Tor  0.4.6.0-alpha-dev
memarea Directory Reference

lib/memarea: A fast arena-style allocator.

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Files

file  memarea.c [code]
 Implementation for memarea_t, an allocator for allocating lots of small objects that will be freed all at once.
 
file  memarea.h [code]
 Header for memarea.c.
 

Detailed Description

lib/memarea: A fast arena-style allocator.

This module has a fast "arena" style allocator, where memory is freed all at once. This kind of allocation is very fast and avoids fragmentation, at the expense of requiring all the data to be freed at the same time. We use this for parsing and diff calculations.

It's often handy to allocate a large number of tiny objects, all of which need to disappear at the same time. You can do this in tor using the memarea.c abstraction, which uses a set of grow-only buffers for allocation, and only supports a single "free" operation at the end.

Using memareas also helps you avoid memory fragmentation. You see, some libc malloc implementations perform badly on the case where a large number of small temporary objects are allocated at the same time as a few long-lived objects of similar size. But if you use tor_malloc() for the long-lived ones and a memarea for the temporary object, the malloc implementation is likelier to do better.

To create a new memarea, use memarea_new(). To drop all the storage from a memarea, and invalidate its pointers, use memarea_drop_all().

The allocation functions memarea_alloc(), memarea_alloc_zero(), memarea_memdup(), memarea_strdup(), and memarea_strndup() are analogous to the similarly-named malloc() functions. There is intentionally no memarea_free() or memarea_realloc().