fix: euroscope freezes when api is unavailable

src/CMakeLists.txt

@@ -36,6 +36,10 @@ set(src_plugin
         plugin/InternalSdk.cpp
         plugin/SdkFactory.cpp ../include/ECFMP/SdkEvents.h plugin/InternalSdkEvents.h)
 
+set(src_thread
+        thread/ThreadPool.cpp
+        thread/ThreadPool.h)
+
 set(src_time time/Clock.cpp time/Clock.h)
 
 set(ALL_FILES
@@ -49,6 +53,7 @@ set(ALL_FILES
         ${src_log}
         ${src_pch}
         ${src_plugin}
+        ${src_thread}
         ${src_time})
 
 add_library(${PROJECT_NAME} STATIC ${ALL_FILES})
@@ -59,17 +64,17 @@ set_property(TARGET ${PROJECT_NAME} PROPERTY CXX_STANDARD 20)
 target_include_directories(${PROJECT_NAME} PRIVATE
         "${CMAKE_CURRENT_SOURCE_DIR}/../third_party/nlohmann;"
         "${CMAKE_CURRENT_SOURCE_DIR}/../third_party/euroscope;"
-        )
+)
 
 target_include_directories(${PROJECT_NAME} PUBLIC
         "${CMAKE_CURRENT_SOURCE_DIR};"
         "${CMAKE_CURRENT_SOURCE_DIR}/../include;"
-        )
+)
 
 # Treat Euroscope as a system include directory to suppress warning, because they have lots
 target_include_directories(${PROJECT_NAME} SYSTEM PRIVATE
         "${CMAKE_CURRENT_SOURCE_DIR}/../third_party/euroscope;"
-        )
+)
 
 target_compile_options(${PROJECT_NAME} PRIVATE
         $<$<CONFIG:Debug>:
@@ -89,4 +94,4 @@ target_compile_options(${PROJECT_NAME} PRIVATE
         /WX;
         -Wno-unused-parameter; # Lots of interfaces don't use everything
         -Wno-missing-field-initializers; # Windows has loads of this sadly
-        )
+)

src/eventbus/AsynchronousEventDispatcher.h

@@ -1,6 +1,7 @@
 #pragma once
 #include "ECFMP/eventbus/EventListener.h"
 #include "EventDispatcher.h"
+#include "thread/ThreadPool.h"
 #include <cassert>
 #include <future>
 
@@ -10,9 +11,13 @@ namespace ECFMP::EventBus {
     class AsynchronousEventDispatcher : public EventDispatcher<EventType>
     {
         public:
-        explicit AsynchronousEventDispatcher(std::shared_ptr<EventListener<EventType>> listener) : listener(listener)
+        explicit AsynchronousEventDispatcher(
+                std::shared_ptr<EventListener<EventType>> listener, std::shared_ptr<Thread::ThreadPool> threadPool
+        )
+            : listener(listener), threadPool(threadPool)
         {
             assert(listener != nullptr && "Listener cannot be null");
+            assert(threadPool != nullptr && "Thread pool cannot be null");
         }
 
         /**
@@ -22,17 +27,19 @@ namespace ECFMP::EventBus {
         {
             // Copy the listener to ensure it is not destroyed before the event is dispatched
             auto listenerCopy = listener;
-            static_cast<void>(std::async(
-                    std::launch::async,
-                    [listenerCopy](const auto& event) {
-                        listenerCopy->OnEvent(event);
-                    },
-                    event
-            ));
+            auto eventCopy = event;
+
+            // Dispatch the event asynchronously using the thread pool
+            threadPool->Schedule([listenerCopy, eventCopy]() {
+                listenerCopy->OnEvent(eventCopy);
+            });
         };
 
         private:
         // The event listener for this dispatcher
         std::shared_ptr<EventListener<EventType>> listener;
+
+        // The thread pool to use for dispatching events
+        std::shared_ptr<Thread::ThreadPool> threadPool;
     };
 }// namespace ECFMP::EventBus

src/eventbus/EventDispatcherFactory.h

@@ -5,16 +5,20 @@
 #include "PendingEuroscopeEvents.h"
 #include "SubscriptionFlags.h"
 #include "SynchronousEventDispatcher.h"
-#include <assert.h>
+#include "thread/ThreadPool.h"
 
 namespace ECFMP::EventBus {
     class EventDispatcherFactory
     {
         public:
-        explicit EventDispatcherFactory(const std::shared_ptr<PendingEuroscopeEvents>& pendingEuroscopeEvents)
-            : pendingEuroscopeEvents(pendingEuroscopeEvents)
+        EventDispatcherFactory(
+                const std::shared_ptr<PendingEuroscopeEvents>& pendingEuroscopeEvents,
+                const std::shared_ptr<Thread::ThreadPool>& threadPool
+        )
+            : pendingEuroscopeEvents(pendingEuroscopeEvents), threadPool(threadPool)
         {
             assert(pendingEuroscopeEvents != nullptr && "pendingEuroscopeEvents cannot be null");
+            assert(threadPool != nullptr && "threadPool cannot be null");
         }
         virtual ~EventDispatcherFactory() = default;
 
