4 files changed, 180 insertions, 242 deletions

diff --git a/platform/linux/src/headless_backend_egl.cpp b/platform/linux/src/headless_backend_egl.cpp
index 0784173af7..7d3a3d1ec1 100644
--- a/platform/linux/src/headless_backend_egl.cpp
+++ b/platform/linux/src/headless_backend_egl.cpp
@@ -1,5 +1,4 @@
 #include <mbgl/gl/headless_backend.hpp>
-#include <mbgl/gl/headless_display.hpp>
 
 #include <mbgl/util/logging.hpp>
 
@@ -9,11 +8,82 @@
 
 namespace mbgl {
 
+// This class provides a singleton that contains information about the configuration used for
+// instantiating new headless rendering contexts.
+class EGLDisplayConfig {
+private:
+    // Key for singleton construction.
+    struct Key { explicit Key() = default; };
+
+public:
+    EGLDisplayConfig(Key) {
+        display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
+        if (display == EGL_NO_DISPLAY) {
+            throw std::runtime_error("Failed to obtain a valid EGL display.\n");
+        }
+
+        EGLint major, minor, numConfigs;
+        if (!eglInitialize(display, &major, &minor)) {
+            throw std::runtime_error("eglInitialize() failed.\n");
+        }
+
+        if (!eglBindAPI(EGL_OPENGL_ES_API)) {
+            mbgl::Log::Error(mbgl::Event::OpenGL, "eglBindAPI(EGL_OPENGL_ES_API) returned error %d",
+                             eglGetError());
+            throw std::runtime_error("eglBindAPI() failed");
+        }
+
+        const EGLint attribs[] = {
+#if MBGL_USE_GLES2
+            EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
+#endif
+            EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
+            EGL_NONE
+        };
+
+        // Note: we're choosing an arbitrary pixel format, since we're not using the default surface
+        // anyway; all rendering will be directed to framebuffers which have their own configuration.
+        if (!eglChooseConfig(display, attribs, &config, 1, &numConfigs) || numConfigs != 1) {
+            throw std::runtime_error("Failed to choose ARGB config.\n");
+        }
+    }
+
+    ~EGLDisplayConfig() {
+        eglTerminate(display);
+    }
+
+    static std::shared_ptr<const EGLDisplayConfig> create() {
+        static std::weak_ptr<const EGLDisplayConfig> instance;
+        auto shared = instance.lock();
+        if (!shared) {
+            instance = shared = std::make_shared<EGLDisplayConfig>(Key{});
+        }
+        return shared;
+    }
+
+public:
+    EGLDisplay display = EGL_NO_DISPLAY;
+    EGLConfig config = 0;
+};
+
 struct EGLImpl : public HeadlessBackend::Impl {
-    EGLImpl(EGLContext glContext_, EGLDisplay display_, EGLConfig config_)
-            : glContext(glContext_),
-              display(display_),
-              config(config_) {
+    EGLImpl() {
+        // EGL initializes the context client version to 1 by default. We want to
+        // use OpenGL ES 2.0 which has the ability to create shader and program
+        // objects and also to write vertex and fragment shaders in the OpenGL ES
+        // Shading Language.
+        const EGLint attribs[] = {
+            EGL_CONTEXT_CLIENT_VERSION, 2,
+            EGL_NONE
+        };
+
+        eglContext = eglCreateContext(eglDisplay->display, eglDisplay->config, EGL_NO_CONTEXT, attribs);
+        if (eglContext == EGL_NO_CONTEXT) {
+            mbgl::Log::Error(mbgl::Event::OpenGL, "eglCreateContext() returned error 0x%04x",
+                             eglGetError());
+            throw std::runtime_error("Error creating the EGL context object.\n");
+        }
+
         // Create a dummy pbuffer. We will render to framebuffers anyway, but we need a pbuffer to
         // activate the context.
         // Note that to be able to create pbuffer surfaces, we need to choose a config that
@@ -25,77 +95,49 @@ struct EGLImpl : public HeadlessBackend::Impl {
             EGL_NONE
         };
 
