https://github.com/qxy11 created 
https://github.com/llvm/llvm-project/pull/163653

## Summary:
This change introduces a DAPSessionManager to enable multiple DAP sessions to 
share debugger instances when needed, for things like child process debugging 
and some scripting hooks that create dynamically new targets.

Changes include:
- Add DAPSessionManager singleton to track and coordinate all active DAP 
sessions
- Support attaching to an existing target via its globally unique target ID 
(targetId parameter)
- Share debugger instances across sessions when new targets are created 
dynamically
- Refactor event thread management to allow sharing event threads between 
sessions
- Add eBroadcastBitNewTargetCreated event to notify when new targets are created
- Extract session names from target creation events
- Defer debugger initialization from 'initialize' request to 'launch'/'attach' 
requests. The only time the debugger is used currently in between its creation 
in `InitializeRequestHandler` and  the `Launch` or `Attach` requests is during 
the `TelemetryDispatcher` destruction call at the end of the 
`DAP::HandleObject` call, so this is safe.

This enables scenarios when new targets are created dynamically so that the 
debug adapter can automatically start a new debug session for the spawned 
target while sharing the debugger instance.

## Tests:
The refactoring maintains backward compatibility. All existing DAP test cases 
pass.

Also added a few basic unit tests for DAPSessionManager
```
>> ninja DAPTests
>> ./tools/lldb/unittests/DAP/DAPTests
>>./bin/llvm-lit -v ../llvm-project/lldb/test/API/tools/lldb-dap/
```


>From 5b94fa5412e8a56ee1ea1fe7e1cd8d9efddcaffb Mon Sep 17 00:00:00 2001
From: qxy11 <[email protected]>
Date: Wed, 15 Oct 2025 15:47:23 -0700
Subject: [PATCH] [lldb-dap] Add multi-session support with shared debugger
 instances

Summary:
This change introduces a DAPSessionManager to enable multiple concurrent
lldb-dap sessions and allow them to share debugger instances when needed.

Key changes:
- Add DAPSessionManager singleton to track and coordinate all active DAP 
sessions
- Support attaching to an existing target via unique target ID (targetId 
parameter)
- Share debugger instances across sessions when spawning new targets (e.g., GPU 
debugging)
- Refactor event thread management to allow sharing event threads between 
sessions
- Add eBroadcastBitNewTargetCreated event to notify when new targets are spawned
- Extract session names from target creation events for better identification
- Defer debugger initialization from 'initialize' request to 'launch'/'attach' 
requests

This enables scenarios where a native process spawns a new target (like a child 
process)
and the debug adapter can automatically start a new debug session for the 
spawned
target while sharing the parent's debugger instance.

Tests:
The refactoring maintains backward compatibility. All existing test cases pass.
---
 lldb/include/lldb/API/SBTarget.h              |   3 +
 lldb/include/lldb/Target/Target.h             |   9 +
 .../test/tools/lldb-dap/dap_server.py         |   3 +
 lldb/source/API/SBTarget.cpp                  |   8 +
 lldb/source/Target/Target.cpp                 |  34 ++-
 .../tools/lldb-dap/attach/TestDAP_attach.py   |  13 +
 lldb/tools/lldb-dap/CMakeLists.txt            |   1 +
 lldb/tools/lldb-dap/DAP.cpp                   | 231 ++++++++++++++----
 lldb/tools/lldb-dap/DAP.h                     |  25 +-
 lldb/tools/lldb-dap/DAPSessionManager.cpp     | 168 +++++++++++++
 lldb/tools/lldb-dap/DAPSessionManager.h       | 119 +++++++++
 .../lldb-dap/Handler/AttachRequestHandler.cpp |  26 +-
 .../Handler/InitializeRequestHandler.cpp      |  58 +----
 .../lldb-dap/Handler/LaunchRequestHandler.cpp |   4 +
 .../lldb-dap/Protocol/ProtocolRequests.cpp    |   3 +-
 .../lldb-dap/Protocol/ProtocolRequests.h      |   3 +
 lldb/tools/lldb-dap/package.json              |   4 +
 lldb/tools/lldb-dap/tool/lldb-dap.cpp         |  53 ++--
 lldb/unittests/DAP/CMakeLists.txt             |   1 +
 lldb/unittests/DAP/DAPSessionManagerTest.cpp  | 177 ++++++++++++++
 .../gn/secondary/lldb/tools/lldb-dap/BUILD.gn |   1 +
 21 files changed, 802 insertions(+), 142 deletions(-)
 create mode 100644 lldb/tools/lldb-dap/DAPSessionManager.cpp
 create mode 100644 lldb/tools/lldb-dap/DAPSessionManager.h
 create mode 100644 lldb/unittests/DAP/DAPSessionManagerTest.cpp

diff --git a/lldb/include/lldb/API/SBTarget.h b/lldb/include/lldb/API/SBTarget.h
index 173fd05b54a13..1d251763a826a 100644
--- a/lldb/include/lldb/API/SBTarget.h
+++ b/lldb/include/lldb/API/SBTarget.h
@@ -44,6 +44,7 @@ class LLDB_API SBTarget {
     eBroadcastBitWatchpointChanged = (1 << 3),
     eBroadcastBitSymbolsLoaded = (1 << 4),
     eBroadcastBitSymbolsChanged = (1 << 5),
+    eBroadcastBitNewTargetCreated = (1 << 6),
   };
 
   // Constructors
@@ -69,6 +70,8 @@ class LLDB_API SBTarget {
   static lldb::SBModule GetModuleAtIndexFromEvent(const uint32_t idx,
                                                   const lldb::SBEvent &event);
 
+  static const char *GetSessionNameFromEvent(const SBEvent &event);
+
   static const char *GetBroadcasterClassName();
 
   lldb::SBProcess GetProcess();
diff --git a/lldb/include/lldb/Target/Target.h 
b/lldb/include/lldb/Target/Target.h
index f4a09237ce897..86349897762f4 100644
--- a/lldb/include/lldb/Target/Target.h
+++ b/lldb/include/lldb/Target/Target.h
@@ -537,6 +537,7 @@ class Target : public std::enable_shared_from_this<Target>,
     eBroadcastBitWatchpointChanged = (1 << 3),
     eBroadcastBitSymbolsLoaded = (1 << 4),
     eBroadcastBitSymbolsChanged = (1 << 5),
+    eBroadcastBitNewTargetCreated = (1 << 6),
   };
 
   // These two functions fill out the Broadcaster interface:
@@ -556,6 +557,11 @@ class Target : public std::enable_shared_from_this<Target>,
     TargetEventData(const lldb::TargetSP &target_sp,
                     const ModuleList &module_list);
 
+    TargetEventData(const lldb::TargetSP &target_sp, std::string session_name);
+
+    TargetEventData(const lldb::TargetSP &target_sp,
+                    const ModuleList &module_list, std::string session_name);
+
     ~TargetEventData() override;
 
     static llvm::StringRef GetFlavorString();
@@ -564,6 +570,8 @@ class Target : public std::enable_shared_from_this<Target>,
       return TargetEventData::GetFlavorString();
     }
 
+    static llvm::StringRef GetSessionNameFromEvent(const Event *event_ptr);
+
     void Dump(Stream *s) const override;
 
     static const TargetEventData *GetEventDataFromEvent(const Event 
*event_ptr);
@@ -579,6 +587,7 @@ class Target : public std::enable_shared_from_this<Target>,
   private:
     lldb::TargetSP m_target_sp;
     ModuleList m_module_list;
+    std::string m_session_name;
 
     TargetEventData(const TargetEventData &) = delete;
     const TargetEventData &operator=(const TargetEventData &) = delete;
diff --git a/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py 
b/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py
index 8eb64b4ab8b2b..b52aaf558aa24 100644
--- a/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py
+++ b/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py
@@ -785,6 +785,7 @@ def request_attach(
         *,
         program: Optional[str] = None,
         pid: Optional[int] = None,
+        targetId: Optional[int] = None,
         waitFor=False,
         initCommands: Optional[list[str]] = None,
         preRunCommands: Optional[list[str]] = None,
@@ -804,6 +805,8 @@ def request_attach(
             args_dict["pid"] = pid
         if program is not None:
             args_dict["program"] = program
+        if targetId is not None:
+            args_dict["targetId"] = targetId
         if waitFor:
             args_dict["waitFor"] = waitFor
         args_dict["initCommands"] = self.init_commands
diff --git a/lldb/source/API/SBTarget.cpp b/lldb/source/API/SBTarget.cpp
index 98d10aa07c53f..0f4508c772ee4 100644
--- a/lldb/source/API/SBTarget.cpp
+++ b/lldb/source/API/SBTarget.cpp
@@ -145,6 +145,14 @@ SBModule SBTarget::GetModuleAtIndexFromEvent(const 
uint32_t idx,
   return SBModule(module_list.GetModuleAtIndex(idx));
 }
 
