Squashed 'src/ipc/libmultiprocess/' changes from 13424cf2ecc1..47d79db8a552

47d79db8a552 Merge bitcoin-core/libmultiprocess#201: bug: fix mptest hang, ProxyClient<Thread> deadlock in disconnect handler
f15ae9c9b9fb Merge bitcoin-core/libmultiprocess#211: Add .gitignore
4a269b21b8c8 bug: fix ProxyClient<Thread> deadlock if disconnected as IPC call is returning
85df96482c49 Use try_emplace in SetThread instead of threads.find
ca9b380ea91a Use std::optional in ConnThreads to allow shortening locks
9b0799113557 doc: describe ThreadContext struct and synchronization requirements
d60db601ed9b proxy-io.h: add Waiter::m_mutex thread safety annotations
4e365b019a9f ci: Use -Wthread-safety not -Wthread-safety-analysis
15d7bafbb001 Add .gitignore
fe1cd8c76131 Merge bitcoin-core/libmultiprocess#208: ci: Test minimum cmake version in olddeps job
b713a0b7bfbc Merge bitcoin-core/libmultiprocess#207: ci: output CMake version in CI script
0f580397c913 ci: Test minimum cmake version in olddeps job
d603dcc0eef0 ci: output CMake version in CI script

git-subtree-dir: src/ipc/libmultiprocess
git-subtree-split: 47d79db8a5528097b408e18f7b0bae11a6702d26

.gitignore

@@ -0,0 +1,5 @@
+# CMake artifacts
+/*build*
+
+# Git artifacts
+*.patch

ci/configs/llvm.bash

@@ -2,7 +2,7 @@ CI_DESC="CI job using LLVM-based libraries and tools (clang, libc++, clang-tidy,
 CI_DIR=build-llvm
 NIX_ARGS=(--arg enableLibcxx true)
 export CXX=clang++
-export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wthread-safety-analysis -Wno-unused-parameter"
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wthread-safety -Wno-unused-parameter"
 CMAKE_ARGS=(
   -G Ninja
   -DMP_ENABLE_CLANG_TIDY=ON

ci/configs/olddeps.bash

@@ -1,5 +1,5 @@
-CI_DESC="CI job using old Cap'n Proto version"
+CI_DESC="CI job using old Cap'n Proto and cmake versions"
 CI_DIR=build-olddeps
 export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-error=array-bounds"
-NIX_ARGS=(--argstr capnprotoVersion "0.7.1")
+NIX_ARGS=(--argstr capnprotoVersion "0.7.1" --argstr cmakeVersion "3.12.4")
 BUILD_ARGS=(-k)

ci/configs/sanitize.bash

@@ -1,7 +1,7 @@
 CI_DESC="CI job running ThreadSanitizer"
 CI_DIR=build-sanitize
 export CXX=clang++
-export CXXFLAGS="-ggdb -Werror -Wall -Wextra -Wpedantic -Wthread-safety-analysis -Wno-unused-parameter -fsanitize=thread"
+export CXXFLAGS="-ggdb -Werror -Wall -Wextra -Wpedantic -Wthread-safety -Wno-unused-parameter -fsanitize=thread"
 CMAKE_ARGS=()
 BUILD_ARGS=(-k -j4)
 BUILD_TARGETS=(mptest)

ci/scripts/ci.sh

@@ -17,6 +17,21 @@ fi
 
 [ -n "${CI_CLEAN-}" ] && rm -rf "${CI_DIR}"
 
-cmake -B "$CI_DIR" "${CMAKE_ARGS[@]+"${CMAKE_ARGS[@]}"}"
+cmake --version
-cmake --build "$CI_DIR" -t "${BUILD_TARGETS[@]}" -- "${BUILD_ARGS[@]+"${BUILD_ARGS[@]}"}"
+cmake_ver=$(cmake --version | awk '/version/{print $3; exit}')
-ctest --test-dir "$CI_DIR" --output-on-failure
+ver_ge() { [ "$(printf '%s\n' "$2" "$1" | sort -V | head -n1)" = "$2" ]; }
+
+src_dir=$PWD
+mkdir -p "$CI_DIR"
+cd "$CI_DIR"
+cmake "$src_dir" "${CMAKE_ARGS[@]+"${CMAKE_ARGS[@]}"}"
+if ver_ge "$cmake_ver" "3.15"; then
+  cmake --build . -t "${BUILD_TARGETS[@]}" -- "${BUILD_ARGS[@]+"${BUILD_ARGS[@]}"}"
+else
+  # Older versions of cmake can only build one target at a time with --target,
+  # and do not support -t shortcut
+  for t in "${BUILD_TARGETS[@]}"; do
+    cmake --build . --target "$t" -- "${BUILD_ARGS[@]+"${BUILD_ARGS[@]}"}"
+  done
+fi
+ctest --output-on-failure

