Re: [RFC v2 6/7] tracepoint: use new hashtable implementation

Mathieu Desnoyers
2012-08-05T17:12:57Z

* Sasha Levin (levinsasha928@gmail.com) wrote:
[...]
> > Other than that, it looks good!
> >
> > Thanks!
> >
> > Mathieu
> >
>
> Thanks for the review Mathieu!

No problem! By the way, if you want to have a look at another hash table
API for ideas, here is the RCU lock-free hash table API, within the
Userspace RCU tree:

from git://git.lttng.org/userspace-rcu.git
branch: master
API: urcu/rculfhash.h
core code: rculfhash.c
hash table index memory management:
rculfhash-mm-chunk.c, rculfhash-mm-mmap.c, rculfhash-mm-order.c

The git tree is down today due to electrical maintenance, so I am
appending the hash table API below.

#ifndef _URCU_RCULFHASH_H
#define _URCU_RCULFHASH_H

/*
* urcu/rculfhash.h
*
* Userspace RCU library - Lock-Free RCU Hash Table
*
* Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
* Copyright 2011 - Lai Jiangshan <laijs@cn.fujitsu.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Include this file _after_ including your URCU flavor.
*/

#include <stdint.h>
#include <urcu/compiler.h>
#include <urcu-call-rcu.h>
#include <urcu-flavor.h>

#ifdef __cplusplus
extern "C" {
#endif

/*
* cds_lfht_node: Contains the next pointers and reverse-hash
* value required for lookup and traversal of the hash table.
*
* struct cds_lfht_node should be aligned on 8-bytes boundaries because
* the three lower bits are used as flags. It is worth noting that the
* information contained within these three bits could be represented on
* two bits by re-using the same bit for REMOVAL_OWNER_FLAG and
* BUCKET_FLAG. This can be done if we ensure that no iterator nor
* updater check the BUCKET_FLAG after it detects that the REMOVED_FLAG
* is set. Given the minimum size of struct cds_lfht_node is 8 bytes on
* 32-bit architectures, we choose to go for simplicity and reserve
* three bits.
*
* struct cds_lfht_node can be embedded into a structure (as a field).
* caa_container_of() can be used to get the structure from the struct
* cds_lfht_node after a lookup.
*
* The structure which embeds it typically holds the key (or key-value
* pair) of the object. The caller code is responsible for calculation
* of the hash value for cds_lfht APIs.
*/
struct cds_lfht_node {
struct cds_lfht_node *next; /* ptr | REMOVAL_OWNER_FLAG | BUCKET_FLAG | REMOVED_FLAG */
unsigned long reverse_hash;
} __attribute__((aligned(8)));

/* cds_lfht_iter: Used to track state while traversing a hash chain. */
struct cds_lfht_iter {
struct cds_lfht_node *node, *next;
};

static inline
struct cds_lfht_node *cds_lfht_iter_get_node(struct cds_lfht_iter *iter)
{
return iter->node;
}

struct cds_lfht;

/*
* Caution !
* Ensure reader and writer threads are registered as urcu readers.
*/

typedef int (*cds_lfht_match_fct)(struct cds_lfht_node *node, const void *key);

/*
* cds_lfht_node_init - initialize a hash table node
* @node: the node to initialize.
*
* This function is kept to be eventually used for debugging purposes
* (detection of memory corruption).
*/
static inline
void cds_lfht_node_init(struct cds_lfht_node *node)
{
}

/*
* Hash table creation flags.
*/
enum {
CDS_LFHT_AUTO_RESIZE = (1U << 0),
CDS_LFHT_ACCOUNTING = (1U << 1),
};

struct cds_lfht_mm_type {
struct cds_lfht *(*alloc_cds_lfht)(unsigned long min_nr_alloc_buckets,
unsigned long max_nr_buckets);
void (*alloc_bucket_table)(struct cds_lfht *ht, unsigned long order);
void (*free_bucket_table)(struct cds_lfht *ht, unsigned long order);
struct cds_lfht_node *(*bucket_at)(struct cds_lfht *ht,
unsigned long index);
};

extern const struct cds_lfht_mm_type cds_lfht_mm_order;
extern const struct cds_lfht_mm_type cds_lfht_mm_chunk;
extern const struct cds_lfht_mm_type cds_lfht_mm_mmap;

