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// Copyright (c) 2012-2017 The Starwels developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or
#include <sync.h>
#include <algorithm>
#include <vector>
#include <boost/thread/condition_variable.hpp>
#include <boost/thread/mutex.hpp>
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
//! Mutex to protect the inner state
boost::mutex mutex;
//! Worker threads block on this when out of work
boost::condition_variable condWorker;
//! Master thread blocks on this when out of work
boost::condition_variable condMaster;
//! 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;
//! The number of workers (including the master) that are idle.
int nIdle;
//! The total number of workers (including the master).
int nTotal;
//! The temporary evaluation result.
bool fAllOk;
* 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;
//! The maximum number of elements to be processed in one batch
unsigned int nBatchSize;
/** Internal function that does bulk of the verification work. */
bool Loop(bool fMaster = false)
boost::condition_variable& cond = fMaster ? condMaster : condWorker;
std::vector<T> vChecks;
unsigned int nNow = 0;
bool fOk = true;
do {
boost::unique_lock<boost::mutex> lock(mutex);
// 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
} else {
// first iteration
// logically, the do loop starts here
while (queue.empty()) {
if (fMaster && nTodo == 0) {
bool fRet = fAllOk;
// reset the status for new work later
if (fMaster)
fAllOk = true;
// return the current status
return fRet;
cond.wait(lock); // wait
// 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)));
for (unsigned int i = 0; i < nNow; i++) {
// We want the lock on the mutex to be as short as possible, so swap jobs from the global
// queue to the local batch vector instead of copying.
// Check whether we need to do work at all
fOk = fAllOk;
// execute work
for (T& check : vChecks)
if (fOk)
fOk = check();
} while (true);
//! Mutex to ensure only one concurrent CCheckQueueControl
boost::mutex ControlMutex;
//! Create a new check queue
explicit CCheckQueue(unsigned int nBatchSizeIn) : nIdle(0), nTotal(0), fAllOk(true), nTodo(0), nBatchSize(nBatchSizeIn) {}
//! Worker thread
void Thread()
//! Wait until execution finishes, and return whether all evaluations were successful.
bool Wait()
return Loop(true);
//! Add a batch of checks to the queue
void Add(std::vector<T>& vChecks)
boost::unique_lock<boost::mutex> lock(mutex);
for (T& check : vChecks) {
nTodo += vChecks.size();
if (vChecks.size() == 1)
else if (vChecks.size() > 1)
* RAII-style controller object for a CCheckQueue that guarantees the passed
* queue is finished before continuing.
template <typename T>
class CCheckQueueControl
CCheckQueue<T> * const pqueue;
bool fDone;
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) {
bool Wait()
if (pqueue == nullptr)
return true;
bool fRet = pqueue->Wait();
fDone = true;
return fRet;
void Add(std::vector<T>& vChecks)
if (pqueue != nullptr)
if (!fDone)
if (pqueue != nullptr) {