include/mp/proxy-io.h

@@ -66,8 +66,6 @@ struct ProxyClient<Thread> : public ProxyClientBase<Thread, ::capnp::Void>
     ProxyClient(const ProxyClient&) = delete;
     ~ProxyClient();
 
-    void setDisconnectCallback(const std::function<void()>& fn);
-
     //! Reference to callback function that is run if there is a sudden
     //! disconnect and the Connection object is destroyed before this
     //! ProxyClient<Thread> object. The callback will destroy this object and
@@ -285,16 +283,16 @@ struct Waiter
     template <typename Fn>
     void post(Fn&& fn)
     {
-        const std::unique_lock<std::mutex> lock(m_mutex);
+        const Lock lock(m_mutex);
         assert(!m_fn);
         m_fn = std::forward<Fn>(fn);
         m_cv.notify_all();
     }
 
     template <class Predicate>
-    void wait(std::unique_lock<std::mutex>& lock, Predicate pred)
+    void wait(Lock& lock, Predicate pred)
     {
-        m_cv.wait(lock, [&] {
+        m_cv.wait(lock.m_lock, [&]() MP_REQUIRES(m_mutex) {
             // Important for this to be "while (m_fn)", not "if (m_fn)" to avoid
             // a lost-wakeup bug. A new m_fn and m_cv notification might be sent
             // after the fn() call and before the lock.lock() call in this loop
@@ -317,9 +315,9 @@ struct Waiter
     //! mutexes than necessary. This mutex can be held at the same time as
     //! EventLoop::m_mutex as long as Waiter::mutex is locked first and
     //! EventLoop::m_mutex is locked second.
-    std::mutex m_mutex;
+    Mutex m_mutex;
     std::condition_variable m_cv;
-    std::optional<kj::Function<void()>> m_fn;
+    std::optional<kj::Function<void()>> m_fn MP_GUARDED_BY(m_mutex);
 };
 
 //! Object holding network & rpc state associated with either an incoming server
@@ -544,29 +542,73 @@ void ProxyServerBase<Interface, Impl>::invokeDestroy()
     CleanupRun(m_context.cleanup_fns);
 }
 
-using ConnThreads = std::map<Connection*, ProxyClient<Thread>>;
+//! Map from Connection to local or remote thread handle which will be used over
+//! that connection. This map will typically only contain one entry, but can
+//! contain multiple if a single thread makes IPC calls over multiple
+//! connections. A std::optional value type is used to avoid the map needing to
+//! be locked while ProxyClient<Thread> objects are constructed, see
+//! ThreadContext "Synchronization note" below.
+using ConnThreads = std::map<Connection*, std::optional<ProxyClient<Thread>>>;
 using ConnThread = ConnThreads::iterator;
 
 // Retrieve ProxyClient<Thread> object associated with this connection from a
 // map, or create a new one and insert it into the map. Return map iterator and
 // inserted bool.
-std::tuple<ConnThread, bool> SetThread(ConnThreads& threads, std::mutex& mutex, Connection* connection, const std::function<Thread::Client()>& make_thread);
+std::tuple<ConnThread, bool> SetThread(GuardedRef<ConnThreads> threads, Connection* connection, const std::function<Thread::Client()>& make_thread);
 
+//! The thread_local ThreadContext g_thread_context struct provides information
+//! about individual threads and a way of communicating between them. Because
+//! it's a thread local struct, each ThreadContext instance is initialized by
+//! the thread that owns it.
+//!
+//! ThreadContext is used for any client threads created externally which make
+//! IPC calls, and for server threads created by
+//! ProxyServer<ThreadMap>::makeThread() which execute IPC calls for clients.
+//!
+//! In both cases, the struct holds information like the thread name, and a
+//! Waiter object where the EventLoop can post incoming IPC requests to execute
+//! on the thread. The struct also holds ConnThread maps associating the thread
+//! with local and remote ProxyClient<Thread> objects.
 struct ThreadContext
 {
     //! Identifying string for debug.
     std::string thread_name;
 
