345 lines
9.5 KiB
C++
345 lines
9.5 KiB
C++
/*
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* Copyright (c) 1996
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* Silicon Graphics Computer Systems, Inc.
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*
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* Permission to use, copy, modify, distribute and sell this software
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* and its documentation for any purpose is hereby granted without fee,
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* provided that the above copyright notice appear in all copies and
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* that both that copyright notice and this permission notice appear
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* in supporting documentation. Silicon Graphics makes no
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* representations about the suitability of this software for any
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* purpose. It is provided "as is" without express or implied warranty.
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*/
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#ifndef __PTHREAD_ALLOC_H
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#define __PTHREAD_ALLOC_H
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// Pthread-specific node allocator.
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// This is similar to the default allocator, except that free-list
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// information is kept separately for each thread, avoiding locking.
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// This should be reasonably fast even in the presence of threads.
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// The down side is that storage may not be well-utilized.
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// It is not an error to allocate memory in thread A and deallocate
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// it n thread B. But this effectively transfers ownership of the memory,
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// so that it can only be reallocated by thread B. Thus this can effectively
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// result in a storage leak if it's done on a regular basis.
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// It can also result in frequent sharing of
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// cache lines among processors, with potentially serious performance
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// consequences.
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#include <stddef.h>
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#include <stdlib.h>
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#include <string.h>
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#include <pthread.h>
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#include <alloc.h>
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#ifndef __RESTRICT
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# define __RESTRICT
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#endif
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// Note that this class has nonstatic members. We instantiate it once
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// per thread.
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template <bool dummy>
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class __pthread_alloc_template {
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private:
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enum {ALIGN = 8};
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enum {MAX_BYTES = 128}; // power of 2
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enum {NFREELISTS = MAX_BYTES/ALIGN};
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union obj {
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union obj * free_list_link;
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char client_data[ALIGN]; /* The client sees this. */
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};
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// Per instance state
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obj* volatile free_list[NFREELISTS];
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__pthread_alloc_template<dummy>* next; // Free list link
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static size_t ROUND_UP(size_t bytes) {
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return (((bytes) + ALIGN-1) & ~(ALIGN - 1));
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}
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static size_t FREELIST_INDEX(size_t bytes) {
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return (((bytes) + ALIGN-1)/ALIGN - 1);
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}
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// Returns an object of size n, and optionally adds to size n free list.
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void *refill(size_t n);
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// Allocates a chunk for nobjs of size size. nobjs may be reduced
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// if it is inconvenient to allocate the requested number.
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static char *chunk_alloc(size_t size, int &nobjs);
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// Chunk allocation state. And other shared state.
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// Protected by chunk_allocator_lock.
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static pthread_mutex_t chunk_allocator_lock;
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static char *start_free;
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static char *end_free;
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static size_t heap_size;
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static __pthread_alloc_template<dummy>* free_allocators;
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static pthread_key_t key;
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static bool key_initialized;
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// Pthread key under which allocator is stored.
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// Allocator instances that are currently unclaimed by any thread.
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static void destructor(void *instance);
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// Function to be called on thread exit to reclaim allocator
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// instance.
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static __pthread_alloc_template<dummy> *new_allocator();
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// Return a recycled or new allocator instance.
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static __pthread_alloc_template<dummy> *get_allocator_instance();
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// ensure that the current thread has an associated
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// allocator instance.
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class lock {
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public:
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lock () { pthread_mutex_lock(&chunk_allocator_lock); }
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~lock () { pthread_mutex_unlock(&chunk_allocator_lock); }
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};
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friend class lock;
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public:
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__pthread_alloc_template() : next(0)
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{
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memset((void *)free_list, 0, NFREELISTS * sizeof(obj *));
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}
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/* n must be > 0 */
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static void * allocate(size_t n)
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{
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obj * volatile * my_free_list;
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obj * __RESTRICT result;
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__pthread_alloc_template<dummy>* a;
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if (n > MAX_BYTES) {
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return(malloc(n));
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}
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if (!key_initialized ||
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!(a = (__pthread_alloc_template<dummy>*)
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pthread_getspecific(key))) {
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a = get_allocator_instance();
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}
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my_free_list = a -> free_list + FREELIST_INDEX(n);
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result = *my_free_list;
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if (result == 0) {
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void *r = a -> refill(ROUND_UP(n));
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return r;
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}
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*my_free_list = result -> free_list_link;
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return (result);
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};
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/* p may not be 0 */
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static void deallocate(void *p, size_t n)
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{
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obj *q = (obj *)p;
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obj * volatile * my_free_list;
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__pthread_alloc_template<dummy>* a;
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if (n > MAX_BYTES) {
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free(p);
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return;
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}
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if (!key_initialized ||
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!(a = (__pthread_alloc_template<dummy>*)
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pthread_getspecific(key))) {
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a = get_allocator_instance();
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}
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my_free_list = a->free_list + FREELIST_INDEX(n);
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q -> free_list_link = *my_free_list;
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*my_free_list = q;
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}
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static void * reallocate(void *p, size_t old_sz, size_t new_sz);
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} ;
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typedef __pthread_alloc_template<false> pthread_alloc;
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template <bool dummy>
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void __pthread_alloc_template<dummy>::destructor(void * instance)
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{
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__pthread_alloc_template<dummy>* a =
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(__pthread_alloc_template<dummy>*)instance;
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a -> next = free_allocators;
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free_allocators = a;
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}
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template <bool dummy>
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__pthread_alloc_template<dummy>*
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__pthread_alloc_template<dummy>::new_allocator()
