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// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2017 Google Inc. All rights reserved.
// http://ceres-solver.org/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
// * Neither the name of Google Inc. nor the names of its contributors may be
// used to endorse or promote products derived from this software without
// specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Author: yp@photonscore.de (Yury Prokazov)
#ifndef CERES_INTERNAL_THREAD_TOKEN_PROVIDER_H_
#define CERES_INTERNAL_THREAD_TOKEN_PROVIDER_H_
#include "ceres/internal/config.h"
#include "ceres/internal/port.h"
#ifdef CERES_USE_CXX_THREADS
#include "ceres/concurrent_queue.h"
#endif
namespace ceres {
namespace internal {
// Helper for C++ thread number identification that is similar to
// omp_get_thread_num() behaviour. This is necessary to support C++
// threading with a sequential thread id. This is used to access preallocated
// resources in the parallelized code parts. The sequence of tokens varies from
// 0 to num_threads - 1 that can be acquired to identify the thread in a thread
// pool.
//
// If CERES_NO_THREADS is defined, Acquire() always returns 0 and Release()
// takes no action.
//
// If CERES_USE_OPENMP, omp_get_thread_num() is used to Acquire() with no action
// in Release()
//
//
// Example usage pseudocode:
//
// ThreadTokenProvider ttp(N); // allocate N tokens
// Spawn N threads {
// int token = ttp.Acquire(); // get unique token
// ...
// ... use token to access resources bound to the thread
// ...
// ttp.Release(token); // return token to the pool
// }
//
class ThreadTokenProvider {
public:
ThreadTokenProvider(int num_threads);
// Returns the first token from the queue. The acquired value must be
// given back by Release().
int Acquire();
// Makes previously acquired token available for other threads.
void Release(int thread_id);
private:
#ifdef CERES_USE_CXX_THREADS
// This queue initially holds a sequence from 0..num_threads-1. Every
// Acquire() call the first number is removed from here. When the token is not
// needed anymore it shall be given back with corresponding Release()
// call. This concurrent queue is more expensive than TBB's version, so you
// should not acquire the thread ID on every for loop iteration.
ConcurrentQueue<int> pool_;
#endif
ThreadTokenProvider(ThreadTokenProvider&);
ThreadTokenProvider& operator=(ThreadTokenProvider&);
};
} // namespace internal
} // namespace ceres
#endif // CERES_INTERNAL_THREAD_TOKEN_PROVIDER_H_
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