Introduce a BUILD_STATIC_UNIQUE_GLOBALS option.

Same as in Corrade. Because BUILD_STATIC is independent between Corrade
and Magnum this option is also independent -- the corner cases and bad
interactions would be otherwise too complex to handle (e.g., in case of
a dynamic Corrade and static Magnum it would be impossible to enable
this option for Magnum etc etc).

CMakeLists.txt

@@ -186,6 +186,7 @@ else()
     set(ON_EXCEPT_EMSCRIPTEN ON)
 endif()
 option(BUILD_STATIC_PIC "Build static libraries and plugins with position-independent code" ${ON_EXCEPT_EMSCRIPTEN})
+cmake_dependent_option(BUILD_STATIC_UNIQUE_GLOBALS "Build static libraries with globals unique across shared libraries" ${ON_EXCEPT_EMSCRIPTEN} "BUILD_STATIC" OFF)
 option(BUILD_PLUGINS_STATIC "Build static plugins (default are dynamic)" OFF)
 option(BUILD_TESTS "Build unit tests" OFF)
 cmake_dependent_option(BUILD_GL_TESTS "Build unit tests for OpenGL code" OFF "BUILD_TESTS;TARGET_GL" OFF)
@@ -219,6 +220,9 @@ endif()
 
 if(BUILD_STATIC)
     set(MAGNUM_BUILD_STATIC 1)
+    if(BUILD_STATIC_UNIQUE_GLOBALS)
+        set(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS 1)
+    endif()
 endif()
 
 # Check dependencies

doc/building.dox

@@ -630,6 +630,11 @@ Options controlling the build:
     code. Enabled by default when building static libraries, disable if you
     don't need this feature. On @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten"
     this option is always off.
+-   `BUILD_STATIC_UNIQUE_GLOBALS` --- Build static libraries in a way that
+    keeps their globals unique even across different shared libraries. Enabled
+    by default for static builds. May introduce additional overhead on some
+    platforms, disable if you will only link static libraries to one final
+    executable and won't use any dynamic plugins.
 -   `BUILD_PLUGINS_STATIC` --- Build plugins as static. By default, plugins are
     built as dynamic. Independent of the `BUILD_STATIC` option to allow having
     static libraries with dynamic plugins and vice versa.

doc/changelog.dox

@@ -317,6 +317,8 @@ See also:
     executable location where possible and use hardcoded paths only if
     explicitly specified. See @ref Trade::AbstractImporter::pluginSearchPaths()
     for more information.
+-   Added an ability to disable unique globals across shared libraries using
+    @ref MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS on static builds that don't need it
 
 @subsubsection changelog-latest-changes-audio Audio library
 

doc/cmake.dox

@@ -308,6 +308,9 @@ are also available as preprocessor variables if including
     included
 -   `MAGNUM_BUILD_STATIC` --- Defined if compiled as static libraries. Default
     are shared libraries.
+-   `MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS` --- Defined if static libraries keep
+    their globals unique even across different shared libraries. Enabled by
+    default for static builds.
 -   `MAGNUM_TARGET_GL` --- Defined if compiled with OpenGL interoperability
     enabled
 -   `MAGNUM_TARGET_GLES` --- Defined if compiled for OpenGL ES

modules/FindMagnum.cmake

@@ -126,6 +126,8 @@
 #  MAGNUM_BUILD_DEPRECATED      - Defined if compiled with deprecated APIs
 #   included
 #  MAGNUM_BUILD_STATIC          - Defined if compiled as static libraries
+#  MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS - Defined if static libraries keep the
+#   globals unique even across different shared libraries
 #  MAGNUM_TARGET_GL             - Defined if compiled with OpenGL interop
 #  MAGNUM_TARGET_GLES           - Defined if compiled for OpenGL ES
 #  MAGNUM_TARGET_GLES2          - Defined if compiled for OpenGL ES 2.0
@@ -249,6 +251,7 @@ string(REGEX REPLACE "\n" ";" _magnumConfigure "${_magnumConfigure}")
 set(_magnumFlags
     BUILD_DEPRECATED
     BUILD_STATIC
+    BUILD_STATIC_UNIQUE_GLOBALS
     TARGET_GL
     TARGET_GLES
     TARGET_GLES2

src/Magnum/Audio/Context.cpp

@@ -41,7 +41,7 @@
 
 #include "Magnum/Audio/Extensions.h"
 