+const char *SBTarget::GetSessionNameFromEvent(const SBEvent &event) {
+  LLDB_INSTRUMENT_VA(event);
+
+  return ConstString(
+             Target::TargetEventData::GetSessionNameFromEvent(event.get()))
+      .AsCString();
+}
+
 const char *SBTarget::GetBroadcasterClassName() {
   LLDB_INSTRUMENT();
 
diff --git a/lldb/source/Target/Target.cpp b/lldb/source/Target/Target.cpp
index e224a12e33463..a13e11c4b3a05 100644
--- a/lldb/source/Target/Target.cpp
+++ b/lldb/source/Target/Target.cpp
@@ -193,6 +193,7 @@ Target::Target(Debugger &debugger, const ArchSpec 
&target_arch,
   SetEventName(eBroadcastBitModulesUnloaded, "modules-unloaded");
   SetEventName(eBroadcastBitWatchpointChanged, "watchpoint-changed");
   SetEventName(eBroadcastBitSymbolsLoaded, "symbols-loaded");
+  SetEventName(eBroadcastBitNewTargetCreated, "new-target-created");
 
   CheckInWithManager();
 
@@ -5169,11 +5170,21 @@ void TargetProperties::SetDebugUtilityExpression(bool 
debug) {
 // Target::TargetEventData
 
 Target::TargetEventData::TargetEventData(const lldb::TargetSP &target_sp)
-    : EventData(), m_target_sp(target_sp), m_module_list() {}
+    : TargetEventData(target_sp, ModuleList(), "") {}
 
 Target::TargetEventData::TargetEventData(const lldb::TargetSP &target_sp,
                                          const ModuleList &module_list)
-    : EventData(), m_target_sp(target_sp), m_module_list(module_list) {}
+    : TargetEventData(target_sp, module_list, "") {}
+
+Target::TargetEventData::TargetEventData(const lldb::TargetSP &target_sp,
+                                         std::string session_name)
+    : TargetEventData(target_sp, ModuleList(), std::move(session_name)) {}
+
+Target::TargetEventData::TargetEventData(const lldb::TargetSP &target_sp,
+                                         const ModuleList &module_list,
+                                         std::string session_name)
+    : EventData(), m_target_sp(target_sp), m_module_list(module_list),
+      m_session_name(std::move(session_name)) {}
 
 Target::TargetEventData::~TargetEventData() = default;
 
@@ -5209,6 +5220,25 @@ TargetSP 
Target::TargetEventData::GetTargetFromEvent(const Event *event_ptr) {
   return target_sp;
 }
 
+llvm::StringRef
+Target::TargetEventData::GetSessionNameFromEvent(const Event *event_ptr) {
+  const TargetEventData *event_data = GetEventDataFromEvent(event_ptr);
+  if (!event_data)
+    return llvm::StringRef();
+
+  if (!event_data->m_session_name.empty())
+    return event_data->m_session_name;
+
+  // Generate default session name if not provided
+  if (event_data->m_target_sp) {
+    lldb::user_id_t target_id = event_data->m_target_sp->GetGloballyUniqueID();
+    std::string default_name = llvm::formatv("Session {0}", target_id).str();
+    return ConstString(default_name).GetStringRef();
+  }
+
+  return llvm::StringRef();
+}
+
 ModuleList
 Target::TargetEventData::GetModuleListFromEvent(const Event *event_ptr) {
   ModuleList module_list;
diff --git a/lldb/test/API/tools/lldb-dap/attach/TestDAP_attach.py 
b/lldb/test/API/tools/lldb-dap/attach/TestDAP_attach.py
index 5331a9f94ef1f..6ca286c12abd2 100644
--- a/lldb/test/API/tools/lldb-dap/attach/TestDAP_attach.py
+++ b/lldb/test/API/tools/lldb-dap/attach/TestDAP_attach.py
@@ -72,3 +72,16 @@ def test_by_name_waitFor(self):
         self.spawn_thread.start()
         self.attach(program=program, waitFor=True)
         self.continue_and_verify_pid()
+
+    def test_attach_with_invalid_targetId(self):
+        """
+        Test that attaching with an invalid targetId fails with the expected
+        error message.
+        """
+        self.build_and_create_debug_adapter()
+
+        resp = self.attach(targetId=99999, expectFailure=True)
+        self.assertFalse(resp["success"])
+        self.assertIn(
+            "Unable to find existing debugger", resp["body"]["error"]["format"]
+        )
diff --git a/lldb/tools/lldb-dap/CMakeLists.txt 
b/lldb/tools/lldb-dap/CMakeLists.txt
index 7db334ca56bcf..2fbdc73a79978 100644
--- a/lldb/tools/lldb-dap/CMakeLists.txt
+++ b/lldb/tools/lldb-dap/CMakeLists.txt
@@ -12,6 +12,7 @@ add_lldb_library(lldbDAP
   DAP.cpp
   DAPError.cpp
   DAPLog.cpp
+  DAPSessionManager.cpp
   EventHelper.cpp
   ExceptionBreakpoint.cpp
   FifoFiles.cpp
diff --git a/lldb/tools/lldb-dap/DAP.cpp b/lldb/tools/lldb-dap/DAP.cpp
index f76656e98ca01..dc681336637e0 100644
--- a/lldb/tools/lldb-dap/DAP.cpp
+++ b/lldb/tools/lldb-dap/DAP.cpp
@@ -7,6 +7,7 @@
 
//===----------------------------------------------------------------------===//
 
 #include "DAP.h"
+#include "CommandPlugins.h"
 #include "DAPLog.h"
 #include "EventHelper.h"
 #include "ExceptionBreakpoint.h"
@@ -241,10 +242,12 @@ llvm::Error DAP::ConfigureIO(std::FILE *overrideOut, 
std::FILE *overrideErr) {
 }
 
 void DAP::StopEventHandlers() {
-  if (event_thread.joinable()) {
-    broadcaster.BroadcastEventByType(eBroadcastBitStopEventThread);
-    event_thread.join();
-  }
+  event_thread_sp.reset();
+
+  // Clean up expired event threads from the session manager.
+  DAPSessionManager::GetInstance().ReleaseExpiredEventThreads();
+
+  // Still handle the progress thread normally since it's per-DAP instance.
   if (progress_event_thread.joinable()) {
     broadcaster.BroadcastEventByType(eBroadcastBitStopProgressThread);
     progress_event_thread.join();
@@ -804,7 +807,8 @@ void DAP::SetTarget(const lldb::SBTarget target) {
             lldb::SBTarget::eBroadcastBitModulesLoaded |
             lldb::SBTarget::eBroadcastBitModulesUnloaded |
             lldb::SBTarget::eBroadcastBitSymbolsLoaded |
-            lldb::SBTarget::eBroadcastBitSymbolsChanged);
+            lldb::SBTarget::eBroadcastBitSymbolsChanged |
+            lldb::SBTarget::eBroadcastBitNewTargetCreated);
     listener.StartListeningForEvents(this->broadcaster,
                                      eBroadcastBitStopEventThread);
   }
@@ -1289,13 +1293,91 @@ protocol::Capabilities DAP::GetCustomCapabilities() {
 }
 
 void DAP::StartEventThread() {
-  event_thread = std::thread(&DAP::EventThread, this);
+  // Get event thread for this debugger (creates it if it doesn't exist).
+  event_thread_sp = DAPSessionManager::GetInstance().GetEventThreadForDebugger(
+      debugger, this);
 }
 
 void DAP::StartProgressEventThread() {
   progress_event_thread = std::thread(&DAP::ProgressEventThread, this);
 }
 
