
 
   WaitForSingleObject(pi.hProcess, INFINITE);
 
-  if (GetOverlappedResult(m_conpty_output, &ov, &read, FALSE) && read > 0) {
+  std::string accumulated;
+  while (GetOverlappedResult(m_conpty_output, &ov, &read, /*bWait=*/TRUE) &&
+         read > 0) {
+    accumulated.append(buf, read);
+    if (accumulated.find(s_drain_marker) != std::string::npos)
+      break;
     ResetEvent(ov.hEvent);
     ReadFile(m_conpty_output, buf, sizeof(buf), &read, &ov);
   }