They say you try and suppress your worst memories, which explains why I can't remember anything much worse than this: On Symbian OS, the window manager managed

They say you try and suppress your worst memories, which explains why I can't remember anything much worse than this: On Symbian OS, the window manager managed all the screen drawing. All visible apps would be asked to send draw ops to the WM and it would draw them clipped to the apps's windows. And at UIQ we were adding theme wallpapers and memory hungry graphics faster than out licensees were adding RAM. And a real problem was running out of RAM drawing the screen. Doing rectangle intersections actually requires allocation, so drawing isn't constant memory. To speed up drawing we made the WM retain the draw ops. This was transparent to the apps, but a massive performance win. We made a 'transition engine' to smoothly slide between windows and smooth scroll windows and things, at a time when some Nokians confidently told me it wasn't possible :) But what if our cleverness caused an out-of-memory in the WM? I had a cunning plan... We intercepted the malloc and, if it failed, we called out a memory manager app to start zapping things. And if a second alloc attempt failed, we started discarding draw op buffers and unloading theme assets. And this seemingly worked! By making our graphics adapt dynamically to RAM usage rather than ring fencing we got much better app switching because background apps weren't getting unloaded. And then, just as the first phone with this tech was being tested (manually, by a small army), it would sometimes crash with meaningless stacks. My team jumped into the challenge thinking we were elite clever sods and all bugs were shallow. After a few days, I had to start making excuses; we were stumped. The thousand monkey tests should no pattern, only that it was often. Where was the crash coming from? A lunchtime walk cleared our heads a bit and suddenly the horrid realisation was before us: if the allocation that failed was a bitmap data block, the bitmap itself may be reaped but the stack would resume initialising RAM that malloc didn't think it had any more and in the end some other random bit of data would be interpreted as a memory address and eventually the WM would blit to it... The phone never shipped because the plug was pulled on UIQ, but I think this bug was fixed and forgotten before then.