/*
* _cds_lfht_new - API used by cds_lfht_new wrapper. Do not use directly.
*/
struct cds_lfht *_cds_lfht_new(unsigned long init_size,
unsigned long min_nr_alloc_buckets,
unsigned long max_nr_buckets,
int flags,
const struct cds_lfht_mm_type *mm,
const struct rcu_flavor_struct *flavor,
pthread_attr_t *attr);

/*
* cds_lfht_new - allocate a hash table.
* @init_size: number of buckets to allocate initially. Must be power of two.
* @min_nr_alloc_buckets: the minimum number of allocated buckets.
* (must be power of two)
* @max_nr_buckets: the maximum number of hash table buckets allowed.
* (must be power of two)
* @flags: hash table creation flags (can be combined with bitwise or: '|').
* 0: no flags.
* CDS_LFHT_AUTO_RESIZE: automatically resize hash table.
* CDS_LFHT_ACCOUNTING: count the number of node addition
* and removal in the table
* @attr: optional resize worker thread attributes. NULL for default.
*
* Return NULL on error.
* Note: the RCU flavor must be already included before the hash table header.
*
* The programmer is responsible for ensuring that resize operation has a
* priority equal to hash table updater threads. It should be performed by
* specifying the appropriate priority in the pthread "attr" argument, and,
* for CDS_LFHT_AUTO_RESIZE, by ensuring that call_rcu worker threads also have
* this priority level. Having lower priority for call_rcu and resize threads
* does not pose any correctness issue, but the resize operations could be
* starved by updates, thus leading to long hash table bucket chains.
* Threads calling cds_lfht_new are NOT required to be registered RCU
* read-side threads. It can be called very early. (e.g. before RCU is
* initialized)
*/
static inline
struct cds_lfht *cds_lfht_new(unsigned long init_size,
unsigned long min_nr_alloc_buckets,
unsigned long max_nr_buckets,
int flags,
pthread_attr_t *attr)
{
return _cds_lfht_new(init_size, min_nr_alloc_buckets, max_nr_buckets,
flags, NULL, &rcu_flavor, attr);
}

/*
* cds_lfht_destroy - destroy a hash table.
* @ht: the hash table to destroy.
* @attr: (output) resize worker thread attributes, as received by cds_lfht_new.
* The caller will typically want to free this pointer if dynamically
* allocated. The attr point can be NULL if the caller does not
* need to be informed of the value passed to cds_lfht_new().
*
* Return 0 on success, negative error value on error.
* Threads calling this API need to be registered RCU read-side threads.
*/
int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr);

/*
* cds_lfht_count_nodes - count the number of nodes in the hash table.
* @ht: the hash table.
* @split_count_before: sample the node count split-counter before traversal.
* @count: traverse the hash table, count the number of nodes observed.
* @split_count_after: sample the node count split-counter after traversal.
*
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
*/
void cds_lfht_count_nodes(struct cds_lfht *ht,
long *split_count_before,
unsigned long *count,
long *split_count_after);

/*
* cds_lfht_lookup - lookup a node by key.
* @ht: the hash table.
* @hash: the key hash.
* @match: the key match function.
* @key: the current node key.
* @iter: node, if found (output). *iter->node set to NULL if not found.
*
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* This function acts as a rcu_dereference() to read the node pointer.
*/
void cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash,
cds_lfht_match_fct match, const void *key,
struct cds_lfht_iter *iter);

/*
* cds_lfht_next_duplicate - get the next item with same key, after iterator.
* @ht: the hash table.
* @match: the key match function.
* @key: the current node key.
* @iter: input: current iterator.
* output: node, if found. *iter->node set to NULL if not found.
*
* Uses an iterator initialized by a lookup or traversal. Important: the
* iterator _needs_ to be initialized before calling
* cds_lfht_next_duplicate.
* Sets *iter-node to the following node with same key.
* Sets *iter->node to NULL if no following node exists with same key.
* RCU read-side lock must be held across cds_lfht_lookup and
* cds_lfht_next calls, and also between cds_lfht_next calls using the
* node returned by a previous cds_lfht_next.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* This function acts as a rcu_dereference() to read the node pointer.
*/
void cds_lfht_next_duplicate(struct cds_lfht *ht,
cds_lfht_match_fct match, const void *key,
struct cds_lfht_iter *iter);

