Squashed 'third_party/ceres/' content from commit e51e9b4
Change-Id: I763587619d57e594d3fa158dc3a7fe0b89a1743b
git-subtree-dir: third_party/ceres
git-subtree-split: e51e9b46f6ca88ab8b2266d0e362771db6d98067
diff --git a/internal/ceres/thread_pool.cc b/internal/ceres/thread_pool.cc
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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_CXX11_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_CXX11_THREADS