lruhash.h File Reference

This file contains a hashtable with LRU keeping of entries. More...

#include "util/locks.h"

Data Structures
struct	lruhash
	Hash table that keeps LRU list of entries. More...
struct	lruhash_bin
	A single bin with a linked list of entries in it. More...
struct	lruhash_entry
	An entry into the hash table. More...

Macros
#define	HASH_DEFAULT_STARTARRAY   1024 /* entries in array */
	default start size for hash arrays
#define	HASH_DEFAULT_MAXMEM   4*1024*1024 /* bytes */
	default max memory for hash arrays

Typedefs
typedef uint32_t	hashvalue_type
	the type of a hash value
typedef size_t(*	lruhash_sizefunc_type) (void *, void *)
	Type of function that calculates the size of an entry. More...
typedef int(*	lruhash_compfunc_type) (void *, void *)
	type of function that compares two keys. More...
typedef void(*	lruhash_delkeyfunc_type) (void *, void *)
	old keys are deleted. More...
typedef void(*	lruhash_deldatafunc_type) (void *, void *)
	old data is deleted. More...
typedef void(*	lruhash_markdelfunc_type) (void *)
	mark a key as pending to be deleted (and not to be used by anyone). More...

Functions
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)
	Create new hash table. More...
void	lruhash_delete (struct lruhash *table)
	Delete hash table. More...
void	lruhash_clear (struct lruhash *table)
	Clear hash table. More...
void	lruhash_insert (struct lruhash *table, hashvalue_type hash, struct lruhash_entry *entry, void *data, void *cb_override)
	Insert a new element into the hashtable. More...
struct lruhash_entry *	lruhash_lookup (struct lruhash *table, hashvalue_type hash, void *key, int wr)
	Lookup an entry in the hashtable. More...
void	lru_touch (struct lruhash *table, struct lruhash_entry *entry)
	Touch entry, so it becomes the most recently used in the LRU list. More...
void	lruhash_setmarkdel (struct lruhash *table, lruhash_markdelfunc_type md)
	Set the markdelfunction (or NULL)
void	lru_demote (struct lruhash *table, struct lruhash_entry *entry)
	Demote entry, so it becomes the least recently used in the LRU list. More...
struct lruhash_entry *	lruhash_insert_or_retrieve (struct lruhash *table, hashvalue_type hash, struct lruhash_entry *entry, void *data, void *cb_arg)
	Insert a new element into the hashtable, or retrieve the corresponding element of it exits. More...
void	lruhash_remove (struct lruhash *table, hashvalue_type hash, void *key)
	Remove entry from hashtable. More...
void	bin_init (struct lruhash_bin *array, size_t size)
	init the hash bins for the table
void	bin_delete (struct lruhash *table, struct lruhash_bin *bin)
	delete the hash bin and entries inside it
struct lruhash_entry *	bin_find_entry (struct lruhash *table, struct lruhash_bin *bin, hashvalue_type hash, void *key, size_t *collisions)
	Find entry in hash bin. More...
void	bin_overflow_remove (struct lruhash_bin *bin, struct lruhash_entry *entry)
	Remove entry from bin overflow chain. More...
void	bin_split (struct lruhash *table, struct lruhash_bin *newa, int newmask)
	Split hash bin into two new ones. More...
void	reclaim_space (struct lruhash *table, struct lruhash_entry **list)
	Try to make space available by deleting old entries. More...
void	table_grow (struct lruhash *table)
	Grow the table lookup array. More...
void	lru_front (struct lruhash *table, struct lruhash_entry *entry)
	Put entry at front of lru. More...
void	lru_remove (struct lruhash *table, struct lruhash_entry *entry)
	Remove entry from lru list. More...
void	lruhash_status (struct lruhash *table, const char *id, int extended)
	Output debug info to the log as to state of the hash table. More...
size_t	lruhash_get_mem (struct lruhash *table)
	Get memory in use now by the lruhash table. More...
void	lruhash_traverse (struct lruhash *h, int wr, void(*func)(struct lruhash_entry *, void *), void *arg)
	Traverse a lruhash. More...

Detailed Description

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.