-#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS_RT)
+#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(CORRADE_TARGET_WINDOWS_RT)
 #include "Magnum/Implementation/WindowsWeakSymbol.h"
 #endif
 
@@ -119,7 +119,7 @@ std::vector<std::string> Context::deviceSpecifierStrings() {
     return list;
 }
 
-#if !defined(MAGNUM_BUILD_STATIC) || defined(CORRADE_TARGET_WINDOWS)
+#if !defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) || defined(CORRADE_TARGET_WINDOWS)
 /* (Of course) can't be in an unnamed namespace in order to export it below
    (except for Windows, where we do extern "C" so this doesn't matter) */
 namespace {
@@ -127,8 +127,9 @@ namespace {
 
 /* Unlike GL, this isn't thread-local. Would need to implement
    ALC_EXT_thread_local_context first */
-#if !defined(MAGNUM_BUILD_STATIC) || (defined(MAGNUM_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS))
+/* What the hell is going on here with the #ifdefs?! */
-#ifdef MAGNUM_BUILD_STATIC
+#if !defined(MAGNUM_BUILD_STATIC) || !defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) || (defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(CORRADE_TARGET_WINDOWS))
+#ifdef MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS
 /* On static builds that get linked to multiple shared libraries and then used
    in a single app we want to ensure there's just one global symbol. On Linux
    it's apparently enough to just export, macOS needs the weak attribute.
@@ -152,7 +153,7 @@ extern "C" {
 }
 #endif
 
-#if !defined(MAGNUM_BUILD_STATIC) || defined(CORRADE_TARGET_WINDOWS)
+#if !defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) || defined(CORRADE_TARGET_WINDOWS)
 }
 #endif
 
@@ -161,7 +162,7 @@ extern "C" {
    pick up the same symbol of the final exe independently of the DLL it was
    called from. To avoid #ifdef hell in code below, the currentContext is
    redefined to return a value from this uniqueness-ensuring function. */
-#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS_RT)
+#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(CORRADE_TARGET_WINDOWS_RT)
 namespace {
 
 Context*& windowsCurrentContext() {

src/Magnum/Audio/Test/GlobalStateAcrossLibrariesALTest.cpp

@@ -42,9 +42,19 @@ GlobalStateAcrossLibrariesALTest::GlobalStateAcrossLibrariesALTest() {
 }
 
 void GlobalStateAcrossLibrariesALTest::test() {
+    #if defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(MAGNUM_BUILD_STATIC)
+    CORRADE_VERIFY(!"MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS enabled but MAGNUM_BUILD_STATIC not");
+    #endif
+
     Context context;
     CORRADE_VERIFY(Context::hasCurrent());
-    CORRADE_COMPARE(currentContextInALibrary(), &context);
+
+    {
+        #ifndef MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS
+        CORRADE_EXPECT_FAIL("MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS not enabled.");
+        #endif
+        CORRADE_COMPARE(currentContextInALibrary(), &context);
+    }
 }
 
 }}}}

src/Magnum/GL/Context.cpp

@@ -65,7 +65,7 @@
 #include "Magnum/GL/Implementation/TransformFeedbackState.h"
 #endif
 
-#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS_RT)
+#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(CORRADE_TARGET_WINDOWS_RT)
 #include "Magnum/Implementation/WindowsWeakSymbol.h"
 #endif
 
@@ -500,7 +500,7 @@ Containers::ArrayView<const Extension> Extension::extensions(Version version) {
     CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */
 }
 
