[Lldb-commits] [lldb] New ThreadPlanSingleThreadTimeout to resolve potential deadlock in single thread stepping (PR #90930)

[via lldb-commits]

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@@ -0,0 +1,93 @@
+//===-- ThreadPlanSingleThreadTimeout.h -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_TARGET_THREADPLANSINGLETHREADTIMEOUT_H
+#define LLDB_TARGET_THREADPLANSINGLETHREADTIMEOUT_H
+
+#include "lldb/Target/Thread.h"
+#include "lldb/Target/ThreadPlan.h"
+#include "lldb/Utility/Event.h"
+#include "lldb/Utility/LLDBLog.h"
+#include "lldb/Utility/State.h"
+
+#include <thread>
+
+namespace lldb_private {
+
+//
+// Thread plan used by single thread execution to issue timeout. This is useful
+// to detect potential deadlock in single thread execution. The timeout measures
+// the elapsed time from the last internal stop and got reset by each internal
+// stops to ensure we are accurately detecting execution not moving forward.
+// This means this thread plan  can be created/destroyed multiple times by the
+// parent execution plan.
+//
+// When timeout happens, the thread plan resolves the potential deadlock by
+// issuing a thread specific async interrupt to enter stop state, then all
+// threads execution are resumed to resolve the potential deadlock.
+//
+class ThreadPlanSingleThreadTimeout : public ThreadPlan {
+public:
+  ~ThreadPlanSingleThreadTimeout() override;
+
+  // Create a new instance from fresh new state.
+  static void CreateNew(Thread &thread);
+  // Reset and create a new instance from the previous state.
+  static void ResetFromPrevState(Thread &thread);
+
+  void GetDescription(Stream *s, lldb::DescriptionLevel level) override;
+  bool ValidatePlan(Stream *error) override { return true; }
+  bool WillStop() override;
+  void DidPop() override;
+
+  bool DoPlanExplainsStop(Event *event_ptr) override;
+
+  lldb::StateType GetPlanRunState() override;
+  static void TimeoutThreadFunc(ThreadPlanSingleThreadTimeout *self);
+
+  bool MischiefManaged() override;
+
+  bool ShouldStop(Event *event_ptr) override;
+  void SetStopOthers(bool new_value) override;
+  bool StopOthers() override;
+
+private:
+  ThreadPlanSingleThreadTimeout(Thread &thread);
+
+  static bool IsAlive();
+
+  enum class State {
+    WaitTimeout,    // Waiting for timeout.
+    AsyncInterrupt, // Async interrupt has been issued.
+    Done,           // Finished resume all threads.
+  };
+
+  static std::mutex s_mutex;
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jeffreytan81 wrote:

This is a good point. I was storing some static states so that we can ensure: 
1. Singleton (only one ThreadPlanSingleThreadTimeout is alive/used anytime). 
2. If there is ever a race that, the `ThreadPlanSingleThreadTimeout` is in `State::AsyncInterrupt` but it got popped by another internal stop before async interrupt received. I want to remember the previous/last state, and the newly created `ThreadPlanSingleThreadTimeout` can be re-created from previous state.

Instead, I will look into storing these static states into parent controlling ThreadPlan (ThreadPlanStepOverRange in this case).

https://github.com/llvm/llvm-project/pull/90930