GCC Code Coverage Report


Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2025-07-27 02:42:09
Exec Total Coverage
Lines: 259 263 98.5%
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 <gtest/gtest_prod.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 93444 SmallHashBase() {
43 93444 keys_ = NULL;
44 93444 values_ = NULL;
45 93444 hasher_ = NULL;
46 93444 bytes_allocated_ = 0;
47 93444 num_collisions_ = 0;
48 93444 max_collisions_ = 0;
49
50 // Properly initialized by Init()
51 93444 capacity_ = 0;
52 93444 initial_capacity_ = 0;
53 93444 size_ = 0;
54 93444 }
55
56 93306 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
57
58 93442 void Init(uint32_t expected_size, Key empty,
59 uint32_t (*hasher)(const Key &key)) {
60 93442 hasher_ = hasher;
61 93442 empty_key_ = empty;
62 93442 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
63 93442 / kLoadFactor);
64 93442 initial_capacity_ = capacity_;
65 93442 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
66 93442 AllocMemory();
67 93442 this->DoClear(false);
68 93442 }
69
70 20282860 bool Lookup(const Key &key, Value *value) const {
71 uint32_t bucket;
72 uint32_t collisions;
73
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20282860 const bool found = DoLookup(key, &bucket, &collisions);
74
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20336316 if (found)
75
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12265287 *value = values_[bucket];
76 20336316 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 */
86 504 bool LookupEx(Key *key, Value *value) const {
87 504 uint32_t bucket = ScaleHash(*key);
88
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504 while (!(keys_[bucket] == empty_key_)) {
89
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336 if (keys_[bucket] == *key) {
90 336 *key = keys_[bucket];
91 336 *value = values_[bucket];
92 336 return true;
93 }
94 bucket = (bucket + 1) % capacity_;
95 }
96 168 return false;
97 }
98
99 49040235 bool Contains(const Key &key) const {
100 uint32_t bucket;
101 uint32_t collisions;
102
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49040235 const bool found = DoLookup(key, &bucket, &collisions);
103 49040235 return found;
104 }
105
106 274515098 void Insert(const Key &key, const Value &value) {
107 274515098 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
108 274303514 const bool overwritten = DoInsert(key, value, true);
109 274305312 size_ += !overwritten; // size + 1 if the key was not yet in the map
110 274305312 }
111
112 26232917 bool Erase(const Key &key) {
113 uint32_t bucket;
114 uint32_t collisions;
115
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26232917 const bool found = DoLookup(key, &bucket, &collisions);
116
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26160931 if (found) {
117 26160424 keys_[bucket] = empty_key_;
118 26160424 size_--;
119 26160424 bucket = (bucket + 1) % capacity_;
120
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50882173 while (!(keys_[bucket] == empty_key_)) {
121 24777954 Key rehash = keys_[bucket];
122 24777954 keys_[bucket] = empty_key_;
123
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24777954 DoInsert(rehash, values_[bucket], false);
124 24721749 bucket = (bucket + 1) % capacity_;
125 }
126
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26104219 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
127 }
128 26154609 return found;
129 }
130
131 352 void Clear() { DoClear(true); }
132
133 1624 uint64_t bytes_allocated() const { return bytes_allocated_; }
134 144 static double GetEntrySize() {
135 288 const double unit = sizeof(Key) + sizeof(Value);
136 288 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 7242 Key empty_key() const { return empty_key_; }
148 35664 Key *keys() const { return keys_; }
149 357 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 470472069 uint32_t ScaleHash(const Key &key) const {
156 470472069 const double bucket = (static_cast<double>(hasher_(key))
157 469842953 * static_cast<double>(capacity_)
158 / static_cast<double>(static_cast<uint32_t>(-1)));
159 469842953 return static_cast<uint32_t>(bucket) % capacity_;
160 }
161
162 100068 void AllocMemory() {
163 100068 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
164 100072 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
165
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1463174522 for (uint32_t i = 0; i < capacity_; ++i) {
166 1463074450 /*keys_[i] =*/new (keys_ + i) Key();
167 }
168
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1463459212 for (uint32_t i = 0; i < capacity_; ++i) {
169 1463351228 /*values_[i] =*/new (values_ + i) Value();
170 }
171 107984 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
172 107984 }
173
174 99936 void DeallocMemory(Key *k, Value *v, uint32_t c) {
175
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1463827110 for (uint32_t i = 0; i < c; ++i) {
176 1463727174 k[i].~Key();
177 }
178
