Revive voronoi multi-threaded demo.

native_client_sdk/src/examples/demo/voronoi/threadpool.h

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Simple thread pool class
+
+#ifndef EXAMPLES_DEMO_VORONOI_THREADPOOL_H_
+#define EXAMPLES_DEMO_VORONOI_THREADPOOL_H_
+
+#if !defined(DISABLE_THREADS)
+#include <pthread.h>
+#include <semaphore.h>
+#endif
+
+// typdef helper for work function
+typedef void (*WorkFunction)(int task_index, void *data);
+
+// ThreadPool is a class to manage num_threads and assign
+// them num_tasks of work at a time. Each call
+// to Dispatch(..) will block until all tasks complete.
+
+class ThreadPool {
+#if !defined(DISABLE_THREADS)

[noelallen1, 2013/05/25 00:21:11]

I would recommend removing.   We either should support this everywhere or
nowhere IMO.

[nfullagar1, 2013/05/28 23:11:50]

removed

+ public:
+  void Dispatch(int num_tasks, WorkFunction work, void *data);
+  explicit ThreadPool(int num_threads);
+  ~ThreadPool();
+ private:
+  int DecCounter();
+  void Setup(int counter, WorkFunction work, void *data);
+  void MultiThread(int num_tasks, WorkFunction work, void *data);
+  void SingleThread(int num_tasks, WorkFunction work, void *data);
+  void WorkLoop();
+  static void* WorkerThreadEntry(void *data);
+  void PostExitAndJoinAll();
+  pthread_t *threads_;

[binji, 2013/05/24 21:47:55]

might want to run clang-format on this diff to fix * issues, etc.

[nfullagar1, 2013/05/28 23:11:50]

Done.

+  int counter_;
+  int num_threads_;

[noelallen1, 2013/05/25 00:21:11]

Did you mean to make this one const?

[nfullagar1, 2013/05/28 23:11:50]

yes! thx.

+  bool exiting_;
+  void *user_data_;
+  WorkFunction user_work_function_;
+  pthread_mutex_t mutex_;
+  sem_t work_tasks_;
+  sem_t done_tasks_;
+#else
+ public:
+  void Dispatch(int num_tasks, WorkFunction work, void *data) {
+    for(int i = 0; i < num_tasks; i++) work(i, data); }

[binji, 2013/05/24 21:47:55]

share with SingleThread?

[nfullagar1, 2013/05/28 23:11:50]

Fishing this out and sharing this one line of code is more loc...

+  explicit ThreadPool(int num_threads) { ; }

[binji, 2013/05/24 21:47:55]

nit: {}

[noelallen1, 2013/05/25 00:21:11]

A bit strange that in the DISABLE_THREADS case the .cc is empty.

[nfullagar1, 2013/05/28 23:11:50]

Done.

[nfullagar1, 2013/05/28 23:11:50]

DISABLE_THREADS removed

+  ~ThreadPool() { ; }
+#endif  // DISABLE_THREADS
+};
+#endif  // EXAMPLES_DEMO_VORONOI_THREADPOOL_H_