-#if !defined(MAGNUM_BUILD_STATIC) || defined(CORRADE_TARGET_WINDOWS)
+#if !defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) || defined(CORRADE_TARGET_WINDOWS)
 /* (Of course) can't be in an unnamed namespace in order to export it below
    (except for Windows, where we do extern "C" so this doesn't matter) */
 namespace {
@@ -509,7 +509,7 @@ namespace {
 #ifdef CORRADE_BUILD_MULTITHREADED
 CORRADE_THREAD_LOCAL
 #endif
-#if defined(MAGNUM_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS)
+#if defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(CORRADE_TARGET_WINDOWS)
 /* On static builds that get linked to multiple shared libraries and then used
    in a single app we want to ensure there's just one global symbol. On Linux
    it's apparently enough to just export, macOS needs the weak attribute.
@@ -523,7 +523,7 @@ CORRADE_VISIBILITY_EXPORT
 #endif
 Context* currentContext = nullptr;
 
-#if !defined(MAGNUM_BUILD_STATIC) || defined(CORRADE_TARGET_WINDOWS)
+#if !defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) || defined(CORRADE_TARGET_WINDOWS)
 }
 #endif
 
@@ -535,7 +535,7 @@ Context* currentContext = nullptr;
    pick up the same symbol of the final exe independently of the DLL it was
    called from. To avoid #ifdef hell in code below, the currentContext is
    redefined to return a value from this uniqueness-ensuring function. */
-#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS_RT)
+#if defined(CORRADE_TARGET_WINDOWS) && defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(CORRADE_TARGET_WINDOWS_RT)
 /* Clang-CL complains that the function has a return type incompatible with C.
    I don't care, I only need an unmangled name to look up later at runtime. */
 #ifdef CORRADE_TARGET_CLANG_CL

src/Magnum/GL/Test/GlobalStateAcrossLibrariesGLTest.cpp

@@ -41,8 +41,18 @@ GlobalStateAcrossLibrariesGLTest::GlobalStateAcrossLibrariesGLTest() {
 }
 
 void GlobalStateAcrossLibrariesGLTest::test() {
+    #if defined(MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS) && !defined(MAGNUM_BUILD_STATIC)
+    CORRADE_VERIFY(!"MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS enabled but MAGNUM_BUILD_STATIC not");
+    #endif
+
     CORRADE_VERIFY(GL::Context::hasCurrent());
-    CORRADE_COMPARE(currentContextInALibrary(), &GL::Context::current());
+
+    {
+        #ifndef MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS
+        CORRADE_EXPECT_FAIL("MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS not enabled.");
+        #endif
+        CORRADE_COMPARE(currentContextInALibrary(), &GL::Context::current());
+    }
 }
 
 }}}}

src/Magnum/Magnum.h

@@ -66,6 +66,16 @@ Defined if built as static libraries. Default are shared libraries.
 #define MAGNUM_BUILD_STATIC
 #undef MAGNUM_BUILD_STATIC
 
+/**
+@brief Static library build with globals unique across shared libraries
+@m_since_latest
+
+Enabled by default in a static build.
+@see @ref building, @ref cmake
+*/
+#define MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS
+#undef MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS
+
 #ifdef MAGNUM_BUILD_DEPRECATED
 /** @brief Multi-threaded build
  * @m_deprecated_since{2019,10} Use @ref CORRADE_BUILD_MULTITHREADED instead.

src/Magnum/configure.h.cmake

@@ -27,6 +27,7 @@
 
 #cmakedefine MAGNUM_BUILD_DEPRECATED
 #cmakedefine MAGNUM_BUILD_STATIC
+#cmakedefine MAGNUM_BUILD_STATIC_UNIQUE_GLOBALS
 #cmakedefine MAGNUM_TARGET_GL
 #cmakedefine MAGNUM_TARGET_GLES
 #cmakedefine MAGNUM_TARGET_GLES2