Freeing Freed Memory (FFM)

Memory Profiling for C and C++

An FFM message indicates that the program is trying to free memory that has previously been freed.

This message can occur when one function frees the memory, but a data structure retains a pointer to that memory and later a different function tries to free the same memory. This message can also occur if the heap is corrupted.

Memory Profiling maintains a free queue, whose role is to actually delay memory free calls in order to compare with upcoming free calls. The length of the delay depends on the Free queue length and Free queue threshold Memory Profiling Settings. A large deferred free queue length and threshold increases the chances of catching FFM errors long after the block has been freed. A smaller deferred free queue length and threshold limits the amount of memory on the deferred free queue, taking up less memory at run time but providing a lower level of error detection.