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#pragma once
#include <future>
#include <functional>
#include <algorithm>
#include <sigc++/signal.h>
#include <vector>
namespace parser
{
/**
* Helper class used to asynchronically parse/load def files in a separate thread.
*
* The worker thread itself is ensured to be called in a thread-safe
* way (to prevent the worker from being invoked twice). Subsequent calls to
* get() or start() will not start the loader again, unless the reset() method
* is called.
*
* Client code (even from multiple threads) can retrieve (and wait for) the result
* by calling the get() method.
*/
template <typename ReturnType>
class ThreadedDefLoader
{
public:
using LoadFunction = std::function<ReturnType()>;
using FinishedSignal = sigc::signal<void>;
private:
LoadFunction _loadFunc;
FinishedSignal _finishedSignal;
std::shared_future<ReturnType> _result;
std::shared_future<void> _finisher;
std::mutex _mutex;
bool _loadingStarted;
public:
ThreadedDefLoader(const LoadFunction& loadFunc) :
_loadFunc(loadFunc),
_loadingStarted(false)
{}
virtual ~ThreadedDefLoader()
{
// wait for any worker thread to finish
reset();
}
// Starts the loader in the background. This can be called multiple
// times from separate threads, the worker will only launched once and
// cannot be started a second time unless reset() is called.
void start()
{
ensureLoaderStarted();
}
// Ensures that the worker thread has been started and is done processing
// This will block and wait for the worker execution before returning to the caller.
void ensureFinished()
{
get();
}
// Retrieve the result of the asynchronous worker function
// This will block and wait for the result if worker has not been
// run yet or in case it's still running
ReturnType get()
{
// Make sure we already started the loader
ensureLoaderStarted();
// Wait for the result or return if it's already done.
return _result.get();
}
// Resets the state of the loader to the state it had after construction.
// If a background thread has been started, this will block and wait for it to finish.
void reset()
{
std::lock_guard<std::mutex> lock(_mutex);
// Wait for any running thread to finish
if (_loadingStarted)
{
if (_result.valid())
{
_result.get();
}
if (_finisher.valid())
{
_finisher.get();
}
_result = std::shared_future<ReturnType>();
_finisher = std::shared_future<void>();
_loadingStarted = false;
}
}
FinishedSignal& signal_finished()
{
return _finishedSignal;
}
private:
struct FinishSignalEmitter
{
FinishedSignal& _signal;
std::shared_future<void>& _targetFuture;
FinishSignalEmitter(FinishedSignal& signal, std::shared_future<void>& targetFuture) :
_signal(signal),
_targetFuture(targetFuture)
{}
~FinishSignalEmitter()
{
_targetFuture = std::async(std::launch::async, std::bind(&FinishedSignal::emit, _signal));
}
};
void ensureLoaderStarted()
{
std::lock_guard<std::mutex> lock(_mutex);
if (!_loadingStarted)
{
_loadingStarted = true;
_result = std::async(std::launch::async, [&]()
{
// When going out of scope, this instance invokes the finished signal in a separate thread
FinishSignalEmitter finisher(_finishedSignal, _finisher);
return _loadFunc();
});
}
}
};
}
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