+void DAP::StartEventThreads() {
+  if (clientFeatures.contains(eClientFeatureProgressReporting))
+    StartProgressEventThread();
+
+  StartEventThread();
+}
+
+llvm::Error DAP::InitializeDebugger(std::optional<uint32_t> target_id) {
+  // Initialize debugger instance (shared or individual).
+  if (target_id) {
+    std::optional<lldb::SBDebugger> shared_debugger =
+        DAPSessionManager::GetInstance().GetSharedDebugger(*target_id);
+    // If the target ID is not valid, then we won't find a debugger.
+    if (!shared_debugger) {
+      return llvm::createStringError(
+          "Unable to find existing debugger for target ID");
+    }
+    debugger = shared_debugger.value();
+    StartEventThreads();
+    return llvm::Error::success();
+  }
+
+  debugger = lldb::SBDebugger::Create(/*argument_name=*/false);
+
+  // Configure input/output/error file descriptors.
+  debugger.SetInputFile(in);
+  target = debugger.GetDummyTarget();
+
+  llvm::Expected<int> out_fd = out.GetWriteFileDescriptor();
+  if (!out_fd)
+    return out_fd.takeError();
+  debugger.SetOutputFile(lldb::SBFile(*out_fd, "w", false));
+
+  llvm::Expected<int> err_fd = err.GetWriteFileDescriptor();
+  if (!err_fd)
+    return err_fd.takeError();
+  debugger.SetErrorFile(lldb::SBFile(*err_fd, "w", false));
+
+  // The sourceInitFile option is not part of the DAP specification. It is an
+  // extension used by the test suite to prevent sourcing `.lldbinit` and
+  // changing its behavior. The CLI flag --no-lldbinit takes precedence over
+  // the DAP parameter.
+  bool should_source_init_files = !no_lldbinit && sourceInitFile;
+  if (should_source_init_files) {
+    debugger.SkipLLDBInitFiles(false);
+    debugger.SkipAppInitFiles(false);
+    lldb::SBCommandReturnObject init;
+    auto interp = debugger.GetCommandInterpreter();
+    interp.SourceInitFileInGlobalDirectory(init);
+    interp.SourceInitFileInHomeDirectory(init);
+  }
+
+  // Run initialization commands.
+  if (llvm::Error err = RunPreInitCommands())
+    return err;
+
+  auto cmd = debugger.GetCommandInterpreter().AddMultiwordCommand(
+      "lldb-dap", "Commands for managing lldb-dap.");
+
+  if (clientFeatures.contains(eClientFeatureStartDebuggingRequest)) {
+    cmd.AddCommand(
+        "start-debugging", new StartDebuggingCommand(*this),
+        "Sends a startDebugging request from the debug adapter to the client "
+        "to start a child debug session of the same type as the caller.");
+  }
+
+  cmd.AddCommand(
+      "repl-mode", new ReplModeCommand(*this),
+      "Get or set the repl behavior of lldb-dap evaluation requests.");
+  cmd.AddCommand("send-event", new SendEventCommand(*this),
+                 "Sends an DAP event to the client.");
+
+  StartEventThreads();
+  return llvm::Error::success();
+}
+
 void DAP::ProgressEventThread() {
   lldb::SBListener listener("lldb-dap.progress.listener");
   debugger.GetBroadcaster().AddListener(
@@ -1374,6 +1456,14 @@ void DAP::EventThread() {
       const auto event_mask = event.GetType();
       if (lldb::SBProcess::EventIsProcessEvent(event)) {
         lldb::SBProcess process = lldb::SBProcess::GetProcessFromEvent(event);
+        // Find the DAP instance that owns this process's target.
+        DAP *dap_instance = DAPSessionManager::FindDAP(process.GetTarget());
+        if (!dap_instance) {
+          DAP_LOG(log, "Unable to find DAP instance for process {0}",
+                  process.GetProcessID());
+          continue;
+        }
+
         if (event_mask & lldb::SBProcess::eBroadcastBitStateChanged) {
           auto state = lldb::SBProcess::GetStateFromEvent(event);
           switch (state) {
@@ -1390,89 +1480,138 @@ void DAP::EventThread() {
             // Only report a stopped event if the process was not
             // automatically restarted.
             if (!lldb::SBProcess::GetRestartedFromEvent(event)) {
-              SendStdOutStdErr(*this, process);
-              if (llvm::Error err = SendThreadStoppedEvent(*this))
-                DAP_LOG_ERROR(log, std::move(err),
+              SendStdOutStdErr(*dap_instance, process);
+              if (llvm::Error err = SendThreadStoppedEvent(*dap_instance))
+                DAP_LOG_ERROR(dap_instance->log, std::move(err),
                               "({1}) reporting thread stopped: {0}",
-                              m_client_name);
+                              dap_instance->m_client_name);
             }
             break;
           case lldb::eStateRunning:
           case lldb::eStateStepping:
-            WillContinue();
-            SendContinuedEvent(*this);
+            dap_instance->WillContinue();
+            SendContinuedEvent(*dap_instance);
             break;
           case lldb::eStateExited:
             lldb::SBStream stream;
             process.GetStatus(stream);
-            SendOutput(OutputType::Console, stream.GetData());
+            dap_instance->SendOutput(OutputType::Console, stream.GetData());
 
             // When restarting, we can get an "exited" event for the process we
             // just killed with the old PID, or even with no PID. In that case
             // we don't have to terminate the session.
             if (process.GetProcessID() == LLDB_INVALID_PROCESS_ID ||
-                process.GetProcessID() == restarting_process_id) {
-              restarting_process_id = LLDB_INVALID_PROCESS_ID;
+                process.GetProcessID() == dap_instance->restarting_process_id) 
{
+              dap_instance->restarting_process_id = LLDB_INVALID_PROCESS_ID;
             } else {
               // Run any exit LLDB commands the user specified in the
               // launch.json
-              RunExitCommands();
-              SendProcessExitedEvent(*this, process);
-              SendTerminatedEvent();
+              dap_instance->RunExitCommands();
+              SendProcessExitedEvent(*dap_instance, process);
+              dap_instance->SendTerminatedEvent();
               done = true;
             }
             break;
           }
         } else if ((event_mask & lldb::SBProcess::eBroadcastBitSTDOUT) ||
                    (event_mask & lldb::SBProcess::eBroadcastBitSTDERR)) {
-          SendStdOutStdErr(*this, process);
+          SendStdOutStdErr(*dap_instance, process);
         }
       } else if (lldb::SBTarget::EventIsTargetEvent(event)) {
         if (event_mask & lldb::SBTarget::eBroadcastBitModulesLoaded ||
             event_mask & lldb::SBTarget::eBroadcastBitModulesUnloaded ||
             event_mask & lldb::SBTarget::eBroadcastBitSymbolsLoaded ||
             event_mask & lldb::SBTarget::eBroadcastBitSymbolsChanged) {
+          lldb::SBTarget event_target =
+              lldb::SBTarget::GetTargetFromEvent(event);
+          // Find the DAP instance that owns this target.
+          DAP *dap_instance = DAPSessionManager::FindDAP(event_target);
+          if (!dap_instance)
+            continue;
+
           const uint32_t num_modules =
               lldb::SBTarget::GetNumModulesFromEvent(event);
           const bool remove_module =
               event_mask & lldb::SBTarget::eBroadcastBitModulesUnloaded;
 
-          std::lock_guard<std::mutex> guard(modules_mutex);
+          std::lock_guard<std::mutex> guard(dap_instance->modules_mutex);
           for (uint32_t i = 0; i < num_modules; ++i) {
             lldb::SBModule module =
                 lldb::SBTarget::GetModuleAtIndexFromEvent(i, event);
 
             std::optional<protocol::Module> p_module =
-                CreateModule(target, module, remove_module);
+                CreateModule(dap_instance->target, module, remove_module);
             if (!p_module)
               continue;
 
             llvm::StringRef module_id = p_module->id;
 
