Move thread_pool.h into utils so it can be shared by more than one example.

native_client_sdk/src/libraries/utils/thread_pool.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_
+#ifndef LIBRARY_UTILS_THREAD_POOL_H_
+#define LIBRARY_UTILS_THREAD_POOL_H_
 
 #include <pthread.h>
 #include <semaphore.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "utils/auto_lock.h"
 
 // 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.
-// If 0 is passed in for num_threads, all tasks will be
-// issued on the dispatch thread.
+// 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. If 0 is passed in for num_threads, all tasks will be issued on the
+// dispatch thread.
 
 class ThreadPool {
  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 DispatchMany(int num_tasks, WorkFunction work, void* data);
   void DispatchHere(int num_tasks, WorkFunction work, void* data);
   void WorkLoop();
-  static void* WorkerThreadEntry(void* data);
+  static void* WorkerThreadEntry(void* thiz) {
+    static_cast<ThreadPool*>(thiz)->WorkLoop();
+    return NULL;
+  }
   void PostExitAndJoinAll();
   pthread_t* threads_;
   int counter_;
   const int num_threads_;
   bool exiting_;
   void* user_data_;
   WorkFunction user_work_function_;
+  pthread_mutex_t mutex_;
   sem_t work_sem_;
   sem_t done_sem_;
 };
-#endif  // EXAMPLES_DEMO_VORONOI_THREADPOOL_H_
 
+// Initializes mutex, semaphores and a pool of threads.  If 0 is passed for
+// num_threads, all work will be performed on the dispatch thread.
+ThreadPool::ThreadPool(int num_threads)

[binji, 2013/06/04 23:30:28]

should this all be inline...?

[nfullagar1, 2013/06/04 23:47:09]

I'm on the fence - it's not that much code (compare with STL templates...)  vs.
making utils into a full blown library.  Was hoping to hold off on that for this
round...

+  : threads_(NULL), counter_(0), num_threads_(num_threads), exiting_(false),
+    user_data_(NULL), user_work_function_(NULL) {
+  if (num_threads_ > 0) {
+    int status;
+    status = sem_init(&work_sem_, 0, 0);
+    if (-1 == status) {
+      fprintf(stderr, "Failed to initialize semaphore!\n");
+      exit(-1);
+    }
+    status = sem_init(&done_sem_, 0, 0);
+    if (-1 == status) {
+      fprintf(stderr, "Failed to initialize semaphore!\n");
+      exit(-1);
+    }
+    threads_ = new pthread_t[num_threads_];
+    for (int i = 0; i < num_threads_; i++) {
+      status = pthread_create(&threads_[i], NULL, WorkerThreadEntry, this);
+      if (0 != status) {
+        fprintf(stderr, "Failed to create thread!\n");
+        exit(-1);
+      }
+    }
+  }
+}
+
+// Post exit request, wait for all threads to join, and cleanup.
+ThreadPool::~ThreadPool() {
+  if (num_threads_ > 0) {
+    PostExitAndJoinAll();
+    delete[] threads_;
+    sem_destroy(&done_sem_);
+    sem_destroy(&work_sem_);
+  }
+}
+
+// Dispatch() will invoke the user supplied work function across
+// one or more threads for each task.
+// Note: This function will block until all work has completed.
+inline void ThreadPool::Dispatch(int num_tasks, WorkFunction work, void* data) {
+  if (num_threads_ > 0)
+    DispatchMany(num_tasks, work, data);
+  else
+    DispatchHere(num_tasks, work, data);
+}
+
+// Decrement and get the value of the mutex protected counter.  This function
+// can be called from multiple threads at any given time.
+inline int ThreadPool::DecCounter() {
+#if defined(__native_client__)
+  return __sync_sub_and_fetch(&counter_, 1);
+#else
+  // Slightly more overhead, but more portable mutex guard.
+  static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+  AutoLock(&mutex);
+  return --counter_;
+#endif
+}
+
+// Setup work parameters.  This function is called from the dispatch thread,
+// when all worker threads are sleeping.
+inline void ThreadPool::Setup(int counter, WorkFunction work, void *data) {
+  counter_ = counter;
+  user_work_function_ = work;
+  user_data_ = data;
+}
+
+// DispatchMany() will dispatch a set of tasks across worker threads.
+// Note: This function will block until all work has completed.
+inline void ThreadPool::DispatchMany(int tasks, WorkFunction work, void* data) {
+  // On entry, all worker threads are sleeping.
+  Setup(tasks, work, data);
+  // Wake up the worker threads & have them process tasks.
+  for (int i = 0; i < num_threads_; i++)
+    sem_post(&work_sem_);
+  // Worker threads are now awake and busy.
+  // This dispatch thread will now sleep-wait for the worker threads to finish.
+  for (int i = 0; i < num_threads_; i++)
+    sem_wait(&done_sem_);
+  // On exit, all tasks are done and all worker threads are sleeping again.
+}
+
+//  DispatchHere will dispatch all tasks on this thread.
+inline void ThreadPool::DispatchHere(int tasks, WorkFunction work, void* data) {
+  for (int i = 0; i < tasks; i++)
+    work(i, data);
+}
+
+// Set exit flag, post and join all the threads in the pool.  This function is
+// called only from the dispatch thread, and only when all worker threads are
+// sleeping.
+inline void ThreadPool::PostExitAndJoinAll() {
+  exiting_ = true;
+  // Wake up all the sleeping worker threads.
+  for (int i = 0; i < num_threads_; ++i)
+    sem_post(&work_sem_);
+  void* retval;
+  for (int i = 0; i < num_threads_; ++i)
+    pthread_join(threads_[i], &retval);
+}
+
+// Main work loop - one for each worker thread.
+inline void ThreadPool::WorkLoop() {
+  while (true) {
+    // Wait for work. If no work is availble, this thread will sleep here.
+    sem_wait(&work_sem_);
+    if (exiting_) break;
+    while (true) {
+      // Grab a task index to work on from the counter.
+      int task_index = DecCounter();
+      if (task_index < 0)
+        break;
+      user_work_function_(task_index, user_data_);
+    }
+    // Post to dispatch thread work is done.
+    sem_post(&done_sem_);
+  }
+}
+
+#endif  // LIBRARY_UTILS_THREAD_POOL_H_
+