[quote='879668022, Richie_Wu, /thread/818409?answerId=879668022#879668022, /profile/Richie_Wu'] The crash is not on demand. [/quote] Well, that makes it harder. [quote='879668022, Richie_Wu, /thread/818409?answerId=879668022#879668022, /profile/Richie_Wu'] The code I post is very independent [/quote] It’s not as independent as you think. It relies on a huge chunk of shared mutable state, namely the objects allocated on the heap. It’s very common for problems like this to be caused by memory corruption in a completely different subsystem. For example, if one subsystem over-releases an object then some other completely different subsystem can crash in CFRelease. Such crashes are often very hard to reproduce, just like this one. OTOH, hard-to-reproduce crashes like this can also be caused by concurrency problems )- I want to reiterate my previous suggest: Put your code into a small test project and run it with the standard memory debugging tools. If this is a memory management issue within your code or System Co