85 lines
2.5 KiB
C++
85 lines
2.5 KiB
C++
// Copyright (C) 2011, 2012 Strahinja Val Markovic <val@markovic.io>
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//
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// This file is part of YouCompleteMe.
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//
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// YouCompleteMe is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// YouCompleteMe is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with YouCompleteMe. If not, see <http://www.gnu.org/licenses/>.
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#ifndef CONCURRENTLATESTVALUE_H_SYF1JPPG
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#define CONCURRENTLATESTVALUE_H_SYF1JPPG
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#include <boost/thread.hpp>
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#include <boost/utility.hpp>
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namespace YouCompleteMe
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{
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// This is is basically a multi-consumer single-producer queue, only with the
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// twist that we only care about the latest value set. So the GUI thread is the
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// setter, and the worker threads are the workers. The workers wait in line on
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// the condition variable and when the setter sets a value, a worker is chosen
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// to consume it.
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//
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// The point is that we always want to have one "fresh" worker thread ready to
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// work on our latest value. If a newer value is set, then we don't care what
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// happens to the old values.
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//
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// This implementation is mutex-based and is not lock-free. Normally using a
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// lock-free data structure makes more sense, but since the GUI thread goes
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// through VimL and Python on every keystroke, there's really no point. Those 5
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// nanoseconds it takes to lock a mutex are laughably negligible compared to the
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// VimL/Python overhead.
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template <typename T>
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class ConcurrentLatestValue : boost::noncopyable
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{
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public:
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ConcurrentLatestValue() : empty_( true ) {}
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void Set( const T& data )
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{
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{
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boost::unique_lock< boost::mutex > lock( mutex_ );
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latest_ = data;
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empty_ = false;
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}
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condition_variable_.notify_one();
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}
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T Get()
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{
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boost::unique_lock< boost::mutex > lock( mutex_ );
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while ( empty_ )
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{
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condition_variable_.wait( lock );
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}
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empty_ = true;
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return latest_;
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}
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private:
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T latest_;
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bool empty_;
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boost::mutex mutex_;
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boost::condition_variable condition_variable_;
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};
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} // namespace YouCompleteMe
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#endif /* end of include guard: CONCURRENTLATESTVALUE_H_SYF1JPPG */
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