1 // Copyright (c) 2012-present The Bitcoin Core developers
2 // Distributed under the MIT software license, see the accompanying
3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4 5 #ifndef BITCOIN_CHECKQUEUE_H
6 #define BITCOIN_CHECKQUEUE_H
7 8 #include <sync.h>
9 #include <tinyformat.h>
10 #include <util/log.h>
11 #include <util/threadnames.h>
12 13 #include <algorithm>
14 #include <iterator>
15 #include <optional>
16 #include <vector>
17 18 /**
19 * Queue for verifications that have to be performed.
20 * The verifications are represented by a type T, which must provide an
21 * operator(), returning an std::optional<R>.
22 *
23 * The overall result of the computation is std::nullopt if all invocations
24 * return std::nullopt, or one of the other results otherwise.
25 *
26 * One thread (the master) is assumed to push batches of verifications
27 * onto the queue, where they are processed by N-1 worker threads. When
28 * the master is done adding work, it temporarily joins the worker pool
29 * as an N'th worker, until all jobs are done.
30 *
31 */
32 template <typename T, typename R = std::remove_cvref_t<decltype(std::declval<T>()().value())>>
33 class CCheckQueue
34 {
35 private:
36 //! Mutex to protect the inner state
37 Mutex m_mutex;
38 39 //! Worker threads block on this when out of work
40 std::condition_variable m_worker_cv;
41 42 //! Master thread blocks on this when out of work
43 std::condition_variable m_master_cv;
44 45 //! The queue of elements to be processed.
46 //! As the order of booleans doesn't matter, it is used as a LIFO (stack)
47 std::vector<T> queue GUARDED_BY(m_mutex);
48 49 //! The number of workers (including the master) that are idle.
50 int nIdle GUARDED_BY(m_mutex){0};
51 52 //! The total number of workers (including the master).
53 int nTotal GUARDED_BY(m_mutex){0};
54 55 //! The temporary evaluation result.
56 std::optional<R> m_result GUARDED_BY(m_mutex);
57 58 /**
59 * Number of verifications that haven't completed yet.
60 * This includes elements that are no longer queued, but still in the
61 * worker's own batches.
62 */
63 unsigned int nTodo GUARDED_BY(m_mutex){0};
64 65 //! The maximum number of elements to be processed in one batch
66 const unsigned int nBatchSize;
67 68 std::vector<std::thread> m_worker_threads;
69 bool m_request_stop GUARDED_BY(m_mutex){false};
70 71 /// \anchor checkqueue
72 /** Internal function that does bulk of the verification work. If fMaster, return the final result. */
73 std::optional<R> Loop(bool fMaster) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
74 {
75 std::condition_variable& cond = fMaster ? m_master_cv : m_worker_cv;
76 std::vector<T> vChecks;
77 vChecks.reserve(nBatchSize);
78 unsigned int nNow = 0;
79 std::optional<R> local_result;
80 bool do_work;
81 do {
82 {
83 WAIT_LOCK(m_mutex, lock);
84 // first do the clean-up of the previous loop run (allowing us to do it in the same critsect)
85 if (nNow) {
86 if (local_result.has_value() && !m_result.has_value()) {
87 std::swap(local_result, m_result);
88 }
89 nTodo -= nNow;
90 if (nTodo == 0 && !fMaster) {
91 // We processed the last element; inform the master it can exit and return the result
92 m_master_cv.notify_one();
93 }
94 } else {
95 // first iteration
96 nTotal++;
97 }
98 // logically, the do loop starts here
99 while (queue.empty() && !m_request_stop) {
100 if (fMaster && nTodo == 0) {
101 nTotal--;
102 std::optional<R> to_return = std::move(m_result);
103 // reset the status for new work later
104 m_result = std::nullopt;
105 // return the current status
106 return to_return;
107 }
108 nIdle++;
109 cond.wait(lock); // wait
110 nIdle--;
111 }
112 if (m_request_stop) {
113 // return value does not matter, because m_request_stop is only set in the destructor.
114 return std::nullopt;
115 }
116 117 // Decide how many work units to process now.
118 // * Do not try to do everything at once, but aim for increasingly smaller batches so
119 // all workers finish approximately simultaneously.
120 // * Try to account for idle jobs which will instantly start helping.
121 // * Don't do batches smaller than 1 (duh), or larger than nBatchSize.