/*
* cds_lfht_first - get the first node in the table.
* @ht: the hash table.
* @iter: First node, if exists (output). *iter->node set to NULL if not found.
*
* Output in "*iter". *iter->node set to NULL if table is empty.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* This function acts as a rcu_dereference() to read the node pointer.
*/
void cds_lfht_first(struct cds_lfht *ht, struct cds_lfht_iter *iter);

/*
* cds_lfht_next - get the next node in the table.
* @ht: the hash table.
* @iter: input: current iterator.
* output: next node, if exists. *iter->node set to NULL if not found.
*
* Input/Output in "*iter". *iter->node set to NULL if *iter was
* pointing to the last table node.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* This function acts as a rcu_dereference() to read the node pointer.
*/
void cds_lfht_next(struct cds_lfht *ht, struct cds_lfht_iter *iter);

/*
* cds_lfht_add - add a node to the hash table.
* @ht: the hash table.
* @hash: the key hash.
* @node: the node to add.
*
* This function supports adding redundant keys into the table.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* This function issues a full memory barrier before and after its
* atomic commit.
*/
void cds_lfht_add(struct cds_lfht *ht, unsigned long hash,
struct cds_lfht_node *node);

/*
* cds_lfht_add_unique - add a node to hash table, if key is not present.
* @ht: the hash table.
* @hash: the node's hash.
* @match: the key match function.
* @key: the node's key.
* @node: the node to try adding.
*
* Return the node added upon success.
* Return the unique node already present upon failure. If
* cds_lfht_add_unique fails, the node passed as parameter should be
* freed by the caller. In this case, the caller does NOT need to wait
* for a grace period before freeing the node.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
*
* The semantic of this function is that if only this function is used
* to add keys into the table, no duplicated keys should ever be
* observable in the table. The same guarantee apply for combination of
* add_unique and add_replace (see below).
*
* Upon success, this function issues a full memory barrier before and
* after its atomic commit. Upon failure, this function acts like a
* simple lookup operation: it acts as a rcu_dereference() to read the
* node pointer. The failure case does not guarantee any other memory
* barrier.
*/
struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
unsigned long hash,
cds_lfht_match_fct match,
const void *key,
struct cds_lfht_node *node);

/*
* cds_lfht_add_replace - replace or add a node within hash table.
* @ht: the hash table.
* @hash: the node's hash.
* @match: the key match function.
* @key: the node's key.
* @node: the node to add.
*
* Return the node replaced upon success. If no node matching the key
* was present, return NULL, which also means the operation succeeded.
* This replacement operation should never fail.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* After successful replacement, a grace period must be waited for before
* freeing the memory reserved for the returned node.
*
* The semantic of replacement vs lookups and traversals is the
* following: if lookups and traversals are performed between a key
* unique insertion and its removal, we guarantee that the lookups and
* traversals will always find exactly one instance of the key if it is
* replaced concurrently with the lookups.
*
* Providing this semantic allows us to ensure that replacement-only
* schemes will never generate duplicated keys. It also allows us to
* guarantee that a combination of add_replace and add_unique updates
* will never generate duplicated keys.
*
* This function issues a full memory barrier before and after its
* atomic commit.
*/
struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht,
unsigned long hash,
cds_lfht_match_fct match,
const void *key,
struct cds_lfht_node *node);

