415 lines
15 KiB
C
415 lines
15 KiB
C
/*
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* util/storage/lruhash.h - hashtable, hash function, LRU keeping.
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*
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* Copyright (c) 2007, NLnet Labs. All rights reserved.
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*
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* This software is open source.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* Neither the name of the NLNET LABS nor the names of its contributors may
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* be used to endorse or promote products derived from this software without
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* specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
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* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/**
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* \file
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*
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* This file contains a hashtable with LRU keeping of entries.
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*
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* The hash table keeps a maximum memory size. Old entries are removed
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* to make space for new entries.
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*
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* The locking strategy is as follows:
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* o since (almost) every read also implies a LRU update, the
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* hashtable lock is a spinlock, not rwlock.
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* o the idea is to move every thread through the hash lock quickly,
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* so that the next thread can access the lookup table.
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* o User performs hash function.
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*
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* For read:
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* o lock hashtable.
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* o lookup hash bin.
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* o lock hash bin.
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* o find entry (if failed, unlock hash, unl bin, exit).
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* o swizzle pointers for LRU update.
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* o unlock hashtable.
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* o lock entry (rwlock).
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* o unlock hash bin.
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* o work on entry.
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* o unlock entry.
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*
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* To update an entry, gain writelock and change the entry.
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* (the entry must keep the same hashvalue, so a data update.)
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* (you cannot upgrade a readlock to a writelock, because the item may
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* be deleted, it would cause race conditions. So instead, unlock and
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* relookup it in the hashtable.)
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*
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* To delete an entry:
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* o unlock the entry if you hold the lock already.
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* o lock hashtable.
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* o lookup hash bin.
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* o lock hash bin.
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* o find entry (if failed, unlock hash, unl bin, exit).
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* o remove entry from hashtable bin overflow chain.
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* o unlock hashtable.
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* o lock entry (writelock).
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* o unlock hash bin.
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* o unlock entry (nobody else should be waiting for this lock,
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* since you removed it from hashtable, and you got writelock while
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* holding the hashbinlock so you are the only one.)
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* Note you are only allowed to obtain a lock while holding hashbinlock.
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* o delete entry.
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*
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* The above sequence is:
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* o race free, works with read, write and delete.
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* o but has a queue, imagine someone needing a writelock on an item.
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* but there are still readlocks. The writelocker waits, but holds
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* the hashbinlock. The next thread that comes in and needs the same
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* hashbin will wait for the lock while holding the hashtable lock.
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* thus halting the entire system on hashtable.
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* This is because of the delete protection.
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* Readlocks will be easier on the rwlock on entries.
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* While the writer is holding writelock, similar problems happen with
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* a reader or writer needing the same item.
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* the scenario requires more than three threads.
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* o so the queue length is 3 threads in a bad situation. The fourth is
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* unable to use the hashtable.
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*
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* If you need to acquire locks on multiple items from the hashtable.
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* o you MUST release all locks on items from the hashtable before
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* doing the next lookup/insert/delete/whatever.
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* o To acquire multiple items you should use a special routine that
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* obtains the locks on those multiple items in one go.
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*/
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#ifndef UTIL_STORAGE_LRUHASH_H
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#define UTIL_STORAGE_LRUHASH_H
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#include "util/locks.h"
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struct lruhash_bin;
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struct lruhash_entry;
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/** default start size for hash arrays */
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#define HASH_DEFAULT_STARTARRAY 1024 /* entries in array */
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/** default max memory for hash arrays */
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#define HASH_DEFAULT_MAXMEM 4*1024*1024 /* bytes */
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/** the type of a hash value */
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typedef uint32_t hashvalue_t;
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/**
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* Type of function that calculates the size of an entry.
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* Result must include the size of struct lruhash_entry.
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* Keys that are identical must also calculate to the same size.
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* size = func(key, data).
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*/
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typedef size_t (*lruhash_sizefunc_t)(void*, void*);
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/** type of function that compares two keys. return 0 if equal. */
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typedef int (*lruhash_compfunc_t)(void*, void*);
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/** old keys are deleted.
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* The RRset type has to revoke its ID number, markdel() is used first.
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* This function is called: func(key, userarg) */
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typedef void (*lruhash_delkeyfunc_t)(void*, void*);
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/** old data is deleted. This function is called: func(data, userarg). */
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typedef void (*lruhash_deldatafunc_t)(void*, void*);
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/** mark a key as pending to be deleted (and not to be used by anyone).
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* called: func(key) */
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typedef void (*lruhash_markdelfunc_t)(void*);
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/**
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* Hash table that keeps LRU list of entries.