-            const bool module_exists = modules.contains(module_id);
+            const bool module_exists =
+                dap_instance->modules.contains(module_id);
             if (remove_module && module_exists) {
-              modules.erase(module_id);
-              Send(protocol::Event{
+              dap_instance->modules.erase(module_id);
+              dap_instance->Send(protocol::Event{
                   "module", ModuleEventBody{std::move(p_module).value(),
                                             ModuleEventBody::eReasonRemoved}});
             } else if (module_exists) {
-              Send(protocol::Event{
+              dap_instance->Send(protocol::Event{
                   "module", ModuleEventBody{std::move(p_module).value(),
                                             ModuleEventBody::eReasonChanged}});
             } else if (!remove_module) {
-              modules.insert(module_id);
-              Send(protocol::Event{
+              dap_instance->modules.insert(module_id);
+              dap_instance->Send(protocol::Event{
                   "module", ModuleEventBody{std::move(p_module).value(),
                                             ModuleEventBody::eReasonNew}});
             }
           }
+        } else if (event_mask & lldb::SBTarget::eBroadcastBitNewTargetCreated) 
{
+          auto target = lldb::SBTarget::GetTargetFromEvent(event);
+
+          // Generate unique target ID and set the shared debugger.
+          uint32_t target_id = target.GetGloballyUniqueID();
+          DAPSessionManager::GetInstance().SetSharedDebugger(target_id,
+                                                             debugger);
+
+          // We create an attach config that will select the unique
+          // target ID of the created target. The DAP instance will attach to
+          // this existing target and the debug session will be ready to go.
+          llvm::json::Object attach_config;
+
+          // If we have a process name, add command to attach to the same
+          // process name.
+          attach_config.try_emplace("type", "lldb");
+          attach_config.try_emplace("targetId", target_id);
+          const char *session_name =
+              lldb::SBTarget::GetSessionNameFromEvent(event);
+          attach_config.try_emplace("name", session_name);
+
+          // 2. Construct the main 'startDebugging' request arguments.
+          llvm::json::Object start_debugging_args{
+              {"request", "attach"},
+              {"configuration", std::move(attach_config)}};
+
+          // Send the request. Note that this is a reverse request, so you 
don't
+          // expect a direct response in the same way as a client request.
+          SendReverseRequest<LogFailureResponseHandler>(
+              "startDebugging", std::move(start_debugging_args));
         }
       } else if (lldb::SBBreakpoint::EventIsBreakpointEvent(event)) {
+        lldb::SBBreakpoint bp =
+            lldb::SBBreakpoint::GetBreakpointFromEvent(event);
+        if (!bp.IsValid())
+          continue;
+
+        lldb::SBTarget event_target = bp.GetTarget();
+
+        // Find the DAP instance that owns this target.
+        DAP *dap_instance = DAPSessionManager::FindDAP(event_target);
+        if (!dap_instance)
+          continue;
+
         if (event_mask & lldb::SBTarget::eBroadcastBitBreakpointChanged) {
           auto event_type =
               lldb::SBBreakpoint::GetBreakpointEventTypeFromEvent(event);
-          auto bp = Breakpoint(
-              *this, lldb::SBBreakpoint::GetBreakpointFromEvent(event));
+          auto breakpoint = Breakpoint(*dap_instance, bp);
           // If the breakpoint was set through DAP, it will have the
           // BreakpointBase::kDAPBreakpointLabel. Regardless of whether
           // locations were added, removed, or resolved, the breakpoint isn't
@@ -1480,14 +1619,14 @@ void DAP::EventThread() {
           if ((event_type & lldb::eBreakpointEventTypeLocationsAdded ||
                event_type & lldb::eBreakpointEventTypeLocationsRemoved ||
                event_type & lldb::eBreakpointEventTypeLocationsResolved) &&
-              bp.MatchesName(BreakpointBase::kDAPBreakpointLabel)) {
+              breakpoint.MatchesName(BreakpointBase::kDAPBreakpointLabel)) {
             // As the DAP client already knows the path of this breakpoint, we
             // don't need to send it back as part of the "changed" event. This
             // avoids sending paths that should be source mapped. Note that
             // CreateBreakpoint doesn't apply source mapping and certain
             // implementation ignore the source part of this event anyway.
-            protocol::Breakpoint protocol_bp = bp.ToProtocolBreakpoint();
-
+            protocol::Breakpoint protocol_bp =
+                breakpoint.ToProtocolBreakpoint();
             // "source" is not needed here, unless we add adapter data to be
             // saved by the client.
             if (protocol_bp.source && !protocol_bp.source->adapterData)
@@ -1500,19 +1639,29 @@ void DAP::EventThread() {
             llvm::json::Object bp_event = CreateEventObject("breakpoint");
             bp_event.try_emplace("body", std::move(body));
 
-            SendJSON(llvm::json::Value(std::move(bp_event)));
+            dap_instance->SendJSON(llvm::json::Value(std::move(bp_event)));
           }
         }
       } else if (event_mask & lldb::eBroadcastBitError ||
                  event_mask & lldb::eBroadcastBitWarning) {
-        lldb::SBStructuredData data =
-            lldb::SBDebugger::GetDiagnosticFromEvent(event);
-        if (!data.IsValid())
-          continue;
-        std::string type = GetStringValue(data.GetValueForKey("type"));
-        std::string message = GetStringValue(data.GetValueForKey("message"));
-        SendOutput(OutputType::Important,
-                   llvm::formatv("{0}: {1}", type, message).str());
+        // Global debugger events - send to all DAP instances.
+        std::vector<DAP *> active_instances =
+            DAPSessionManager::GetInstance().GetActiveSessions();
+        for (DAP *dap_instance : active_instances) {
+          if (!dap_instance)
+            continue;
+
+          lldb::SBStructuredData data =
+              lldb::SBDebugger::GetDiagnosticFromEvent(event);
+          if (!data.IsValid())
+            continue;
+
+          std::string type = GetStringValue(data.GetValueForKey("type"));
+          std::string message = GetStringValue(data.GetValueForKey("message"));
+          dap_instance->SendOutput(
+              OutputType::Important,
+              llvm::formatv("{0}: {1}", type, message).str());
+        }
       } else if (event.BroadcasterMatchesRef(broadcaster)) {
         if (event_mask & eBroadcastBitStopEventThread) {
           done = true;
diff --git a/lldb/tools/lldb-dap/DAP.h b/lldb/tools/lldb-dap/DAP.h
index a90ddf59671ee..fdca801d400c0 100644
--- a/lldb/tools/lldb-dap/DAP.h
+++ b/lldb/tools/lldb-dap/DAP.h
@@ -10,6 +10,7 @@
 #define LLDB_TOOLS_LLDB_DAP_DAP_H
 
 #include "DAPForward.h"
+#include "DAPSessionManager.h"
 #include "ExceptionBreakpoint.h"
 #include "FunctionBreakpoint.h"
 #include "InstructionBreakpoint.h"
@@ -47,6 +48,7 @@
 #include <condition_variable>
 #include <cstdint>
 #include <deque>
+#include <map>
 #include <memory>
 #include <mutex>
 #include <optional>
@@ -81,6 +83,8 @@ enum class ReplMode { Variable = 0, Command, Auto };
 using DAPTransport = 
lldb_private::transport::JSONTransport<ProtocolDescriptor>;
 
 struct DAP final : public DAPTransport::MessageHandler {
+  friend class DAPSessionManager;
+
   /// Path to the lldb-dap binary itself.
   static llvm::StringRef debug_adapter_path;
 
@@ -157,6 +161,11 @@ struct DAP final : public DAPTransport::MessageHandler {
   /// Whether to disable sourcing .lldbinit files.
   bool no_lldbinit;
 
+  /// Stores whether the initialize request specified a value for
+  /// lldbExtSourceInitFile. Used by the test suite to prevent sourcing
+  /// `.lldbinit` and changing its behavior.
+  bool sourceInitFile = true;
+
   /// The initial thread list upon attaching.
   std::vector<protocol::Thread> initial_thread_list;
 
@@ -417,6 +426,18 @@ struct DAP final : public DAPTransport::MessageHandler {
   void StartEventThread();
   void StartProgressEventThread();
 
+  /// DAP debugger initialization functions.
+  /// @{
+
+  /// Perform complete DAP initialization in one call.
+  llvm::Error
+  InitializeDebugger(std::optional<uint32_t> target_idx = std::nullopt);
+
+  /// Start event handling threads based on client capabilities.
+  void StartEventThreads();
+
+  /// @}
+
   /// Sets the given protocol `breakpoints` in the given `source`, while
   /// removing any existing breakpoints in the given source if they are not in
   /// `breakpoint`.
@@ -462,7 +483,9 @@ struct DAP final : public DAPTransport::MessageHandler {
   void EventThread();
   void ProgressEventThread();
 
