By default, access to each heap created is serialized, which prevents multiple threads in the same process from simultaneously accessing the heap. There is a small performance cost to serialization, but mutual exclusion must be used whenever two threads heap usage might collide with a strong possibility of causing corruption of the heap.

Setting the HEAP_NO_SERIALIZE flag when the heap is created, or when a particular heap function is used, eliminates this default mutual exclusion on the heap. This flag can be safely set if only one thread accesses the heap or if the process uses another form of mutual exclusion, e.g. a mutex object, to keep multiple threads from accessing the heap at the same time. Specifying the HEAP_NO_SERIALIZE flag improves overall heap performance slightly and means the heap needs less memory overhead to maintain itself.

Interestingly enough, access to the default heap is serialized so there is no need to worry about multiple threads in a process corrupting the default heap.

Specifying the HEAP_GENERATE_EXCEPTIONS flag when the heap is created or when memory is allocated or reallocated from a heap, specifies that the heap manager will raise an exception to indicate a heap allocation function failure, rather than returning NIJLL. This flag is a useful feature if you have exception handling built into your application. Exception handling can be an effective way of triggering special events, such as low memory situations, in your application. Exception values on such exceptions are STATUS_NO_MEMORY if the allocation failed for lack of memory or

STATUS_ACCESS_VIOLATION if the allocation failed because of heap corruption or improper function parameters.

Specifying the HEAP_ZERO_MEMORY flag when memory is allocated or reallocated from a heap, specifies that the allocated memory will be initialized to zero values which is not the default.