-    //! Waiter object used to allow client threads blocked waiting for a server
+    //! Waiter object used to allow remote clients to execute code on this
-    //! response to execute callbacks made from the client's corresponding
+    //! thread. For server threads created by
-    //! server thread.
+    //! ProxyServer<ThreadMap>::makeThread(), this is initialized in that
+    //! function. Otherwise, for client threads created externally, this is
+    //! initialized the first time the thread tries to make an IPC call. Having
+    //! a waiter is necessary for threads making IPC calls in case a server they
+    //! are calling expects them to execute a callback during the call, before
+    //! it sends a response.
+    //!
+    //! For IPC client threads, the Waiter pointer is never cleared and the Waiter
+    //! just gets destroyed when the thread does. For server threads created by
+    //! makeThread(), this pointer is set to null in the ~ProxyServer<Thread> as
+    //! a signal for the thread to exit and destroy itself. In both cases, the
+    //! same Waiter object is used across different calls and only created and
+    //! destroyed once for the lifetime of the thread.
     std::unique_ptr<Waiter> waiter = nullptr;
 
     //! When client is making a request to a server, this is the
     //! `callbackThread` argument it passes in the request, used by the server
     //! in case it needs to make callbacks into the client that need to execute
     //! while the client is waiting. This will be set to a local thread object.
-    ConnThreads callback_threads;
+    //!
+    //! Synchronization note: The callback_thread and request_thread maps are
+    //! only ever accessed internally by this thread's destructor and externally
+    //! by Cap'n Proto event loop threads. Since it's possible for IPC client
+    //! threads to make calls over different connections that could have
+    //! different event loops, these maps are guarded by Waiter::m_mutex in case
+    //! different event loop threads add or remove map entries simultaneously.
+    //! However, individual ProxyClient<Thread> objects in the maps will only be
+    //! associated with one event loop and guarded by EventLoop::m_mutex. So
+    //! Waiter::m_mutex does not need to be held while accessing individual
+    //! ProxyClient<Thread> instances, and may even need to be released to
+    //! respect lock order and avoid locking Waiter::m_mutex before
+    //! EventLoop::m_mutex.
+    ConnThreads callback_threads MP_GUARDED_BY(waiter->m_mutex);
 
     //! When client is making a request to a server, this is the `thread`
     //! argument it passes in the request, used to control which thread on
@@ -575,7 +617,9 @@ struct ThreadContext
     //! by makeThread. If a client call is being made from a thread currently
     //! handling a server request, this will be set to the `callbackThread`
     //! request thread argument passed in that request.
-    ConnThreads request_threads;
+    //!
+    //! Synchronization note: \ref callback_threads note applies here as well.
+    ConnThreads request_threads MP_GUARDED_BY(waiter->m_mutex);
 
     //! Whether this thread is a capnp event loop thread. Not really used except
     //! to assert false if there's an attempt to execute a blocking operation

include/mp/proxy-types.h

@@ -617,7 +617,7 @@ void clientInvoke(ProxyClient& proxy_client, const GetRequest& get_request, Fiel
     const char* disconnected = nullptr;
     proxy_client.m_context.loop->sync([&]() {
         if (!proxy_client.m_context.connection) {
-            const std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
+            const Lock lock(thread_context.waiter->m_mutex);
             done = true;
             disconnected = "IPC client method called after disconnect.";
             thread_context.waiter->m_cv.notify_all();
@@ -644,7 +644,7 @@ void clientInvoke(ProxyClient& proxy_client, const GetRequest& get_request, Fiel
                 } catch (...) {
                     exception = std::current_exception();
                 }
-                const std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
+                const Lock lock(thread_context.waiter->m_mutex);
                 done = true;
                 thread_context.waiter->m_cv.notify_all();
             },
@@ -656,13 +656,13 @@ void clientInvoke(ProxyClient& proxy_client, const GetRequest& get_request, Fiel
                     proxy_client.m_context.loop->logPlain()
                         << "{" << thread_context.thread_name << "} IPC client exception " << kj_exception;
                 }
-                const std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
+                const Lock lock(thread_context.waiter->m_mutex);
                 done = true;
                 thread_context.waiter->m_cv.notify_all();
             }));
     });
 
