GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2025-10-19 02:35:28
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 168670 SmallHashBase() {
43 168670 keys_ = NULL;
44 168670 values_ = NULL;
45 168670 hasher_ = NULL;
46 168670 bytes_allocated_ = 0;
47 168670 num_collisions_ = 0;
48 168670 max_collisions_ = 0;
49
50 // Properly initialized by Init()
51 168670 capacity_ = 0;
52 168670 initial_capacity_ = 0;
53 168670 size_ = 0;
54 168670 }
55
56 168532 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
57
58 168608 void Init(uint32_t expected_size, Key empty,
59 uint32_t (*hasher)(const Key &key)) {
60 168608 hasher_ = hasher;
61 168608 empty_key_ = empty;
62 168608 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
63 168608 / kLoadFactor);
64 168608 initial_capacity_ = capacity_;
65 168608 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
66 168608 AllocMemory();
67 168608 this->DoClear(false);
68 168608 }
69
70 68338307 bool Lookup(const Key &key, Value *value) const {
71 uint32_t bucket;
72 uint32_t collisions;
73
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 68338307 const bool found = DoLookup(key, &bucket, &collisions);
74
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 68348595 if (found)
75
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 65985148 *value = values_[bucket];
76 68348595 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 12 bool LookupEx(Key *key, Value *value) const {
87 12 uint32_t bucket = ScaleHash(*key);
88
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 12 while (!(keys_[bucket] == empty_key_)) {
89
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 8 if (keys_[bucket] == *key) {
90 8 *key = keys_[bucket];
91 8 *value = values_[bucket];
92 8 return true;
93 }
94 ✗ bucket = (bucket + 1) % capacity_;
95 }
96 4 return false;
97 }
98
99 40066401 bool Contains(const Key &key) const {
100 uint32_t bucket;
101 uint32_t collisions;
102
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 40066401 const bool found = DoLookup(key, &bucket, &collisions);
103 40066401 return found;
104 }
105
106 1902394366 void Insert(const Key &key, const Value &value) {
107 1902394366 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
108 1896697696 const bool overwritten = DoInsert(key, value, true);
109 1893987358 size_ += !overwritten; // size + 1 if the key was not yet in the map
110 1893987358 }
111
112 102206151 bool Erase(const Key &key) {
113 uint32_t bucket;
114 uint32_t collisions;
115
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 102206151 const bool found = DoLookup(key, &bucket, &collisions);
116
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 98561914 if (found) {
117 98571580 keys_[bucket] = empty_key_;
118 98571580 size_--;
119 98571580 bucket = (bucket + 1) % capacity_;
120
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 283850730 while (!(keys_[bucket] == empty_key_)) {
121 186462978 Key rehash = keys_[bucket];
122 186462978 keys_[bucket] = empty_key_;
123
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 186462978 DoInsert(rehash, values_[bucket], false);
124 185279150 bucket = (bucket + 1) % capacity_;
125 }
126
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 97387752 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
127 }
128 99944475 return found;
129 }
130
131 1799 void Clear() { DoClear(true); }
132
133 7000 uint64_t bytes_allocated() const { return bytes_allocated_; }
134 2073 static double GetEntrySize() {
135 4146 const double unit = sizeof(Key) + sizeof(Value);
136 4146 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 246026 Key empty_key() const { return empty_key_; }
148 534400 Key *keys() const { return keys_; }
149 239 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 2612878730 uint32_t ScaleHash(const Key &key) const {
156 2612878730 const double bucket = (static_cast<double>(hasher_(key))
157 2603682854 * static_cast<double>(capacity_)
158 / static_cast<double>(static_cast<uint32_t>(-1)));
159 2603682854 return static_cast<uint32_t>(bucket) % capacity_;
160 }
161
162 309026 void AllocMemory() {
163 309026 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
164 309150 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
165
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 3818590798 for (uint32_t i = 0; i < capacity_; ++i) {
166 3818281648 /*keys_[i] =*/new (keys_ + i) Key();
167 }
168
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 3818452848 for (uint32_t i = 0; i < capacity_; ++i) {
169 3818246432 /*values_[i] =*/new (values_ + i) Value();
170 }
171 206416 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
172 206416 }
173
174 309074 void DeallocMemory(Key *k, Value *v, uint32_t c) {
175
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 3827674770 for (uint32_t i = 0; i < c; ++i) {
176 3827365696 k[i].~Key();
177 }
178
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 3828825304 for (uint32_t i = 0; i < c; ++i) {
179 3828516230 v[i].~Value();
180 }
181
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 309074 if (k)