Typedef Documentation

lruhash_sizefunc_type

typedef size_t(* lruhash_sizefunc_type) (void *, void *)

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).

lruhash_compfunc_type

typedef int(* lruhash_compfunc_type) (void *, void *)

type of function that compares two keys.

return 0 if equal.

lruhash_delkeyfunc_type

typedef void(* lruhash_delkeyfunc_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)

lruhash_deldatafunc_type

typedef void(* lruhash_deldatafunc_type) (void *, void *)

old data is deleted.

This function is called: func(data, userarg).

lruhash_markdelfunc_type

typedef void(* lruhash_markdelfunc_type) (void *)

mark a key as pending to be deleted (and not to be used by anyone).

called: func(key)

Function Documentation

lruhash_create()

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
	)

Create new hash table.

Parameters

start_size	size of hashtable array at start, must be power of 2.
maxmem	maximum amount of memory this table is allowed to use.
sizefunc	calculates memory usage of entries.
compfunc	compares entries, 0 on equality.
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.
deldatafunc	deletes data.
arg	user argument that is passed to user function calls.

Returns

: new hash table or NULL on malloc failure.

References lruhash::array, bin_init(), lruhash::cb_arg, lruhash::compfunc, lruhash::deldatafunc, lruhash::delkeyfunc, lruhash::lock, lruhash::lru_end, lruhash::lru_start, lruhash::max_collisions, lruhash::num, lruhash::size, lruhash::size_mask, lruhash::sizefunc, lruhash::space_max, and lruhash::space_used.

Referenced by lruhash_test(), and slabhash_create().

lruhash_delete()

void lruhash_delete

(

struct lruhash *

table

)

Delete hash table.

Entries are all deleted.

Parameters

table

to delete.

References lruhash::array, bin_delete(), lruhash::lock, and lruhash::size.

Referenced by lruhash_test(), and slabhash_delete().

lruhash_clear()

void lruhash_clear

(

struct lruhash *

table

)

Clear hash table.

Entries are all deleted, while locking them before doing so. At end the table is empty.

Parameters

table

to make empty.

References lruhash::array, bin_clear(), lruhash::deldatafunc, lruhash::delkeyfunc, fptr_ok, fptr_whitelist_hash_deldatafunc(), fptr_whitelist_hash_delkeyfunc(), fptr_whitelist_hash_markdelfunc(), lruhash::lock, lruhash::lru_end, lruhash::lru_start, lruhash::markdelfunc, lruhash::num, lruhash::size, and lruhash::space_used.

Referenced by slabhash_clear(), and test_long_table().

lruhash_insert()

void lruhash_insert	(	struct lruhash *	table,
		hashvalue_type	hash,
		struct lruhash_entry *	entry,
		void *	data,
		void *	cb_override
	)

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.

Parameters

table	hash table.
hash	hash value. User calculates the hash.
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.
data	the data.
cb_override	if not null overrides the cb_arg for the deletefunc.

References lruhash::array, bin_find_entry(), lruhash::cb_arg, lruhash::compfunc, lruhash_entry::data, lruhash::deldatafunc, lruhash::delkeyfunc, fptr_ok, fptr_whitelist_hash_compfunc(), fptr_whitelist_hash_deldatafunc(), fptr_whitelist_hash_delkeyfunc(), fptr_whitelist_hash_markdelfunc(), fptr_whitelist_hash_sizefunc(), lruhash_entry::hash, lruhash_entry::key, lruhash::lock, lruhash_bin::lock, lruhash_entry::lock, lru_front(), lru_touch(), lruhash::markdelfunc, lruhash::max_collisions, lruhash::num, lruhash_bin::overflow_list, lruhash_entry::overflow_next, reclaim_space(), lruhash::size, lruhash::size_mask, lruhash::sizefunc, lruhash::space_max, lruhash::space_used, and table_grow().

Referenced by slabhash_insert(), test_short_table(), testadd(), and testadd_unlim().

lruhash_lookup()

struct lruhash_entry* lruhash_lookup	(	struct lruhash *	table,
		hashvalue_type	hash,
		void *	key,
		int	wr
	)

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).

Parameters

table	hash table.
hash	hash of key.
key	what to look for, compared against entries in overflow chain. the hash value must be set, and must work with compare function.
wr	set to true if you desire a writelock on the entry. with a writelock you can update the data part.

Returns

: pointer to the entry or NULL. The entry is locked. The user must unlock the entry when done.

References lruhash::array, bin_find_entry(), lruhash::compfunc, fptr_ok, fptr_whitelist_hash_compfunc(), lruhash::lock, lruhash_bin::lock, lru_touch(), and lruhash::size_mask.