/*
* cds_lfht_replace - replace a node pointed to by iter within hash table.
* @ht: the hash table.
* @old_iter: the iterator position of the node to replace.
* @hash: the node's hash.
* @match: the key match function.
* @key: the node's key.
* @new_node: the new node to use as replacement.
*
* Return 0 if replacement is successful, negative value otherwise.
* Replacing a NULL old node or an already removed node will fail with
* -ENOENT.
* If the hash or value of the node to replace and the new node differ,
* this function returns -EINVAL without proceeding to the replacement.
* Old node can be looked up with cds_lfht_lookup and cds_lfht_next.
* RCU read-side lock must be held between lookup and replacement.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* After successful replacement, a grace period must be waited for before
* freeing the memory reserved for the old node (which can be accessed
* with cds_lfht_iter_get_node).
*
* The semantic of replacement vs lookups is the same as
* cds_lfht_add_replace().
*
* Upon success, this function issues a full memory barrier before and
* after its atomic commit. Upon failure, this function does not issue
* any memory barrier.
*/
int cds_lfht_replace(struct cds_lfht *ht,
struct cds_lfht_iter *old_iter,
unsigned long hash,
cds_lfht_match_fct match,
const void *key,
struct cds_lfht_node *new_node);

/*
* cds_lfht_del - remove node pointed to by iterator from hash table.
* @ht: the hash table.
* @node: the node to delete.
*
* Return 0 if the node is successfully removed, negative value
* otherwise.
* Deleting a NULL node or an already removed node will fail with a
* negative value.
* Node can be looked up with cds_lfht_lookup and cds_lfht_next,
* followed by use of cds_lfht_iter_get_node.
* RCU read-side lock must be held between lookup and removal.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* After successful removal, a grace period must be waited for before
* freeing the memory reserved for old node (which can be accessed with
* cds_lfht_iter_get_node).
* Upon success, this function issues a full memory barrier before and
* after its atomic commit. Upon failure, this function does not issue
* any memory barrier.
*/
int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node);

/*
* cds_lfht_is_node_deleted - query whether a node is removed from hash table.
*
* Return non-zero if the node is deleted from the hash table, 0
* otherwise.
* Node can be looked up with cds_lfht_lookup and cds_lfht_next,
* followed by use of cds_lfht_iter_get_node.
* RCU read-side lock must be held between lookup and call to this
* function.
* Call with rcu_read_lock held.
* Threads calling this API need to be registered RCU read-side threads.
* This function does not issue any memory barrier.
*/
int cds_lfht_is_node_deleted(struct cds_lfht_node *node);

/*
* cds_lfht_resize - Force a hash table resize
* @ht: the hash table.
* @new_size: update to this hash table size.
*
* Threads calling this API need to be registered RCU read-side threads.
* This function does not (necessarily) issue memory barriers.
*/
void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size);

/*
* Note: it is safe to perform element removal (del), replacement, or
* any hash table update operation during any of the following hash
* table traversals.
* These functions act as rcu_dereference() to read the node pointers.
*/
#define cds_lfht_for_each(ht, iter, node) \
for (cds_lfht_first(ht, iter), \
node = cds_lfht_iter_get_node(iter); \
node != NULL; \
cds_lfht_next(ht, iter), \
node = cds_lfht_iter_get_node(iter))

#define cds_lfht_for_each_duplicate(ht, hash, match, key, iter, node) \
for (cds_lfht_lookup(ht, hash, match, key, iter), \
node = cds_lfht_iter_get_node(iter); \
node != NULL; \
cds_lfht_next_duplicate(ht, match, key, iter), \
node = cds_lfht_iter_get_node(iter))

#define cds_lfht_for_each_entry(ht, iter, pos, member) \
for (cds_lfht_first(ht, iter), \
pos = caa_container_of(cds_lfht_iter_get_node(iter), \
__typeof__(*(pos)), member); \
&(pos)->member != NULL; \
cds_lfht_next(ht, iter), \
pos = caa_container_of(cds_lfht_iter_get_node(iter), \
__typeof__(*(pos)), member))

#define cds_lfht_for_each_entry_duplicate(ht, hash, match, key, \
iter, pos, member) \
for (cds_lfht_lookup(ht, hash, match, key, iter), \
pos = caa_container_of(cds_lfht_iter_get_node(iter), \
__typeof__(*(pos)), member); \
&(pos)->member != NULL; \
cds_lfht_next_duplicate(ht, match, key, iter), \
pos = caa_container_of(cds_lfht_iter_get_node(iter), \
__typeof__(*(pos)), member))

#ifdef __cplusplus
}
#endif

#endif /* _URCU_RCULFHASH_H */

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.