GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2025-11-30 02:35:17
Exec Total Coverage
Lines: 260 263 98.9%
Branches: 89 110 80.9%
Line Branch Exec Source
1 /**
2 * This file is part of the CernVM File System.
3 */
4
5 #ifndef CVMFS_SMALLHASH_H_
6 #define CVMFS_SMALLHASH_H_
7
8 #ifndef __STDC_FORMAT_MACROS
9 // NOLINTNEXTLINE
10 #define __STDC_FORMAT_MACROS
11 #endif
12
13 #include "duplex_testing.h"
14 #include <inttypes.h>
15 #include <pthread.h>
16 #include <stdint.h>
17
18 #include <algorithm>
19 #include <cassert>
20 #include <cstdlib>
21 #include <new>
22
23 #include "util/atomic.h"
24 #include "util/murmur.hxx"
25 #include "util/prng.h"
26 #include "util/smalloc.h"
27
28 /**
29 * Hash table with linear probing as collision resolution. Works only for
30 * a fixed (maximum) number of elements, i.e. no resizing. Load factor fixed
31 * to 0.7.
32 */
33 template<class Key, class Value, class Derived>
34 class SmallHashBase {
35 FRIEND_TEST(T_Smallhash, InsertAndCopyMd5Slow);
36
37 public:
38 static const double kLoadFactor; // mainly useless for the dynamic version
39 static const double kThresholdGrow; // only used for resizable version
40 static const double kThresholdShrink; // only used for resizable version
41
42 151159 SmallHashBase() {
43 151159 keys_ = NULL;
44 151159 values_ = NULL;
45 151159 hasher_ = NULL;
46 151159 bytes_allocated_ = 0;
47 151159 num_collisions_ = 0;
48 151159 max_collisions_ = 0;
49
50 // Properly initialized by Init()
51 151159 capacity_ = 0;
52 151159 initial_capacity_ = 0;
53 151159 size_ = 0;
54 151159 }
55
56 151021 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
57
58 151129 void Init(uint32_t expected_size, Key empty,
59 uint32_t (*hasher)(const Key &key)) {
60 151129 hasher_ = hasher;
61 151129 empty_key_ = empty;
62 151129 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
63 151129 / kLoadFactor);
64 151129 initial_capacity_ = capacity_;
65 151129 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
66 151129 AllocMemory();
67 151129 this->DoClear(false);
68 151129 }
69
70 83191780 bool Lookup(const Key &key, Value *value) const {
71 uint32_t bucket;
72 uint32_t collisions;
73
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 83191780 const bool found = DoLookup(key, &bucket, &collisions);
74
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 83308620 if (found)
75
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 60257285 *value = values_[bucket];
76 83308620 return found;
77 }
78
79 /**
80 * Returns both the key and the value. That is useful if Key's equality
81 * operator implements an equivalence relation on Key. In this case, LookupEx
82 * returns the key representing the equivalence class that has been used
83 * during Insert().
84 * Used to return a glue::InodeEx element when looking for an inode.
85 */
86 132 bool LookupEx(Key *key, Value *value) const {
87 132 uint32_t bucket = ScaleHash(*key);
88
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 132 while (!(keys_[bucket] == empty_key_)) {
89
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 88 if (keys_[bucket] == *key) {
90 88 *key = keys_[bucket];
91 88 *value = values_[bucket];
92 88 return true;
93 }
94 ✗ bucket = (bucket + 1) % capacity_;
95 }
96 44 return false;
97 }
98
99 46021436 bool Contains(const Key &key) const {
100 uint32_t bucket;
101 uint32_t collisions;
102
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 46021436 const bool found = DoLookup(key, &bucket, &collisions);
103 46021436 return found;
104 }
105
106 980508642 void Insert(const Key &key, const Value &value) {
107 980508642 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
108 978057556 const bool overwritten = DoInsert(key, value, true);
109 978733510 size_ += !overwritten; // size + 1 if the key was not yet in the map
110 978733510 }
111
112 66328165 bool Erase(const Key &key) {
113 uint32_t bucket;
114 uint32_t collisions;
115
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 66328165 const bool found = DoLookup(key, &bucket, &collisions);
116
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 64584798 if (found) {
117 64590234 keys_[bucket] = empty_key_;
118 64590234 size_--;
119 64590234 bucket = (bucket + 1) % capacity_;
120
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 148086433 while (!(keys_[bucket] == empty_key_)) {
121 84032044 Key rehash = keys_[bucket];
122 84032044 keys_[bucket] = empty_key_;
123
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 84032044 DoInsert(rehash, values_[bucket], false);
124 83496199 bucket = (bucket + 1) % capacity_;
125 }
126
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 64054389 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
127 }
128 64796399 return found;
129 }
130
131 1468 void Clear() { DoClear(true); }
132
133 3014 uint64_t bytes_allocated() const { return bytes_allocated_; }
134 999 static double GetEntrySize() {