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1463646774 for (uint32_t i = 0; i < c; ++i) {
179 1463546838 v[i].~Value();
180 }
181
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99936 if (k)
182 99934 smunmap(k);
183
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99936 if (v)
184 99934 smunmap(v);
185 99936 k = NULL;
186 99936 v = NULL;
187 99936 }
188
189 // Returns true iff the key is overwritten
190 306081193 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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306081193 const bool overwritten = DoLookup(key, &bucket, &collisions);
195
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306068691 if (count_collisions) {
196 274352626 num_collisions_ += collisions;
197 274352626 max_collisions_ = std::max(collisions, max_collisions_);
198 }
199 306027557 keys_[bucket] = key;
200
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306027557 values_[bucket] = value;
201 306027557 return overwritten;
202 }
203
204 470729667 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
205 470729667 *bucket = ScaleHash(key);
206 469801973 *collisions = 0;
207
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10048554265 while (!(keys_[*bucket] == empty_key_)) {
208
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9742392058 if (keys_[*bucket] == key)
209 163639766 return true;
210 9578752292 *bucket = (*bucket + 1) % capacity_;
211 9578752292 (*collisions)++;
212 }
213 306162207 return false;
214 }
215
216 100106 void DoClear(const bool reset_capacity) {
217
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100106 if (reset_capacity)
218 398 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
219
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1463923354 for (uint32_t i = 0; i < capacity_; ++i)
220 1463823248 keys_[i] = empty_key_;
221 100106 size_ = 0;
222 100106 }
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 1590 void SetThresholds() { }
252 98210 void Grow() { }
253 19474 void Shrink() { }
254 34 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 91854 SmallHashDynamic() : Base() {
269 91854 num_migrates_ = 0;
270
271 // Properly set by Init
272 91854 threshold_grow_ = 0;
273 91854 threshold_shrink_ = 0;
274 91854 }
275
276 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
277 num_migrates_ = 0;
278 CopyFrom(other);
279 }
280
281 369 SmallHashDynamic<Key, Value> &operator=(
282 const SmallHashDynamic<Key, Value> &other) {
283
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369 if (&other == this)
284 return *this;
285
286 369 CopyFrom(other);
287 369 return *this;
288 }
289
290 46472872 uint32_t capacity() const { return Base::capacity_; }
291 186219841 uint32_t size() const { return Base::size_; }
292 uint32_t num_migrates() const { return num_migrates_; }
293
294 protected:
295 98474 void SetThresholds() {
296 98474 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
297 98474 * kThresholdGrow);
298 98474 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
299 98476 * kThresholdShrink);
300 98476 }
301
302 274351834 void Grow() {
303
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274351834 if (size() > threshold_grow_)
304 4844 Migrate(capacity() * 2);
305 274250298 }
306
307 26136473 void Shrink() {
308
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26136473 if (size() < threshold_shrink_) {
309 23115647 const uint32_t target_capacity = capacity() / 2;
310
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23113266 if (target_capacity >= Base::initial_capacity_)
311 687 Migrate(target_capacity);
312 }
313 26131089 }
314
315 364 void ResetCapacity() {
316 364 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
317 364 Base::capacity_ = Base::initial_capacity_;
318 364 Base::AllocMemory();
319 364 SetThresholds();
320 364 }
321
322 private:
323 // Returns a random permutation of indices [0..N-1] that is allocated
324 // by smmap (Knuth's shuffle algorithm)
325 1746 uint32_t *ShuffleIndices(const uint32_t N) {
326 1746 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
327 // Init with identity
328
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22577220 for (unsigned i = 0; i < N; ++i)
329 22575474 shuffled[i] = i;
330 // Shuffle (no shuffling for the last element)
331
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21381362 for (unsigned i = 0; i < N - 1; ++i) {
332 21384506 const uint32_t swap_idx = i + g_prng.Next(N - i);
333 21379616 const uint32_t tmp = shuffled[i];
334 21379616 shuffled[i] = shuffled[swap_idx];
335 21379616 shuffled[swap_idx] = tmp;
336 }
337 369 return shuffled;
338 }
339
340 6216 void Migrate(const uint32_t new_capacity) {
341 6216 Key *old_keys = Base::keys_;
342 6216 Value *old_values = Base::values_;
343 6216 const uint32_t old_capacity = capacity();
344 6216 const uint32_t old_size = size();
345
346 6216 Base::capacity_ = new_capacity;
347 6216 SetThresholds();
348 6218 Base::AllocMemory();
349 6224 Base::DoClear(false);
350
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6224 if (new_capacity < old_capacity) {
