About custom memory managers

An important part of Purify's error detection involves tracking malloc and free calls. If you use custom memory-management layers rather than calling malloc or free directly, you might need to modify them slightly to make them compatible with Purify.

You can preserve your custom memory manager's semantics and implementation during normal operation, but provide an alternate implementation that uses malloc and free when the program is Purify'd.

Types of custom memory managers

There are five categories of custom memory managers:

• Malloc veneers are layers over malloc and free that check error returns so that the callers do not have to. You do not need to modify malloc veneers when you use Purify because the actual allocation and freeing is still done by malloc and free.

• Improved mallocs are allocation packages that are better than the malloc and free in the C library. For example, they can reduce memory fragmentation or perform garbage collection. Improved mallocs present the same interface as the standard malloc and free functions.
  
  You do not need to modify improved mallocs when you use Purify because Purify does not replace the malloc, it merely intercepts calls to it.
   

• Fixed-size allocators work by requesting a large block of memory using malloc and then allocating many fixed size sub-blocks. These allocators are more efficient than malloc because the sub-blocks do not need any size overhead.
  
  You must make minor changes to fixed-size allocators when you use Purify.
  

• Pool allocators allow an application to specify a location identifier in addition to a size when making a memory allocation request, thus reducing the amount of paging. These memory managers can also support pool-level operations, such as printing or freeing an entire pool.
  
  You must make minor changes to pool allocators when you use Purify.
   

• Sbrk allocators have application-specific semantics and use the system call sbrk to allocate memory rather than using malloc. To preserve compatibility with library routines, sbrk allocators generally implement a malloc interface in addition to their application-specific interface.
  
  You must make several changes to sbrk allocators when you use Purify.