GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2026-04-26 02:35:59
Exec Total Coverage
Lines: 259 263 98.5%
Branches: 88 110 80.0%
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 175756 SmallHashBase() {
43 175756 keys_ = NULL;
44 175756 values_ = NULL;
45 175756 hasher_ = NULL;
46 175756 bytes_allocated_ = 0;
47 175756 num_collisions_ = 0;
48 175756 max_collisions_ = 0;
49
50 // Properly initialized by Init()
51 175756 capacity_ = 0;
52 175756 initial_capacity_ = 0;
53 175756 size_ = 0;
54 175756 }
55
56 175618 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
57
58 175746 void Init(uint32_t expected_size, Key empty,
59 uint32_t (*hasher)(const Key &key)) {
60 175746 hasher_ = hasher;
61 175746 empty_key_ = empty;
62 175746 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
63 175746 / kLoadFactor);
64 175746 initial_capacity_ = capacity_;
65 175746 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
66 175746 AllocMemory();
67 175746 this->DoClear(false);
68 175746 }
69
70 56646071 bool Lookup(const Key &key, Value *value) const {
71 uint32_t bucket;
72 uint32_t collisions;
73
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 56646071 const bool found = DoLookup(key, &bucket, &collisions);
74
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 56896802 if (found)
75
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 37129461 *value = values_[bucket];
76 56896802 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 */
86 520 bool LookupEx(Key *key, Value *value) const {
87 520 uint32_t bucket = ScaleHash(*key);
88
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 520 while (!(keys_[bucket] == empty_key_)) {
89
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 348 if (keys_[bucket] == *key) {
90 348 *key = keys_[bucket];
91 348 *value = values_[bucket];
92 348 return true;
93 }
94 ✗ bucket = (bucket + 1) % capacity_;
95 }
96 172 return false;
97 }
98
99 34073929 bool Contains(const Key &key) const {
100 uint32_t bucket;
101 uint32_t collisions;
102
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 34073929 const bool found = DoLookup(key, &bucket, &collisions);
103 34073929 return found;
104 }
105
106 481461678 void Insert(const Key &key, const Value &value) {
107 481461678 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
108 480574003 const bool overwritten = DoInsert(key, value, true);
109 480234524 size_ += !overwritten; // size + 1 if the key was not yet in the map
110 480234524 }
111
112 47512855 bool Erase(const Key &key) {
113 uint32_t bucket;
114 uint32_t collisions;
115
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 47512855 const bool found = DoLookup(key, &bucket, &collisions);
116
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 47339569 if (found) {
117 47354326 keys_[bucket] = empty_key_;
118 47354326 size_--;
119 47354326 bucket = (bucket + 1) % capacity_;
120
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 117344138 while (!(keys_[bucket] == empty_key_)) {
121 70253212 Key rehash = keys_[bucket];
122 70253212 keys_[bucket] = empty_key_;
123
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 70253212 DoInsert(rehash, values_[bucket], false);
124 69989812 bucket = (bucket + 1) % capacity_;
125 }
126
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 47090926 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
127 }
128 47163788 return found;
129 }
130
131 1004 void Clear() { DoClear(true); }
132
133 6121 uint64_t bytes_allocated() const { return bytes_allocated_; }
134 1359 static double GetEntrySize() {
135 2718 const double unit = sizeof(Key) + sizeof(Value);
136 2718 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 210192 Key empty_key() const { return empty_key_; }
148 451200 Key *keys() const { return keys_; }
149 602 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 780803790 uint32_t ScaleHash(const Key &key) const {
156 780803790 const double bucket = (static_cast<double>(hasher_(key))
157 780713776 * static_cast<double>(capacity_)
158 / static_cast<double>(static_cast<uint32_t>(-1)));
159 780713776 return static_cast<uint32_t>(bucket) % capacity_;
160 }
161
162 202239 void AllocMemory() {
163 202239 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
164 202239 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
165
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 1480805392 for (uint32_t i = 0; i < capacity_; ++i) {
166 1480603153 /*keys_[i] =*/new (keys_ + i) Key();
167 }
168
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 1483420402 for (uint32_t i = 0; i < capacity_; ++i) {
169 1483197713 /*values_[i] =*/new (values_ + i) Value();
170 }
171 222689 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
172 222689 }
173
174 202111 void DeallocMemory(Key *k, Value *v, uint32_t c) {
175
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 1484105408 for (uint32_t i = 0; i < c; ++i) {
176 1483903297 k[i].~Key();
177 }
178
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 1484373408 for (uint32_t i = 0; i < c; ++i) {