@@ -26,7 +30,7 @@ namespace ECFMP::EventBus {
             case EventDispatchMode::Sync:
                 return std::make_shared<SynchronousEventDispatcher<EventType>>(listener);
             case EventDispatchMode::Async:
-                return std::make_shared<AsynchronousEventDispatcher<EventType>>(listener);
+                return std::make_shared<AsynchronousEventDispatcher<EventType>>(listener, threadPool);
             case EventDispatchMode::Euroscope:
                 return std::make_shared<EuroscopeEventDispatcher<EventType>>(listener, pendingEuroscopeEvents);
             default:
@@ -37,5 +41,8 @@ namespace ECFMP::EventBus {
         private:
         // A place that stores events that should be dispatched on the Euroscope thread.
         std::shared_ptr<PendingEuroscopeEvents> pendingEuroscopeEvents;
+
+        // The thread pool to use for dispatching events
+        std::shared_ptr<Thread::ThreadPool> threadPool;
     };
 }// namespace ECFMP::EventBus

src/eventbus/InternalEventBusFactory.cpp

@@ -1,12 +1,15 @@
 #include "eventbus/InternalEventBusFactory.h"
 #include "eventbus/PendingEuroscopeEvents.h"
 #include "plugin/InternalSdkEvents.h"
+#include "thread/ThreadPool.h"
 
 namespace ECFMP::EventBus {
     [[nodiscard]] auto MakeEventBus() -> std::shared_ptr<InternalEventBus>
     {
+        // Thread pool will get stopped when the eventbus is destroyed
+        auto threadPool = std::make_shared<Thread::ThreadPool>();
         auto pendingEuroscopeEvents = std::make_shared<PendingEuroscopeEvents>();
-        auto eventDispatcherFactory = std::make_shared<EventDispatcherFactory>(pendingEuroscopeEvents);
+        auto eventDispatcherFactory = std::make_shared<EventDispatcherFactory>(pendingEuroscopeEvents, threadPool);
 
         auto eventBus = std::make_shared<InternalEventBus>(eventDispatcherFactory);
         eventBus->SubscribeSync<Plugin::EuroscopeTimerTickEvent>(pendingEuroscopeEvents);

src/pch.h

@@ -1,5 +1,6 @@
 #pragma once
 #include <Windows.h>
+#include <algorithm>
 #include <cassert>
 #include <chrono>
 #include <functional>

src/plugin/InternalSdk.cpp

@@ -19,6 +19,7 @@ namespace ECFMP::Plugin {
 
     void InternalSdk::Destroy()
     {
+        // Resetting the event bus naturally means we wait for threads to finish.
         eventBus.reset();
     }
 

src/thread/ThreadPool.cpp

@@ -0,0 +1,84 @@
+#include "ThreadPool.h"
+#include <condition_variable>
+#include <mutex>
+#include <queue>
+#include <thread>
+
+namespace ECFMP::Thread {
+    struct ThreadPool::Impl {
+        std::vector<std::thread> threads;
+
+        std::mutex mutex;
+
+        std::condition_variable condition;
+
+        std::queue<std::function<void()>> tasks;
+
+        bool running = true;
+    };
+
+    ThreadPool::ThreadPool() : impl(std::make_unique<ThreadPool::Impl>())
+    {
+        // Create 2 threads in the pool
+        for (int i = 0; i < 2; i++) {
+            impl->threads.emplace_back([this]() {
+                while (true) {
+                    std::function<void()> task;
+
+                    // Run this block in a lock
+                    {
+                        std::unique_lock<std::mutex> lock(impl->mutex);
+
+                        // Wait for a task to be available, or for the pool to be stopped
+                        impl->condition.wait(lock, [this]() {
+                            return !impl->running || !impl->tasks.empty();
+                        });
+
+                        // If the pool is stopped, exit
+                        if (!impl->running) {
+                            return;
+                        }
+
+                        // If the pool doesn't have a task, continue
+                        if (impl->tasks.empty()) {
+                            continue;
+                        }
+
+                        // Grab the next task
+                        task = std::move(impl->tasks.front());
+                        impl->tasks.pop();
+                    }
+
+                    // Run the task
+                    task();
+                }
+            });
+        }
+    }
+
+    ThreadPool::~ThreadPool()
+    {
+        // Join all threads
+        {
+            std::unique_lock<std::mutex> lock(impl->mutex);
+            impl->running = false;
+        }
+
+        impl->condition.notify_all();
+        for (auto& thread: impl->threads) {
+            thread.join();
+        }
+    }
+
+    void ThreadPool::Schedule(const std::function<void()>& function)
+    {
+        // Run this block in a lock, add the task to the queue
+        {
+            std::unique_lock<std::mutex> lock(impl->mutex);
+            impl->tasks.emplace(function);
+        }
+
+        // Notify a thread that a task is available
+        impl->condition.notify_one();
+    }
+}// namespace ECFMP::Thread