351 1376 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
352
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353
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19326230 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
354 4855298 Base::Insert(old_keys[shuffled_indices[i]],
355 4855298 old_values[shuffled_indices[i]]);
356 }
357 }
358 smunmap(shuffled_indices);
359 } else {
360
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94881414 for (uint32_t i = 0; i < old_capacity; ++i) {
361
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94877250 if (old_keys[i] != Base::empty_key_)
362 71171432 Base::Insert(old_keys[i], old_values[i]);
363 }
364 }
365
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5540 assert(size() == old_size);
366
367 6224 Base::DeallocMemory(old_keys, old_values, old_capacity);
368 6224 num_migrates_++;
369 6224 }
370
371 369 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
372 369 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
373
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1384353 for (uint32_t i = 0; i < other.capacity_; ++i) {
374
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1383984 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
375 1000000 this->Insert(other.keys_[shuffled_indices[i]],
376 1000000 other.values_[shuffled_indices[i]]);
377 }
378 }
379 369 smunmap(shuffled_indices);
380 369 }
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 10 MultiHash() {
397 10 num_hashmaps_ = 0;
398 10 hashmaps_ = NULL;
399 10 locks_ = NULL;
400 10 }
401
402 10 void Init(const uint8_t num_hashmaps, const Key &empty_key,
403 uint32_t (*hasher)(const Key &key)) {
404
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10 assert(num_hashmaps > 0);
405 10 const uint8_t N = num_hashmaps;
406 10 num_hashmaps_ = N;
407
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430 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
408 10 locks_ = static_cast<pthread_mutex_t *>(
409 10 smalloc(N * sizeof(pthread_mutex_t)));
410
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430 for (uint8_t i = 0; i < N; ++i) {
411 420 int retval = pthread_mutex_init(&locks_[i], NULL);
412
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420 assert(retval == 0);
413 420 hashmaps_[i].Init(128, empty_key, hasher);
414 }
415 10 }
416
417 10 ~MultiHash() {
418
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430 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
419 420 pthread_mutex_destroy(&locks_[i]);
420 }
421 10 free(locks_);
422
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430 delete[] hashmaps_;
423 10 }
424
425 1000000 bool Lookup(const Key &key, Value *value) {
426 1000000 uint8_t target = SelectHashmap(key);
427 1000000 Lock(target);
428 1000000 const bool result = hashmaps_[target].Lookup(key, value);
429 1000000 Unlock(target);
430 1000000 return result;
431 }
432
433 3739289 void Insert(const Key &key, const Value &value) {
434 3739289 uint8_t target = SelectHashmap(key);
435 3635480 Lock(target);
436 3783069 hashmaps_[target].Insert(key, value);
437 3603161 Unlock(target);
438 3892150 }
439
440 1808374 void Erase(const Key &key) {
441 1808374 uint8_t target = SelectHashmap(key);
442 1728613 Lock(target);
443 1851886 hashmaps_[target].Erase(key);
444 1675572 Unlock(target);
445 1874711 }
446
447 1 void Clear() {
448
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43 for (uint8_t i = 0; i < num_hashmaps_; ++i)
449 42 Lock(i);
450
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43 for (uint8_t i = 0; i < num_hashmaps_; ++i)
451 42 hashmaps_[i].Clear();
452
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43 for (uint8_t i = 0; i < num_hashmaps_; ++i)
453 42 Unlock(i);
454 1 }
455
456 10 uint8_t num_hashmaps() const { return num_hashmaps_; }
457
458 8 void GetSizes(uint32_t *sizes) {
459
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344 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
460 336 Lock(i);
461 336 sizes[i] = hashmaps_[i].size();
462 336 Unlock(i);
463 }
464 8 }
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 6502426 inline uint8_t SelectHashmap(const Key &key) {
476 6502426 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
477 6395470 double bucket = static_cast<double>(hash)
478 6395470 * static_cast<double>(num_hashmaps_)
479 / static_cast<double>(static_cast<uint32_t>(-1));
480 6395470 return static_cast<uint32_t>(bucket) % num_hashmaps_;
481 }
482
483 6439731 inline void Lock(const uint8_t target) {
484 6439731 int retval = pthread_mutex_lock(&locks_[target]);
485
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6871273 assert(retval == 0);
486 6871273 }
487
488 6279316 inline void Unlock(const uint8_t target) {
489 6279316 int retval = pthread_mutex_unlock(&locks_[target]);
490
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6888395 assert(retval == 0);
491 6888395 }
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