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// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2018 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: vitus@google.com (Michael Vitus)
// This include must come before any #ifndef check on Ceres compile options.
#include "ceres/internal/port.h"
#ifdef CERES_USE_CXX_THREADS
#include "ceres/thread_pool.h"
#include <cmath>
#include <limits>
namespace ceres {
namespace internal {
namespace {
// Constrain the total number of threads to the amount the hardware can support.
int GetNumAllowedThreads(int requested_num_threads) {
return std::min(requested_num_threads, ThreadPool::MaxNumThreadsAvailable());
}
} // namespace
int ThreadPool::MaxNumThreadsAvailable() {
const int num_hardware_threads = std::thread::hardware_concurrency();
// hardware_concurrency() can return 0 if the value is not well defined or not
// computable.
return num_hardware_threads == 0
? std::numeric_limits<int>::max()
: num_hardware_threads;
}
ThreadPool::ThreadPool() { }
ThreadPool::ThreadPool(int num_threads) {
Resize(num_threads);
}
ThreadPool::~ThreadPool() {
std::lock_guard<std::mutex> lock(thread_pool_mutex_);
// Signal the thread workers to stop and wait for them to finish all scheduled
// tasks.
Stop();
for (std::thread& thread : thread_pool_) {
thread.join();
}
}
void ThreadPool::Resize(int num_threads) {
std::lock_guard<std::mutex> lock(thread_pool_mutex_);
const int num_current_threads = thread_pool_.size();
if (num_current_threads >= num_threads) {
return;
}
const int create_num_threads =
GetNumAllowedThreads(num_threads) - num_current_threads;
for (int i = 0; i < create_num_threads; ++i) {
thread_pool_.push_back(std::thread(&ThreadPool::ThreadMainLoop, this));
}
}
void ThreadPool::AddTask(const std::function<void()>& func) {
task_queue_.Push(func);
}
int ThreadPool::Size() {
std::lock_guard<std::mutex> lock(thread_pool_mutex_);
return thread_pool_.size();
}
void ThreadPool::ThreadMainLoop() {
std::function<void()> task;
while (task_queue_.Wait(&task)) {
task();
}
}
void ThreadPool::Stop() {
task_queue_.StopWaiters();
}
} // namespace internal
} // namespace ceres
#endif // CERES_USE_CXX_THREADS
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