Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 59)

CS485G Spring 2015 59

ii. Every free region has tags and also is linked into a list of

free regions (the link is in the region itself).

iii. To allocate, traverse the free list until a good region is found.

Split it into an allocated region and a free region, adjusting

pointers and tags.

iv. To deallocate, coalesce the region into the ones before and

after if they are free; otherwise, place the region on the free

list.

(b) Slab allocator

i. For every size of allocation, maintain a slab, which is a large

region that can be subdivided into units of the given size.

ii. Each slab also has a header indicating the size and which

units are currently allocated.

iii. To allocate, ﬁnd the right slab and allocate one of its units.

If the slab is fully allocated or does not exist, start a new

slab.

iv. To deallocate, mark the unit free. If all units are free in a

slab, the entire slab may be deallocated.

(d) Buddy system

57 Garbage collection

1. Explicit free() calls are fragile.

(a) One might forget to free space, leading to a memory leak.

(b) One might free space and keep using it, perhaps through an

alias, leading to memory corruption.

need that assumption, use calloc().

(d) Returning a pointer to a local variable.

(e) Freeing a block more than once.

2. Standard alternative: automatic garbage collection.

(a) Part of the run-time library of many languages, like Java, Perl,

Macsyma.

(b) Let allocation continue until there is insufﬁcient free space.

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Cirrus Logic CS485 Manual de usuario Pagina 59