Replace std::lock_guard and std::lock with std::scoped_lock (#1758)

std::scoped_lock was introduced in C++17 and is strictly better than
std::lock_guard as it supports locking any number of mutexes safely.
It's also easier to use than std::lock for locking multiple mutexes at
once.

wpiutil/src/main/native/cpp/SafeThread.cpp

@@ -29,7 +29,7 @@ detail::SafeThreadOwnerBase::~SafeThreadOwnerBase() {
 }
 
 void detail::SafeThreadOwnerBase::Start(std::shared_ptr<SafeThread> thr) {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   if (auto thr = m_thread.lock()) return;
   m_stdThread = std::thread([=] { thr->Main(); });
   thr->m_threadId = m_stdThread.get_id();
@@ -37,7 +37,7 @@ void detail::SafeThreadOwnerBase::Start(std::shared_ptr<SafeThread> thr) {
 }
 
 void detail::SafeThreadOwnerBase::Stop() {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   if (auto thr = m_thread.lock()) {
     thr->m_active = false;
     thr->m_cond.notify_all();
@@ -63,26 +63,24 @@ void detail::SafeThreadOwnerBase::Join() {
 void detail::swap(SafeThreadOwnerBase& lhs, SafeThreadOwnerBase& rhs) noexcept {
   using std::swap;
   if (&lhs == &rhs) return;
-  std::lock(lhs.m_mutex, rhs.m_mutex);
-  std::lock_guard lock_lhs(lhs.m_mutex, std::adopt_lock);
-  std::lock_guard lock_rhs(rhs.m_mutex, std::adopt_lock);
+  std::scoped_lock lock(lhs.m_mutex, rhs.m_mutex);
   std::swap(lhs.m_stdThread, rhs.m_stdThread);
   std::swap(lhs.m_thread, rhs.m_thread);
 }
 
 detail::SafeThreadOwnerBase::operator bool() const {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   return !m_thread.expired();
 }
 
 std::thread::native_handle_type
 detail::SafeThreadOwnerBase::GetNativeThreadHandle() {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   return m_stdThread.native_handle();
 }
 
 std::shared_ptr<SafeThread> detail::SafeThreadOwnerBase::GetThreadSharedPtr()
     const {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   return m_thread.lock();
 }

wpiutil/src/main/native/cpp/TCPConnector_parallel.cpp

@@ -74,7 +74,7 @@ std::unique_ptr<NetworkStream> TCPConnector::connect_parallel(
     // don't start a new worker if we had a previously still-active connection
     // attempt to the same server
     {
-      std::lock_guard lock(local->mtx);
+      std::scoped_lock lock(local->mtx);
       if (local->active.count(active_tracker) > 0) continue;  // already in set
     }
 
@@ -85,7 +85,7 @@ std::unique_ptr<NetworkStream> TCPConnector::connect_parallel(
       if (!result->done) {
         // add to global state
         {
-          std::lock_guard lock(local->mtx);
+          std::scoped_lock lock(local->mtx);
           local->active.insert(active_tracker);
         }
 
@@ -95,13 +95,13 @@ std::unique_ptr<NetworkStream> TCPConnector::connect_parallel(
 
         // remove from global state
         {
-          std::lock_guard lock(local->mtx);
+          std::scoped_lock lock(local->mtx);
           local->active.erase(active_tracker);
         }
 
         // successful connection
         if (stream) {
-          std::lock_guard lock(result->mtx);
+          std::scoped_lock lock(result->mtx);
           if (!result->done.exchange(true)) result->stream = std::move(stream);
         }
       }

wpiutil/src/main/native/cpp/llvm/ErrorHandling.cpp

@@ -55,14 +55,14 @@ static std::mutex BadAllocErrorHandlerMutex;
 
 void wpi::install_fatal_error_handler(fatal_error_handler_t handler,
                                       void *user_data) {
-  std::lock_guard Lock(ErrorHandlerMutex);
+  std::scoped_lock Lock(ErrorHandlerMutex);
   assert(!ErrorHandler && "Error handler already registered!\n");
   ErrorHandler = handler;
   ErrorHandlerUserData = user_data;
 }
 
 void wpi::remove_fatal_error_handler() {
-  std::lock_guard Lock(ErrorHandlerMutex);
+  std::scoped_lock Lock(ErrorHandlerMutex);
   ErrorHandler = nullptr;
   ErrorHandlerUserData = nullptr;
 }
@@ -85,7 +85,7 @@ void wpi::report_fatal_error(const Twine &Reason, bool GenCrashDiag) {
   {
     // Only acquire the mutex while reading the handler, so as not to invoke a
     // user-supplied callback under a lock.
-    std::lock_guard Lock(ErrorHandlerMutex);
+    std::scoped_lock Lock(ErrorHandlerMutex);
     handler = ErrorHandler;
     handlerData = ErrorHandlerUserData;
   }
@@ -113,14 +113,14 @@ void wpi::report_fatal_error(const Twine &Reason, bool GenCrashDiag) {
 
