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53 lines
1.6 KiB
C
53 lines
1.6 KiB
C
#include "likely.h"
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#include <stdlib.h>
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#include <fcntl.h>
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#include <sys/mman.h>
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#include <unistd.h>
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#include "iarray.h"
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#ifdef __dietlibc__
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#include <sys/atomic.h>
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#else
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#define __CAS(ptr,oldval,newval) __sync_val_compare_and_swap(ptr,oldval,newval)
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#endif
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static iarray_page* new_page(size_t pagesize) {
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void* x=mmap(0,pagesize,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_PRIVATE,-1,0);
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if (x==MAP_FAILED) return 0;
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return (iarray_page*)x;
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}
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void* iarray_allocate(iarray* ia,size_t pos) {
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size_t index,prevlen=ia->len;
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/* first, find the linked list of pages */
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iarray_page** p=&ia->pages[pos%(sizeof(ia->pages)/sizeof(ia->pages[0]))];
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/* this is here so we don't munmap and then re-mmap pages when a
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* certain path makes it necessary to mmap several pages into the
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* linked list and we are competing with another thread that does the
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* same thing */
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iarray_page* newpage=0;
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/* since we have a fan-out of 16, on page 0 the elements are 0, 16, 32, ...
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* so we divide pos by the fan-out here */
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size_t realpos=pos;
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pos /= sizeof(ia->pages)/sizeof(ia->pages[0]);
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/* now walk the linked list of pages until we reach the one we want */
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for (index=0; ; index+=ia->elemperpage) {
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if (!*p) {
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if (!newpage)
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if (!(newpage=new_page(ia->bytesperpage))) return 0;
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if (__CAS(p,0,newpage)==0)
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newpage=0;
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}
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if (index+ia->elemperpage>pos)
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break;
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p=&(*p)->next;
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}
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if (newpage) munmap(newpage,ia->bytesperpage);
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{
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size_t l;
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do {
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l=__CAS(&ia->len,prevlen,realpos);
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} while (l<realpos);
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}
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return &(*p)->data[(pos-index)*ia->elemsize];
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}
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