-    std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
+    Lock lock(thread_context.waiter->m_mutex);
     thread_context.waiter->wait(lock, [&done]() { return done; });
     if (exception) std::rethrow_exception(exception);
     if (!kj_exception.empty()) proxy_client.m_context.loop->raise() << kj_exception;

include/mp/type-context.h

@@ -25,7 +25,7 @@ void CustomBuildField(TypeList<>,
     // Also store the Thread::Client reference in the callback_threads map so
     // future calls over this connection can reuse it.
     auto [callback_thread, _]{SetThread(
-        thread_context.callback_threads, thread_context.waiter->m_mutex, &connection,
+        GuardedRef{thread_context.waiter->m_mutex, thread_context.callback_threads}, &connection,
         [&] { return connection.m_threads.add(kj::heap<ProxyServer<Thread>>(thread_context, std::thread{})); })};
 
     // Call remote ThreadMap.makeThread function so server will create a
@@ -43,12 +43,12 @@ void CustomBuildField(TypeList<>,
         return request.send().getResult(); // Nonblocking due to capnp request pipelining.
     }};
     auto [request_thread, _1]{SetThread(
-        thread_context.request_threads, thread_context.waiter->m_mutex,
+        GuardedRef{thread_context.waiter->m_mutex, thread_context.request_threads},
         &connection, make_request_thread)};
 
     auto context = output.init();
-    context.setThread(request_thread->second.m_client);
+    context.setThread(request_thread->second->m_client);
-    context.setCallbackThread(callback_thread->second.m_client);
+    context.setCallbackThread(callback_thread->second->m_client);
 }
 
 //! PassField override for mp.Context arguments. Return asynchronously and call
@@ -89,29 +89,39 @@ auto PassField(Priority<1>, TypeList<>, ServerContext& server_context, const Fn&
                     // need to update the map.
                     auto& thread_context = g_thread_context;
                     auto& request_threads = thread_context.request_threads;
-                    auto [request_thread, inserted]{SetThread(
+                    ConnThread request_thread;
-                        request_threads, thread_context.waiter->m_mutex,
+                    bool inserted;
-                        server.m_context.connection,
+                    server.m_context.loop->sync([&] {
-                        [&] { return context_arg.getCallbackThread(); })};
+                        std::tie(request_thread, inserted) = SetThread(
+                            GuardedRef{thread_context.waiter->m_mutex, request_threads}, server.m_context.connection,
+                            [&] { return context_arg.getCallbackThread(); });
+                    });
 
-                    // If an entry was inserted into the requests_threads map,
+                    // If an entry was inserted into the request_threads map,
                     // remove it after calling fn.invoke. If an entry was not
                     // inserted, one already existed, meaning this must be a
                     // recursive call (IPC call calling back to the caller which
                     // makes another IPC call), so avoid modifying the map.
                     const bool erase_thread{inserted};
                     KJ_DEFER(if (erase_thread) {
-                        std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
+                        // Erase the request_threads entry on the event loop
-                        // Call erase here with a Connection* argument instead
+                        // thread with loop->sync(), so if the connection is
-                        // of an iterator argument, because the `request_thread`
+                        // broken there is not a race between this thread and
-                        // iterator may be invalid if the connection is closed
+                        // the disconnect handler trying to destroy the thread
-                        // during this function call. More specifically, the
+                        // client object.
-                        // iterator may be invalid because SetThread adds a
+                        server.m_context.loop->sync([&] {
-                        // cleanup callback to the Connection destructor that
+                            // Look up the thread again without using existing
-                        // erases the thread from the map, and also because the
+                            // iterator since entry may no longer be there after
-                        // ProxyServer<Thread> destructor calls
+                            // a disconnect. Destroy node after releasing
-                        // request_threads.clear().
+                            // Waiter::m_mutex, so the ProxyClient<Thread>
-                        request_threads.erase(server.m_context.connection);
+                            // destructor is able to use EventLoop::mutex
+                            // without violating lock order.
+                            ConnThreads::node_type removed;
+                            {
+                                Lock lock(thread_context.waiter->m_mutex);
+                                removed = request_threads.extract(server.m_context.connection);
+                            }
+                        });
                     });
                     fn.invoke(server_context, args...);
                 }

include/mp/util.h

@@ -182,6 +182,17 @@ public:
     std::unique_lock<std::mutex> m_lock;
 };
 
