Revive voronoi multi-threaded demo.

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

+// 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.
+
+#include "threadpool.h"
+
+#include <pthread.h>
+#include <semaphore.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+// TODO(nfullagar): Switch DecCounter to use atomic decrement.
+
+// 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)
+    : threads_(NULL), counter_(0), num_threads_(num_threads), exiting_(false),
+      user_data_(NULL), user_work_function_(NULL) {
+  if (num_threads_ > 0) {
+    int status;
+    status = pthread_mutex_init(&mutex_, NULL);
+    if (0 != status) {
+      fprintf(stderr, "Failed to initialize mutex!\n");
+      exit(-1);
+    }
+    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_ > 1) {
+    PostExitAndJoinAll();
+    delete[] threads_;
+    sem_destroy(&done_sem_);
+    sem_destroy(&work_sem_);
+    pthread_mutex_destroy(&mutex_);
+  }
+}
+
+// Setup work parameters.  This function is called from the dispatch thread,
+// when all worker threads are sleeping.
+void ThreadPool::Setup(int counter, WorkFunction work, void *data) {
+  counter_ = counter;
+  user_work_function_ = work;
+  user_data_ = data;
+}
+
+// Decrement and get the value of the mutex protected counter.  This function
+// can be called from multiple threads at any given time.
+int ThreadPool::DecCounter() {
+  int v;
+  pthread_mutex_lock(&mutex_);
+  {
+    v = --counter_;
+  }
+  pthread_mutex_unlock(&mutex_);
+  return v;
+}
+
+// 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.
+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.
+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_);
+  }
+}
+
+// pthread entry point for a worker thread.
+void* ThreadPool::WorkerThreadEntry(void* thiz) {
+  static_cast<ThreadPool*>(thiz)->WorkLoop();
+  return NULL;
+}
+
+// DispatchMany() will dispatch a set of tasks across worker threads.
+// Note: This function will block until all work has completed.
+void ThreadPool::DispatchMany(int num_tasks, WorkFunction work, void* data) {
+  // On entry, all worker threads are sleeping.
+  Setup(num_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.
+void ThreadPool::DispatchHere(int num_tasks, WorkFunction work, void* data) {
+  for (int i = 0; i < num_tasks; i++)
+    work(i, data);
+}
+
+// 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.
+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);
+}
+