135 1998 const double unit = sizeof(Key) + sizeof(Value);
136 1998 return unit / kLoadFactor;
137 }
138
139 void GetCollisionStats(uint64_t *num_collisions,
140 uint32_t *max_collisions) const {
141 *num_collisions = num_collisions_;
142 *max_collisions = max_collisions_;
143 }
144
145 // Careful with the direct access TODO: iterator
146 uint32_t capacity() const { return capacity_; }
147 67936 Key empty_key() const { return empty_key_; }
148 155426 Key *keys() const { return keys_; }
149 165 Value *values() const { return values_; }
150
151 // Only needed by compat
152 ✗ void SetHasher(uint32_t (*hasher)(const Key &key)) { hasher_ = hasher; }
153
154 protected:
155 1433316960 uint32_t ScaleHash(const Key &key) const {
156 1433316960 const double bucket = (static_cast<double>(hasher_(key))
157 1429083918 * static_cast<double>(capacity_)
158 / static_cast<double>(static_cast<uint32_t>(-1)));
159 1429083918 return static_cast<uint32_t>(bucket) % capacity_;
160 }
161
162 218912 void AllocMemory() {
163 218912 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
164 218942 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
165
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 2464170688 for (uint32_t i = 0; i < capacity_; ++i) {
166 2463951746 /*keys_[i] =*/new (keys_ + i) Key();
167 }
168
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 2467176058 for (uint32_t i = 0; i < capacity_; ++i) {
169 2466989846 /*values_[i] =*/new (values_ + i) Value();
170 }
171 186212 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
172 186212 }
173
174 218834 void DeallocMemory(Key *k, Value *v, uint32_t c) {
175
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 2469508624 for (uint32_t i = 0; i < c; ++i) {
176 2469289790 k[i].~Key();
177 }
178
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 2474790544 for (uint32_t i = 0; i < c; ++i) {
179 2474571710 v[i].~Value();
180 }
181
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 218834 if (k)
182 218804 smunmap(k);
183
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 218834 if (v)
184 218804 smunmap(v);
185 218834 k = NULL;
186 218834 v = NULL;
187 218834 }
188
189 // Returns true iff the key is overwritten
190 1131351667 bool DoInsert(const Key &key, const Value &value,
191 const bool count_collisions) {
192 uint32_t bucket;
193 uint32_t collisions;
194
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 1131351667 const bool overwritten = DoLookup(key, &bucket, &collisions);
195
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 1133222427 if (count_collisions) {
196 980181776 num_collisions_ += collisions;
197 980181776 max_collisions_ = std::max(collisions, max_collisions_);
198 }
199 1131896809 keys_[bucket] = key;
200
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 1131896809 values_[bucket] = value;
201 1131896809 return overwritten;
202 }
203
204 1434839994 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
205 1434839994 *bucket = ScaleHash(key);
206 1431132592 *collisions = 0;
207
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 9750447836 while (!(keys_[*bucket] == empty_key_)) {
208
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 8628662515 if (keys_[*bucket] == key)
209 309347271 return true;
210 8319315244 *bucket = (*bucket + 1) % capacity_;
211 8319315244 (*collisions)++;
212 }
213 1121785321 return false;
214 }
215
216 218972 void DoClear(const bool reset_capacity) {
217
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 218972 if (reset_capacity)
218 2124 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
219
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 2469022228 for (uint32_t i = 0; i < capacity_; ++i)
220 2468803256 keys_[i] = empty_key_;
221 218972 size_ = 0;
222 218972 }
223
224 // Methods for resizable version
225 void SetThresholds() { }
226 void Grow() { }
227 void Shrink() { }
228 void ResetCapacity() { }
229
230 // Separate key and value arrays for better locality
231 Key *keys_;
232 Value *values_;
233 uint32_t capacity_;
234 uint32_t initial_capacity_;
235 uint32_t size_;
236 uint32_t (*hasher_)(const Key &key);
237 uint64_t bytes_allocated_;
238 uint64_t num_collisions_;
239 uint32_t max_collisions_; /**< maximum collisions for a single insert */
240 Key empty_key_;
241 };
242
243
244 template<class Key, class Value>
245 class SmallHashFixed
246 : public SmallHashBase<Key, Value, SmallHashFixed<Key, Value> > {
247 friend class SmallHashBase<Key, Value, SmallHashFixed<Key, Value> >;
248
249 protected:
250 // No-ops
251 2984 void SetThresholds() { }
252 302198 void Grow() { }
253 13984 void Shrink() { }
254 30 void ResetCapacity() { }
255 };
256
257
258 template<class Key, class Value>
259 class SmallHashDynamic
260 : public SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > {
261 friend class SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> >;
262
263 public:
264 typedef SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > Base;