-  std::thread event_thread;
+  /// Event thread is a shared pointer in case we have a multiple
+  /// DAP instances sharing the same event thread.
+  std::shared_ptr<ManagedEventThread> event_thread_sp;
   std::thread progress_event_thread;
   /// @}
 
diff --git a/lldb/tools/lldb-dap/DAPSessionManager.cpp 
b/lldb/tools/lldb-dap/DAPSessionManager.cpp
new file mode 100644
index 0000000000000..5fd6e7e810fcc
--- /dev/null
+++ b/lldb/tools/lldb-dap/DAPSessionManager.cpp
@@ -0,0 +1,168 @@
+//===-- DAPSessionManager.cpp ----------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+#include "DAPSessionManager.h"
+#include "DAP.h"
+#include "lldb/API/SBBroadcaster.h"
+#include "lldb/API/SBEvent.h"
+#include "lldb/API/SBTarget.h"
+#include "lldb/Host/MainLoopBase.h"
+#include "llvm/Support/Threading.h"
+#include "llvm/Support/WithColor.h"
+
+#include <chrono>
+#include <mutex>
+
+namespace lldb_dap {
+
+ManagedEventThread::ManagedEventThread(lldb::SBBroadcaster broadcaster,
+                                       std::thread t)
+    : m_broadcaster(broadcaster), m_event_thread(std::move(t)) {}
+
+ManagedEventThread::~ManagedEventThread() {
+  if (m_event_thread.joinable()) {
+    m_broadcaster.BroadcastEventByType(eBroadcastBitStopEventThread);
+    m_event_thread.join();
+  }
+}
+
+DAPSessionManager &DAPSessionManager::GetInstance() {
+  // NOTE: intentional leak to avoid issues with C++ destructor chain
+  // Use std::call_once for thread-safe initialization.
+  static std::once_flag initialized;
+  static DAPSessionManager *instance = nullptr;
+
+  std::call_once(initialized, []() { instance = new DAPSessionManager(); });
+
+  return *instance;
+}
+
+void DAPSessionManager::RegisterSession(lldb_private::MainLoop *loop,
+                                        DAP *dap) {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+  m_active_sessions[loop] = dap;
+}
+
+void DAPSessionManager::UnregisterSession(lldb_private::MainLoop *loop) {
+  std::unique_lock<std::mutex> lock(m_sessions_mutex);
+  m_active_sessions.erase(loop);
+
+  // Clean up shared resources when the last session exits.
+  if (m_active_sessions.empty())
+    CleanupSharedResources();
+
+  std::notify_all_at_thread_exit(m_sessions_condition, std::move(lock));
+}
+
+std::vector<DAP *> DAPSessionManager::GetActiveSessions() {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+  std::vector<DAP *> sessions;
+  for (const auto &[loop, dap] : m_active_sessions)
+    if (dap)
+      sessions.emplace_back(dap);
+  return sessions;
+}
+
+void DAPSessionManager::DisconnectAllSessions() {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+  m_client_failed = false;
+  for (auto [loop, dap] : m_active_sessions) {
+    if (dap) {
+      if (llvm::Error error = dap->Disconnect()) {
+        m_client_failed = true;
+        llvm::WithColor::error() << "DAP client disconnected failed: "
+                                 << llvm::toString(std::move(error)) << "\n";
+      }
+      loop->AddPendingCallback(
+          [](lldb_private::MainLoopBase &loop) { loop.RequestTermination(); });
+    }
+  }
+}
+
+llvm::Error DAPSessionManager::WaitForAllSessionsToDisconnect() {
+  std::unique_lock<std::mutex> lock(m_sessions_mutex);
+  m_sessions_condition.wait(lock, [this] { return m_active_sessions.empty(); 
});
+
+  // Check if any disconnection failed and return appropriate error.
+  if (m_client_failed)
+    return llvm::make_error<llvm::StringError>(
+        "disconnecting all clients failed", llvm::inconvertibleErrorCode());
+
+  return llvm::Error::success();
+}
+
+std::shared_ptr<ManagedEventThread>
+DAPSessionManager::GetEventThreadForDebugger(lldb::SBDebugger debugger,
+                                             DAP *requesting_dap) {
+  lldb::user_id_t debugger_id = debugger.GetID();
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+
+  // Try to use shared event thread, if it exists.
+  if (auto it = m_debugger_event_threads.find(debugger_id);
+      it != m_debugger_event_threads.end()) {
+    if (auto thread_sp = it->second.lock())
+      return thread_sp;
+    // Our weak pointer has expired.
+    m_debugger_event_threads.erase(it);
+  }
+
+  // Create a new event thread and store it.
+  auto new_thread_sp = std::make_shared<ManagedEventThread>(
+      requesting_dap->broadcaster,
+      std::thread(&DAP::EventThread, requesting_dap));
+  m_debugger_event_threads[debugger_id] = new_thread_sp;
+  return new_thread_sp;
+}
+
+void DAPSessionManager::SetSharedDebugger(uint32_t target_id,
+                                          lldb::SBDebugger debugger) {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+  m_target_to_debugger_map[target_id] = debugger;
+}
+
+std::optional<lldb::SBDebugger>
+DAPSessionManager::GetSharedDebugger(uint32_t target_id) {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+  auto pos = m_target_to_debugger_map.find(target_id);
+  if (pos == m_target_to_debugger_map.end())
+    return std::nullopt;
+  lldb::SBDebugger debugger = pos->second;
+  m_target_to_debugger_map.erase(pos);
+  return debugger;
+}
+
+DAP *DAPSessionManager::FindDAPForTarget(lldb::SBTarget target) {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+
+  for (const auto &[loop, dap] : m_active_sessions)
+    if (dap && dap->target.IsValid() && dap->target == target)
+      return dap;
+
+  return nullptr;
+}
+
+void DAPSessionManager::CleanupSharedResources() {
+  // SBDebugger destructors will handle cleanup when the map entries are
+  // destroyed.
+  m_target_to_debugger_map.clear();
+}
+
+void DAPSessionManager::ReleaseExpiredEventThreads() {
+  std::lock_guard<std::mutex> lock(m_sessions_mutex);
+  for (auto it = m_debugger_event_threads.begin();
+       it != m_debugger_event_threads.end();) {
+    // Check if the weak_ptr has expired (no DAP instances are using it
+    // anymore).
+    if (it->second.expired()) {
+      it = m_debugger_event_threads.erase(it);
+    } else {
+      ++it;
+    }
+  }
+}
+
+} // namespace lldb_dap
diff --git a/lldb/tools/lldb-dap/DAPSessionManager.h 
b/lldb/tools/lldb-dap/DAPSessionManager.h
new file mode 100644
index 0000000000000..d547f3036a9b2
--- /dev/null
+++ b/lldb/tools/lldb-dap/DAPSessionManager.h
@@ -0,0 +1,119 @@
+//===-- 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.
+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.
+  void UnregisterSession(lldb_private::MainLoop *loop);
+
+  /// Get all active DAP sessions.
+  std::vector<DAP *> GetActiveSessions();
+
+  /// Disconnect all active sessions.
+  void DisconnectAllSessions();
+
+  /// Wait for all sessions to finish disconnecting.
+  /// Returns an error if any client disconnection failed, otherwise success.
+  llvm::Error WaitForAllSessionsToDisconnect();
+
+  /// Set the shared debugger instance for a unique target ID.
+  void SetSharedDebugger(uint32_t target_id, lldb::SBDebugger debugger);
+
+  /// Get the shared debugger instance for a unique target ID.
+  std::optional<lldb::SBDebugger> GetSharedDebugger(uint32_t target_id);
+
+  /// Get or create event thread for a specific debugger.
+  std::shared_ptr<ManagedEventThread>
+  GetEventThreadForDebugger(lldb::SBDebugger debugger, DAP *requesting_dap);
+
+  /// Find the DAP instance that owns the given target.
+  DAP *FindDAPForTarget(lldb::SBTarget target);
+
+  /// Static convenience method for FindDAPForTarget.
+  static DAP *FindDAP(lldb::SBTarget target) {
+    return GetInstance().FindDAPForTarget(target);
+  }
+
+  /// Clean up shared resources when the last session exits.
+  void CleanupSharedResources();
+
+  /// Clean up expired event threads from the collection.
+  void ReleaseExpiredEventThreads();
+
+private:
+  DAPSessionManager() = default;
+  ~DAPSessionManager() = default;
+
+  // Non-copyable and non-movable.
+  DAPSessionManager(const DAPSessionManager &) = delete;
+  DAPSessionManager &operator=(const DAPSessionManager &) = delete;
+  DAPSessionManager(DAPSessionManager &&) = delete;
+  DAPSessionManager &operator=(DAPSessionManager &&) = delete;
+
+  bool m_client_failed = false;
+  std::mutex m_sessions_mutex;
+  std::condition_variable m_sessions_condition;
+  std::map<lldb_private::MainLoop *, DAP *> m_active_sessions;
+
+  /// Optional map from target ID to shared debugger set when the native
+  /// process creates a new target.
+  std::map<uint32_t, lldb::SBDebugger> m_target_to_debugger_map;
+
+  /// Map from debugger ID to its event thread used for when
+  /// multiple DAP sessions are using the same debugger instance.
+  std::map<lldb::user_id_t, std::weak_ptr<ManagedEventThread>>
+      m_debugger_event_threads;
+};
+
+} // namespace lldb_dap
+
+#endif // LLDB_TOOLS_LLDB_DAP_DAPSESSIONMANAGER_H
diff --git a/lldb/tools/lldb-dap/Handler/AttachRequestHandler.cpp 
b/lldb/tools/lldb-dap/Handler/AttachRequestHandler.cpp
index 371349a26866e..cd30fc5b6325f 100644
--- a/lldb/tools/lldb-dap/Handler/AttachRequestHandler.cpp
+++ b/lldb/tools/lldb-dap/Handler/AttachRequestHandler.cpp
@@ -17,6 +17,7 @@
 #include "lldb/lldb-defines.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
+#include <cstdint>
 
