[lldb] [llvm] [lldb-dap] Add multi-session support with shared debugger instances (PR #163653)

[John Harrison via llvm-commits]

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+//===-- DAPSessionManager.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_TOOLS_LLDB_DAP_DAPSESSIONMANAGER_H
+#define LLDB_TOOLS_LLDB_DAP_DAPSESSIONMANAGER_H
+
+#include "lldb/API/SBBroadcaster.h"
+#include "lldb/API/SBDebugger.h"
+#include "lldb/API/SBTarget.h"
+#include "lldb/Host/MainLoop.h"
+#include "lldb/lldb-types.h"
+#include "llvm/Support/Error.h"
+#include <condition_variable>
+#include <map>
+#include <memory>
+#include <mutex>
+#include <optional>
+#include <thread>
+#include <vector>
+
+namespace lldb_dap {
+
+// Forward declarations
+struct DAP;
+
+class ManagedEventThread {
+public:
+  // Constructor declaration
+  ManagedEventThread(lldb::SBBroadcaster broadcaster, std::thread t);
+
+  ~ManagedEventThread();
+
+  ManagedEventThread(const ManagedEventThread &) = delete;
+  ManagedEventThread &operator=(const ManagedEventThread &) = delete;
+
+private:
+  lldb::SBBroadcaster m_broadcaster;
+  std::thread m_event_thread;
+};
+
+/// Global DAP session manager that manages multiple concurrent DAP sessions in
+/// a single lldb-dap process. Handles session lifecycle tracking, coordinates
+/// shared debugger event threads, and facilitates target handoff between
+/// sessions for dynamically created targets.
+class DAPSessionManager {
+public:
+  /// Get the singleton instance of the DAP session manager.
+  static DAPSessionManager &GetInstance();
+
+  /// Register a DAP session.
+  void RegisterSession(lldb_private::MainLoop *loop, DAP *dap);
+
+  /// Unregister a DAP session. Called by sessions when they complete their
+  /// disconnection, which unblocks WaitForAllSessionsToDisconnect().
+  void UnregisterSession(lldb_private::MainLoop *loop);
+
+  /// Get all active DAP sessions.
+  std::vector<DAP *> GetActiveSessions();
+
+  /// Disconnect all registered sessions by calling Disconnect() on
+  /// each and requesting their event loops to terminate. Used during
+  /// shutdown to force all sessions to begin disconnecting.
+  void DisconnectAllSessions();
+
+  /// Block until all sessions disconnect and unregister. Returns an error if
+  /// DisconnectAllSessions() was called and any disconnection failed.
+  llvm::Error WaitForAllSessionsToDisconnect();
+
+  /// Store a target for later retrieval by another session.
+  void StoreTargetById(uint32_t target_id, lldb::SBTarget target);
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ashgti wrote:

I'm not sure I understand this part, why do we need to store them separately and the `TakeTargetById`, why does that remove them from the list of targets?

https://github.com/llvm/llvm-project/pull/163653