265 static const double kThresholdGrow;
266 static const double kThresholdShrink;
267
268 148175 SmallHashDynamic() : Base() {
269 148175 num_migrates_ = 0;
270
271 // Properly set by Init
272 148175 threshold_grow_ = 0;
273 148175 threshold_shrink_ = 0;
274 148175 }
275
276 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
277 num_migrates_ = 0;
278 CopyFrom(other);
279 }
280
281 55 SmallHashDynamic<Key, Value> &operator=(
282 const SmallHashDynamic<Key, Value> &other) {
283
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 55 if (&other == this)
284 ✗ return *this;
285
286 55 CopyFrom(other);
287 55 return *this;
288 }
289
290 50311396 uint32_t capacity() const { return Base::capacity_; }
291 577658662 uint32_t size() const { return Base::size_; }
292 uint32_t num_migrates() const { return num_migrates_; }
293
294 protected:
295 215868 void SetThresholds() {
296 215868 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
297 215868 * kThresholdGrow);
298 215868 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
299 215868 * kThresholdShrink);
300 215868 }
301
302 978833341 void Grow() {
303
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 978833341 if (size() > threshold_grow_)
304 45068 Migrate(capacity() * 2);
305 977980091 }
306
307 64704180 void Shrink() {
308
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 64704180 if (size() < threshold_shrink_) {
309 24781825 const uint32_t target_capacity = capacity() / 2;
310
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 24780675 if (target_capacity >= Base::initial_capacity_)
311 10305 Migrate(target_capacity);
312 }
313 64794634 }
314
315 2094 void ResetCapacity() {
316 2094 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
317 2094 Base::capacity_ = Base::initial_capacity_;
318 2094 Base::AllocMemory();
319 2094 SetThresholds();
320 2094 }
321
322 private:
323 // Returns a random permutation of indices [0..N-1] that is allocated
324 // by smmap (Knuth's shuffle algorithm)
325 20710 uint32_t *ShuffleIndices(const uint32_t N) {
326 20710 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
327 // Init with identity
328
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 336288670 for (unsigned i = 0; i < N; ++i)
329 336267960 shuffled[i] = i;
330 // Shuffle (no shuffling for the last element)
331
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 321945000 for (unsigned i = 0; i < N - 1; ++i) {
332 322719650 const uint32_t swap_idx = i + g_prng.Next(N - i);
333 321924290 const uint32_t tmp = shuffled[i];
334 321924290 shuffled[i] = shuffled[swap_idx];
335 321924290 shuffled[swap_idx] = tmp;
336 }
337 55 return shuffled;
338 }
339
340 65648 void Migrate(const uint32_t new_capacity) {
341 65648 Key *old_keys = Base::keys_;
342 65648 Value *old_values = Base::values_;
343 65648 const uint32_t old_capacity = capacity();
344 65648 const uint32_t old_size = size();
345
346 65618 Base::capacity_ = new_capacity;
347 65618 SetThresholds();
348 65648 Base::AllocMemory();
349 65708 Base::DoClear(false);
350
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 65708 if (new_capacity < old_capacity) {
351 20640 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
352
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 291305070 for (uint32_t i = 0; i < old_capacity; ++i) {
353
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 291301440 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
354 73004280 Base::Insert(old_keys[shuffled_indices[i]],
355 73004280 old_values[shuffled_indices[i]]);
356 }
357 }
358 3630 smunmap(shuffled_indices);
359 } else {
360
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 550951010 for (uint32_t i = 0; i < old_capacity; ++i) {
361
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 550938552 if (old_keys[i] != Base::empty_key_)
362 413386872 Base::Insert(old_keys[i], old_values[i]);
363 }
364 }
365
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 33098 assert(size() == old_size);
366
367 65708 Base::DeallocMemory(old_keys, old_values, old_capacity);
368 65708 num_migrates_++;
369 65708 }
370
371 55 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
372 55 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
373
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 20644735 for (uint32_t i = 0; i < other.capacity_; ++i) {
374
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 20644680 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
375 15000000 this->Insert(other.keys_[shuffled_indices[i]],
376 15000000 other.values_[shuffled_indices[i]]);
377 }
378 }
379 55 smunmap(shuffled_indices);
380 55 }
381
382 uint32_t num_migrates_;
383 uint32_t threshold_grow_;
384 uint32_t threshold_shrink_;
385 static Prng g_prng;
386 };
387
388
389 /**
390 * Distributes the key-value pairs over $n$ dynamic hash maps with individual
391 * mutexes. Hence low mutex contention, and benefits from multiple processors.