 using namespace llvm;
 using namespace lldb_dap::protocol;
@@ -29,14 +30,20 @@ namespace lldb_dap {
 /// Since attaching is debugger/runtime specific, the arguments for this 
request
 /// are not part of this specification.
 Error AttachRequestHandler::Run(const AttachRequestArguments &args) const {
+  // Initialize DAP debugger and related components if not sharing previously
+  // launched debugger.
+  std::optional<uint32_t> target_id = args.targetId;
+  if (Error err = dap.InitializeDebugger(target_id))
+    return err;
+
   // Validate that we have a well formed attach request.
   if (args.attachCommands.empty() && args.coreFile.empty() &&
       args.configuration.program.empty() &&
       args.pid == LLDB_INVALID_PROCESS_ID &&
-      args.gdbRemotePort == LLDB_DAP_INVALID_PORT)
+      args.gdbRemotePort == LLDB_DAP_INVALID_PORT && !target_id.has_value())
     return make_error<DAPError>(
         "expected one of 'pid', 'program', 'attachCommands', "
-        "'coreFile' or 'gdb-remote-port' to be specified");
+        "'coreFile', 'gdb-remote-port', or target_id to be specified");
 
   // Check if we have mutually exclusive arguments.
   if ((args.pid != LLDB_INVALID_PROCESS_ID) &&
@@ -64,7 +71,18 @@ Error AttachRequestHandler::Run(const AttachRequestArguments 
&args) const {
   dap.ConfigureSourceMaps();
 
   lldb::SBError error;
-  lldb::SBTarget target = dap.CreateTarget(error);
+  lldb::SBTarget target;
+  if (target_id) {
+    // Use the unique target ID to get the target.
+    target = dap.debugger.FindTargetByGloballyUniqueID(*target_id);
+    if (!target.IsValid()) {
+      error.SetErrorStringWithFormat("invalid target_id %u in attach config",
+                                     *target_id);
+    }
+  } else {
+    target = dap.CreateTarget(error);
+  }
+
   if (error.Fail())
     return ToError(error);
 
@@ -114,7 +132,7 @@ Error AttachRequestHandler::Run(const 
AttachRequestArguments &args) const {
       connect_url += std::to_string(args.gdbRemotePort);
       dap.target.ConnectRemote(listener, connect_url.c_str(), "gdb-remote",
                                error);
-    } else {
+    } else if (!target_id.has_value()) {
       // Attach by pid or process name.
       lldb::SBAttachInfo attach_info;
       if (args.pid != LLDB_INVALID_PROCESS_ID)
diff --git a/lldb/tools/lldb-dap/Handler/InitializeRequestHandler.cpp 
b/lldb/tools/lldb-dap/Handler/InitializeRequestHandler.cpp
index 9069de4a3a690..53e1810a5b0e0 100644
--- a/lldb/tools/lldb-dap/Handler/InitializeRequestHandler.cpp
+++ b/lldb/tools/lldb-dap/Handler/InitializeRequestHandler.cpp
@@ -21,63 +21,9 @@ using namespace lldb_dap::protocol;
 /// Initialize request; value of command field is 'initialize'.
 llvm::Expected<InitializeResponse> InitializeRequestHandler::Run(
     const InitializeRequestArguments &arguments) const {
+  // Store initialization arguments for later use in Launch/Attach.
   dap.clientFeatures = arguments.supportedFeatures;
-
-  // Do not source init files until in/out/err are configured.
-  dap.debugger = lldb::SBDebugger::Create(false);
-  dap.debugger.SetInputFile(dap.in);
-  dap.target = dap.debugger.GetDummyTarget();
-
-  llvm::Expected<int> out_fd = dap.out.GetWriteFileDescriptor();
-  if (!out_fd)
-    return out_fd.takeError();
-  dap.debugger.SetOutputFile(lldb::SBFile(*out_fd, "w", false));
-
-  llvm::Expected<int> err_fd = dap.err.GetWriteFileDescriptor();
-  if (!err_fd)
-    return err_fd.takeError();
-  dap.debugger.SetErrorFile(lldb::SBFile(*err_fd, "w", false));
-
-  auto interp = dap.debugger.GetCommandInterpreter();
-
-  // The sourceInitFile option is not part of the DAP specification. It is an
-  // extension used by the test suite to prevent sourcing `.lldbinit` and
-  // changing its behavior. The CLI flag --no-lldbinit takes precedence over
-  // the DAP parameter.
-  bool should_source_init_files =
-      !dap.no_lldbinit && arguments.lldbExtSourceInitFile.value_or(true);
-  if (should_source_init_files) {
-    dap.debugger.SkipLLDBInitFiles(false);
-    dap.debugger.SkipAppInitFiles(false);
-    lldb::SBCommandReturnObject init;
-    interp.SourceInitFileInGlobalDirectory(init);
-    interp.SourceInitFileInHomeDirectory(init);
-  }
-
-  if (llvm::Error err = dap.RunPreInitCommands())
-    return err;
-
-  auto cmd = dap.debugger.GetCommandInterpreter().AddMultiwordCommand(
-      "lldb-dap", "Commands for managing lldb-dap.");
-  if (arguments.supportedFeatures.contains(
-          eClientFeatureStartDebuggingRequest)) {
-    cmd.AddCommand(
-        "start-debugging", new StartDebuggingCommand(dap),
-        "Sends a startDebugging request from the debug adapter to the client "
-        "to start a child debug session of the same type as the caller.");
-  }
-  cmd.AddCommand(
-      "repl-mode", new ReplModeCommand(dap),
-      "Get or set the repl behavior of lldb-dap evaluation requests.");
-  cmd.AddCommand("send-event", new SendEventCommand(dap),
-                 "Sends an DAP event to the client.");
-
-  if (arguments.supportedFeatures.contains(eClientFeatureProgressReporting))
-    dap.StartProgressEventThread();
-
-  // Start our event thread so we can receive events from the debugger, target,
-  // process and more.
-  dap.StartEventThread();
+  dap.sourceInitFile = arguments.lldbExtSourceInitFile.value_or(true);
 
   return dap.GetCapabilities();
 }
diff --git a/lldb/tools/lldb-dap/Handler/LaunchRequestHandler.cpp 
b/lldb/tools/lldb-dap/Handler/LaunchRequestHandler.cpp
index 553cbeaf849e2..329f0a7bf6453 100644
--- a/lldb/tools/lldb-dap/Handler/LaunchRequestHandler.cpp
+++ b/lldb/tools/lldb-dap/Handler/LaunchRequestHandler.cpp
@@ -22,6 +22,10 @@ namespace lldb_dap {
 
