Introduce BUILD_MULTITHREADED CMake option.

Enabled by default, makes the current Magnum context a thread-local
variable instead of a global one, so it's possible to have multiple
thread-local contexts. Might have some performance implications, that's
why it's possible to disable it (but enabled by default is the safer
option).

GCC 4.7 and Apple platforms don't support thread_local, but __thread
does the job too (though on iOS not until Xcode 7.3). Also had to move
it to file-local because MSVC doesn't like having thread local variables
as part of DLL interface. (And there is *of course* no way to disable
exporting one particular member. F' that.)

CMakeLists.txt

@@ -138,6 +138,11 @@ if(BUILD_DEPRECATED)
     set(MAGNUM_BUILD_DEPRECATED 1)
 endif()
 
+option(BUILD_MULTITHREADED "Build in a way that makes it possible to use multiple thread-local Magnum contexts" ON)
+if(BUILD_MULTITHREADED)
+    set(MAGNUM_BUILD_MULTITHREADED 1)
+endif()
+
 option(BUILD_STATIC "Build static libraries (default are shared)" OFF)
 option(BUILD_STATIC_PIC "Build static libraries and plugins with position-independent code" ON)
 option(BUILD_PLUGINS_STATIC "Build static plugins (default are dynamic)" OFF)

doc/building.dox

@@ -173,6 +173,11 @@ available for desktop OpenGL only, see @ref requires-gl.
     Supported mainly on OpenGL ES drivers, for desktop OpenGL the only driver
     that supports this configuration is NVidia >= 355.
 
+By default the engine is built in a way that allows having multiple
+thread-local Magnum contents. This might cause some performance penalties -- if
+you are sure that you will never need such feature, you can disable it via the
+`BUILD_MULTITHREADED` option.
+
 The features used can be conveniently detected in depending projects both in
 CMake and C++ sources, see @ref cmake and @ref Magnum/Magnum.h for more
 information. See also @ref corrade-cmake and @ref Corrade/Corrade.h for
@@ -542,6 +547,10 @@ static libraries. You might also have problems using dynamic plugins, enable
 `BUILD_PLUGINS_STATIC` to build also plugins as static. OpenGL ES 2.0 is
 enabled by default, switch to 3.0 by disabling `TARGET_GLES2`.
 
+Please note that `BUILD_MULTITHREADED` is supported only since Xcode 7.3 and
+doesn't work on `i386` iOS Simulator, you need to disable it in order to build
+for older platforms.
+
     mkdir build-ios && cd build-ios
     cmake .. \
         -DCMAKE_TOOLCHAIN_FILE=../toolchains/generic/iOS.cmake \

doc/cmake.dox

@@ -180,6 +180,8 @@ are also available as preprocessor variables if including
     included
 -   `MAGNUM_BUILD_STATIC` -- Defined if compiled as static libraries. Default
     are shared libraries.
+-   `MAGNUM_BUILD_MULTITHREADED` -- Defined if compiled in a way that allows
+    having multiple thread-local Magnum contexts. The default.
 -   `MAGNUM_TARGET_GLES` -- Defined if compiled for OpenGL ES
 -   `MAGNUM_TARGET_GLES2` -- Defined if compiled for OpenGL ES 2.0
 -   `MAGNUM_TARGET_GLES3` -- Defined if compiled for OpenGL ES 3.0

modules/FindMagnum.cmake

@@ -105,6 +105,8 @@
 #  MAGNUM_BUILD_DEPRECATED      - Defined if compiled with deprecated APIs
 #   included
 #  MAGNUM_BUILD_STATIC          - Defined if compiled as static libraries
+#  MAGNUM_BUILD_MULTITHREADED   - Defined if compiled in a way that allows
+#   having multiple thread-local Magnum contexts
 #  MAGNUM_TARGET_GLES           - Defined if compiled for OpenGL ES
 #  MAGNUM_TARGET_GLES2          - Defined if compiled for OpenGL ES 2.0
 #  MAGNUM_TARGET_GLES3          - Defined if compiled for OpenGL ES 3.0
@@ -206,6 +208,7 @@ file(READ ${_MAGNUM_CONFIGURE_FILE} _magnumConfigure)
 set(_magnumFlags
     BUILD_DEPRECATED
     BUILD_STATIC
+    BUILD_MULTITHREADED
     TARGET_GLES
     TARGET_GLES2
     TARGET_GLES3

