GDI handle leak using TGIFImage in a second thread

Question

I have a background thread which loads images (either from disk or a server), with the goal of eventually passing them to the main thread to draw. When this second thread i

Answer 1

Unfortunately, the fix is very, very ugly. The basic idea is that the background thread must acquire a lock that the main thread holds when it's between messages.

The naive implementation is like this:

1. Lock canvas mutex.
2. Spawn background thread.
3. Wait for message.
4. Release canvas mutex.
5. Process message.
6. Lock canvas mutex.
7. Go to step 3.

Note that this means the background thread can only access GDI objects while the main thread is busy, not while it's waiting for a message. And this means the background thread cannot own any canvasses while it does not hold the mutex. These two requirements tend to be too painful. So you may need to refine the algorithm.

One refinement is to have the background thread send the main thread a message when it needs to use a canvas. This will cause the main thread to more quickly release the canvas mutex so the background thread can get it.

I think this will be enough to make you give up this idea. Instead, perhaps, read the file from the background thread but process it in the main thread.