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*/
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struct lruhash {
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/** lock for exclusive access, to the lookup array */
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lock_quick_t lock;
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/** the size function for entries in this table */
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lruhash_sizefunc_t sizefunc;
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/** the compare function for entries in this table. */
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lruhash_compfunc_t compfunc;
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/** how to delete keys. */
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lruhash_delkeyfunc_t delkeyfunc;
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/** how to delete data. */
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lruhash_deldatafunc_t deldatafunc;
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/** how to mark a key pending deletion */
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lruhash_markdelfunc_t markdelfunc;
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/** user argument for user functions */
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void* cb_arg;
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/** the size of the lookup array */
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size_t size;
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/** size bitmask - since size is a power of 2 */
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int size_mask;
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/** lookup array of bins */
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struct lruhash_bin* array;
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/** the lru list, start and end, noncyclical double linked list. */
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struct lruhash_entry* lru_start;
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/** lru list end item (least recently used) */
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struct lruhash_entry* lru_end;
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/** the number of entries in the hash table. */
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size_t num;
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/** the amount of space used, roughly the number of bytes in use. */
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size_t space_used;
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/** the amount of space the hash table is maximally allowed to use. */
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size_t space_max;
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};
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/**
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* A single bin with a linked list of entries in it.
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*/
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struct lruhash_bin {
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/**
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* Lock for exclusive access to the linked list
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* This lock makes deletion of items safe in this overflow list.
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*/
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lock_quick_t lock;
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/** linked list of overflow entries */
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struct lruhash_entry* overflow_list;
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};
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/**
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* An entry into the hash table.
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* To change overflow_next you need to hold the bin lock.
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* To change the lru items you need to hold the hashtable lock.
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* This structure is designed as part of key struct. And key pointer helps
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* to get the surrounding structure. Data should be allocated on its own.
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*/
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struct lruhash_entry {
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/**
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* rwlock for access to the contents of the entry
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* Note that it does _not_ cover the lru_ and overflow_ ptrs.
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* Even with a writelock, you cannot change hash and key.
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* You need to delete it to change hash or key.
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*/
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lock_rw_t lock;
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/** next entry in overflow chain. Covered by hashlock and binlock. */
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struct lruhash_entry* overflow_next;
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/** next entry in lru chain. covered by hashlock. */
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struct lruhash_entry* lru_next;
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/** prev entry in lru chain. covered by hashlock. */
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struct lruhash_entry* lru_prev;
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/** hash value of the key. It may not change, until entry deleted. */
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hashvalue_t hash;
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/** key */
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void* key;
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/** data */
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void* data;
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};
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/**
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* Create new hash table.
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* @param start_size: size of hashtable array at start, must be power of 2.
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* @param maxmem: maximum amount of memory this table is allowed to use.
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* @param sizefunc: calculates memory usage of entries.
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* @param compfunc: compares entries, 0 on equality.
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* @param delkeyfunc: deletes key.
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* Calling both delkey and deldata will also free the struct lruhash_entry.
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* Make it part of the key structure and delete it in delkeyfunc.
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* @param deldatafunc: deletes data.
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* @param arg: user argument that is passed to user function calls.
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* @return: new hash table or NULL on malloc failure.
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*/
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struct lruhash* lruhash_create(size_t start_size, size_t maxmem,
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lruhash_sizefunc_t sizefunc, lruhash_compfunc_t compfunc,
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lruhash_delkeyfunc_t delkeyfunc, lruhash_deldatafunc_t deldatafunc,
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void* arg);
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/**
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* Delete hash table. Entries are all deleted.
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* @param table: to delete.
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*/
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void lruhash_delete(struct lruhash* table);
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/**
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* Clear hash table. Entries are all deleted, while locking them before
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* doing so. At end the table is empty.
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* @param table: to make empty.
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*/
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void lruhash_clear(struct lruhash* table);
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/**
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* Insert a new element into the hashtable.
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* If key is already present data pointer in that entry is updated.
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* The space calculation function is called with the key, data.
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* If necessary the least recently used entries are deleted to make space.
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* If necessary the hash array is grown up.
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*
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* @param table: hash table.
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* @param hash: hash value. User calculates the hash.
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* @param entry: identifies the entry.
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* If key already present, this entry->key is deleted immediately.
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* But entry->data is set to NULL before deletion, and put into
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* the existing entry. The data is then freed.
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* @param data: the data.
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* @param cb_override: if not null overrides the cb_arg for the deletefunc.
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*/
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void lruhash_insert(struct lruhash* table, hashvalue_t hash,
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struct lruhash_entry* entry, void* data, void* cb_override);
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/**
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* Lookup an entry in the hashtable.
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* At the end of the function you hold a (read/write)lock on the entry.
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* The LRU is updated for the entry (if found).
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* @param table: hash table.
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* @param hash: hash of key.
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* @param key: what to look for, compared against entries in overflow chain.
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* the hash value must be set, and must work with compare function.