 /// Launch request; value of command field is 'launch'.
 Error LaunchRequestHandler::Run(const LaunchRequestArguments &arguments) const 
{
+  // Initialize DAP debugger.
+  if (Error err = dap.InitializeDebugger())
+    return err;
+
   // Validate that we have a well formed launch request.
   if (!arguments.launchCommands.empty() &&
       arguments.console != protocol::eConsoleInternal)
diff --git a/lldb/tools/lldb-dap/Protocol/ProtocolRequests.cpp 
b/lldb/tools/lldb-dap/Protocol/ProtocolRequests.cpp
index b9393356b4e01..77a23df411428 100644
--- a/lldb/tools/lldb-dap/Protocol/ProtocolRequests.cpp
+++ b/lldb/tools/lldb-dap/Protocol/ProtocolRequests.cpp
@@ -316,7 +316,8 @@ bool fromJSON(const json::Value &Params, 
AttachRequestArguments &ARA,
          O.mapOptional("waitFor", ARA.waitFor) &&
          O.mapOptional("gdb-remote-port", ARA.gdbRemotePort) &&
          O.mapOptional("gdb-remote-hostname", ARA.gdbRemoteHostname) &&
-         O.mapOptional("coreFile", ARA.coreFile);
+         O.mapOptional("coreFile", ARA.coreFile) &&
+         O.mapOptional("targetId", ARA.targetId);
 }
 
 bool fromJSON(const json::Value &Params, ContinueArguments &CA, json::Path P) {
diff --git a/lldb/tools/lldb-dap/Protocol/ProtocolRequests.h 
b/lldb/tools/lldb-dap/Protocol/ProtocolRequests.h
index 92dada2295841..a762071cb61c5 100644
--- a/lldb/tools/lldb-dap/Protocol/ProtocolRequests.h
+++ b/lldb/tools/lldb-dap/Protocol/ProtocolRequests.h
@@ -349,6 +349,9 @@ struct AttachRequestArguments {
   /// Path to the core file to debug.
   std::string coreFile;
 
+  /// Unique ID of an existing target to attach to.
+  std::optional<uint32_t> targetId;
+
   /// @}
 };
 bool fromJSON(const llvm::json::Value &, AttachRequestArguments &,
diff --git a/lldb/tools/lldb-dap/package.json b/lldb/tools/lldb-dap/package.json
index e961c2e48b258..b008a24137216 100644
--- a/lldb/tools/lldb-dap/package.json
+++ b/lldb/tools/lldb-dap/package.json
@@ -775,6 +775,10 @@
                 "description": "Custom commands that are executed instead of 
attaching to a process ID or to a process by name. These commands may 
optionally create a new target and must perform an attach. A valid process must 
exist after these commands complete or the \"attach\" will fail.",
                 "default": []
               },
+              "targetId": {
+                "type": "number",
+                "description": "The globally unique target id to attach to. 
Used when a target is dynamically created."
+              },
               "initCommands": {
                 "type": "array",
                 "items": {
diff --git a/lldb/tools/lldb-dap/tool/lldb-dap.cpp 
b/lldb/tools/lldb-dap/tool/lldb-dap.cpp
index 93446c051eb54..eeb3e45e07b32 100644
--- a/lldb/tools/lldb-dap/tool/lldb-dap.cpp
+++ b/lldb/tools/lldb-dap/tool/lldb-dap.cpp
@@ -320,12 +320,8 @@ static llvm::Error serveConnection(
                            g_connection_timeout_time_point,
                            connection_timeout_seconds.value());
   std::condition_variable dap_sessions_condition;
-  std::mutex dap_sessions_mutex;
-  std::map<MainLoop *, DAP *> dap_sessions;
   unsigned int clientCount = 0;
-  auto handle = listener->Accept(g_loop, [=, &dap_sessions_condition,
-                                          &dap_sessions_mutex, &dap_sessions,
-                                          &clientCount](
+  auto handle = listener->Accept(g_loop, [=, &clientCount](
                                              std::unique_ptr<Socket> sock) {
     // Reset the keep alive timer, because we won't be killing the server
     // while this connection is being served.
@@ -339,8 +335,7 @@ static llvm::Error serveConnection(
 
     // Move the client into a background thread to unblock accepting the next
     // client.
-    std::thread client([=, &dap_sessions_condition, &dap_sessions_mutex,
-                        &dap_sessions]() {
+    std::thread client([=]() {
       llvm::set_thread_name(client_name + ".runloop");
       MainLoop loop;
       Transport transport(client_name, log, io, io);
@@ -353,10 +348,8 @@ static llvm::Error serveConnection(
         return;
       }
 
-      {
-        std::scoped_lock<std::mutex> lock(dap_sessions_mutex);
-        dap_sessions[&loop] = &dap;
-      }
+      // Register the DAP session with the global manager.
+      DAPSessionManager::GetInstance().RegisterSession(&loop, &dap);
 
       if (auto Err = dap.Loop()) {
         llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(),
@@ -365,10 +358,8 @@ static llvm::Error serveConnection(
       }
 
       DAP_LOG(log, "({0}) client disconnected", client_name);
-      std::unique_lock<std::mutex> lock(dap_sessions_mutex);
-      dap_sessions.erase(&loop);
-      std::notify_all_at_thread_exit(dap_sessions_condition, std::move(lock));
-
+      // Unregister the DAP session from the global manager.
+      DAPSessionManager::GetInstance().UnregisterSession(&loop);
       // Start the countdown to kill the server at the end of each connection.
       if (connection_timeout_seconds)
         TrackConnectionTimeout(g_loop, g_connection_timeout_mutex,
@@ -391,29 +382,11 @@ static llvm::Error serveConnection(
       log,
       "lldb-dap server shutdown requested, disconnecting remaining 
clients...");
 
-  bool client_failed = false;
-  {
-    std::scoped_lock<std::mutex> lock(dap_sessions_mutex);
-    for (auto [loop, dap] : dap_sessions) {
-      if (llvm::Error error = dap->Disconnect()) {
-        client_failed = true;
-        llvm::WithColor::error() << "DAP client disconnected failed: "
-                                 << llvm::toString(std::move(error)) << "\n";
-      }
-      loop->AddPendingCallback(
-          [](MainLoopBase &loop) { loop.RequestTermination(); });
-    }
-  }
-
-  // Wait for all clients to finish disconnecting.
-  std::unique_lock<std::mutex> lock(dap_sessions_mutex);
-  dap_sessions_condition.wait(lock, [&] { return dap_sessions.empty(); });
+  // Disconnect all active sessions using the global manager.
+  DAPSessionManager::GetInstance().DisconnectAllSessions();
 
-  if (client_failed)
-    return llvm::make_error<llvm::StringError>(
-        "disconnecting all clients failed", llvm::inconvertibleErrorCode());
-
-  return llvm::Error::success();
+  // Wait for all clients to finish disconnecting and return any errors.
+  return DAPSessionManager::GetInstance().WaitForAllSessionsToDisconnect();
 }
 
 int main(int argc, char *argv[]) {
@@ -641,6 +614,10 @@ int main(int argc, char *argv[]) {
     return EXIT_FAILURE;
   }
 