-        glSurface = eglCreatePbufferSurface(display, config, surfAttribs);
-        if (glSurface == EGL_NO_SURFACE) {
+        eglSurface = eglCreatePbufferSurface(eglDisplay->display, eglDisplay->config, surfAttribs);
+        if (eglSurface == EGL_NO_SURFACE) {
             throw std::runtime_error("Could not create surface: " + std::to_string(eglGetError()));
         }
     }
 
-    ~EGLImpl() {
-        if (glSurface != EGL_NO_SURFACE) {
-            if (!eglDestroySurface(display, glSurface)) {
-                throw std::runtime_error("Failed to destroy EGL surface.\n");
+    ~EGLImpl() final {
+        if (eglSurface != EGL_NO_SURFACE) {
+            if (!eglDestroySurface(eglDisplay->display, eglSurface)) {
+                Log::Error(Event::OpenGL, "Failed to destroy EGL surface.");
             }
-            glSurface = EGL_NO_SURFACE;
+            eglSurface = EGL_NO_SURFACE;
         }
-        if (!eglDestroyContext(display, glContext)) {
-            throw std::runtime_error("Failed to destroy EGL context.\n");
+        if (!eglDestroyContext(eglDisplay->display, eglContext)) {
+            Log::Error(Event::OpenGL, "Failed to destroy EGL context.");
         }
     }
 
     void activateContext() final {
-        if (!eglMakeCurrent(display, glSurface, glSurface, glContext)) {
+        if (!eglMakeCurrent(eglDisplay->display, eglSurface, eglSurface, eglContext)) {
             throw std::runtime_error("Switching OpenGL context failed.\n");
         }
     }
 
     void deactivateContext() final {
-        if (!eglMakeCurrent(display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT)) {
+        if (!eglMakeCurrent(eglDisplay->display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT)) {
             throw std::runtime_error("Removing OpenGL context failed.\n");
         }
     }
 
-    EGLContext glContext = EGL_NO_CONTEXT;
-    EGLDisplay display = EGL_NO_DISPLAY;
-    EGLConfig config = 0;
-    EGLSurface glSurface = EGL_NO_SURFACE;
+private:
+    const std::shared_ptr<const EGLDisplayConfig> eglDisplay = EGLDisplayConfig::create();
+    EGLContext eglContext = EGL_NO_CONTEXT;
+    EGLSurface eglSurface = EGL_NO_SURFACE;
 };
 
 gl::ProcAddress HeadlessBackend::initializeExtension(const char* name) {
     return eglGetProcAddress(name);
 }
 
-bool HeadlessBackend::hasDisplay() {
-    if (!display) {
-        display = HeadlessDisplay::create();
-    }
-    return bool(display);
-};
-
 void HeadlessBackend::createContext() {
     assert(!hasContext());
-    assert(hasDisplay());
-
-    EGLDisplay display_ = display->attribute<EGLDisplay>();
-    EGLConfig& config = display->attribute<EGLConfig&>();
-
-    // EGL initializes the context client version to 1 by default. We want to
-    // use OpenGL ES 2.0 which has the ability to create shader and program
-    // objects and also to write vertex and fragment shaders in the OpenGL ES
-    // Shading Language.
-    const EGLint attribs[] = {
-        EGL_CONTEXT_CLIENT_VERSION, 2,
-        EGL_NONE
-    };
-
-    EGLContext glContext = eglCreateContext(display_, config, EGL_NO_CONTEXT, attribs);
-    if (glContext == EGL_NO_CONTEXT) {
-        mbgl::Log::Error(mbgl::Event::OpenGL, "eglCreateContext() returned error 0x%04x",
-                         eglGetError());
-        throw std::runtime_error("Error creating the EGL context object.\n");
-    }
-
-    impl.reset(new EGLImpl(glContext, display_, config));
+    impl = std::make_unique<EGLImpl>();
 }
 
 } // namespace mbgl
diff --git a/platform/linux/src/headless_backend_glx.cpp b/platform/linux/src/headless_backend_glx.cpp
index 0ba7f08630..6d2939da0f 100644
--- a/platform/linux/src/headless_backend_glx.cpp
+++ b/platform/linux/src/headless_backend_glx.cpp
@@ -1,5 +1,4 @@
 #include <mbgl/gl/headless_backend.hpp>
-#include <mbgl/gl/headless_display.hpp>
 
