Replaced TransientContextLock implementation with a more elaborate one which relies on locking a single mutex and thus avoids lock order inversion. Fixes #1165.

include/SFML/Window/GlResource.hpp

@@ -75,9 +75,6 @@ protected:
         ///
         ////////////////////////////////////////////////////////////
         ~TransientContextLock();
-
-    private:
-        Context* m_context; ///< Temporary context, in case we needed to create one
     };
 };
 

src/SFML/Window/GlContext.cpp

@@ -26,6 +26,7 @@
 // Headers
 ////////////////////////////////////////////////////////////
 #include <SFML/Window/GlContext.hpp>
+#include <SFML/Window/Context.hpp>
 #include <SFML/System/ThreadLocalPtr.hpp>
 #include <SFML/System/Mutex.hpp>
 #include <SFML/System/Lock.hpp>
@@ -131,18 +132,70 @@ namespace
     // We need to make sure that no operating system context
     // or pixel format operations are performed simultaneously
     // This mutex is also used to protect the shared context
-    // from being locked on multiple threads
+    // from being locked on multiple threads and for managing
+    // the resource count
     sf::Mutex mutex;
 
+    // OpenGL resources counter
+    unsigned int resourceCount = 0;
+
     // This per-thread variable holds the current context for each thread
     sf::ThreadLocalPtr<sf::priv::GlContext> currentContext(NULL);
 
     // The hidden, inactive context that will be shared with all other contexts
     ContextType* sharedContext = NULL;
 
-    // This per-thread variable is set to point to the shared context
-    // if we had to acquire it when a TransientContextLock was required
-    sf::ThreadLocalPtr<sf::priv::GlContext> currentSharedContext(NULL);
+    // This structure contains all the state necessary to
+    // track TransientContext usage
+    struct TransientContext : private sf::NonCopyable
+    {
+        ////////////////////////////////////////////////////////////
+        /// \brief Constructor
+        ///
+        ////////////////////////////////////////////////////////////
+        TransientContext() :
+        referenceCount   (0),
+        context          (0),
+        sharedContextLock(0),
+        useSharedContext (false)
+        {
+            if (resourceCount == 0)
+            {
+                context = new sf::Context;
+            }
+            else if (!currentContext)
+            {
+                sharedContextLock = new sf::Lock(mutex);
+                useSharedContext = true;
+                sharedContext->setActive(true);
+            }
+        }
+
+        ////////////////////////////////////////////////////////////
+        /// \brief Destructor
+        ///
+        ////////////////////////////////////////////////////////////
+        ~TransientContext()
+        {
+            if (useSharedContext)
+                sharedContext->setActive(false);
+
+            delete sharedContextLock;
+            delete context;
+        }
+
+        ///////////////////////////////////////////////////////////
+        // Member data
+        ////////////////////////////////////////////////////////////
+        unsigned int referenceCount;
+        sf::Context* context;
+        sf::Lock*    sharedContextLock;
+        bool         useSharedContext;
+    };
+
+    // This per-thread variable tracks if and how a transient
+    // context is currently being used on the current thread
+    sf::ThreadLocalPtr<TransientContext> transientContext(NULL);
 
     // Supported OpenGL extensions
     std::vector<std::string> extensions;
@@ -154,12 +207,21 @@ namespace sf
 namespace priv
 {
 ////////////////////////////////////////////////////////////
-void GlContext::globalInit()
+void GlContext::initResource()
 {
+    // Protect from concurrent access
     Lock lock(mutex);
 
+    // If this is the very first resource, trigger the global context initialization
+    if (resourceCount == 0)
+    {
         if (sharedContext)
+        {
+            // Increment the resources counter
+            resourceCount++;
+
             return;
+        }
 
         // Create the shared context
         sharedContext = new ContextType(NULL);
@@ -215,12 +277,23 @@ void GlContext::globalInit()
         sharedContext->setActive(false);
     }
 
+    // Increment the resources counter
+    resourceCount++;
+}
+
 
 ////////////////////////////////////////////////////////////
-void GlContext::globalCleanup()
+void GlContext::cleanupResource()
 {
+    // Protect from concurrent access
     Lock lock(mutex);
 
+    // Decrement the resources counter
+    resourceCount--;
+
+    // If there's no more resource alive, we can trigger the global context cleanup
+    if (resourceCount == 0)
+    {
         if (!sharedContext)
             return;
 
@@ -228,33 +301,44 @@ void GlContext::globalCleanup()
         delete sharedContext;
         sharedContext = NULL;
     }
+}
 
 
 ////////////////////////////////////////////////////////////
 void GlContext::acquireTransientContext()
 {
-    // If a capable context is already active on this thread
-    // there is no need to use the shared context for the operation
-    if (currentContext)
-    {
-        currentSharedContext = NULL;
-        return;
-    }
+    // Protect from concurrent access
+    Lock lock(mutex);
 
