[Lldb-commits] [lldb] [lldb-dap] Fix mutex acquisition order for modules event. (PR #163821)

[Ebuka Ezike via lldb-commits]

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@@ -1437,7 +1437,12 @@ void DAP::EventThread() {
           const bool remove_module =
               event_mask & lldb::SBTarget::eBroadcastBitModulesUnloaded;
 
-          std::lock_guard<std::mutex> guard(modules_mutex);
+          // NOTE: Both mutexes must be acquired (API mutex first, then modules
+          // mutex) to prevent deadlock when handling `modules_request`, which
+          // also requires both locks.
+          lldb::SBMutex api_mutex = GetAPIMutex();
+          std::lock_guard api_guard(api_mutex);
+          std::lock_guard modules_guard(modules_mutex);
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da-viper wrote:

I wanted to use that but, locking two mutex with [std::scoped_lock](https://en.cppreference.com/w/cpp/thread/scoped_lock.html)  requires the mutex to implement  `Lockable` `try_lock` so we have to add it to SBMutex public api. not sure if it is something we want to support. 

https://github.com/llvm/llvm-project/pull/163821