Referenced by slabhash_lookup(), test_short_table(), testlookup(), and testlookup_unlim().

lru_touch()

void lru_touch	(	struct lruhash *	table,
		struct lruhash_entry *	entry
	)

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.

Parameters

table	hash table.
entry	entry to make first in LRU.

References log_assert, lru_front(), lru_remove(), and lruhash::lru_start.

Referenced by lruhash_insert(), lruhash_lookup(), and rrset_cache_touch().

lru_demote()

void lru_demote	(	struct lruhash *	table,
		struct lruhash_entry *	entry
	)

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.

Parameters

table	hash table.
entry	entry to make last in LRU.

References log_assert, lruhash::lru_end, lruhash_entry::lru_next, lru_remove(), and lruhash::lru_start.

lruhash_insert_or_retrieve()

struct lruhash_entry* lruhash_insert_or_retrieve	(	struct lruhash *	table,
		hashvalue_type	hash,
		struct lruhash_entry *	entry,
		void *	data,
		void *	cb_arg
	)

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.

Parameters

table	hash table.
hash	hash value. User calculates the hash.
entry	identifies the entry.
data	the data.
cb_arg	if not null overrides the cb_arg for the deletefunc.

Returns

: pointer to the existing entry if the key was already present, or to the entry argument if it was not.

References lruhash::array, bin_find_entry(), lruhash::cb_arg, lruhash::compfunc, lruhash_entry::data, lruhash::deldatafunc, lruhash::delkeyfunc, fptr_ok, fptr_whitelist_hash_compfunc(), fptr_whitelist_hash_deldatafunc(), fptr_whitelist_hash_delkeyfunc(), fptr_whitelist_hash_markdelfunc(), fptr_whitelist_hash_sizefunc(), lruhash_entry::hash, lruhash_entry::key, lruhash::lock, lruhash_bin::lock, lruhash_entry::lock, lru_front(), lruhash::markdelfunc, lruhash::max_collisions, lruhash::num, lruhash_bin::overflow_list, lruhash_entry::overflow_next, reclaim_space(), lruhash::size, lruhash::size_mask, lruhash::sizefunc, lruhash::space_max, lruhash::space_used, and table_grow().

lruhash_remove()

void lruhash_remove	(	struct lruhash *	table,
		hashvalue_type	hash,
		void *	key
	)

Remove entry from hashtable.

Does nothing if not found in hashtable. Delfunc is called for the entry.

Parameters

table	hash table.
hash	hash of key.
key	what to look for.

References lruhash::array, bin_find_entry(), bin_overflow_remove(), lruhash::cb_arg, lruhash::compfunc, lruhash::deldatafunc, lruhash::delkeyfunc, fptr_ok, fptr_whitelist_hash_compfunc(), fptr_whitelist_hash_deldatafunc(), fptr_whitelist_hash_delkeyfunc(), fptr_whitelist_hash_markdelfunc(), fptr_whitelist_hash_sizefunc(), lruhash::lock, lruhash_bin::lock, lru_remove(), lruhash::markdelfunc, lruhash::num, lruhash::size_mask, lruhash::sizefunc, and lruhash::space_used.

Referenced by slabhash_remove(), test_short_table(), testremove(), and testremove_unlim().

bin_find_entry()

struct lruhash_entry* bin_find_entry	(	struct lruhash *	table,
		struct lruhash_bin *	bin,
		hashvalue_type	hash,
		void *	key,
		size_t *	collisions
	)

Find entry in hash bin.

You must have locked the bin.

Parameters

table	hash table with function pointers.
bin	hash bin to look into.
hash	hash value to look for.
key	key to look for.
collisions	how many collisions were found during the search.

Returns

: the entry or NULL if not found.

References lruhash::compfunc, lruhash_entry::hash, lruhash_entry::key, lruhash_bin::overflow_list, and lruhash_entry::overflow_next.

Referenced by lruhash_insert(), lruhash_insert_or_retrieve(), lruhash_lookup(), lruhash_remove(), and test_bin_find_entry().

bin_overflow_remove()

void bin_overflow_remove	(	struct lruhash_bin *	bin,
		struct lruhash_entry *	entry
	)

Remove entry from bin overflow chain.

You must have locked the bin.

Parameters

bin	hash bin to look into.
entry	entry ptr that needs removal.