179 1484171297 v[i].~Value();
180 }
181
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 202111 if (k)
182 202101 smunmap(k);
183
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 202111 if (v)
184 202101 smunmap(v);
185 202111 k = NULL;
186 202111 v = NULL;
187 202111 }
188
189 // Returns true iff the key is overwritten
190 574789285 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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 574789285 const bool overwritten = DoLookup(key, &bucket, &collisions);
195
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 574571841 if (count_collisions) {
196 480526239 num_collisions_ += collisions;
197 480526239 max_collisions_ = std::max(collisions, max_collisions_);
198 }
199 574320607 keys_[bucket] = key;
200
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 574320607 values_[bucket] = value;
201 574320607 return overwritten;
202 }
203
204 781177646 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
205 781177646 *bucket = ScaleHash(key);
206 780309356 *collisions = 0;
207
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 25106629947 while (!(keys_[*bucket] == empty_key_)) {
208
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 24535169560 if (keys_[*bucket] == key)
209 208848969 return true;
210 24326320591 *bucket = (*bucket + 1) % capacity_;
211 24326320591 (*collisions)++;
212 }
213 571460387 return false;
214 }
215
216 202327 void DoClear(const bool reset_capacity) {
217
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 202327 if (reset_capacity)
218 1257 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
219
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 1484261270 for (uint32_t i = 0; i < capacity_; ++i)
220 1484058943 keys_[i] = empty_key_;
221 202327 size_ = 0;
222 202327 }
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 6033 void SetThresholds() { }
252 1271961 void Grow() { }
253 48348 void Shrink() { }
254 88 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 169723 SmallHashDynamic() : Base() {
269 169723 num_migrates_ = 0;
270
271 // Properly set by Init
272 169723 threshold_grow_ = 0;
273 169723 threshold_shrink_ = 0;
274 169723 }
275
276 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
277 num_migrates_ = 0;
278 CopyFrom(other);
279 }
280
281 317 SmallHashDynamic<Key, Value> &operator=(
282 const SmallHashDynamic<Key, Value> &other) {
283
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 317 if (&other == this)
284 ✗ return *this;
285
286 317 CopyFrom(other);
287 317 return *this;
288 }
289
290 68612695 uint32_t capacity() const { return Base::capacity_; }
291 319503960 uint32_t size() const { return Base::size_; }
292 uint32_t num_migrates() const { return num_migrates_; }
293
294 protected:
295 196206 void SetThresholds() {
296 196206 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
297 196206 * kThresholdGrow);
298 196206 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
299 196206 * kThresholdShrink);
300 196206 }
301
302 479687058 void Grow() {
303
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 479687058 if (size() > threshold_grow_)
304 18400 Migrate(capacity() * 2);
305 479396023 }
306
307 47234242 void Shrink() {
308
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 47234242 if (size() < threshold_shrink_) {
309 33801747 const uint32_t target_capacity = capacity() / 2;
310
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 33774213 if (target_capacity >= Base::initial_capacity_)
311 3435 Migrate(target_capacity);
312 }
313 47166248 }
314
315 1169 void ResetCapacity() {
316 1169 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
317 1169 Base::capacity_ = Base::initial_capacity_;
318 1169 Base::AllocMemory();
319 1169 SetThresholds();
320 1169 }
321
322 private:
323 // Returns a random permutation of indices [0..N-1] that is allocated
324 // by smmap (Knuth's shuffle algorithm)
325 7202 uint32_t *ShuffleIndices(const uint32_t N) {
326 7202 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
327 // Init with identity
328
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 111747724 for (unsigned i = 0; i < N; ++i)
329 111740522 shuffled[i] = i;
330 // Shuffle (no shuffling for the last element)
331
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 105235512 for (unsigned i = 0; i < N - 1; ++i) {
332 105276640 const uint32_t swap_idx = i + g_prng.Next(N - i);
333 105228310 const uint32_t tmp = shuffled[i];
334 105228310 shuffled[i] = shuffled[swap_idx];
335 105228310 shuffled[swap_idx] = tmp;
336 }
337 317 return shuffled;
338 }
339
340 25270 void Migrate(const uint32_t new_capacity) {
341 25270 Key *old_keys = Base::keys_;
342 25270 Value *old_values = Base::values_;
343 25270 const uint32_t old_capacity = capacity();
344 25270 const uint32_t old_size = size();
345
346 25270 Base::capacity_ = new_capacity;
347 25270 SetThresholds();
348 25280 Base::AllocMemory();
349 25280 Base::DoClear(false);
350