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* @param wr: set to true if you desire a writelock on the entry.
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* with a writelock you can update the data part.
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* @return: pointer to the entry or NULL. The entry is locked.
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* The user must unlock the entry when done.
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*/
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struct lruhash_entry* lruhash_lookup(struct lruhash* table, hashvalue_t hash,
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void* key, int wr);
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/**
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* Touch entry, so it becomes the most recently used in the LRU list.
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* Caller must hold hash table lock. The entry must be inserted already.
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* @param table: hash table.
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* @param entry: entry to make first in LRU.
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*/
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void lru_touch(struct lruhash* table, struct lruhash_entry* entry);
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/**
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* Set the markdelfunction (or NULL)
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*/
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void lruhash_setmarkdel(struct lruhash* table, lruhash_markdelfunc_t md);
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/************************* Internal functions ************************/
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/*** these are only exposed for unit tests. ***/
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/**
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* Remove entry from hashtable. Does nothing if not found in hashtable.
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* Delfunc is called for the entry.
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* @param table: hash table.
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* @param hash: hash of key.
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* @param key: what to look for.
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*/
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void lruhash_remove(struct lruhash* table, hashvalue_t hash, void* key);
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/** init the hash bins for the table */
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void bin_init(struct lruhash_bin* array, size_t size);
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/** delete the hash bin and entries inside it */
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void bin_delete(struct lruhash* table, struct lruhash_bin* bin);
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/**
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* Find entry in hash bin. You must have locked the bin.
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* @param table: hash table with function pointers.
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* @param bin: hash bin to look into.
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* @param hash: hash value to look for.
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* @param key: key to look for.
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* @return: the entry or NULL if not found.
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*/
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struct lruhash_entry* bin_find_entry(struct lruhash* table,
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struct lruhash_bin* bin, hashvalue_t hash, void* key);
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/**
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* Remove entry from bin overflow chain.
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* You must have locked the bin.
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* @param bin: hash bin to look into.
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* @param entry: entry ptr that needs removal.
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*/
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void bin_overflow_remove(struct lruhash_bin* bin,
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struct lruhash_entry* entry);
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/**
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* Split hash bin into two new ones. Based on increased size_mask.
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* Caller must hold hash table lock.
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* At the end the routine acquires all hashbin locks (in the old array).
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* This makes it wait for other threads to finish with the bins.
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* So the bins are ready to be deleted after this function.
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* @param table: hash table with function pointers.
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* @param newa: new increased array.
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* @param newmask: new lookup mask.
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*/
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void bin_split(struct lruhash* table, struct lruhash_bin* newa,
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int newmask);
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/**
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* Try to make space available by deleting old entries.
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* Assumes that the lock on the hashtable is being held by caller.
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* Caller must not hold bin locks.
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* @param table: hash table.
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* @param list: list of entries that are to be deleted later.
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* Entries have been removed from the hash table and writelock is held.
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*/
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void reclaim_space(struct lruhash* table, struct lruhash_entry** list);
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/**
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* Grow the table lookup array. Becomes twice as large.
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* Caller must hold the hash table lock. Must not hold any bin locks.
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* Tries to grow, on malloc failure, nothing happened.
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* @param table: hash table.
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*/
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void table_grow(struct lruhash* table);
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/**
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* Put entry at front of lru. entry must be unlinked from lru.
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* Caller must hold hash table lock.
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* @param table: hash table with lru head and tail.
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* @param entry: entry to make most recently used.
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*/
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void lru_front(struct lruhash* table, struct lruhash_entry* entry);
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/**
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* Remove entry from lru list.
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* Caller must hold hash table lock.
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* @param table: hash table with lru head and tail.
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* @param entry: entry to remove from lru.
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*/
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void lru_remove(struct lruhash* table, struct lruhash_entry* entry);
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/**
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* Output debug info to the log as to state of the hash table.
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* @param table: hash table.
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* @param id: string printed with table to identify the hash table.
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* @param extended: set to true to print statistics on overflow bin lengths.
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*/
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void lruhash_status(struct lruhash* table, const char* id, int extended);
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/**
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* Get memory in use now by the lruhash table.
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* @param table: hash table. Will be locked before use. And unlocked after.
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* @return size in bytes.
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*/
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size_t lruhash_get_mem(struct lruhash* table);
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/**
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* Traverse a lruhash. Call back for every element in the table.
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* @param h: hash table. Locked before use.
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* @param wr: if true writelock is obtained on element, otherwise readlock.
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* @param func: function for every element. Do not lock or unlock elements.
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* @param arg: user argument to func.
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*/
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void lruhash_traverse(struct lruhash* h, int wr,
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void (*func)(struct lruhash_entry*, void*), void* arg);
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#endif /* UTIL_STORAGE_LRUHASH_H */
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