122 nNow = std::max(1U, std::min(nBatchSize, (unsigned int)queue.size() / (nTotal + nIdle + 1)));
123 auto start_it = queue.end() - nNow;
124 vChecks.assign(std::make_move_iterator(start_it), std::make_move_iterator(queue.end()));
125 queue.erase(start_it, queue.end());
126 // Check whether we need to do work at all
127 do_work = !m_result.has_value();
128 }
129 // execute work
130 if (do_work) {
131 for (T& check : vChecks) {
132 local_result = check();
133 if (local_result.has_value()) break;
134 }
135 }
136 vChecks.clear();
137 } while (true);
138 }
139 140 public:
141 //! Mutex to ensure only one concurrent CCheckQueueControl
142 Mutex m_control_mutex;
143 144 //! Create a new check queue
145 explicit CCheckQueue(unsigned int batch_size, int worker_threads_num)
146 : nBatchSize(batch_size)
147 {
148 LogInfo("Script verification uses %d additional threads", worker_threads_num);
149 m_worker_threads.reserve(worker_threads_num);
150 for (int n = 0; n < worker_threads_num; ++n) {
151 m_worker_threads.emplace_back([this, n]() {
152 util::ThreadRename(strprintf("scriptch.%02i", n));
153 Loop(false /* worker thread */);
154 });
155 }
156 }
157 158 // Since this class manages its own resources, which is a thread
159 // pool `m_worker_threads`, copy and move operations are not appropriate.
160 CCheckQueue(const CCheckQueue&) = delete;
161 CCheckQueue& operator=(const CCheckQueue&) = delete;
162 CCheckQueue(CCheckQueue&&) = delete;
163 CCheckQueue& operator=(CCheckQueue&&) = delete;
164 165 //! Join the execution until completion. If at least one evaluation wasn't successful, return
166 //! its error.
167 std::optional<R> Complete() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
168 {
169 return Loop(true /* master thread */);
170 }
171 172 //! Add a batch of checks to the queue
173 void Add(std::vector<T>&& vChecks) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
174 {
175 if (vChecks.empty()) {
176 return;
177 }
178 179 {
180 LOCK(m_mutex);
181 queue.insert(queue.end(), std::make_move_iterator(vChecks.begin()), std::make_move_iterator(vChecks.end()));
182 nTodo += vChecks.size();
183 }
184 185 if (vChecks.size() == 1) {
186 m_worker_cv.notify_one();
187 } else {
188 m_worker_cv.notify_all();
189 }
190 }
191 192 ~CCheckQueue()
193 {
194 WITH_LOCK(m_mutex, m_request_stop = true);
195 m_worker_cv.notify_all();
196 for (std::thread& t : m_worker_threads) {
197 t.join();
198 }
199 }
200 201 bool HasThreads() const { return !m_worker_threads.empty(); }
202 };
203 204 /**
205 * RAII-style controller object for a CCheckQueue that guarantees the passed
206 * queue is finished before continuing.
207 */
208 template <typename T, typename R = std::remove_cvref_t<decltype(std::declval<T>()().value())>>
209 class SCOPED_LOCKABLE CCheckQueueControl
210 {
211 private:
212 CCheckQueue<T, R>& m_queue;
213 UniqueLock<Mutex> m_lock;
214 bool fDone;
215 216 public:
217 CCheckQueueControl() = delete;
218 CCheckQueueControl(const CCheckQueueControl&) = delete;
219 CCheckQueueControl& operator=(const CCheckQueueControl&) = delete;
220 explicit CCheckQueueControl(CCheckQueue<T>& queueIn) EXCLUSIVE_LOCK_FUNCTION(queueIn.m_control_mutex) : m_queue(queueIn), m_lock(LOCK_ARGS(queueIn.m_control_mutex)), fDone(false) {}
221 222 std::optional<R> Complete()
223 {
224 auto ret = m_queue.Complete();
225 fDone = true;
226 return ret;
227 }
228 229 void Add(std::vector<T>&& vChecks)
230 {
231 m_queue.Add(std::move(vChecks));
232 }
233 234 ~CCheckQueueControl() UNLOCK_FUNCTION()
235 {
236 if (!fDone)
237 Complete();
238 }
239 };
240 241 #endif // BITCOIN_CHECKQUEUE_H
242