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 25280 if (new_capacity < old_capacity) {
351 6880 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
352
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353
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 96438500 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
354 24214840 Base::Insert(old_keys[shuffled_indices[i]],
355 24214840 old_values[shuffled_indices[i]]);
356 }
357 }
358 ✗ smunmap(shuffled_indices);
359 } else {
360
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361
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 236113598 if (old_keys[i] != Base::empty_key_)
362 177135506 Base::Insert(old_keys[i], old_values[i]);
363 }
364 }
365
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 15250 assert(size() == old_size);
366
367 25280 Base::DeallocMemory(old_keys, old_values, old_capacity);
368 25280 num_migrates_++;
369 25280 }
370
371 317 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
372 317 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
373
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 6888149 for (uint32_t i = 0; i < other.capacity_; ++i) {
374
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 6887832 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
375 5000000 this->Insert(other.keys_[shuffled_indices[i]],
376 5000000 other.values_[shuffled_indices[i]]);
377 }
378 }
379 317 smunmap(shuffled_indices);
380 317 }
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 50 MultiHash() {
397 50 num_hashmaps_ = 0;
398 50 hashmaps_ = NULL;
399 50 locks_ = NULL;
400 50 }
401
402 50 void Init(const uint8_t num_hashmaps, const Key &empty_key,
403 uint32_t (*hasher)(const Key &key)) {
404
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 50 assert(num_hashmaps > 0);
405 50 const uint8_t N = num_hashmaps;
406 50 num_hashmaps_ = N;
407
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 2150 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
408 50 locks_ = static_cast<pthread_mutex_t *>(
409 50 smalloc(N * sizeof(pthread_mutex_t)));
410
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 2150 for (uint8_t i = 0; i < N; ++i) {
411 2100 int retval = pthread_mutex_init(&locks_[i], NULL);
412
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 2100 assert(retval == 0);
413 2100 hashmaps_[i].Init(128, empty_key, hasher);
414 }
415 50 }
416
417 50 ~MultiHash() {
418
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 2150 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
419 2100 pthread_mutex_destroy(&locks_[i]);
420 }
421 50 free(locks_);
422
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 2150 delete[] hashmaps_;
423 50 }
424
425 5000000 bool Lookup(const Key &key, Value *value) {
426 5000000 uint8_t target = SelectHashmap(key);
427 5000000 Lock(target);
428 5000000 const bool result = hashmaps_[target].Lookup(key, value);
429 5000000 Unlock(target);
430 5000000 return result;
431 }
432
433 18509460 void Insert(const Key &key, const Value &value) {
434 18509460 uint8_t target = SelectHashmap(key);
435 18048260 Lock(target);
436 18723720 hashmaps_[target].Insert(key, value);
437 17714130 Unlock(target);
438 19016360 }
439
440 8992970 void Erase(const Key &key) {
441 8992970 uint8_t target = SelectHashmap(key);
442 8557050 Lock(target);
443 9113375 hashmaps_[target].Erase(key);
444 8342435 Unlock(target);
445 9255710 }
446
447 5 void Clear() {
448
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 215 for (uint8_t i = 0; i < num_hashmaps_; ++i)
449 210 Lock(i);
450
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 215 for (uint8_t i = 0; i < num_hashmaps_; ++i)
451 210 hashmaps_[i].Clear();
452
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 215 for (uint8_t i = 0; i < num_hashmaps_; ++i)
453 210 Unlock(i);
454 5 }
455
456 50 uint8_t num_hashmaps() const { return num_hashmaps_; }
457
458 40 void GetSizes(uint32_t *sizes) {
459
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 1720 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
460 1680 Lock(i);
461 1680 sizes[i] = hashmaps_[i].size();
462 1680 Unlock(i);
463 }
464 40 }
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 32306475 inline uint8_t SelectHashmap(const Key &key) {
476 32306475 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
477 31749015 double bucket = static_cast<double>(hash)
478 31749015 * static_cast<double>(num_hashmaps_)
479 / static_cast<double>(static_cast<uint32_t>(-1));
480 31749015 return static_cast<uint32_t>(bucket) % num_hashmaps_;
481 }
482
483 31474870 inline void Lock(const uint8_t target) {
484 31474870 int retval = pthread_mutex_lock(&locks_[target]);
485
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 34123355 assert(retval == 0);
486 34123355 }
487
488 31058620 inline void Unlock(const uint8_t target) {
489 31058620 int retval = pthread_mutex_unlock(&locks_[target]);
490
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 34212520 assert(retval == 0);
491 34212520 }
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