Remove utterly useless multithreading switch

Since we're using OpenGL, everything has to be done in the same thread anyways. Besides that, the actual "multithreading" implementation was basically starting an empty thread that did absolutely nothing, then wait synchronously for it to complete and join it on the next frame.

Author: kblaschke

BUILDING-cmake.md

@@ -118,7 +118,6 @@ developing libprojectM, trying experimental features or building the library for
 | CMake option           | Default | Required dependencies          | Description                                                                                                                                                   |
 |------------------------|---------|--------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `ENABLE_SDL_UI`        | `ON`    | `SDL2`                         | Builds the SDL-based test application. Only used for development testing, will not be installed.                                                              |
-| `ENABLE_THREADING`     | `ON`    |                                | Enable multithreading support for preset loading if available.                                                                                                |
 | `ENABLE_INSTALL`       | `OFF`   | Building as a CMake subproject | Enable projectM install targets when built as a subproject via `add_subdirectory()`.                                                                          |
 | `ENABLE_DEBUG_POSTFIX` | `ON`    |                                | Adds `d` (by default) to the name of any binary file in debug builds.                                                                                         |
 | `ENABLE_SYSTEM_GLM`    | `OFF`   |                                | Builds against a system-installed GLM library.                                                                                                                |

CMakeLists.txt

@@ -64,7 +64,6 @@ cmake_dependent_option(BUILD_SHARED_LIBS "Build and install libprojectM as a sha
 option(ENABLE_PLAYLIST "Enable building the playlist management library" ON)
 cmake_dependent_option(ENABLE_SDL_UI "Build the SDL2-based developer test UI" OFF "NOT ENABLE_EMSCRIPTEN" OFF)
 cmake_dependent_option(ENABLE_GLES "Enable OpenGL ES support" OFF "NOT ENABLE_EMSCRIPTEN AND NOT CMAKE_SYSTEM_NAME STREQUAL Android" ON)
-cmake_dependent_option(ENABLE_THREADING "Enable multithreading support." ON "NOT ENABLE_EMSCRIPTEN" OFF)
 option(ENABLE_BOOST_FILESYSTEM "Force the use of boost::filesystem, even if the compiler supports C++17." OFF)
 cmake_dependent_option(ENABLE_INSTALL "Enable installing projectM libraries and headers." OFF "NOT PROJECT_IS_TOP_LEVEL" ON)
 option(ENABLE_SYSTEM_GLM "Enable use of system-install GLM library" OFF)
@@ -118,13 +117,6 @@ if(ENABLE_EMSCRIPTEN)
             "SHELL:-s NO_DISABLE_EXCEPTION_CATCHING"
             )
 
-    if(ENABLE_THREADING)
-        message(AUTHOR_WARNING "Threading on emscripten is deemed stable, but may have issues. Use with care.\n"
-                "See https://emscripten.org/docs/porting/pthreads.html for more information.")
-        add_compile_options(-pthread)
-        add_link_options(-pthread)
-    endif()
-
     set(USE_GLES ON)
 else()
     if(ENABLE_SDL_UI)
@@ -168,12 +160,6 @@ else()
             endif()
         endif()
     endif()
-
-    if(ENABLE_THREADING)
-        find_package(Threads REQUIRED)
-        set(PROJECTM_USE_THREADS YES)
-    endif()
-
 endif()
 
 if(ENABLE_CXX_INTERFACE)
@@ -216,7 +202,6 @@ message(STATUS "Features:")
 message(STATUS "==============================================")
 message(STATUS "")
 message(STATUS "    Build shared libraries:  ${BUILD_SHARED_LIBS}")
-message(STATUS "    Threading:               ${ENABLE_THREADING}")
 if(ENABLE_BOOST_FILESYSTEM)
     message(STATUS "    Filesystem support:      Boost")
     message(STATUS "        Boost version:       ${Boost_VERSION}")

src/libprojectM/BackgroundWorker.hpp

@@ -128,13 +128,6 @@ if(ENABLE_INSTALL)
             )
 
     if(ENABLE_CXX_INTERFACE)
-        if(ENABLE_THREADING)
-            target_compile_definitions(projectM
-                    INTERFACE
-                    PROJECTM_USE_THREADS
-                    )
-        endif()
-
         install(FILES
                 Audio/PCM.hpp
                 ProjectM.hpp

src/libprojectM/CMakeLists.txt

@@ -32,27 +32,17 @@
 #include "Renderer/TextureManager.hpp"
 #include "Renderer/TransitionShaderManager.hpp"
 
-#if PROJECTM_USE_THREADS
-#include "libprojectM/BackgroundWorker.hpp"
-#endif
-
 namespace libprojectM {
 
