[lldb-dap] Fixing a race during disconnect.

[ashgti]

While attempting to disconnect the DAP transport reader thread is setting
disconnecting as soon as it sees a disconnect request.

However, if it is processing another request when this disconnect arrives the DAP::Loop handler may exit the loop without replying to the disconnect request.

There has been some instability on the CI jobs due to this race, for example https://lab.llvm.org/buildbot/#/builders/59/builds/16076

To address this, ensure we only return from DAP::Loop once we've emptied the queue.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: John Harrison (ashgti)

Changes

While attempting to disconnect the DAP transport reader thread is setting
disconnecting as soon as it sees a disconnect request.

However, if it is processing another request when ths disconnect arrives the DAP::Loop handler may exit the loop without replying to the disconnect request.

There has been some instability on the CI jobs due to this race, for example https://lab.llvm.org/buildbot/#/builders/59/builds/16076

To address this, ensure we only return from DAP::Loop once we've emptied the queue.

---

Full diff: https://github.com/llvm/llvm-project/pull/135872.diff

1 Files Affected:

• (modified) lldb/tools/lldb-dap/DAP.cpp (+1-1)

diff --git a/lldb/tools/lldb-dap/DAP.cpp b/lldb/tools/lldb-dap/DAP.cpp
index b752e9cfaeb85..597fe3a1e323b 100644
--- a/lldb/tools/lldb-dap/DAP.cpp
+++ b/lldb/tools/lldb-dap/DAP.cpp
@@ -921,7 +921,7 @@ llvm::Error DAP::Loop() {
     StopEventHandlers();
   });
 
-  while (!disconnecting) {
+  while (!disconnecting || !m_queue.empty()) {
     std::unique_lock<std::mutex> lock(m_queue_mutex);
     m_queue_cv.wait(lock, [&] { return disconnecting || !m_queue.empty(); });