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Window / SFML 2.4.0, Ubuntu 16.04.2: memory leaks from GlxContext

« on: August 15, 2016, 03:29:08 am »

Hi,

I've run into what looks like memory leaks in SFML 2.4.0's GlxContext.  The last part of this post is a patch that seems to address these leaks.

Compiler information:

$ g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609
 

The following program linked against SFML 2.4.0 and compiled with -fsanitize=address emits LeakSanitizer memory leak warnings on exit.  No memory leak warnings are emitted under SFML 2.3.2.

#include <SFML/Window.hpp>

int main()
{
    sf::Window window(sf::VideoMode(640, 480), "Test window");

    window.setVisible(true);

    bool running = true;

    while (running) {
        sf::Event event;

        while (window.pollEvent(event)) {
            switch (event.type) {
                case sf::Event::Closed:
                    running = false;
                    break;
                default:
                    break;
            }
        }

        window.display();
    }

    window.close();

    return 0;
}
 

The LeakSanitizer output looks like this:

$ ./a.out

=================================================================
==10307==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 1280 byte(s) in 2 object(s) allocated from:
    #0 0x7f5089977602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
    #1 0x7f5087ed9174 in XGetVisualInfo (/usr/lib/x86_64-linux-gnu/libX11.so.6+0x3b174)
    #2 0x8e  (<unknown module>)

Direct leak of 640 byte(s) in 1 object(s) allocated from:
    #0 0x7f5089977602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
    #1 0x7f5087ed9174 in XGetVisualInfo (/usr/lib/x86_64-linux-gnu/libX11.so.6+0x3b174)
    #2 0x1f  (<unknown module>)
    #3 0x5e85223a446818ff  (<unknown module>)

Direct leak of 640 byte(s) in 1 object(s) allocated from:
    #0 0x7f5089977602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
    #1 0x7f5087ed9174 in XGetVisualInfo (/usr/lib/x86_64-linux-gnu/libX11.so.6+0x3b174)
    #2 0x1f  (<unknown module>)

(...similar warnings elided...)
 

The full compile/run session can be found at https://gitlab.peach-bun.com/snippets/27.

It looks like there are some missing XFree calls in GlxContext.cpp.  (The LeakSanitizer output unfortunately runs into la-la memory space, but valgrind gives us a better picture.) The below diff applied to SFML commit 8df84935152b89a0f569058bb66e9e1bdc095bfa seems to fix the issue:

diff --git a/src/SFML/Window/Unix/GlxContext.cpp b/src/SFML/Window/Unix/GlxContext.cpp
index 7251db2..4d4d831 100644
--- a/src/SFML/Window/Unix/GlxContext.cpp
+++ b/src/SFML/Window/Unix/GlxContext.cpp
@@ -482,8 +482,11 @@ void GlxContext::createSurface(GlxContext* shared, unsigned int width, unsigned
                 if (visual->visualid == visualInfo.visualid)
                 {
                     config = &configs[i];
+                    XFree(visual);
                     break;
                 }
+
+                XFree(visual);
             }
 
             if (config)
@@ -640,8 +643,11 @@ void GlxContext::createContext(GlxContext* shared)
             if (visual->visualid == visualInfo->visualid)
             {
                 config = &configs[i];
+                XFree(visual);
                 break;
             }
+
+            XFree(visual);
         }
 
         if (!config)
 

As far as I can tell, glXGetVisualFromFBConfig's return value is caller-owned.  The inserted XFree calls are intended to take care of that.