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