forked from 0ad/0ad
97 lines
2.7 KiB
C
97 lines
2.7 KiB
C
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/**
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* =========================================================================
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* File : bucket.h
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* Project : 0 A.D.
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* Description : bucket allocator
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#ifndef INCLUDED_BUCKET
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#define INCLUDED_BUCKET
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/**
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* allocator design goals:
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* - either fixed- or variable-sized blocks;
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* - allow freeing individual blocks if they are all fixed-size;
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* - never relocates;
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* - no fixed limit.
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*
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* note: this type of allocator is called "region-based" in the literature
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* and is also known as "obstack"; see "Reconsidering Custom Memory
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* Allocation" (Berger, Zorn, McKinley).
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* if individual variable-size elements must be freeable, consider "reaps":
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* basically a combination of region and heap, where frees go to the heap and
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* allocs exhaust that memory first and otherwise use the region.
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*
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* opaque! do not read/write any fields!
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**/
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struct Bucket
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{
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/**
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* currently open bucket.
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**/
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u8* bucket;
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/**
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* offset of free space at end of current bucket (i.e. # bytes in use).
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**/
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size_t pos;
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void* freelist;
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size_t el_size : 16;
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/**
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* records # buckets allocated; verifies the list of buckets is correct.
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**/
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uint num_buckets : 16;
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};
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/**
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* ready the Bucket object for use.
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*
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* @param Bucket*
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* @param el_size 0 to allow variable-sized allocations (which cannot be
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* freed individually); otherwise, it specifies the number of bytes that
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* will be returned by bucket_alloc (whose size parameter is then ignored).
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* @return LibError.
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**/
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extern LibError bucket_create(Bucket* b, size_t el_size);
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/**
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* free all memory that ensued from <b>.
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*
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* future alloc and free calls on this Bucket will fail.
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*
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* @param Bucket*
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**/
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extern void bucket_destroy(Bucket* b);
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/**
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* Dole out memory from the Bucket.
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* exhausts the freelist before returning new entries to improve locality.
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*
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* @param Bucket*
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* @param size bytes to allocate; ignored if bucket_create's el_size was not 0.
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* @return allocated memory, or 0 if the Bucket would have to be expanded and
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* there isn't enough memory to do so.
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**/
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extern void* bucket_alloc(Bucket* b, size_t size);
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/**
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* make an entry available for reuse in the given Bucket.
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*
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* this is not allowed if created for variable-size elements.
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* rationale: avoids having to pass el_size here and compare with size when
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* allocating; also prevents fragmentation and leaking memory.
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*
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* @param Bucket*
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* @param el entry allocated via bucket_alloc.
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**/
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extern void bucket_free(Bucket* b, void* el);
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#endif // #ifndef INCLUDED_BUCKET
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