1 /*------------------------------------------------------------------------
2 Junction: Concurrent data structures in C++
3 Copyright (c) 2016 Jeff Preshing
5 Distributed under the Simplified BSD License.
6 Original location: https://github.com/preshing/junction
8 This software is distributed WITHOUT ANY WARRANTY; without even the
9 implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
10 See the LICENSE file for more information.
11 ------------------------------------------------------------------------*/
13 #ifndef JUNCTION_CONCURRENTMAP_LINEAR_H
14 #define JUNCTION_CONCURRENTMAP_LINEAR_H
16 #include <junction/Core.h>
17 #include <junction/details/Linear.h>
18 #include <junction/QSBR.h>
19 #include <turf/Heap.h>
20 #include <turf/Trace.h>
24 TURF_TRACE_DECLARE(ConcurrentMap_Linear, 17)
26 template <typename K, typename V, class KT = DefaultKeyTraits<K>, class VT = DefaultValueTraits<V> >
27 class ConcurrentMap_Linear {
32 typedef VT ValueTraits;
33 typedef typename turf::util::BestFit<Key>::Unsigned Hash;
34 typedef details::Linear<ConcurrentMap_Linear> Details;
37 turf::Atomic<typename Details::Table*> m_root;
40 ConcurrentMap_Linear(ureg capacity = Details::InitialSize) : m_root(Details::Table::create(capacity)) {
43 ~ConcurrentMap_Linear() {
44 typename Details::Table* table = m_root.loadNonatomic();
48 // publishTableMigration() is called by exactly one thread from Details::TableMigration::run()
49 // after all the threads participating in the migration have completed their work.
50 void publishTableMigration(typename Details::TableMigration* migration) {
51 // There are no racing calls to this function.
52 typename Details::Table* oldRoot = m_root.loadNonatomic();
53 m_root.store(migration->m_destination, turf::Release);
54 TURF_ASSERT(oldRoot == migration->getSources()[0].table);
55 // Caller will GC the TableMigration and the source table.
58 // A Mutator represents a known cell in the hash table.
59 // It's meant for manipulations within a temporary function scope.
60 // Obviously you must not call QSBR::Update while holding a Mutator.
61 // Any operation that modifies the table (exchangeValue, eraseValue)
62 // may be forced to follow a redirected cell, which changes the Mutator itself.
63 // Note that even if the Mutator was constructed from an existing cell,
64 // exchangeValue() can still trigger a resize if the existing cell was previously marked deleted,
65 // or if another thread deletes the key between the two steps.
68 friend class ConcurrentMap_Linear;
70 ConcurrentMap_Linear& m_map;
71 typename Details::Table* m_table;
72 typename Details::Cell* m_cell;
75 // Constructor: Find existing cell
76 Mutator(ConcurrentMap_Linear& map, Key key, bool) : m_map(map), m_value(Value(ValueTraits::NullValue)) {
77 TURF_TRACE(ConcurrentMap_Linear, 0, "[Mutator] find constructor called", uptr(m_table), uptr(key));
78 Hash hash = KeyTraits::hash(key);
80 m_table = m_map.m_root.load(turf::Consume);
81 m_cell = Details::find(hash, m_table);
84 m_value = m_cell->value.load(turf::Consume);
85 if (m_value != Value(ValueTraits::Redirect))
86 return; // Found an existing value
87 // We've encountered a Redirect value. Help finish the migration.
88 TURF_TRACE(ConcurrentMap_Linear, 1, "[Mutator] find was redirected", uptr(m_table), 0);
89 m_table->jobCoordinator.participate();
90 // Try again using the latest root.
94 // Constructor: Insert cell
95 Mutator(ConcurrentMap_Linear& map, Key key)
96 : m_map(map), m_table(map.m_root.load(turf::Consume)), m_value(Value(ValueTraits::NullValue)) {
97 TURF_TRACE(ConcurrentMap_Linear, 2, "[Mutator] insert constructor called", uptr(m_table), uptr(key));
98 Hash hash = KeyTraits::hash(key);
100 m_table = m_map.m_root.load(turf::Consume);
101 switch (Details::insert(hash, m_table, m_cell)) { // Modifies m_cell
102 case Details::InsertResult_InsertedNew: {
103 // We've inserted a new cell. Don't load m_cell->value.
106 case Details::InsertResult_AlreadyFound: {
107 // The hash was already found in the table.
