tor includes its own memory allocator.  The allocator obtains
memory from the system in a platform-dependent way.  Under UNIX, it
uses either <TT>malloc</tt>, <TT>sbrk</tt>, or <TT>mmap</tt>.
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Most static data used by the allocator, as well as that needed by the
rest of the garbage collector is stored inside the
<TT>_GC_arrays</tt> structure.
This allows the garbage collector to easily ignore the collectors own
data structures when it searches for root pointers.  Other allocator
and collector internal da