 ProjectM::ProjectM()
     : m_presetFactoryManager(std::make_unique<PresetFactoryManager>())
-#if PROJECTM_USE_THREADS
-    , m_workerSync(std::make_unique<BackgroundWorkerSync>())
-#endif
 {
     Initialize();
 }
 
 ProjectM::~ProjectM()
 {
-#if PROJECTM_USE_THREADS
-    m_workerSync->FinishUp();
-    m_workerThread.join();
-#endif
+    // Can't use "=default" in the header due to unique_ptr requiring the actual type declarations.
 }
 
 void ProjectM::PresetSwitchRequestedEvent(bool) const
@@ -113,22 +103,6 @@ void ProjectM::ResetTextures()
     m_textureManager = std::make_unique<Renderer::TextureManager>(m_textureSearchPaths);
 }
 
-#if PROJECTM_USE_THREADS
-
-void ProjectM::ThreadWorker()
-{
-    while (true)
-    {
-        if (!m_workerSync->WaitForWork())
-        {
-            return;
-        }
-        m_workerSync->FinishedWork();
-    }
-}
-
-#endif
-
 void ProjectM::RenderFrame()
 {
     // Don't render if window area is zero.
@@ -137,10 +111,6 @@ void ProjectM::RenderFrame()
         return;
     }
 
-#if PROJECTM_USE_THREADS
-    std::lock_guard<std::recursive_mutex> guard(m_presetSwitchMutex);
-#endif
-
     // Update FPS and other timer values.
     m_timeKeeper->UpdateTimers();
 
@@ -181,12 +151,6 @@ void ProjectM::RenderFrame()
 
     if (m_timeKeeper->IsSmoothing() && m_transitioningPreset != nullptr)
     {
-#if PROJECTM_USE_THREADS
-        m_workerSync->WakeUpBackgroundTask();
-        // FIXME: Instead of waiting after a single render pass, check every frame if it's done.
-        m_workerSync->WaitForBackgroundTaskToFinish();
-#endif
-
         // ToDo: check if new preset is loaded.
 
         if (m_timeKeeper->SmoothRatio() >= 1.0)
@@ -256,11 +220,6 @@ void ProjectM::Initialize()
 
     LoadIdlePreset();
 
-#if PROJECTM_USE_THREADS
-    m_workerSync->Reset();
-    m_workerThread = std::thread(&ProjectM::ThreadWorker, this);
-#endif
-
     m_timeKeeper->StartPreset();
 }
 

src/libprojectM/ProjectM.cpp

@@ -40,21 +40,8 @@
 #include <string>
 #include <vector>
 
-#if PROJECTM_USE_THREADS
-
-#include <mutex>
-#include <thread>
-
-#endif
-
 namespace libprojectM {
 
-class BackgroundWorkerSync;
-
-namespace Audio {
-class BeatDetect;
-} // namespace Audio
-
 namespace Renderer {
 class CopyTexture;
 class PresetTransition;
@@ -207,13 +194,6 @@ class PROJECTM_EXPORT ProjectM
 
     auto GetRenderContext() -> Renderer::RenderContext;
 
-#if PROJECTM_USE_THREADS
-
-    void ThreadWorker();
-
-#endif
-
-
     uint32_t m_meshX{32};              //!< Per-point mesh horizontal resolution.
     uint32_t m_meshY{24};              //!< Per-point mesh vertical resolution.
     uint32_t m_targetFps{35};          //!< Target frames per second.
@@ -247,12 +227,6 @@ class PROJECTM_EXPORT ProjectM
     std::unique_ptr<Preset> m_transitioningPreset;                                //!< Destination preset when smooth preset switching.
     std::unique_ptr<Renderer::PresetTransition> m_transition;                     //!< Transition effect used for blending.
     std::unique_ptr<TimeKeeper> m_timeKeeper;                                     //!< Keeps the different timers used to render and switch presets.
-
-#if PROJECTM_USE_THREADS
-    mutable std::recursive_mutex m_presetSwitchMutex;   //!< Mutex for locking preset switching while rendering and vice versa.
-    std::thread m_workerThread;                         //!< Background worker for preloading presets.
-    std::unique_ptr<BackgroundWorkerSync> m_workerSync; //!< Background work synchronizer.
-#endif
 };
 
 } // namespace libprojectM

src/libprojectM/ProjectM.hpp

@@ -12,9 +12,6 @@ if(NOT "@ENABLE_EMSCRIPTEN@") # ENABLE_EMSCRIPTEN
         find_dependency(OpenGL)
     endif()
 endif()
-if("@ENABLE_THREADING@") # ENABLE_THREADING
-     find_dependency(Threads)
-endif()
 if("@ENABLE_BOOST_FILESYSTEM@") # ENABLE_BOOST_FILESYSTEM
     find_dependency(Boost COMPONENTS Filesystem)
 endif()