 #include <mbgl/util/logging.hpp>
 
@@ -9,79 +8,122 @@
 
 namespace mbgl {
 
+// This class provides a singleton that contains information about the configuration used for
+// instantiating new headless rendering contexts.
+class GLXDisplayConfig {
+private:
+    // Key for singleton construction.
+    struct Key { explicit Key() = default; };
+
+public:
+    GLXDisplayConfig(Key) {
+        if (!XInitThreads()) {
+            throw std::runtime_error("Failed to XInitThreads.");
+        }
+
+        xDisplay = XOpenDisplay(nullptr);
+        if (xDisplay == nullptr) {
+            throw std::runtime_error("Failed to open X display.");
+        }
+
+        const auto* extensions = reinterpret_cast<const char*>(
+            glXQueryServerString(xDisplay, DefaultScreen(xDisplay), GLX_EXTENSIONS));
+        if (!extensions) {
+            throw std::runtime_error("Cannot read GLX extensions.");
+        }
+        if (!strstr(extensions, "GLX_SGIX_fbconfig")) {
+            throw std::runtime_error("Extension GLX_SGIX_fbconfig was not found.");
+        }
+        if (!strstr(extensions, "GLX_SGIX_pbuffer")) {
+            throw std::runtime_error("Cannot find glXCreateContextAttribsARB.");
+        }
+
+        // We're creating a dummy pbuffer anyway that we're not using.
+        static int pixelFormat[] = { GLX_DRAWABLE_TYPE, GLX_PBUFFER_BIT, None };
+
+        int configs = 0;
+        fbConfigs = glXChooseFBConfig(xDisplay, DefaultScreen(xDisplay), pixelFormat, &configs);
+        if (fbConfigs == nullptr) {
+            throw std::runtime_error("Failed to glXChooseFBConfig.");
+        }
+        if (configs <= 0) {
+            throw std::runtime_error("No Framebuffer configurations.");
+        }
+    }
+
+    ~GLXDisplayConfig() {
+        XFree(fbConfigs);
+        XCloseDisplay(xDisplay);
+    }
+
+    static std::shared_ptr<const GLXDisplayConfig> create() {
+        static std::weak_ptr<const GLXDisplayConfig> instance;
+        auto shared = instance.lock();
+        if (!shared) {
+            instance = shared = std::make_shared<GLXDisplayConfig>(Key{});
+        }
+        return shared;
+    }
+
+public:
+    Display* xDisplay = nullptr;
+    GLXFBConfig* fbConfigs = nullptr;
+};
+
 struct GLXImpl : public HeadlessBackend::Impl {
-    GLXImpl(GLXContext glContext_, GLXPbuffer glxPbuffer_, Display* xDisplay_, GLXFBConfig* fbConfigs_)
-            : glContext(glContext_),
-              glxPbuffer(glxPbuffer_),
-              xDisplay(xDisplay_),
-              fbConfigs(fbConfigs_) {
+    GLXImpl() {
+        // Try to create a legacy context.
+        glContext = glXCreateNewContext(glxDisplay->xDisplay, glxDisplay->fbConfigs[0],
+                                        GLX_RGBA_TYPE, None, True);
+        if (glContext && !glXIsDirect(glxDisplay->xDisplay, glContext)) {
+            Log::Error(Event::OpenGL, "failed to create direct OpenGL Legacy context");
+            glXDestroyContext(glxDisplay->xDisplay, glContext);
+            glContext = nullptr;
+        }
+        if (glContext == nullptr) {
+            throw std::runtime_error("Error creating GL context object.");
+        }
+
+        // Create a dummy pbuffer. We will render to framebuffers anyway, but we need a pbuffer to
+        // activate the context.
+        int pbufferAttributes[] = { GLX_PBUFFER_WIDTH, 8, GLX_PBUFFER_HEIGHT, 8, None };
+        glxPbuffer =
+            glXCreatePbuffer(glxDisplay->xDisplay, glxDisplay->fbConfigs[0], pbufferAttributes);
     }
 
