ThreadLocal container that does not rely on thread local storage

unsupported/test/CMakeLists.txt

@@ -201,6 +201,7 @@ if(EIGEN_TEST_CXX11)
   ei_add_test(cxx11_tensor_shuffling)
   ei_add_test(cxx11_tensor_striding)
   ei_add_test(cxx11_tensor_notification "-pthread" "${CMAKE_THREAD_LIBS_INIT}")
+  ei_add_test(cxx11_tensor_thread_local "-pthread" "${CMAKE_THREAD_LIBS_INIT}")
   ei_add_test(cxx11_tensor_thread_pool "-pthread" "${CMAKE_THREAD_LIBS_INIT}")
   ei_add_test(cxx11_tensor_executor "-pthread" "${CMAKE_THREAD_LIBS_INIT}")
   ei_add_test(cxx11_tensor_ref)

unsupported/test/cxx11_tensor_thread_local.cpp

@@ -0,0 +1,158 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// 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/.
+
+#define EIGEN_USE_THREADS
+
+#include <iostream>
+#include <unordered_set>
+
+#include "main.h"
+#include <Eigen/CXX11/ThreadPool>
+
+class Counter {
+ public:
+  Counter() : Counter(0) {}
+  explicit Counter(int value)
+      : created_by_(std::this_thread::get_id()), value_(value) {}
+
+  void inc() {
+    // Check that mutation happens only in a thread that created this counter.
+    VERIFY_IS_EQUAL(std::this_thread::get_id(), created_by_);
+    value_++;
+  }
+  int value() { return value_; }
+
+ private:
+  std::thread::id created_by_;
+  int value_;
+};
+
+struct CounterFactory {
+  using T = Counter;
+
+  T Allocate() { return Counter(0); }
+  void Release(T&) {}
+};
+
+void test_simple_thread_local() {
+  CounterFactory factory;
+  int num_threads = internal::random<int>(4, 32);
+  Eigen::ThreadPool thread_pool(num_threads);
+  Eigen::ThreadLocal<CounterFactory> counter(factory, num_threads);
+
+  int num_tasks = 3 * num_threads;
+  Eigen::Barrier barrier(num_tasks);
+
+  for (int i = 0; i < num_tasks; ++i) {
+    thread_pool.Schedule([&counter, &barrier]() {
+      Counter& local = counter.local();
+      local.inc();
+
+      std::this_thread::sleep_for(std::chrono::milliseconds(100));
+      barrier.Notify();
+    });
+  }
+
+  barrier.Wait();
+
+  counter.ForEach(
+      [](std::thread::id, Counter& cnt) { VERIFY_IS_EQUAL(cnt.value(), 3); });
+}
+
+void test_zero_sized_thread_local() {
+  CounterFactory factory;
+  Eigen::ThreadLocal<CounterFactory> counter(factory, 0);
+
+  Counter& local = counter.local();
+  local.inc();
+
+  int total = 0;
+  counter.ForEach([&total](std::thread::id, Counter& cnt) {
+    total += cnt.value();
+    VERIFY_IS_EQUAL(cnt.value(), 1);
+  });
+
+  VERIFY_IS_EQUAL(total, 1);
+}
+
+// All thread local values fits into the lock-free storage.
+void test_large_number_of_tasks_no_spill() {
+  CounterFactory factory;
+  int num_threads = internal::random<int>(4, 32);
+  Eigen::ThreadPool thread_pool(num_threads);
+  Eigen::ThreadLocal<CounterFactory> counter(factory, num_threads);
+
+  int num_tasks = 10000;
+  Eigen::Barrier barrier(num_tasks);
+
+  for (int i = 0; i < num_tasks; ++i) {
+    thread_pool.Schedule([&counter, &barrier]() {
+      Counter& local = counter.local();
+      local.inc();
+      barrier.Notify();
+    });
+  }
+
+  barrier.Wait();
+
+  int total = 0;
+  std::unordered_set<std::thread::id> unique_threads;
+
+  counter.ForEach([&](std::thread::id id, Counter& cnt) {
+    total += cnt.value();
+    unique_threads.insert(id);
+  });
+
+  VERIFY_IS_EQUAL(total, num_tasks);
+  // Not all threads in a pool might be woken up to execute submitted tasks.
+  // Also thread_pool.Schedule() might use current thread if queue is full.
+  VERIFY_IS_EQUAL(
+      unique_threads.size() <= (static_cast<size_t>(num_threads + 1)), true);
+}
+
+// Lock free thread local storage is too small to fit all the unique threads,
+// and it spills to a map guarded by a mutex.
+void test_large_number_of_tasks_with_spill() {
+  CounterFactory factory;
+  int num_threads = internal::random<int>(4, 32);
+  Eigen::ThreadPool thread_pool(num_threads);
+  Eigen::ThreadLocal<CounterFactory> counter(factory, 1);  // This is too small
+
+  int num_tasks = 10000;
+  Eigen::Barrier barrier(num_tasks);
+
+  for (int i = 0; i < num_tasks; ++i) {
+    thread_pool.Schedule([&counter, &barrier]() {
+      Counter& local = counter.local();
+      local.inc();
+      barrier.Notify();
+    });
+  }
+
+  barrier.Wait();
+
+  int total = 0;
+  std::unordered_set<std::thread::id> unique_threads;
+
+  counter.ForEach([&](std::thread::id id, Counter& cnt) {
+    total += cnt.value();
+    unique_threads.insert(id);
+  });
+
+  VERIFY_IS_EQUAL(total, num_tasks);
+  // Not all threads in a pool might be woken up to execute submitted tasks.
+  // Also thread_pool.Schedule() might use current thread if queue is full.
+  VERIFY_IS_EQUAL(
+      unique_threads.size() <= (static_cast<size_t>(num_threads + 1)), true);
+}
+
+EIGEN_DECLARE_TEST(cxx11_tensor_thread_local) {
+  CALL_SUBTEST(test_simple_thread_local());
+  CALL_SUBTEST(test_zero_sized_thread_local());
+  CALL_SUBTEST(test_large_number_of_tasks_no_spill());
+  CALL_SUBTEST(test_large_number_of_tasks_with_spill());
+}