+template<typename T>
+struct GuardedRef
+{
+    Mutex& mutex;
+    T& ref MP_GUARDED_BY(mutex);
+};
+
+// CTAD for Clang 16: GuardedRef{mutex, x} -> GuardedRef<decltype(x)>
+template <class U>
+GuardedRef(Mutex&, U&) -> GuardedRef<U>;
+
 //! Analog to std::lock_guard that unlocks instead of locks.
 template <typename Lock>
 struct UnlockGuard

shell.nix

@@ -3,6 +3,7 @@
 , enableLibcxx ? false # Whether to use libc++ toolchain and libraries instead of libstdc++
 , minimal ? false # Whether to create minimal shell without extra tools (faster when cross compiling)
 , capnprotoVersion ? null
+, cmakeVersion ? null
 }:
 
 let
@@ -37,12 +38,23 @@ let
   capnproto = capnprotoBase.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
   clang = if enableLibcxx then llvm.libcxxClang else llvm.clang;
   clang-tools = llvm.clang-tools.override { inherit enableLibcxx; };
+  cmakeHashes = {
+    "3.12.4" = "sha256-UlVYS/0EPrcXViz/iULUcvHA5GecSUHYS6raqbKOMZQ=";
+  };
+  cmakeBuild = if cmakeVersion == null then pkgs.cmake else (pkgs.cmake.overrideAttrs (old: {
+    version = cmakeVersion;
+    src = pkgs.fetchurl {
+      url = "https://cmake.org/files/v${lib.versions.majorMinor cmakeVersion}/cmake-${cmakeVersion}.tar.gz";
+      hash = lib.attrByPath [cmakeVersion] "" cmakeHashes;
+    };
+    patches = [];
+  })).override { isMinimalBuild = true; };
 in crossPkgs.mkShell {
   buildInputs = [
     capnproto
   ];
   nativeBuildInputs = with pkgs; [
-    cmake
+    cmakeBuild
     include-what-you-use
     ninja
   ] ++ lib.optionals (!minimal) [

src/mp/proxy.cpp

@@ -12,6 +12,7 @@
 
 #include <atomic>
 #include <capnp/capability.h>
+#include <capnp/common.h> // IWYU pragma: keep
 #include <capnp/rpc.h>
 #include <condition_variable>
 #include <functional>
@@ -25,7 +26,6 @@
 #include <kj/memory.h>
 #include <map>
 #include <memory>
-#include <mutex>
 #include <optional>
 #include <stdexcept>
 #include <string>
@@ -81,6 +81,11 @@ ProxyContext::ProxyContext(Connection* connection) : connection(connection), loo
 
 Connection::~Connection()
 {
+    // Connection destructor is always called on the event loop thread. If this
+    // is a local disconnect, it will trigger I/O, so this needs to run on the
+    // event loop thread, and if there was a remote disconnect, this is called
+    // by an onDisconnect callback directly from the event loop thread.
+    assert(std::this_thread::get_id() == m_loop->m_thread_id);
     // Shut down RPC system first, since this will garbage collect any
     // ProxyServer objects that were not freed before the connection was closed.
     // Typically all ProxyServer objects associated with this connection will be
@@ -156,6 +161,9 @@ CleanupIt Connection::addSyncCleanup(std::function<void()> fn)
 
 void Connection::removeSyncCleanup(CleanupIt it)
 {
+    // Require cleanup functions to be removed on the event loop thread to avoid
+    // needing to deal with them being removed in the middle of a disconnect.
+    assert(std::this_thread::get_id() == m_loop->m_thread_id);
     const Lock lock(m_loop->m_mutex);
     m_sync_cleanup_fns.erase(it);
 }
@@ -305,29 +313,34 @@ bool EventLoop::done() const
     return m_num_clients == 0 && m_async_fns->empty();
 }
 