-    ~GLXImpl() override {
+    ~GLXImpl() final {
         if (glxPbuffer) {
-            glXDestroyPbuffer(xDisplay, glxPbuffer);
+            glXDestroyPbuffer(glxDisplay->xDisplay, glxPbuffer);
         }
-        glXDestroyContext(xDisplay, glContext);
+        glXDestroyContext(glxDisplay->xDisplay, glContext);
     }
 
     void activateContext() final {
-        if (!glXMakeContextCurrent(xDisplay, glxPbuffer, glxPbuffer, glContext)) {
+        if (!glXMakeContextCurrent(glxDisplay->xDisplay, glxPbuffer, glxPbuffer, glContext)) {
             throw std::runtime_error("Switching OpenGL context failed.\n");
         }
     }
 
     void deactivateContext() final {
-        if (!glXMakeContextCurrent(xDisplay, 0, 0, nullptr)) {
+        if (!glXMakeContextCurrent(glxDisplay->xDisplay, 0, 0, nullptr)) {
             throw std::runtime_error("Removing OpenGL context failed.\n");
         }
     }
 
+private:
+    const std::shared_ptr<const GLXDisplayConfig> glxDisplay = GLXDisplayConfig::create();
+
     GLXContext glContext = nullptr;
     GLXPbuffer glxPbuffer = 0;
-
-    // Needed for ImplDeleter.
-    Display* xDisplay = nullptr;
-    GLXFBConfig* fbConfigs = nullptr;
 };
 
 gl::ProcAddress HeadlessBackend::initializeExtension(const char* name) {
     return glXGetProcAddress(reinterpret_cast<const GLubyte*>(name));
 }
 
-bool HeadlessBackend::hasDisplay() {
-    if (!display) {
-        display = HeadlessDisplay::create();
-    }
-    return bool(display);
-};
-
 void HeadlessBackend::createContext() {
     assert(!hasContext());
-
-    auto* xDisplay = display->attribute<Display*>();
-    auto* fbConfigs = display->attribute<GLXFBConfig*>();
-
-    // Try to create a legacy context.
-    GLXContext glContext = glXCreateNewContext(xDisplay, fbConfigs[0], GLX_RGBA_TYPE, None, True);
-    if (glContext && !glXIsDirect(xDisplay, glContext)) {
-        Log::Error(Event::OpenGL, "failed to create direct OpenGL Legacy context");
-        glXDestroyContext(xDisplay, glContext);
-        glContext = nullptr;
-    }
-    if (glContext == nullptr) {
-        throw std::runtime_error("Error creating GL context object.");
-    }
-
-    // Create a dummy pbuffer. We will render to framebuffers anyway, but we need a pbuffer to
-    // activate the context.
-    int pbufferAttributes[] = {
-        GLX_PBUFFER_WIDTH, 8,
-        GLX_PBUFFER_HEIGHT, 8,
-        None
-    };
-    GLXPbuffer glxPbuffer = glXCreatePbuffer(xDisplay, fbConfigs[0], pbufferAttributes);
-
-    impl = std::make_unique<mbgl::GLXImpl>(glContext, glxPbuffer, xDisplay, fbConfigs);
+    impl = std::make_unique<GLXImpl>();
 }
 