src/thread/ThreadPool.h

@@ -0,0 +1,16 @@
+#pragma once
+
+namespace ECFMP::Thread {
+    class ThreadPool
+    {
+        public:
+        ThreadPool();
+        ~ThreadPool();
+
+        void Schedule(const std::function<void()>& function);
+
+        private:
+        struct Impl;
+        std::unique_ptr<Impl> impl;
+    };
+}// namespace ECFMP::Thread

test/CMakeLists.txt

@@ -32,7 +32,7 @@ set(test__eventbus
 
 set(test__flightinformationregion
         flightinformationregion/ConcreteFlightInformationRegionTest.cpp
-        )
+)
 
 set(test__flowmeasure
         flowmeasure/ConcreteAirportFilterTest.cpp
@@ -46,7 +46,7 @@ set(test__flowmeasure
 
 set(test__log
         log/LogDecoratorTest.cpp
-        )
+)
 
 set(test__mock
         mock/MockEuroscopeAircraft.h
@@ -57,12 +57,15 @@ set(test__mock
 set(test__pch
         pch/pch.cpp
         pch/pch.h
-        )
+)
 
 set(test__plugin
         plugin/SdkFactoryTest.cpp
         plugin/InternalSdkTest.cpp)
 
+set(test__thread
+        thread/ThreadPoolTest.cpp)
+
 set(test__other
         main.cpp
         pch/pch.cpp pch/pch.h
@@ -80,8 +83,9 @@ add_executable(${PROJECT_NAME}
         ${test__log}
         ${test__mock}
         ${test__plugin}
+        ${test__thread}
         ${test__other}
-        )
+)
 add_test(NAME ${PROJECT_NAME} COMMAND ${PROJECT_NAME})
 target_precompile_headers(${PROJECT_NAME} PRIVATE "pch/pch.h")
 
@@ -90,7 +94,7 @@ add_dependencies(${PROJECT_NAME}
         ecfmp_sdk
         gtest
         gmock
-        )
+)
 
 #### INCLUDES
 target_include_directories(${PROJECT_NAME} PUBLIC
@@ -99,12 +103,12 @@ target_include_directories(${PROJECT_NAME} PUBLIC
         "${CMAKE_CURRENT_SOURCE_DIR}/../include;"
         "${CMAKE_CURRENT_SOURCE_DIR}/../third_party/googletest/googlemock/include;"
         "${CMAKE_CURRENT_SOURCE_DIR}/../third_party/nlohmann;"
-        )
+)
 
 # Treat Euroscope as a system include directory to suppress warning, because they have lots
 target_include_directories(${PROJECT_NAME} SYSTEM PRIVATE
         "${CMAKE_CURRENT_SOURCE_DIR}/../third_party/euroscope;"
-        )
+)
 
 #### LINKS
 target_link_directories(
@@ -117,7 +121,7 @@ target_link_libraries(${PROJECT_NAME} PRIVATE
         gmock
         ecfmp_sdk
         "EuroScopePlugInDll;"
-        )
+)
 
 set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS " -m32" LINK_FLAGS "-m32" JSON_MultipleHeaders "ON ")
 
@@ -142,7 +146,7 @@ target_compile_options(${PROJECT_NAME} PRIVATE
         -Wno-unused-parameter; # Lots of interfaces don't use everything
         -Wno-missing-field-initializers; # Windows has loads of this sadly
         /EHa;
-        )
+)
 
 #### LINK OPTIONS
 target_link_options(${PROJECT_NAME} PRIVATE
@@ -159,10 +163,10 @@ target_link_options(${PROJECT_NAME} PRIVATE
         >
         /NODEFAULTLIB:LIBCMT;
         /SUBSYSTEM:CONSOLE;
-        )
+)
 
 # Post-build copy the EuroScope binary
 add_custom_command(TARGET ${PROJECT_NAME} POST_BUILD
         COMMAND ${CMAKE_COMMAND} -E copy "${CMAKE_CURRENT_SOURCE_DIR}/../lib/EuroScopePlugInDll.dll" "${PROJECT_BINARY_DIR}/EuroScopePlugInDll.dll"
         COMMENT "Copied EuroScope shared library to ${PROJECT_BINARY_DIR}/EuroScopePlugInDll.dll"
-        )
+)