+  // Register the DAP session with the global manager for stdio mode.
+  // This is needed for the event handling to find the correct DAP instance.
+  DAPSessionManager::GetInstance().RegisterSession(&loop, &dap);
+
   // used only by TestVSCode_redirection_to_console.py
   if (getenv("LLDB_DAP_TEST_STDOUT_STDERR_REDIRECTION") != nullptr)
     redirection_test();
@@ -650,7 +627,9 @@ int main(int argc, char *argv[]) {
             llvm::toStringWithoutConsuming(Err));
     llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(),
                                 "DAP session error: ");
+    DAPSessionManager::GetInstance().UnregisterSession(&loop);
     return EXIT_FAILURE;
   }
+  DAPSessionManager::GetInstance().UnregisterSession(&loop);
   return EXIT_SUCCESS;
 }
diff --git a/lldb/unittests/DAP/CMakeLists.txt 
b/lldb/unittests/DAP/CMakeLists.txt
index a08414c30e6cd..cc81479c7f024 100644
--- a/lldb/unittests/DAP/CMakeLists.txt
+++ b/lldb/unittests/DAP/CMakeLists.txt
@@ -1,5 +1,6 @@
 add_lldb_unittest(DAPTests
   DAPErrorTest.cpp
+  DAPSessionManagerTest.cpp
   DAPTest.cpp
   DAPTypesTest.cpp
   FifoFilesTest.cpp
diff --git a/lldb/unittests/DAP/DAPSessionManagerTest.cpp 
b/lldb/unittests/DAP/DAPSessionManagerTest.cpp
new file mode 100644
index 0000000000000..4b30d749d028b
--- /dev/null
+++ b/lldb/unittests/DAP/DAPSessionManagerTest.cpp
@@ -0,0 +1,177 @@
+//===-- DAPSessionManagerTest.cpp ----------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "DAPSessionManager.h"
+#include "TestBase.h"
+#include "lldb/API/SBDebugger.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+using namespace lldb_dap;
+using namespace lldb;
+using namespace lldb_dap_tests;
+
+class DAPSessionManagerTest : public DAPTestBase {};
+
+TEST_F(DAPSessionManagerTest, GetInstanceReturnsSameSingleton) {
+  DAPSessionManager &instance1 = DAPSessionManager::GetInstance();
+  DAPSessionManager &instance2 = DAPSessionManager::GetInstance();
+
+  EXPECT_EQ(&instance1, &instance2);
+}
+
+TEST_F(DAPSessionManagerTest, SharedDebuggerSetAndGet) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  SBDebugger debugger = SBDebugger::Create();
+  ASSERT_TRUE(debugger.IsValid());
+
+  uint32_t target_id = 12345;
+  manager.SetSharedDebugger(target_id, debugger);
+
+  // Retrieval consumes the debugger (removes from map).
+  std::optional<SBDebugger> retrieved = manager.GetSharedDebugger(target_id);
+  ASSERT_TRUE(retrieved.has_value());
+  EXPECT_TRUE(retrieved->IsValid());
+  EXPECT_EQ(retrieved->GetID(), debugger.GetID());
+
+  // Second retrieval should fail.
+  std::optional<SBDebugger> second_retrieval =
+      manager.GetSharedDebugger(target_id);
+  EXPECT_FALSE(second_retrieval.has_value());
+
+  SBDebugger::Destroy(debugger);
+}
+
+TEST_F(DAPSessionManagerTest, GetSharedDebuggerWithInvalidId) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  std::optional<SBDebugger> result = manager.GetSharedDebugger(99999);
+
+  EXPECT_FALSE(result.has_value());
+}
+
+TEST_F(DAPSessionManagerTest, MultipleSharedDebuggersWithDifferentIds) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  SBDebugger debugger1 = SBDebugger::Create();
+  SBDebugger debugger2 = SBDebugger::Create();
+  ASSERT_TRUE(debugger1.IsValid());
+  ASSERT_TRUE(debugger2.IsValid());
+
+  uint32_t target_id_1 = 1001;
+  uint32_t target_id_2 = 1002;
+
+  manager.SetSharedDebugger(target_id_1, debugger1);
+  manager.SetSharedDebugger(target_id_2, debugger2);
+
+  std::optional<SBDebugger> retrieved1 = 
manager.GetSharedDebugger(target_id_1);
+  ASSERT_TRUE(retrieved1.has_value());
+  EXPECT_EQ(retrieved1->GetID(), debugger1.GetID());
+
+  std::optional<SBDebugger> retrieved2 = 
manager.GetSharedDebugger(target_id_2);
+  ASSERT_TRUE(retrieved2.has_value());
+  EXPECT_EQ(retrieved2->GetID(), debugger2.GetID());
+
+  SBDebugger::Destroy(debugger1);
+  SBDebugger::Destroy(debugger2);
+}
+
+TEST_F(DAPSessionManagerTest, CleanupSharedResources) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  SBDebugger debugger = SBDebugger::Create();
+  ASSERT_TRUE(debugger.IsValid());
+  manager.SetSharedDebugger(5555, debugger);
+  std::optional<SBDebugger> initial_result = manager.GetSharedDebugger(5555);
+  ASSERT_TRUE(initial_result.has_value());
+
+  manager.CleanupSharedResources();
+
+  std::optional<SBDebugger> result = manager.GetSharedDebugger(5555);
+  EXPECT_FALSE(result.has_value());
+
+  SBDebugger::Destroy(debugger);
+}
+
+// UnregisterSession uses std::notify_all_at_thread_exit, so it must be called
+// from a separate thread to properly release the mutex on thread exit.
+TEST_F(DAPSessionManagerTest, RegisterAndUnregisterSession) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  // Initially not registered.
+  std::vector<DAP *> sessions_before = manager.GetActiveSessions();
+  EXPECT_EQ(
+      std::count(sessions_before.begin(), sessions_before.end(), dap.get()), 
0);
+
+  manager.RegisterSession(&loop, dap.get());
+
+  // Should be in active sessions after registration.
+  std::vector<DAP *> sessions_after = manager.GetActiveSessions();
+  EXPECT_EQ(std::count(sessions_after.begin(), sessions_after.end(), 
dap.get()),
+            1);
+
+  // Unregister.
+  std::thread unregister_thread([&]() { manager.UnregisterSession(&loop); });
+
+  unregister_thread.join();
+
+  // There should no longer be active sessions.
+  std::vector<DAP *> sessions_final = manager.GetActiveSessions();
+  EXPECT_EQ(std::count(sessions_final.begin(), sessions_final.end(), 
dap.get()),
+            0);
+}
+
+TEST_F(DAPSessionManagerTest, DisconnectAllSessions) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  manager.RegisterSession(&loop, dap.get());
+
+  std::vector<DAP *> sessions = manager.GetActiveSessions();
+  EXPECT_EQ(std::count(sessions.begin(), sessions.end(), dap.get()), 1);
+
+  manager.DisconnectAllSessions();
+
+  // DisconnectAllSessions shutdown but doesn't wait for
+  // sessions to complete or remove them from the active sessions map.
+  sessions = manager.GetActiveSessions();
+  EXPECT_EQ(std::count(sessions.begin(), sessions.end(), dap.get()), 1);
+
+  std::thread unregister_thread([&]() { manager.UnregisterSession(&loop); });
+  unregister_thread.join();
+}
+
+TEST_F(DAPSessionManagerTest, WaitForAllSessionsToDisconnect) {
+  DAPSessionManager &manager = DAPSessionManager::GetInstance();
+
+  manager.RegisterSession(&loop, dap.get());
+
+  std::vector<DAP *> sessions = manager.GetActiveSessions();
+  EXPECT_EQ(std::count(sessions.begin(), sessions.end(), dap.get()), 1);
+
+  // Unregister after a delay to test blocking behavior.
+  std::thread unregister_thread([&]() {
+    std::this_thread::sleep_for(std::chrono::milliseconds(100));
+    manager.UnregisterSession(&loop);
+  });
+
+  // WaitForAllSessionsToDisconnect should block until unregistered.
+  auto start = std::chrono::steady_clock::now();
+  llvm::Error err = manager.WaitForAllSessionsToDisconnect();
+  EXPECT_FALSE(err);
+  auto duration = std::chrono::steady_clock::now() - start;
+
+  // Verify it waited at least 100ms.
+  EXPECT_GE(duration, std::chrono::milliseconds(100));
+
+  // Session should be unregistered now.
+  sessions = manager.GetActiveSessions();
+  EXPECT_EQ(std::count(sessions.begin(), sessions.end(), dap.get()), 0);
+
+  unregister_thread.join();
+}
diff --git a/llvm/utils/gn/secondary/lldb/tools/lldb-dap/BUILD.gn 
b/llvm/utils/gn/secondary/lldb/tools/lldb-dap/BUILD.gn
index a42f781271a21..74e1e9bfc4a53 100644
--- a/llvm/utils/gn/secondary/lldb/tools/lldb-dap/BUILD.gn
+++ b/llvm/utils/gn/secondary/lldb/tools/lldb-dap/BUILD.gn
@@ -25,6 +25,7 @@ static_library("lib") {
     "DAP.cpp",
     "DAPError.cpp",
     "DAPLog.cpp",
+    "DAPSessionManager.cpp",
     "EventHelper.cpp",
     "ExceptionBreakpoint.cpp",
     "FifoFiles.cpp",

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