 } // namespace mbgl
diff --git a/platform/linux/src/headless_display_egl.cpp b/platform/linux/src/headless_display_egl.cpp
deleted file mode 100644
index b746211924..0000000000
--- a/platform/linux/src/headless_display_egl.cpp
+++ /dev/null
@@ -1,68 +0,0 @@
-#include <mbgl/gl/headless_display.hpp>
-#include <mbgl/util/logging.hpp>
-#include <mbgl/util/string.hpp>
-
-#include <EGL/egl.h>
-
-namespace mbgl {
-
-class HeadlessDisplay::Impl {
-public:
-    Impl();
-    ~Impl();
-
-    EGLDisplay display = EGL_NO_DISPLAY;
-    EGLConfig config = 0;
-};
-
-HeadlessDisplay::Impl::Impl() {
-    display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
-    if (display == EGL_NO_DISPLAY) {
-        throw std::runtime_error("Failed to obtain a valid EGL display.\n");
-    }
-
-    EGLint major, minor, numConfigs;
-    if (!eglInitialize(display, &major, &minor)) {
-        throw std::runtime_error("eglInitialize() failed.\n");
-    }
-
-    if (!eglBindAPI(EGL_OPENGL_ES_API)) {
-        mbgl::Log::Error(mbgl::Event::OpenGL, "eglBindAPI(EGL_OPENGL_ES_API) returned error %d", eglGetError());
-        throw std::runtime_error("eglBindAPI() failed");
-    }
-
-    const EGLint attribs[] = {
-#if MBGL_USE_GLES2
-        EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
-#endif
-        EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
-        EGL_NONE
-    };
-
-    if (!eglChooseConfig(display, attribs, &config, 1, &numConfigs) || numConfigs != 1) {
-        throw std::runtime_error("Failed to choose ARGB config.\n");
-    }
-}
-
-HeadlessDisplay::Impl::~Impl() {
-    eglTerminate(display);
-}
-
-template <>
-EGLDisplay HeadlessDisplay::attribute() const {
-    return impl->display;
-}
-
-template <>
-EGLConfig& HeadlessDisplay::attribute() const {
-    return impl->config;
-}
-
-HeadlessDisplay::HeadlessDisplay()
-    : impl(std::make_unique<Impl>()) {
-}
-
-HeadlessDisplay::~HeadlessDisplay() {
-}
-
-} // namespace mbgl
diff --git a/platform/linux/src/headless_display_glx.cpp b/platform/linux/src/headless_display_glx.cpp
deleted file mode 100644
index 5dc342154d..0000000000
--- a/platform/linux/src/headless_display_glx.cpp
+++ /dev/null
@@ -1,78 +0,0 @@
-#include <mbgl/gl/headless_display.hpp>
-
-#include <GL/glx.h>
-
-#include <cstring>
-#include <stdexcept>
-#include <string>
-
-namespace mbgl {
-
-class HeadlessDisplay::Impl {
-public:
-    Impl();
-    ~Impl();
-
-    Display* xDisplay = nullptr;
-    GLXFBConfig* fbConfigs = nullptr;
-};
-
-HeadlessDisplay::Impl::Impl() {
-    if (!XInitThreads()) {
-        throw std::runtime_error("Failed to XInitThreads.");
-    }
-
-    xDisplay = XOpenDisplay(nullptr);
-    if (xDisplay == nullptr) {
-        throw std::runtime_error("Failed to open X display.");
-    }
-
-    const auto *extensions = reinterpret_cast<const char *>(glXQueryServerString(xDisplay, DefaultScreen(xDisplay), GLX_EXTENSIONS));
-    if (!extensions) {
-        throw std::runtime_error("Cannot read GLX extensions.");
-    }
-    if (!strstr(extensions,"GLX_SGIX_fbconfig")) {
-        throw std::runtime_error("Extension GLX_SGIX_fbconfig was not found.");
-    }
-    if (!strstr(extensions, "GLX_SGIX_pbuffer")) {
-        throw std::runtime_error("Cannot find glXCreateContextAttribsARB.");
-    }
-
-    // We're creating a dummy pbuffer anyway that we're not using.
-    static int pixelFormat[] = {
-        GLX_DRAWABLE_TYPE, GLX_PBUFFER_BIT,
-        None
-    };
-
-    int configs = 0;
-    fbConfigs = glXChooseFBConfig(xDisplay, DefaultScreen(xDisplay), pixelFormat, &configs);
-    if (fbConfigs == nullptr) {
-        throw std::runtime_error("Failed to glXChooseFBConfig.");
-    }
-    if (configs <= 0) {
-        throw std::runtime_error("No Framebuffer configurations.");
-    }
-}
-
-HeadlessDisplay::Impl::~Impl() {
-    XFree(fbConfigs);
-    XCloseDisplay(xDisplay);
-}
-
-template <>
-Display* HeadlessDisplay::attribute() const {
-    return impl->xDisplay;
-}
-
-template <>
-GLXFBConfig* HeadlessDisplay::attribute() const {
-    return impl->fbConfigs;
-}
-
-HeadlessDisplay::HeadlessDisplay()
-    : impl(std::make_unique<Impl>()) {
-}
-
-HeadlessDisplay::~HeadlessDisplay() = default;
-
-} // namespace mbgl