108 m_value = m_cell->value.load(turf::Consume);
109 if (m_value == Value(ValueTraits::Redirect)) {
110 // We've encountered a Redirect value.
111 TURF_TRACE(ConcurrentMap_Linear, 3, "[Mutator] insert was redirected", uptr(m_table), uptr(m_value));
112 break; // Help finish the migration.
114 return; // Found an existing value
116 case Details::InsertResult_Overflow: {
117 Details::beginTableMigration(m_map, m_table);
121 // A migration has been started (either by us, or another thread). Participate until it's complete.
122 m_table->jobCoordinator.participate();
123 // Try again using the latest root.
128 Value getValue() const {
129 // Return previously loaded value. Don't load it again.
130 return Value(m_value);
133 Value exchangeValue(Value desired) {
134 TURF_ASSERT(desired != Value(ValueTraits::NullValue));
135 TURF_ASSERT(m_cell); // Cell must have been found or inserted
136 TURF_TRACE(ConcurrentMap_Linear, 4, "[Mutator::exchangeValue] called", uptr(m_table), uptr(m_value));
138 Value oldValue = m_value;
139 if (m_cell->value.compareExchangeStrong(m_value, desired, turf::ConsumeRelease)) {
140 // Exchange was successful. Return previous value.
141 TURF_TRACE(ConcurrentMap_Linear, 5, "[Mutator::exchangeValue] exchanged Value", uptr(m_value), uptr(desired));
142 Value result = m_value;
143 m_value = desired; // Leave the mutator in a valid state
146 // The CAS failed and m_value has been updated with the latest value.
147 if (m_value != Value(ValueTraits::Redirect)) {
148 TURF_TRACE(ConcurrentMap_Linear, 6, "[Mutator::exchangeValue] detected race to write value", uptr(m_table),
150 if (oldValue == Value(ValueTraits::NullValue) && m_value != Value(ValueTraits::NullValue)) {
151 TURF_TRACE(ConcurrentMap_Linear, 7, "[Mutator::exchangeValue] racing write inserted new value",
152 uptr(m_table), uptr(m_value));
154 // There was a racing write (or erase) to this cell.
155 // Pretend we exchanged with ourselves, and just let the racing write win.
158 // We've encountered a Redirect value. Help finish the migration.
159 TURF_TRACE(ConcurrentMap_Linear, 8, "[Mutator::exchangeValue] was redirected", uptr(m_table), uptr(m_value));
160 Hash hash = m_cell->hash.load(turf::Relaxed);
162 // Help complete the migration.
163 m_table->jobCoordinator.participate();
164 // Try again in the new table.
165 m_table = m_map.m_root.load(turf::Consume);
166 m_value = Value(ValueTraits::NullValue);
167 switch (Details::insert(hash, m_table, m_cell)) { // Modifies m_cell
168 case Details::InsertResult_AlreadyFound:
169 m_value = m_cell->value.load(turf::Consume);
170 if (m_value == Value(ValueTraits::Redirect)) {
171 TURF_TRACE(ConcurrentMap_Linear, 9, "[Mutator::exchangeValue] was re-redirected", uptr(m_table),
176 case Details::InsertResult_InsertedNew:
178 case Details::InsertResult_Overflow:
179 TURF_TRACE(ConcurrentMap_Linear, 10, "[Mutator::exchangeValue] overflow after redirect", uptr(m_table), 0);
180 Details::beginTableMigration(m_map, m_table);
183 // We were redirected... again
186 // Try again in the new table.
190 void setValue(Value desired) {
191 exchangeValue(desired);
195 TURF_ASSERT(m_cell); // Cell must have been found or inserted
196 TURF_TRACE(ConcurrentMap_Linear, 11, "[Mutator::eraseValue] called", uptr(m_table), m_cell - m_table->getCells());
198 if (m_value == Value(ValueTraits::NullValue))
199 return Value(m_value);
200 TURF_ASSERT(m_cell); // m_value is non-NullValue, therefore cell must have been found or inserted.
201 if (m_cell->value.compareExchangeStrong(m_value, Value(ValueTraits::NullValue), turf::Consume)) {
202 // Exchange was successful and a non-NULL value was erased and returned by reference in m_value.
203 TURF_ASSERT(m_value != ValueTraits::NullValue); // Implied by the test at the start of the loop.
204 Value result = m_value;
205 m_value = Value(ValueTraits::NullValue); // Leave the mutator in a valid state
208 // The CAS failed and m_value has been updated with the latest value.