392 */
393 template<class Key, class Value>
394 class MultiHash {
395 public:
396 150 MultiHash() {
397 150 num_hashmaps_ = 0;
398 150 hashmaps_ = NULL;
399 150 locks_ = NULL;
400 150 }
401
402 150 void Init(const uint8_t num_hashmaps, const Key &empty_key,
403 uint32_t (*hasher)(const Key &key)) {
404
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 150 assert(num_hashmaps > 0);
405 150 const uint8_t N = num_hashmaps;
406 150 num_hashmaps_ = N;
407
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 6450 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
408 150 locks_ = static_cast<pthread_mutex_t *>(
409 150 smalloc(N * sizeof(pthread_mutex_t)));
410
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 6450 for (uint8_t i = 0; i < N; ++i) {
411 6300 int retval = pthread_mutex_init(&locks_[i], NULL);
412
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 6300 assert(retval == 0);
413 6300 hashmaps_[i].Init(128, empty_key, hasher);
414 }
415 150 }
416
417 150 ~MultiHash() {
418
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 6450 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
419 6300 pthread_mutex_destroy(&locks_[i]);
420 }
421 150 free(locks_);
422
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 6450 delete[] hashmaps_;
423 150 }
424
425 15000000 bool Lookup(const Key &key, Value *value) {
426 15000000 uint8_t target = SelectHashmap(key);
427 15000000 Lock(target);
428 15000000 const bool result = hashmaps_[target].Lookup(key, value);
429 15000000 Unlock(target);
430 15000000 return result;
431 }
432
433 56391870 void Insert(const Key &key, const Value &value) {
434 56391870 uint8_t target = SelectHashmap(key);
435 54487305 Lock(target);
436 56558250 hashmaps_[target].Insert(key, value);
437 54517665 Unlock(target);
438 57350880 }
439
440 27131925 void Erase(const Key &key) {
441 27131925 uint8_t target = SelectHashmap(key);
442 25842390 Lock(target);
443 27617970 hashmaps_[target].Erase(key);
444 25012950 Unlock(target);
445 27961425 }
446
447 15 void Clear() {
448
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 645 for (uint8_t i = 0; i < num_hashmaps_; ++i)
449 630 Lock(i);
450
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 645 for (uint8_t i = 0; i < num_hashmaps_; ++i)
451 630 hashmaps_[i].Clear();
452
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 645 for (uint8_t i = 0; i < num_hashmaps_; ++i)
453 630 Unlock(i);
454 15 }
455
456 150 uint8_t num_hashmaps() const { return num_hashmaps_; }
457
458 120 void GetSizes(uint32_t *sizes) {
459
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 5160 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
460 5040 Lock(i);
461 5040 sizes[i] = hashmaps_[i].size();
462 5040 Unlock(i);
463 }
464 120 }
465
466 void GetCollisionStats(uint64_t *num_collisions, uint32_t *max_collisions) {
467 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
468 Lock(i);
469 hashmaps_[i].GetCollisionStats(&num_collisions[i], &max_collisions[i]);
470 Unlock(i);
471 }
472 }
473
474 private:
475 98002860 inline uint8_t SelectHashmap(const Key &key) {
476 98002860 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
477 96094920 double bucket = static_cast<double>(hash)
478 96094920 * static_cast<double>(num_hashmaps_)
479 / static_cast<double>(static_cast<uint32_t>(-1));
480 96094920 return static_cast<uint32_t>(bucket) % num_hashmaps_;
481 }
482
483 96548220 inline void Lock(const uint8_t target) {
484 96548220 int retval = pthread_mutex_lock(&locks_[target]);
485
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 103059975 assert(retval == 0);
486 103059975 }
487
488 94468890 inline void Unlock(const uint8_t target) {
489 94468890 int retval = pthread_mutex_unlock(&locks_[target]);
490
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 103494645 assert(retval == 0);
491 103494645 }
492
493 uint8_t num_hashmaps_;
494 SmallHashDynamic<Key, Value> *hashmaps_;
495 pthread_mutex_t *locks_;
496 };
497
498
499 // initialize the static fields
500 template<class Key, class Value>
501 Prng SmallHashDynamic<Key, Value>::g_prng;
502
503 template<class Key, class Value, class Derived>
504 const double SmallHashBase<Key, Value, Derived>::kLoadFactor = 0.75;
505
506 template<class Key, class Value>
507 const double SmallHashDynamic<Key, Value>::kThresholdGrow = 0.75;
508
509 template<class Key, class Value>
510 const double SmallHashDynamic<Key, Value>::kThresholdShrink = 0.25;
511
512 #endif // CVMFS_SMALLHASH_H_
513