 void wpi::install_bad_alloc_error_handler(fatal_error_handler_t handler,
                                           void *user_data) {
-  std::lock_guard Lock(BadAllocErrorHandlerMutex);
+  std::scoped_lock Lock(BadAllocErrorHandlerMutex);
   assert(!ErrorHandler && "Bad alloc error handler already registered!\n");
   BadAllocErrorHandler = handler;
   BadAllocErrorHandlerUserData = user_data;
 }
 
 void wpi::remove_bad_alloc_error_handler() {
-  std::lock_guard Lock(BadAllocErrorHandlerMutex);
+  std::scoped_lock Lock(BadAllocErrorHandlerMutex);
   BadAllocErrorHandler = nullptr;
   BadAllocErrorHandlerUserData = nullptr;
 }
@@ -131,7 +131,7 @@ void wpi::report_bad_alloc_error(const char *Reason, bool GenCrashDiag) {
   {
     // Only acquire the mutex while reading the handler, so as not to invoke a
     // user-supplied callback under a lock.
-    std::lock_guard Lock(BadAllocErrorHandlerMutex);
+    std::scoped_lock Lock(BadAllocErrorHandlerMutex);
     Handler = BadAllocErrorHandler;
     HandlerData = BadAllocErrorHandlerUserData;
   }

wpiutil/src/main/native/cpp/llvm/ManagedStatic.cpp

@@ -33,7 +33,7 @@ static wpi::mutex* getManagedStaticMutex() {
 void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);
-  std::lock_guard Lock(*getManagedStaticMutex());
+  std::scoped_lock Lock(*getManagedStaticMutex());
 
   if (!Ptr.load(std::memory_order_relaxed)) {
     void *Tmp = Creator();
@@ -65,7 +65,7 @@ void ManagedStaticBase::destroy() const {
 
 /// wpi_shutdown - Deallocate and destroy all ManagedStatic variables.
 void wpi::wpi_shutdown() {
-  std::lock_guard Lock(*getManagedStaticMutex());
+  std::scoped_lock Lock(*getManagedStaticMutex());
 
   while (StaticList)
     StaticList->destroy();

wpiutil/src/main/native/include/wpi/Signal.h

@@ -548,9 +548,7 @@ public:
     }
 
     SignalBase & operator=(SignalBase && o) {
-        lock_type lock1(m_mutex, std::defer_lock);
-        lock_type lock2(o.m_mutex, std::defer_lock);
-        std::lock(lock1, lock2);
+        std::scoped_lock lock(m_mutex, o.m_mutex);
 
         std::swap(m_func, o.m_func);
         m_block.store(o.m_block.exchange(m_block.load()));

wpiutil/src/main/native/include/wpi/priority_mutex.h

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2016-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2016-2019 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -7,7 +7,7 @@
 
 #pragma once
 
-// Allows usage with std::lock_guard without including <mutex> separately
+// Allows usage with std::scoped_lock without including <mutex> separately
 #ifdef __linux__
 #include <pthread.h>
 #endif

wpiutil/src/main/native/include/wpi/uv/Async.h

@@ -68,7 +68,7 @@ class Async final : public HandleImpl<Async<T...>, uv_async_t> {
     int err =
         uv_async_init(loop->GetRaw(), h->GetRaw(), [](uv_async_t* handle) {
           auto& h = *static_cast<Async*>(handle->data);
-          std::lock_guard lock(h.m_mutex);
+          std::scoped_lock lock(h.m_mutex);
           for (auto&& v : h.m_data) std::apply(h.wakeup, v);
           h.m_data.clear();
         });
@@ -96,7 +96,7 @@ class Async final : public HandleImpl<Async<T...>, uv_async_t> {
     }
 
     {
-      std::lock_guard lock(m_mutex);
+      std::scoped_lock lock(m_mutex);
       m_data.emplace_back(std::forward_as_tuple(std::forward<U>(u)...));
     }
     if (loop) this->Invoke(&uv_async_send, this->GetRaw());

wpiutil/src/main/native/include/wpi/uv/AsyncFunction.h

@@ -132,7 +132,7 @@ class AsyncFunction<R(T...)> final
 
     // add the parameters to the input queue
     {
-      std::lock_guard lock(m_mutex);
+      std::scoped_lock lock(m_mutex);
       m_params.emplace_back(std::piecewise_construct,
                             std::forward_as_tuple(req),
                             std::forward_as_tuple(std::forward<U>(u)...));