182 309012 smunmap(k);
183
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 309074 if (v)
184 309012 smunmap(v);
185 309074 k = NULL;
186 309074 v = NULL;
187 309074 }
188
189 // Returns true iff the key is overwritten
190 2227301564 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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 2227301564 const bool overwritten = DoLookup(key, &bucket, &collisions);
195
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 2223331520 if (count_collisions) {
196 1893746008 num_collisions_ += collisions;
197 1893746008 max_collisions_ = std::max(collisions, max_collisions_);
198 }
199 2223393792 keys_[bucket] = key;
200
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 2223393792 values_[bucket] = value;
201 2223393792 return overwritten;
202 }
203
204 2614955056 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
205 2614955056 *bucket = ScaleHash(key);
206 2602292130 *collisions = 0;
207
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 25560353496 while (!(keys_[*bucket] == empty_key_)) {
208
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 23363957627 if (keys_[*bucket] == key)
209 405896261 return true;
210 22958061366 *bucket = (*bucket + 1) % capacity_;
211 22958061366 (*collisions)++;
212 }
213 2196395869 return false;
214 }
215
216 309226 void DoClear(const bool reset_capacity) {
217
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 309226 if (reset_capacity)
218 3165 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
219
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 3821356398 for (uint32_t i = 0; i < capacity_; ++i)
220 3821047172 keys_[i] = empty_key_;
221 309226 size_ = 0;
222 309226 }
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 6924 void SetThresholds() { }
252 627154 void Grow() { }
253 42953 void Shrink() { }
254 76 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 161746 SmallHashDynamic() : Base() {
269 161746 num_migrates_ = 0;
270
271 // Properly set by Init
272 161746 threshold_grow_ = 0;
273 161746 threshold_shrink_ = 0;
274 161746 }
275
276 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
277 num_migrates_ = 0;
278 CopyFrom(other);
279 }
280
281 351 SmallHashDynamic<Key, Value> &operator=(
282 const SmallHashDynamic<Key, Value> &other) {
283
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 351 if (&other == this)
284 ✗ return *this;
285
286 351 CopyFrom(other);
287 351 return *this;
288 }
289
290 34995367 uint32_t capacity() const { return Base::capacity_; }
291 1064691529 uint32_t size() const { return Base::size_; }
292 uint32_t num_migrates() const { return num_migrates_; }
293
294 protected:
295 302102 void SetThresholds() {
296 302102 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
297 302102 * kThresholdGrow);
298 302102 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
299 302102 * kThresholdShrink);
300 302102 }
301
302 1898791833 void Grow() {
303
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 1898791833 if (size() > threshold_grow_)
304 94610 Migrate(capacity() * 2);
305 1896519989 }
306
307 98843121 void Shrink() {
308
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 98843121 if (size() < threshold_shrink_) {
309 16714731 const uint32_t target_capacity = capacity() / 2;
310
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 16715128 if (target_capacity >= Base::initial_capacity_)
311 21297 Migrate(target_capacity);
312 }
313 99069375 }
314
315 3089 void ResetCapacity() {
316 3089 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
317 3089 Base::capacity_ = Base::initial_capacity_;
318 3089 Base::AllocMemory();
319 3089 SetThresholds();
320 3089 }
321
322 private:
323 // Returns a random permutation of indices [0..N-1] that is allocated
324 // by smmap (Knuth's shuffle algorithm)
325 43038 uint32_t *ShuffleIndices(const uint32_t N) {
326 43038 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
327 // Init with identity
328
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 701059764 for (unsigned i = 0; i < N; ++i)
329 701016726 shuffled[i] = i;
330 // Shuffle (no shuffling for the last element)
331
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 672439872 for (unsigned i = 0; i < N - 1; ++i) {
332 673035930 const uint32_t swap_idx = i + g_prng.Next(N - i);
333 672396834 const uint32_t tmp = shuffled[i];
334 672396834 shuffled[i] = shuffled[swap_idx];
335 672396834 shuffled[swap_idx] = tmp;
336 }
337 351 return shuffled;
338 }
339
340 137266 void Migrate(const uint32_t new_capacity) {
341 137266 Key *old_keys = Base::keys_;
342 137266 Value *old_values = Base::values_;
343 137266 const uint32_t old_capacity = capacity();
344 137266 const uint32_t old_size = size();
345
346 137328 Base::capacity_ = new_capacity;
347 137328 SetThresholds();
348 137328 Base::AllocMemory();
349 137452 Base::DoClear(false);
350
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 137452 if (new_capacity < old_capacity) {
351 42656 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
