1 files changed, 33 insertions, 19 deletions

diff --git a/lldb/tools/lldb-dap/DAP.cpp b/lldb/tools/lldb-dap/DAP.cpp
index 61226cc..3c4f225 100644
--- a/lldb/tools/lldb-dap/DAP.cpp
+++ b/lldb/tools/lldb-dap/DAP.cpp
@@ -26,6 +26,7 @@
 #include "lldb/API/SBEvent.h"
 #include "lldb/API/SBLanguageRuntime.h"
 #include "lldb/API/SBListener.h"
+#include "lldb/API/SBMutex.h"
 #include "lldb/API/SBProcess.h"
 #include "lldb/API/SBStream.h"
 #include "lldb/Host/JSONTransport.h"
@@ -266,40 +267,49 @@ void DAP::SendJSON(const llvm::json::Value &json) {
   Send(message);
 }
 
-void DAP::Send(const Message &message) {
-  if (const protocol::Event *event = std::get_if<protocol::Event>(&message)) {
+Id DAP::Send(const Message &message) {
+  std::lock_guard<std::mutex> guard(call_mutex);
+  Message msg = std::visit(
+      [this](auto &&msg) -> Message {
+        if (msg.seq == kCalculateSeq)
+          msg.seq = seq++;
+        return msg;
+      },
+      Message(message));
+
+  if (const protocol::Event *event = std::get_if<protocol::Event>(&msg)) {
     if (llvm::Error err = transport.Send(*event))
       DAP_LOG_ERROR(log, std::move(err), "({0}) sending event failed",
                     m_client_name);
-    return;
+    return event->seq;
   }
 
-  if (const Request *req = std::get_if<Request>(&message)) {
+  if (const Request *req = std::get_if<Request>(&msg)) {
     if (llvm::Error err = transport.Send(*req))
       DAP_LOG_ERROR(log, std::move(err), "({0}) sending request failed",
                     m_client_name);
-    return;
+    return req->seq;
   }
 
-  if (const Response *resp = std::get_if<Response>(&message)) {
+  if (const Response *resp = std::get_if<Response>(&msg)) {
     // FIXME: After all the requests have migrated from LegacyRequestHandler >
     // RequestHandler<> this should be handled in RequestHandler<>::operator().
     // If the debugger was interrupted, convert this response into a
     // 'cancelled' response because we might have a partial result.
-    llvm::Error err =
-        (debugger.InterruptRequested())
-            ? transport.Send({/*request_seq=*/resp->request_seq,
-                              /*command=*/resp->command,
-                              /*success=*/false,
-                              /*message=*/eResponseMessageCancelled,
-                              /*body=*/std::nullopt})
-            : transport.Send(*resp);
-    if (err) {
+    llvm::Error err = (debugger.InterruptRequested())
+                          ? transport.Send({
+                                /*request_seq=*/resp->request_seq,
+                                /*command=*/resp->command,
+                                /*success=*/false,
+                                /*message=*/eResponseMessageCancelled,
+                                /*body=*/std::nullopt,
+                                /*seq=*/resp->seq,
+                            })
+                          : transport.Send(*resp);
+    if (err)
       DAP_LOG_ERROR(log, std::move(err), "({0}) sending response failed",
                     m_client_name);
-      return;
-    }
-    return;
+    return resp->seq;
   }
 
   llvm_unreachable("Unexpected message type");
@@ -1443,7 +1453,11 @@ 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 to prevent deadlock when
+          // handling `modules_request`, which also requires both locks.
+          lldb::SBMutex api_mutex = GetAPIMutex();
+          const std::scoped_lock<lldb::SBMutex, std::mutex> guard(
+              api_mutex, modules_mutex);
           for (uint32_t i = 0; i < num_modules; ++i) {
             lldb::SBModule module =
                 lldb::SBTarget::GetModuleAtIndexFromEvent(i, event);