package/ci/travis.yml

@@ -14,10 +14,12 @@ matrix:
     compiler: clang
     env: TARGET=desktop
   - os: osx
+    osx_image: xcode7.3
     env:
     - TARGET=ios-simulator
     - TARGET_GLES2=ON
   - os: osx
+    osx_image: xcode7.3
     env:
     - TARGET=ios-simulator
     - TARGET_GLES2=OFF
@@ -59,13 +61,14 @@ install:
 - if [ "$TRAVIS_OS_NAME" == "linux" ]; then export PLATFORM_GL_API=GLX; fi
 - if [ "$TRAVIS_OS_NAME" == "osx" ]; then export PLATFORM_GL_API=CGL; fi
 - if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "ios-simulator" ]; then gem install xcpretty; fi
-- if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "ios-simulator" ]; then brew upgrade cmake; fi
+# Xcode 7.2 image doesn't have cmake installed using Homebrew, so we can't use `upgrade`
+- if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "ios-simulator" ]; then brew install cmake; fi
 - if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "emscripten" ]; then brew install emscripten && export LLVM=/usr/local/opt/emscripten/libexec/llvm/bin && emcc; fi
 - if [ "$TARGET" == "desktop" ]; then printf "[General]\ndrivers=null" > ~/.alsoftrc; fi
 
 # SDL (cached)
 - if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "desktop" ]; then brew install sdl2; fi
-- if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "ios-simulator" ]; then curl -O https://www.libsdl.org/release/SDL2-2.0.4.tar.gz && tar -xzvf SDL2-2.0.4.tar.gz && cd SDL2-2.0.4/Xcode-iOS/SDL && xcodebuild -sdk iphonesimulator8.1 | xcpretty && mkdir -p ../../../sdl2/lib && cp build/Release-iphonesimulator/libSDL2.a ../../../sdl2/lib && mkdir -p ../../../sdl2/include/SDL2 && cp -R ../../include/* ../../../sdl2/include/SDL2 && cd ../../..; fi
+- if [ "$TRAVIS_OS_NAME" == "osx" ] && [ "$TARGET" == "ios-simulator" ]; then curl -O https://www.libsdl.org/release/SDL2-2.0.4.tar.gz && tar -xzvf SDL2-2.0.4.tar.gz && cd SDL2-2.0.4/Xcode-iOS/SDL && xcodebuild -sdk iphonesimulator9.3 | xcpretty && mkdir -p ../../../sdl2/lib && cp build/Release-iphonesimulator/libSDL2.a ../../../sdl2/lib && mkdir -p ../../../sdl2/include/SDL2 && cp -R ../../include/* ../../../sdl2/include/SDL2 && cd ../../..; fi
 - if [ "$TRAVIS_OS_NAME" == "linux" ] && [ ! -e "$HOME/sdl2/include" ]; then curl -O http://www.libsdl.org/release/SDL2-2.0.4.tar.gz && tar -xzvf SDL2-2.0.4.tar.gz && cd SDL2-2.0.4 && mkdir build && cd build && cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/sdl2 -DCMAKE_BUILD_TYPE=Release && cmake --build . --target install && cd ../..; fi
 
 # GLFW (cached)

src/Magnum/Context.cpp

@@ -409,13 +409,22 @@ const std::vector<Extension>& Extension::extensions(Version version) {
     CORRADE_ASSERT_UNREACHABLE();
 }
 
-Context* Context::_current = nullptr;
+namespace {
+    #ifdef MAGNUM_BUILD_MULTITHREADED
+    #if !defined(CORRADE_GCC47_COMPATIBILITY) && !defined(CORRADE_TARGET_APPLE)
+    thread_local
+    #else
+    __thread
+    #endif
+    #endif
+    Context* currentContext = nullptr;
+}
 
-bool Context::hasCurrent() { return _current; }
+bool Context::hasCurrent() { return currentContext; }
 