-    mutex.lock();
-    currentSharedContext = sharedContext;
-    sharedContext->setActive(true);
+    // If this is the first TransientContextLock on this thread
+    // construct the state object
+    if (!transientContext)
+        transientContext = new TransientContext;
+
+    // Increase the reference count
+    transientContext->referenceCount++;
 }
 
 
 ////////////////////////////////////////////////////////////
 void GlContext::releaseTransientContext()
 {
-    if (!currentSharedContext)
-        return;
+    // Protect from concurrent access
+    Lock lock(mutex);
 
-    sharedContext->setActive(false);
-    mutex.unlock();
+    // Make sure a matching acquireTransientContext() was called
+    assert(transientContext);
+
+    // Decrease the reference count
+    transientContext->referenceCount--;
+
+    // If this is the last TransientContextLock that is released
+    // destroy the state object
+    if (transientContext->referenceCount == 0)
+    {
+        delete transientContext;
+        transientContext = NULL;
+    }
 }
 
 

src/SFML/Window/GlContext.hpp

@@ -49,28 +49,25 @@ class GlContext : NonCopyable
 public:
 
     ////////////////////////////////////////////////////////////
-    /// \brief Perform the global initialization
+    /// \brief Perform resource initialization
     ///
-    /// This function is called once, before the very first OpenGL
-    /// resource is created. It makes sure that everything is ready
-    /// for contexts to work properly.
-    /// Note: this function doesn't need to be thread-safe, as it
-    /// can be called only once.
+    /// This function is called every time an OpenGL resource is
+    /// created. When the first resource is initialized, it makes
+    /// sure that everything is ready for contexts to work properly.
     ///
     ////////////////////////////////////////////////////////////
-    static void globalInit();
+    static void initResource();
 
     ////////////////////////////////////////////////////////////
-    /// \brief Perform the global cleanup
+    /// \brief Perform resource cleanup
     ///
-    /// This function is called after the very last OpenGL resource
-    /// is destroyed. It makes sure that everything that was
-    /// created by initialize() is properly released.
-    /// Note: this function doesn't need to be thread-safe, as it
-    /// can be called only once.
+    /// This function is called every time an OpenGL resource is
+    /// destroyed. When the last resource is destroyed, it makes
+    /// sure that everything that was created by initResource()
+    /// is properly released.
     ///
     ////////////////////////////////////////////////////////////
-    static void globalCleanup();
+    static void cleanupResource();
 
     ////////////////////////////////////////////////////////////
     /// \brief Acquires a context for short-term use on the current thread

src/SFML/Window/GlResource.cpp

@@ -27,17 +27,6 @@
 ////////////////////////////////////////////////////////////
 #include <SFML/Window/GlResource.hpp>
 #include <SFML/Window/GlContext.hpp>
-#include <SFML/Window/Context.hpp>
-#include <SFML/System/Mutex.hpp>
-#include <SFML/System/Lock.hpp>
-
-
-namespace
-{
-    // OpenGL resources counter and its mutex
-    unsigned int count = 0;
-    sf::Mutex mutex;
-}
 
 
 namespace sf
@@ -45,45 +34,20 @@ namespace sf
 ////////////////////////////////////////////////////////////
 GlResource::GlResource()
 {
-    // Protect from concurrent access
-    Lock lock(mutex);
-
-    // If this is the very first resource, trigger the global context initialization
-    if (count == 0)
-        priv::GlContext::globalInit();
-
-    // Increment the resources counter
-    count++;
+    priv::GlContext::initResource();
 }
 
 
 ////////////////////////////////////////////////////////////
 GlResource::~GlResource()
 {
-    // Protect from concurrent access
-    Lock lock(mutex);
-
-    // Decrement the resources counter
-    count--;
-
-    // If there's no more resource alive, we can trigger the global context cleanup
-    if (count == 0)
-        priv::GlContext::globalCleanup();
+    priv::GlContext::cleanupResource();
 }
 
 
 ////////////////////////////////////////////////////////////
-GlResource::TransientContextLock::TransientContextLock() :
-m_context(0)
+GlResource::TransientContextLock::TransientContextLock()
 {
-    Lock lock(mutex);
-
-    if (count == 0)
-    {
-        m_context = new Context;
-        return;
-    }
-
     priv::GlContext::acquireTransientContext();
 }
 
@@ -91,12 +55,6 @@ m_context(0)
 ////////////////////////////////////////////////////////////
 GlResource::TransientContextLock::~TransientContextLock()
 {
-    if (m_context)
-    {
-        delete m_context;
-        return;
-    }
-
     priv::GlContext::releaseTransientContext();
 }