[ltt-dev] [PATCH 3/7] rculfhash: make cds_lfht_lookup() more generic

[mathieu.desnoyers@efficios.com (Mathieu Desnoyers)]

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> On 11/03/2011 01:23 AM, Mathieu Desnoyers wrote:
> > * Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> >> We use hash value to determine the range of the object
> >> and use cds_lfht_lookup_fct to lookup them.
> >>
> >> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> >> ---
> >>  rculfhash.c            |    8 ++++----
> >>  tests/test_urcu_hash.c |   25 ++++++++++++++++++++++---
> >>  urcu/rculfhash.h       |    4 +++-
> >>  3 files changed, 29 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/rculfhash.c b/rculfhash.c
> >> index d1a1766..29054cd 100644
> >> --- a/rculfhash.c
> >> +++ b/rculfhash.c
> >> @@ -1391,14 +1391,14 @@ struct cds_lfht *_cds_lfht_new(cds_lfht_hash_fct hash_fct,
> >>  	return ht;
> >>  }
> >>  
> >> -void cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len,
> >> +void cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash,
> >> +		cds_lfht_lookup_fct match, void *arg,
> > 
> > arg -> key ?
> > 
> > for "match", our approach is to provide this function as parameter to
> > cds_lfht_new rather than pass it as parameter each time a lookup is
> > performed. What is the reason why we should pass it here as a parameter?
> > 
> 
> Allow the user define it.
> In the test, I pass match = a function always returns true when need,
> thus cds_lfht_lookup() returns the first node of same-hash-value-chain.

This looks like an interesting debug and testing feature, but I don't
really see why we should complicate the API to include this. Is there a
real-life use-case you have in mind besides testing ?

If we only need this for testing, we can use a static variable in the
test program to influence the behavior of cds_lfht_test_lookup.

The other patches look fine, I'm just concerned about this one because
it adds complexity to the API which does not seem useful to end-users.

Thanks!

Mathieu

> 
> thanks,
> lai
> 
> 
> > 
> >>  		struct cds_lfht_iter *iter)
> >>  {
> >>  	struct cds_lfht_node *node, *next, *dummy_node;
> >>  	struct _cds_lfht_node *lookup;
> >> -	unsigned long hash, reverse_hash, size;
> >> +	unsigned long reverse_hash, size;
> >>  
> >> -	hash = ht->hash_fct(key, key_len, ht->hash_seed);
> >>  	reverse_hash = bit_reverse_ulong(hash);
> >>  
> >>  	size = rcu_dereference(ht->t.size);
> >> @@ -1421,7 +1421,7 @@ void cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len,
> >>  		if (caa_likely(!is_removed(next))
> >>  		    && !is_dummy(next)
> >>  		    && node->p.reverse_hash == reverse_hash
> >> -		    && caa_likely(!ht->compare_fct(node->key, node->key_len, key, key_len))) {
> >> +		    && caa_likely(match(node, arg))) {
> >>  				break;
> >>  		}
> >>  		node = clear_flag(next);
> >> diff --git a/tests/test_urcu_hash.c b/tests/test_urcu_hash.c
> >> index e28c14a..4c45573 100644
> >> --- a/tests/test_urcu_hash.c
> >> +++ b/tests/test_urcu_hash.c
> >> @@ -41,6 +41,8 @@
> >>  #define DEFAULT_MIN_ALLOC_SIZE	1
> >>  #define DEFAULT_RAND_POOL	1000000
> >>  
> >> +#define TEST_HASH_SEED	0x42UL
> >> +
> >>  /* Make this big enough to include the POWER5+ L3 cacheline size of 256B */
> >>  #define CACHE_LINE_SIZE 4096
> >>  
> >> @@ -419,6 +421,23 @@ unsigned long test_compare(void *key1, size_t key1_len,
> >>  		return 1;
> >>  }
> >>  
> >> +static
> >> +int test_match(struct cds_lfht_node *node, void *arg)
> >> +{
> >> +	return !test_compare(node->key, node->key_len,
> >> +			arg, sizeof(unsigned long));
> >> +}
> >> +
> >> +static
> >> +void cds_lfht_test_lookup(struct cds_lfht *ht, void *key, size_t key_len,
> >> +		struct cds_lfht_iter *iter)
> >> +{
> >> +	assert(key_len == sizeof(unsigned long));
> >> +
> >> +	cds_lfht_lookup(ht, test_hash(key, key_len, TEST_HASH_SEED),
> >> +			test_match, key, iter);
> >> +}
> >> +
> >>  void *thr_count(void *arg)
> >>  {
> >>  	printf_verbose("thread_begin %s, thread id : %lx, tid %lu\n",
> >> @@ -479,7 +498,7 @@ void *thr_reader(void *_count)
> >>  
> >>  	for (;;) {
> >>  		rcu_read_lock();
> >> -		cds_lfht_lookup(test_ht,
> >> +		cds_lfht_test_lookup(test_ht,
> >>  			(void *)(((unsigned long) rand_r(&rand_lookup) % lookup_pool_size) + lookup_pool_offset),
> >>  			sizeof(void *), &iter);
> >>  		node = cds_lfht_iter_get_test_node(&iter);
> >> @@ -574,7 +593,7 @@ void *thr_writer(void *_count)
> >>  		} else {
> >>  			/* May delete */
> >>  			rcu_read_lock();
> >> -			cds_lfht_lookup(test_ht,
> >> +			cds_lfht_test_lookup(test_ht,
> >>  				(void *)(((unsigned long) rand_r(&rand_lookup) % write_pool_size) + write_pool_offset),
> >>  				sizeof(void *), &iter);
> >>  			ret = cds_lfht_del(test_ht, &iter);
> >> @@ -932,7 +951,7 @@ int main(int argc, char **argv)
> >>  	 * thread from the point of view of resize.
> >>  	 */
> >>  	rcu_register_thread();
> >> -	test_ht = cds_lfht_new(test_hash, test_compare, 0x42UL,
> >> +	test_ht = cds_lfht_new(test_hash, test_compare, TEST_HASH_SEED,
> >>  			init_hash_size, min_hash_alloc_size,
> >>  			(opt_auto_resize ? CDS_LFHT_AUTO_RESIZE : 0) |
> >>  			CDS_LFHT_ACCOUNTING, NULL);
> >> diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h
> >> index f4f3373..b56fe56 100644
> >> --- a/urcu/rculfhash.h
> >> +++ b/urcu/rculfhash.h
> >> @@ -86,6 +86,7 @@ typedef unsigned long (*cds_lfht_hash_fct)(void *key, size_t length,
> >>  					unsigned long seed);
> >>  typedef unsigned long (*cds_lfht_compare_fct)(void *key1, size_t key1_len,
> >>  					void *key2, size_t key2_len);
> >> +typedef int (*cds_lfht_lookup_fct)(struct cds_lfht_node *node, void *arg);
> >>  
> >>  /*
> >>   * cds_lfht_node_init - initialize a hash table node
> >> @@ -203,7 +204,8 @@ void cds_lfht_count_nodes(struct cds_lfht *ht,
> >>   * Call with rcu_read_lock held.
> >>   * Threads calling this API need to be registered RCU read-side threads.
> >>   */
> >> -void cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len,
> >> +void cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash,
> >> +		cds_lfht_lookup_fct match, void *arg,
> >>  		struct cds_lfht_iter *iter);
> >>  
> >>  /*
> >> -- 
> >> 1.7.4.4
> >>
> > 
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com