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// Copyright (c) 2012-2018 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_CHECKQUEUE_H
#define BITCOIN_CHECKQUEUE_H
#include <sync.h>
#include <tinyformat.h>
#include <util/threadnames.h>
#include <algorithm>
#include <iterator>
#include <vector>
template <typename T> class CCheckQueueControl;
/**
* Queue for verifications that have to be performed.
* The verifications are represented by a type T, which must provide an
* operator(), returning a bool.
*
* One thread (the master) is assumed to push batches of verifications onto the
* queue, where they are processed by N-1 worker threads. When the master is
* done adding work, it temporarily joins the worker pool as an N'th worker,
* until all jobs are done.
*/
template <typename T> class CCheckQueue {
private:
//! Mutex to protect the inner state
Mutex m_mutex;
//! Worker threads block on this when out of work
std::condition_variable m_worker_cv;
//! Master thread blocks on this when out of work
std::condition_variable m_master_cv;
//! The queue of elements to be processed.
//! As the order of booleans doesn't matter, it is used as a LIFO (stack)
std::vector<T> queue GUARDED_BY(m_mutex);
//! The number of workers (including the master) that are idle.
int nIdle GUARDED_BY(m_mutex){0};
//! The total number of workers (including the master).
int nTotal GUARDED_BY(m_mutex){0};
//! The temporary evaluation result.
bool fAllOk GUARDED_BY(m_mutex){true};
/**
* Number of verifications that haven't completed yet.
* This includes elements that are no longer queued, but still in the
* worker's own batches.
*/
unsigned int nTodo GUARDED_BY(m_mutex){0};
//! The maximum number of elements to be processed in one batch
const unsigned int nBatchSize;
std::vector<std::thread> m_worker_threads;
bool m_request_stop GUARDED_BY(m_mutex){false};
/** Internal function that does bulk of the verification work. */
bool Loop(bool fMaster) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex) {
std::condition_variable &cond = fMaster ? m_master_cv : m_worker_cv;
std::vector<T> vChecks;
vChecks.reserve(nBatchSize);
unsigned int nNow = 0;
bool fOk = true;
do {
{
WAIT_LOCK(m_mutex, lock);
// first do the clean-up of the previous loop run (allowing us
// to do it in the same critsect)
if (nNow) {
fAllOk &= fOk;
nTodo -= nNow;
if (nTodo == 0 && !fMaster) {
// We processed the last element; inform the master it
// can exit and return the result
m_master_cv.notify_one();
}
} else {
// first iteration
nTotal++;
}
// logically, the do loop starts here
while (queue.empty() && !m_request_stop) {
if (fMaster && nTodo == 0) {
nTotal--;
bool fRet = fAllOk;
// reset the status for new work later
fAllOk = true;
// return the current status
return fRet;
}
nIdle++;
cond.wait(lock); // wait
nIdle--;
}
if (m_request_stop) {
return false;
}
// Decide how many work units to process now.
// * Do not try to do everything at once, but aim for
// increasingly smaller batches so all workers finish
// approximately simultaneously.
// * Try to account for idle jobs which will instantly start
// helping.
// * Don't do batches smaller than 1 (duh), or larger than
// nBatchSize.
nNow = std::max(
1U, std::min(nBatchSize, (unsigned int)queue.size() /
(nTotal + nIdle + 1)));
auto start_it = queue.end() - nNow;
vChecks.assign(std::make_move_iterator(start_it),
std::make_move_iterator(queue.end()));
queue.erase(start_it, queue.end());
// Check whether we need to do work at all
fOk = fAllOk;
}
// execute work
for (T &check : vChecks) {
if (fOk) {
fOk = check();
}
}
vChecks.clear();
} while (true);
}
public:
//! Mutex to ensure only one concurrent CCheckQueueControl
Mutex m_control_mutex;
//! Create a new check queue
explicit CCheckQueue(unsigned int nBatchSizeIn)
: nBatchSize(nBatchSizeIn) {}
//! Create a pool of new worker threads.
void StartWorkerThreads(const int threads_num)
EXCLUSIVE_LOCKS_REQUIRED(!m_mutex) {
{
LOCK(m_mutex);
nIdle = 0;
nTotal = 0;
fAllOk = true;
}
assert(m_worker_threads.empty());
for (int n = 0; n < threads_num; ++n) {
m_worker_threads.emplace_back([this, n]() {
util::ThreadRename(strprintf("scriptch.%i", n));
Loop(false /* worker thread */);
});
}
}
//! Wait until execution finishes, and return whether all evaluations were
//! successful.
bool Wait() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex) {
return Loop(true /* master thread */);
}
//! Add a batch of checks to the queue
void Add(std::vector<T> &&vChecks) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex) {
LOCK(m_mutex);
queue.insert(queue.end(), std::make_move_iterator(vChecks.begin()),
std::make_move_iterator(vChecks.end()));
nTodo += vChecks.size();
if (vChecks.size() == 1) {
m_worker_cv.notify_one();
} else if (vChecks.size() > 1) {
m_worker_cv.notify_all();
}
}
//! Stop all of the worker threads.
void StopWorkerThreads() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex) {
WITH_LOCK(m_mutex, m_request_stop = true);
m_worker_cv.notify_all();
for (std::thread &t : m_worker_threads) {
t.join();
}
m_worker_threads.clear();
WITH_LOCK(m_mutex, m_request_stop = false);
}
~CCheckQueue() { assert(m_worker_threads.empty()); }
};
/**
* RAII-style controller object for a CCheckQueue that guarantees the passed
* queue is finished before continuing.
*/
template <typename T> class CCheckQueueControl {
private:
CCheckQueue<T> *const pqueue;
bool fDone;
public:
CCheckQueueControl() = delete;
CCheckQueueControl(const CCheckQueueControl &) = delete;
CCheckQueueControl &operator=(const CCheckQueueControl &) = delete;
explicit CCheckQueueControl(CCheckQueue<T> *const pqueueIn)
: pqueue(pqueueIn), fDone(false) {
// passed queue is supposed to be unused, or nullptr
if (pqueue != nullptr) {
ENTER_CRITICAL_SECTION(pqueue->m_control_mutex);
}
}
bool Wait() {
if (pqueue == nullptr) {
return true;
}
bool fRet = pqueue->Wait();
fDone = true;
return fRet;
}
void Add(std::vector<T> &&vChecks) {
if (pqueue != nullptr) {
pqueue->Add(std::move(vChecks));
}
}
~CCheckQueueControl() {
if (!fDone) {
Wait();
}
if (pqueue != nullptr) {
LEAVE_CRITICAL_SECTION(pqueue->m_control_mutex);
}
}
};
#endif // BITCOIN_CHECKQUEUE_H

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