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diff --git a/unsupported/Eigen/CXX11/src/ThreadPool/SimpleThreadPool.h b/unsupported/Eigen/CXX11/src/ThreadPool/SimpleThreadPool.h
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+++ b/unsupported/Eigen/CXX11/src/ThreadPool/SimpleThreadPool.h
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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2014 Benoit Steiner <benoit.steiner.goog@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef EIGEN_CXX11_THREADPOOL_SIMPLE_THREAD_POOL_H
+#define EIGEN_CXX11_THREADPOOL_SIMPLE_THREAD_POOL_H
+
+namespace Eigen {
+
+// The implementation of the ThreadPool type ensures that the Schedule method
+// runs the functions it is provided in FIFO order when the scheduling is done
+// by a single thread.
+// Environment provides a way to create threads and also allows to intercept
+// task submission and execution.
+template <typename Environment>
+class SimpleThreadPoolTempl : public ThreadPoolInterface {
+ public:
+  // Construct a pool that contains "num_threads" threads.
+  explicit SimpleThreadPoolTempl(int num_threads, Environment env = Environment())
+      : env_(env), threads_(num_threads), waiters_(num_threads) {
+    for (int i = 0; i < num_threads; i++) {
+      threads_.push_back(env.CreateThread([this, i]() { WorkerLoop(i); }));
+    }
+  }
+
+  // Wait until all scheduled work has finished and then destroy the
+  // set of threads.
+  ~SimpleThreadPoolTempl() {
+    {
+      // Wait for all work to get done.
+      std::unique_lock<std::mutex> l(mu_);
+      while (!pending_.empty()) {
+        empty_.wait(l);
+      }
+      exiting_ = true;
+
+      // Wakeup all waiters.
+      for (auto w : waiters_) {
+        w->ready = true;
+        w->task.f = nullptr;
+        w->cv.notify_one();
+      }
+    }
+
+    // Wait for threads to finish.
+    for (auto t : threads_) {
+      delete t;
+    }
+  }
+
+  // Schedule fn() for execution in the pool of threads. The functions are
+  // executed in the order in which they are scheduled.
+  void Schedule(std::function<void()> fn) final {
+    Task t = env_.CreateTask(std::move(fn));
+    std::unique_lock<std::mutex> l(mu_);
+    if (waiters_.empty()) {
+      pending_.push_back(std::move(t));
+    } else {
+      Waiter* w = waiters_.back();
+      waiters_.pop_back();
+      w->ready = true;
+      w->task = std::move(t);
+      w->cv.notify_one();
+    }
+  }
+
+  int NumThreads() const final {
+    return static_cast<int>(threads_.size());
+  }
+
+  int CurrentThreadId() const final {
+    const PerThread* pt = this->GetPerThread();
+    if (pt->pool == this) {
+      return pt->thread_id;
+    } else {
+      return -1;
+    }
+  }
+
+ protected:
+  void WorkerLoop(int thread_id) {
+    std::unique_lock<std::mutex> l(mu_);
+    PerThread* pt = GetPerThread();
+    pt->pool = this;
+    pt->thread_id = thread_id;
+    Waiter w;
+    Task t;
+    while (!exiting_) {
+      if (pending_.empty()) {
+        // Wait for work to be assigned to me
+        w.ready = false;
+        waiters_.push_back(&w);
+        while (!w.ready) {
+          w.cv.wait(l);
+        }
+        t = w.task;
+        w.task.f = nullptr;
+      } else {
+        // Pick up pending work
+        t = std::move(pending_.front());
+        pending_.pop_front();
+        if (pending_.empty()) {
+          empty_.notify_all();
+        }
+      }
+      if (t.f) {
+        mu_.unlock();
+        env_.ExecuteTask(t);
+        t.f = nullptr;
+        mu_.lock();
+      }
+    }
+  }
+
+ private:
+  typedef typename Environment::Task Task;
+  typedef typename Environment::EnvThread Thread;
+
+  struct Waiter {
+    std::condition_variable cv;
+    Task task;
+    bool ready;
+  };
+
+  struct PerThread {
+    constexpr PerThread() : pool(NULL), thread_id(-1) { }
+    SimpleThreadPoolTempl* pool;  // Parent pool, or null for normal threads.
+    int thread_id;                // Worker thread index in pool.
+  };
+
+  Environment env_;
+  std::mutex mu_;
+  MaxSizeVector<Thread*> threads_;  // All threads
+  MaxSizeVector<Waiter*> waiters_;  // Stack of waiting threads.
+  std::deque<Task> pending_;        // Queue of pending work
+  std::condition_variable empty_;   // Signaled on pending_.empty()
+  bool exiting_ = false;
+
+  PerThread* GetPerThread() const {
+    EIGEN_THREAD_LOCAL PerThread per_thread;
+    return &per_thread;
+  }
+};
+
+typedef SimpleThreadPoolTempl<StlThreadEnvironment> SimpleThreadPool;
+
+}  // namespace Eigen
+
+#endif  // EIGEN_CXX11_THREADPOOL_SIMPLE_THREAD_POOL_H