Merge lp:~alan-griffiths/miral/fix-1575211 into lp:miral

[Alan Griffiths]

examples: fix racy code that failed to ensure buffers are posted exactly once

examples: fix racy code that failed to ensure buffers are posted exactly once

[Cemil Azizoglu (cemil-azizoglu)]

yep

review: Approve

[Alan Griffiths (alan-griffiths)]

same fix has landed in Mir

=== modified file 'miral-shell/titlebar/canonical_window_management_policy_data.cpp'
--- miral-shell/titlebar/canonical_window_management_policy_data.cpp	2016-04-16 23:13:59 +0000
+++ miral-shell/titlebar/canonical_window_management_policy_data.cpp	2016-04-27 12:03:25 +0000
@@ -43,29 +43,29 @@
     SwappingPainter(std::shared_ptr<mir::frontend::BufferStream> const& buffer_stream) :
         buffer_stream{buffer_stream}, buffer{nullptr}
     {
-        swap_buffers();
+        swap_buffers(nullptr);
     }
 
-    void swap_buffers()
+    void swap_buffers(mir::graphics::Buffer* buf)
     {
         auto const callback = [this](mir::graphics::Buffer* new_buffer)
             {
-            buffer.store(new_buffer);
+                buffer.store(new_buffer);
             };
 
-        buffer_stream->swap_buffers(buffer, callback);
+        buffer_stream->swap_buffers(buf, callback);
     }
 
     void paint(int intensity) override
     {
-        if (auto const buf = buffer.load())
+        if (auto const buf = buffer.exchange(nullptr))
         {
             auto const format = buffer_stream->pixel_format();
             auto const sz = buf->size().height.as_int() *
                             buf->size().width.as_int() * MIR_BYTES_PER_PIXEL(format);
             std::vector<unsigned char> pixels(sz, intensity);
             buf->write(pixels.data(), sz);
-            swap_buffers();
+            swap_buffers(buf);
         }
     }