-std::tuple<ConnThread, bool> SetThread(ConnThreads& threads, std::mutex& mutex, Connection* connection, const std::function<Thread::Client()>& make_thread)
+std::tuple<ConnThread, bool> SetThread(GuardedRef<ConnThreads> threads, Connection* connection, const std::function<Thread::Client()>& make_thread)
 {
-    const std::unique_lock<std::mutex> lock(mutex);
+    assert(std::this_thread::get_id() == connection->m_loop->m_thread_id);
-    auto thread = threads.find(connection);
+    ConnThread thread;
-    if (thread != threads.end()) return {thread, false};
+    bool inserted;
-    thread = threads.emplace(
+    {
-        std::piecewise_construct, std::forward_as_tuple(connection),
+        const Lock lock(threads.mutex);
-        std::forward_as_tuple(make_thread(), connection, /* destroy_connection= */ false)).first;
+        std::tie(thread, inserted) = threads.ref.try_emplace(connection);
-    thread->second.setDisconnectCallback([&threads, &mutex, thread] {
+    }
-        // Note: it is safe to use the `thread` iterator in this cleanup
+    if (inserted) {
-        // function, because the iterator would only be invalid if the map entry
+        thread->second.emplace(make_thread(), connection, /* destroy_connection= */ false);
-        // was removed, and if the map entry is removed the ProxyClient<Thread>
+        thread->second->m_disconnect_cb = connection->addSyncCleanup([threads, thread] {
-        // destructor unregisters the cleanup.
+            // Note: it is safe to use the `thread` iterator in this cleanup
+            // function, because the iterator would only be invalid if the map entry
+            // was removed, and if the map entry is removed the ProxyClient<Thread>
+            // destructor unregisters the cleanup.
 
-        // Connection is being destroyed before thread client is, so reset
+            // Connection is being destroyed before thread client is, so reset
-        // thread client m_disconnect_cb member so thread client destructor does not
+            // thread client m_disconnect_cb member so thread client destructor does not
-        // try to unregister this callback after connection is destroyed.
+            // try to unregister this callback after connection is destroyed.
-        // Remove connection pointer about to be destroyed from the map
+            thread->second->m_disconnect_cb.reset();
-        const std::unique_lock<std::mutex> lock(mutex);
+
-        thread->second.m_disconnect_cb.reset();
+            // Remove connection pointer about to be destroyed from the map
-        threads.erase(thread);
+            const Lock lock(threads.mutex);
-    });
+            threads.ref.erase(thread);
-    return {thread, true};
+        });
+    }
+    return {thread, inserted};
 }
 
 ProxyClient<Thread>::~ProxyClient()
@@ -336,17 +349,18 @@ ProxyClient<Thread>::~ProxyClient()
     // cleanup callback that was registered to handle the connection being
     // destroyed before the thread being destroyed.
     if (m_disconnect_cb) {
-        m_context.connection->removeSyncCleanup(*m_disconnect_cb);
+        // Remove disconnect callback on the event loop thread with
+        // loop->sync(), so if the connection is broken there is not a race
+        // between this thread trying to remove the callback and the disconnect
+        // handler attempting to call it.
+        m_context.loop->sync([&]() {
+            if (m_disconnect_cb) {
+                m_context.connection->removeSyncCleanup(*m_disconnect_cb);
+            }
+        });
     }
 }
 
-void ProxyClient<Thread>::setDisconnectCallback(const std::function<void()>& fn)
-{
-    assert(fn);
-    assert(!m_disconnect_cb);
-    m_disconnect_cb = m_context.connection->addSyncCleanup(fn);
-}
-
 ProxyServer<Thread>::ProxyServer(ThreadContext& thread_context, std::thread&& thread)
     : m_thread_context(thread_context), m_thread(std::move(thread))
 {
@@ -364,7 +378,7 @@ ProxyServer<Thread>::~ProxyServer()
     assert(m_thread_context.waiter.get());
     std::unique_ptr<Waiter> waiter;
     {
-        const std::unique_lock<std::mutex> lock(m_thread_context.waiter->m_mutex);
+        const Lock lock(m_thread_context.waiter->m_mutex);
         //! Reset thread context waiter pointer, as shutdown signal for done
         //! lambda passed as waiter->wait() argument in makeThread code below.
         waiter = std::move(m_thread_context.waiter);
@@ -398,7 +412,7 @@ kj::Promise<void> ProxyServer<ThreadMap>::makeThread(MakeThreadContext context)
         g_thread_context.thread_name = ThreadName(m_connection.m_loop->m_exe_name) + " (from " + from + ")";
         g_thread_context.waiter = std::make_unique<Waiter>();
         thread_context.set_value(&g_thread_context);
-        std::unique_lock<std::mutex> lock(g_thread_context.waiter->m_mutex);
+        Lock lock(g_thread_context.waiter->m_mutex);
         // Wait for shutdown signal from ProxyServer<Thread> destructor (signal
         // is just waiter getting set to null.)
         g_thread_context.waiter->wait(lock, [] { return !g_thread_context.waiter; });