209 TURF_TRACE(ConcurrentMap_Linear, 12, "[Mutator::eraseValue] detected race to write value", uptr(m_table),
210 m_cell - m_table->getCells());
211 if (m_value != Value(ValueTraits::Redirect)) {
212 // There was a racing write (or erase) to this cell.
213 // Pretend we erased nothing, and just let the racing write win.
214 return Value(ValueTraits::NullValue);
216 // We've been redirected to a new table.
217 TURF_TRACE(ConcurrentMap_Linear, 13, "[Mutator::eraseValue] was redirected", uptr(m_table),
218 m_cell - m_table->getCells());
219 Hash hash = m_cell->hash.load(turf::Relaxed); // Re-fetch hash
221 // Help complete the migration.
222 m_table->jobCoordinator.participate();
223 // Try again in the new table.
224 m_table = m_map.m_root.load(turf::Consume);
225 m_cell = Details::find(hash, m_table);
227 m_value = Value(ValueTraits::NullValue);
230 m_value = m_cell->value.load(turf::Relaxed);
231 if (m_value != Value(ValueTraits::Redirect))
233 TURF_TRACE(ConcurrentMap_Linear, 14, "[Mutator::eraseValue] was re-redirected", uptr(m_table),
234 m_cell - m_table->getCells());
240 Mutator insert(Key key) {
241 return Mutator(*this, key);
244 Mutator find(Key key) {
245 return Mutator(*this, key, false);
248 // Lookup without creating a temporary Mutator.
250 Hash hash = KeyTraits::hash(key);
251 TURF_TRACE(ConcurrentMap_Linear, 15, "[get] called", uptr(this), uptr(hash));
253 typename Details::Table* table = m_root.load(turf::Consume);
254 typename Details::Cell* cell = Details::find(hash, table);
256 return Value(ValueTraits::NullValue);
257 Value value = cell->value.load(turf::Consume);
258 if (value != Value(ValueTraits::Redirect))
259 return value; // Found an existing value
260 // We've been redirected to a new table. Help with the migration.
261 TURF_TRACE(ConcurrentMap_Linear, 16, "[get] was redirected", uptr(table), uptr(cell));
262 table->jobCoordinator.participate();
263 // Try again in the new table.
267 Value insert(Key key, Value desired) {
268 Mutator iter(*this, key);
269 return iter.exchangeValue(desired);
272 Value exchange(Key key, Value desired) {
273 Mutator iter(*this, key);
274 return iter.exchangeValue(desired);
277 Value erase(Key key) {
278 Mutator iter(*this, key, false);
279 return iter.eraseValue();
282 // The easiest way to implement an Iterator is to prevent all Redirects.
283 // The currrent Iterator does that by forbidding concurrent inserts.
284 // To make it work with concurrent inserts, we'd need a way to block TableMigrations.
287 typename Details::Table* m_table;
293 Iterator(ConcurrentMap_Linear& map) {
294 // Since we've forbidden concurrent inserts (for now), nonatomic would suffice here, but let's plan ahead:
295 m_table = map.m_root.load(turf::Consume);
301 TURF_ASSERT(m_table);
302 TURF_ASSERT(isValid() || m_idx == -1); // Either the Iterator is already valid, or we've just started iterating.
303 while (++m_idx <= m_table->sizeMask) {
304 // Index still inside range of table.
305 typename Details::Cell* cell = m_table->getCells() + m_idx;
306 m_hash = cell->hash.load(turf::Relaxed);
307 if (m_hash != KeyTraits::NullHash) {
308 // Cell has been reserved.
309 m_value = cell->value.load(turf::Relaxed);
310 TURF_ASSERT(m_value != Value(ValueTraits::Redirect));
311 if (m_value != Value(ValueTraits::NullValue))
312 return; // Yield this cell.
315 // That's the end of the map.
316 m_hash = KeyTraits::NullHash;
317 m_value = ValueTraits::NullValue;
320 bool isValid() const {
321 return m_value != Value(ValueTraits::NullValue);
325 TURF_ASSERT(isValid());
326 // Since we've forbidden concurrent inserts (for now), nonatomic would suffice here, but let's plan ahead:
327 return KeyTraits::dehash(m_hash);
330 Value getValue() const {
331 TURF_ASSERT(isValid());
337 } // namespace junction
339 #endif // JUNCTION_CONCURRENTMAP_LINEAR_H