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{
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if (0 != free_allocators) {
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__pthread_alloc_template<dummy>* result = free_allocators;
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free_allocators = free_allocators -> next;
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return result;
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} else {
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return new __pthread_alloc_template<dummy>;
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}
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}
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template <bool dummy>
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__pthread_alloc_template<dummy>*
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__pthread_alloc_template<dummy>::get_allocator_instance()
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{
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__pthread_alloc_template<dummy>* result;
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if (!key_initialized) {
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/*REFERENCED*/
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lock lock_instance;
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if (!key_initialized) {
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if (pthread_key_create(&key, destructor)) {
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abort(); // failed
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}
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key_initialized = true;
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}
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}
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result = new_allocator();
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if (pthread_setspecific(key, result)) abort();
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return result;
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}
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/* We allocate memory in large chunks in order to avoid fragmenting */
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/* the malloc heap too much. */
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/* We assume that size is properly aligned. */
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template <bool dummy>
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char *__pthread_alloc_template<dummy>
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::chunk_alloc(size_t size, int &nobjs)
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{
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{
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char * result;
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size_t total_bytes;
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size_t bytes_left;
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/*REFERENCED*/
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lock lock_instance; // Acquire lock for this routine
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total_bytes = size * nobjs;
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bytes_left = end_free - start_free;
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if (bytes_left >= total_bytes) {
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result = start_free;
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start_free += total_bytes;
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return(result);
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} else if (bytes_left >= size) {
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nobjs = bytes_left/size;
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total_bytes = size * nobjs;
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result = start_free;
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start_free += total_bytes;
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return(result);
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} else {
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size_t bytes_to_get = 2 * total_bytes + ROUND_UP(heap_size >> 4);
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// Try to make use of the left-over piece.
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if (bytes_left > 0) {
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__pthread_alloc_template<dummy>* a =
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(__pthread_alloc_template<dummy>*)pthread_getspecific(key);
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obj * volatile * my_free_list =
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a->free_list + FREELIST_INDEX(bytes_left);
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((obj *)start_free) -> free_list_link = *my_free_list;
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*my_free_list = (obj *)start_free;
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}
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# ifdef _SGI_SOURCE
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// Try to get memory that's aligned on something like a
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// cache line boundary, so as to avoid parceling out
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// parts of the same line to different threads and thus
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// possibly different processors.
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{
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const int cache_line_size = 128; // probable upper bound
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bytes_to_get &= ~(cache_line_size-1);
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start_free = (char *)memalign(cache_line_size, bytes_to_get);
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if (0 == start_free) {
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start_free = (char *)malloc_alloc::allocate(bytes_to_get);
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}
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}
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# else /* !SGI_SOURCE */
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start_free = (char *)malloc_alloc::allocate(bytes_to_get);
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# endif
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heap_size += bytes_to_get;
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end_free = start_free + bytes_to_get;
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}
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}
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// lock is released here
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return(chunk_alloc(size, nobjs));
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}
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/* Returns an object of size n, and optionally adds to size n free list.*/
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/* We assume that n is properly aligned. */
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/* We hold the allocation lock. */
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template <bool dummy>
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void *__pthread_alloc_template<dummy>
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::refill(size_t n)
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{
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int nobjs = 128;
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char * chunk = chunk_alloc(n, nobjs);
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obj * volatile * my_free_list;
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obj * result;
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obj * current_obj, * next_obj;
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int i;
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if (1 == nobjs) {
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return(chunk);
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}
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my_free_list = free_list + FREELIST_INDEX(n);
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/* Build free list in chunk */
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result = (obj *)chunk;
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*my_free_list = next_obj = (obj *)(chunk + n);
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for (i = 1; ; i++) {
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current_obj = next_obj;
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next_obj = (obj *)((char *)next_obj + n);
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if (nobjs - 1 == i) {
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current_obj -> free_list_link = 0;
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break;
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} else {
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current_obj -> free_list_link = next_obj;
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}
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}
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return(result);
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}
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template <bool dummy>
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void *__pthread_alloc_template<dummy>
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::reallocate(void *p, size_t old_sz, size_t new_sz)
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{
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void * result;
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size_t copy_sz;
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if (old_sz > MAX_BYTES && new_sz > MAX_BYTES) {
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return(realloc(p, new_sz));
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}
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if (ROUND_UP(old_sz) == ROUND_UP(new_sz)) return(p);
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result = allocate(new_sz);
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copy_sz = new_sz > old_sz? old_sz : new_sz;
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memcpy(result, p, copy_sz);
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deallocate(p, old_sz);
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return(result);
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}
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template <bool dummy>
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__pthread_alloc_template<dummy> *
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__pthread_alloc_template<dummy>::free_allocators = 0;
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template <bool dummy>
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pthread_key_t __pthread_alloc_template<dummy>::key;
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template <bool dummy>
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bool __pthread_alloc_template<dummy>::key_initialized = false;
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template <bool dummy>
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pthread_mutex_t __pthread_alloc_template<dummy>::chunk_allocator_lock
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= PTHREAD_MUTEX_INITIALIZER;
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template <bool dummy>
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char *__pthread_alloc_template<dummy>
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::start_free = 0;
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template <bool dummy>
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char *__pthread_alloc_template<dummy>
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::end_free = 0;
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template <bool dummy>
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size_t __pthread_alloc_template<dummy>
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::heap_size = 0;
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#endif /* __NODE_ALLOC_H */
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