References lruhash_bin::overflow_list, and lruhash_entry::overflow_next.

Referenced by lruhash_remove(), reclaim_space(), and test_bin_find_entry().

bin_split()

void bin_split	(	struct lruhash *	table,
		struct lruhash_bin *	newa,
		int	newmask
	)

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.

Parameters

table	hash table with function pointers.
newa	new increased array.
newmask	new lookup mask.

References lruhash::array, lruhash_entry::hash, lruhash_bin::lock, lruhash_bin::overflow_list, lruhash_entry::overflow_next, lruhash::size, and lruhash::size_mask.

Referenced by table_grow().

reclaim_space()

void reclaim_space	(	struct lruhash *	table,
		struct lruhash_entry **	list
	)

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.

Parameters

table	hash table.
list	list of entries that are to be deleted later. Entries have been removed from the hash table and writelock is held.

References lruhash::array, bin_overflow_remove(), lruhash_entry::data, lruhash_entry::hash, lruhash_entry::key, lruhash_bin::lock, lruhash_entry::lock, log_assert, lruhash::lru_end, lruhash_entry::lru_next, lruhash_entry::lru_prev, lruhash::markdelfunc, lruhash::num, lruhash_entry::overflow_next, lruhash::size_mask, lruhash::sizefunc, lruhash::space_max, and lruhash::space_used.

Referenced by lruhash_insert(), and lruhash_insert_or_retrieve().

table_grow()

void table_grow

(

struct lruhash *

table

)

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.

Parameters

table

hash table.

References lruhash::array, bin_init(), bin_split(), lruhash::lock, lruhash_bin::lock, log_err(), lruhash::size, and lruhash::size_mask.

Referenced by lruhash_insert(), and lruhash_insert_or_retrieve().

lru_front()

void lru_front	(	struct lruhash *	table,
		struct lruhash_entry *	entry
	)

Put entry at front of lru.

entry must be unlinked from lru. Caller must hold hash table lock.

Parameters

table	hash table with lru head and tail.
entry	entry to make most recently used.

References lruhash::lru_end, lruhash_entry::lru_prev, and lruhash::lru_start.

Referenced by lru_touch(), lruhash_insert(), lruhash_insert_or_retrieve(), and test_lru().

lru_remove()

void lru_remove	(	struct lruhash *	table,
		struct lruhash_entry *	entry
	)

Remove entry from lru list.

Caller must hold hash table lock.

Parameters

table	hash table with lru head and tail.
entry	entry to remove from lru.

References lruhash::lru_end, and lruhash::lru_start.

Referenced by lru_demote(), lru_touch(), lruhash_remove(), and test_lru().

lruhash_status()

void lruhash_status	(	struct lruhash *	table,
		const char *	id,
		int	extended
	)

Output debug info to the log as to state of the hash table.

Parameters

table	hash table.
id	string printed with table to identify the hash table.
extended	set to true to print statistics on overflow bin lengths.

References lruhash::array, lruhash::lock, lruhash_bin::lock, log_info(), lruhash::num, lruhash_bin::overflow_list, lruhash_entry::overflow_next, lruhash::size, lruhash::size_mask, lruhash::space_max, and lruhash::space_used.

Referenced by slabhash_status(), test_long_table(), test_thr_main(), and test_threaded_table().

lruhash_get_mem()

size_t lruhash_get_mem

(

struct lruhash *

table

)

Get memory in use now by the lruhash table.

Parameters

table

hash table. Will be locked before use. And unlocked after.

Returns

size in bytes.

References lruhash::array, lruhash::lock, lruhash_bin::lock, lruhash::size, and lruhash::space_used.

Referenced by slabhash_get_mem().

lruhash_traverse()

void lruhash_traverse	(	struct lruhash *	h,
		int	wr,
		void(*)(struct lruhash_entry *, void *)	func,
		void *	arg
	)

Traverse a lruhash.

Call back for every element in the table.

Parameters

h	hash table. Locked before use.
wr	if true writelock is obtained on element, otherwise readlock.
func	function for every element. Do not lock or unlock elements.
arg	user argument to func.

References lruhash::array, lruhash::lock, lruhash_bin::lock, lruhash_entry::lock, lruhash_bin::overflow_list, lruhash_entry::overflow_next, and lruhash::size.

Referenced by slabhash_traverse().