GL: test for multithreaded behavior of GL::Context.

src/Magnum/GL/Test/CMakeLists.txt

@@ -106,7 +106,6 @@ endif()
 if(BUILD_GL_TESTS)
     corrade_add_test(GLAbstractTextureGLTest AbstractTextureGLTest.cpp LIBRARIES MagnumOpenGLTester)
     corrade_add_test(GLBufferGLTest BufferGLTest.cpp LIBRARIES MagnumOpenGLTester)
-    corrade_add_test(GLContextGLTest ContextGLTest.cpp LIBRARIES MagnumOpenGLTester)
     corrade_add_test(GLCubeMapTextureGLTest CubeMapTextureGLTest.cpp LIBRARIES MagnumOpenGLTester)
     corrade_add_test(GLFramebufferGLTest FramebufferGLTest.cpp LIBRARIES MagnumOpenGLTester)
     corrade_add_test(GLMeshGLTest MeshGLTest.cpp LIBRARIES MagnumOpenGLTesterTestLib)
@@ -120,6 +119,12 @@ if(BUILD_GL_TESTS)
         ${GLAbstractShaderProgramGLTest_RES}
         LIBRARIES MagnumOpenGLTester)
 
+    corrade_add_test(GLContextGLTest ContextGLTest.cpp LIBRARIES MagnumOpenGLTester)
+    if(NOT CORRADE_TARGET_EMSCRIPTEN)
+        find_package(Threads REQUIRED)
+        target_link_libraries(GLContextGLTest PRIVATE Threads::Threads)
+    endif()
+
     if(CORRADE_TARGET_EMSCRIPTEN OR CORRADE_TARGET_ANDROID)
         set(SHADERGLTEST_FILES_DIR "ShaderGLTestFiles")
     else()

src/Magnum/GL/Test/ContextGLTest.cpp

@@ -29,11 +29,19 @@
 #include "Magnum/GL/Extensions.h"
 #include "Magnum/GL/OpenGLTester.h"
 
+#ifndef CORRADE_TARGET_EMSCRIPTEN
+#include <thread>
+#endif
+
 namespace Magnum { namespace GL { namespace Test { namespace {
 
 struct ContextGLTest: OpenGLTester {
     explicit ContextGLTest();
 
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
+    void multithreaded();
+    #endif
+
     void isVersionSupported();
     #ifndef MAGNUM_TARGET_GLES
     void isVersionSupportedES();
@@ -44,15 +52,51 @@ struct ContextGLTest: OpenGLTester {
 };
 
 ContextGLTest::ContextGLTest() {
-    addTests({&ContextGLTest::isVersionSupported,
-              #ifndef MAGNUM_TARGET_GLES
-              &ContextGLTest::isVersionSupportedES,
-              #endif
-              &ContextGLTest::supportedVersion,
-              &ContextGLTest::isExtensionSupported,
-              &ContextGLTest::isExtensionDisabled});
+    addTests({
+        #ifndef CORRADE_TARGET_EMSCRIPTEN
+        &ContextGLTest::multithreaded,
+        #endif
+
+        &ContextGLTest::isVersionSupported,
+        #ifndef MAGNUM_TARGET_GLES
+        &ContextGLTest::isVersionSupportedES,
+        #endif
+        &ContextGLTest::supportedVersion,
+        &ContextGLTest::isExtensionSupported,
+        &ContextGLTest::isExtensionDisabled});
 }
 
+#ifndef CORRADE_TARGET_EMSCRIPTEN
+void ContextGLTest::multithreaded() {
+    CORRADE_VERIFY(Context::hasCurrent());
+    Containers::Optional<bool> otherThreadHasCurrent;
+
+    std::thread t{[](Containers::Optional<bool>& hasCurrent) {
+        hasCurrent = Context::hasCurrent();
+    }, std::ref(otherThreadHasCurrent)};
+
+    t.join();
+
+    CORRADE_VERIFY(otherThreadHasCurrent);
+
+    Debug{} << "MAGNUM_BUILD_MULTITHREADED defined:" <<
+        #ifdef MAGNUM_BUILD_MULTITHREADED
+        true
+        #else
+        false
+        #endif
+        ;
+
+    Debug{} << "Current context visible in another thread:" << *otherThreadHasCurrent;
+
+    #ifdef MAGNUM_BUILD_MULTITHREADED
+    CORRADE_VERIFY(!*otherThreadHasCurrent);
+    #else
+    CORRADE_VERIFY(*otherThreadHasCurrent);
+    #endif
+}
+#endif
+
 void ContextGLTest::isVersionSupported() {
     const Version v = Context::current().version();
     CORRADE_VERIFY(Context::current().isVersionSupported(v));