352
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353
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 599167256 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
354 150358308 Base::Insert(old_keys[shuffled_indices[i]],
355 150358308 old_values[shuffled_indices[i]]);
356 }
357 }
358 ✗ smunmap(shuffled_indices);
359 } else {
360
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 1179191322 for (uint32_t i = 0; i < old_capacity; ++i) {
361
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 1179127650 if (old_keys[i] != Base::empty_key_)
362 884579772 Base::Insert(old_keys[i], old_values[i]);
363 }
364 }
365
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 106328 assert(size() == old_size);
366
367 137452 Base::DeallocMemory(old_keys, old_values, old_capacity);
368 137452 num_migrates_++;
369 137452 }
370
371 351 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
372 351 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
373
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 42671007 for (uint32_t i = 0; i < other.capacity_; ++i) {
374
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 42670656 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
375 31000000 this->Insert(other.keys_[shuffled_indices[i]],
376 31000000 other.values_[shuffled_indices[i]]);
377 }
378 }
379 351 smunmap(shuffled_indices);
380 351 }
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:
396 310 MultiHash() {
397 310 num_hashmaps_ = 0;
398 310 hashmaps_ = NULL;
399 310 locks_ = NULL;
400 310 }
401
402 310 void Init(const uint8_t num_hashmaps, const Key &empty_key,
403 uint32_t (*hasher)(const Key &key)) {
404
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 310 assert(num_hashmaps > 0);
405 310 const uint8_t N = num_hashmaps;
406 310 num_hashmaps_ = N;
407
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 13330 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
408 310 locks_ = static_cast<pthread_mutex_t *>(
409 310 smalloc(N * sizeof(pthread_mutex_t)));
410
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 13330 for (uint8_t i = 0; i < N; ++i) {
411 13020 int retval = pthread_mutex_init(&locks_[i], NULL);
412
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 13020 assert(retval == 0);
413 13020 hashmaps_[i].Init(128, empty_key, hasher);
414 }
415 310 }
416
417 310 ~MultiHash() {
418
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 13330 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
419 13020 pthread_mutex_destroy(&locks_[i]);
420 }
421 310 free(locks_);
422
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 13330 delete[] hashmaps_;
423 310 }
424
425 31000000 bool Lookup(const Key &key, Value *value) {
426 31000000 uint8_t target = SelectHashmap(key);
427 31000000 Lock(target);
428 31000000 const bool result = hashmaps_[target].Lookup(key, value);
429 31000000 Unlock(target);
430 31000000 return result;
431 }
432
433 116119397 void Insert(const Key &key, const Value &value) {
434 116119397 uint8_t target = SelectHashmap(key);
435 112311202 Lock(target);
436 116572524 hashmaps_[target].Insert(key, value);
437 110163801 Unlock(target);
438 118275540 }
439
440 56037522 void Erase(const Key &key) {
441 56037522 uint8_t target = SelectHashmap(key);
442 53332772 Lock(target);
443 57040620 hashmaps_[target].Erase(key);
444 52258188 Unlock(target);
445 57737283 }
446
447 31 void Clear() {
448
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 1333 for (uint8_t i = 0; i < num_hashmaps_; ++i)
449 1302 Lock(i);
450
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 1333 for (uint8_t i = 0; i < num_hashmaps_; ++i)
451 1302 hashmaps_[i].Clear();
452
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 1333 for (uint8_t i = 0; i < num_hashmaps_; ++i)
453 1302 Unlock(i);
454 31 }
455
456 310 uint8_t num_hashmaps() const { return num_hashmaps_; }
457
458 248 void GetSizes(uint32_t *sizes) {
459
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 10664 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
460 10416 Lock(i);
461 10416 sizes[i] = hashmaps_[i].size();
462 10416 Unlock(i);
463 }
464 248 }
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 202102361 inline uint8_t SelectHashmap(const Key &key) {
476 202102361 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
477 198089876 double bucket = static_cast<double>(hash)
478 198089876 * static_cast<double>(num_hashmaps_)
479 / static_cast<double>(static_cast<uint32_t>(-1));
480 198089876 return static_cast<uint32_t>(bucket) % num_hashmaps_;
481 }
482
483 198504160 inline void Lock(const uint8_t target) {
484 198504160 int retval = pthread_mutex_lock(&locks_[target]);
485
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 212730122 assert(retval == 0);
486 212730122 }
487
488 193577206 inline void Unlock(const uint8_t target) {
489 193577206 int retval = pthread_mutex_unlock(&locks_[target]);
490
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 213800149 assert(retval == 0);
491 213800149 }
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