 Context& Context::current() {
-    CORRADE_ASSERT(_current, "Context::current(): no current context", *_current);
-    return *_current;
+    CORRADE_ASSERT(currentContext, "Context::current(): no current context", *currentContext);
+    return *currentContext;
 }
 
 Context::Context(NoCreateT, Int argc, char** argv, void functionLoader()): _functionLoader{functionLoader}, _version{Version::None} {
@@ -448,13 +457,13 @@ Context::Context(Context&& other): _version{std::move(other._version)},
     _detectedDrivers{std::move(other._detectedDrivers)}
 {
     other._state = nullptr;
-    if(_current == &other) _current = this;
+    if(currentContext == &other) currentContext = this;
 }
 
 Context::~Context() {
     delete _state;
 
-    if(_current == this) _current = nullptr;
+    if(currentContext == this) currentContext = nullptr;
 }
 
 void Context::create() {
@@ -640,8 +649,8 @@ bool Context::tryCreate() {
     setupDriverWorkarounds();
 
     /* Set this context as current */
-    CORRADE_ASSERT(!_current, "Context: Another context currently active", false);
-    _current = this;
+    CORRADE_ASSERT(!currentContext, "Context: Another context currently active", false);
+    currentContext = this;
 
     /* Print some info and initialize state tracker (which also prints some
        more info) */

src/Magnum/Context.h

@@ -244,6 +244,8 @@ class MAGNUM_EXPORT Context {
         /**
          * @brief Whether there is any current context
          *
+         * If Magnum is built with @ref MAGNUM_BUILD_MULTITHREADED, current
+         * context is thread-local instead of global (the default).
          * @see @ref current()
          */
         static bool hasCurrent();
@@ -251,7 +253,9 @@ class MAGNUM_EXPORT Context {
         /**
          * @brief Current context
          *
-         * Expect that there is current context.
+         * Expect that there is current context. If Magnum is built with
+         * @ref MAGNUM_BUILD_MULTITHREADED, current context is thread-local
+         * instead of global (the default).
          * @see @ref hasCurrent()
          */
         static Context& current();
@@ -501,8 +505,6 @@ class MAGNUM_EXPORT Context {
         Implementation::State& state() { return *_state; }
 
     private:
-        MAGNUM_LOCAL static Context* _current;
-
         explicit Context(NoCreateT, Int argc, char** argv, void functionLoader());
 
         bool tryCreate();

src/Magnum/Magnum.h

@@ -91,6 +91,16 @@ Defined if built as static libraries. Default are shared libraries.
 #define MAGNUM_BUILD_STATIC
 #undef MAGNUM_BUILD_STATIC
 
+/**
+@brief Multi-threaded build
+
+Defined if the library is built in a way that allows multiple thread-local
+Magnum contexts. Enabled by default.
+@see @ref building, @ref cmake, @ref Context::current()
+*/
+#define MAGNUM_BUILD_MULTITHREADED
+#undef MAGNUM_BUILD_MULTITHREADED
+
 /**
 @brief OpenGL ES target
 

src/Magnum/Platform/magnum-info.cpp

@@ -246,6 +246,9 @@ MagnumInfo::MagnumInfo(const Arguments& arguments): Platform::WindowlessApplicat
     #ifdef MAGNUM_BUILD_STATIC
     Debug() << "    MAGNUM_BUILD_STATIC";
     #endif
+    #ifdef MAGNUM_BUILD_MULTITHREADED
+    Debug() << "    MAGNUM_BUILD_MULTITHREADED";
+    #endif
     #ifdef MAGNUM_TARGET_GLES
     Debug() << "    MAGNUM_TARGET_GLES";
     #endif

src/Magnum/configure.h.cmake

@@ -25,6 +25,7 @@
 
 #cmakedefine MAGNUM_BUILD_DEPRECATED
 #cmakedefine MAGNUM_BUILD_STATIC
+#cmakedefine MAGNUM_BUILD_MULTITHREADED
 #cmakedefine MAGNUM_TARGET_GLES
 #cmakedefine MAGNUM_TARGET_GLES2
 #cmakedefine MAGNUM_TARGET_GLES3