Implement ThreadPool.

runtime/vm/thread_pool.cc

Index: runtime/vm/thread_pool.cc
===================================================================
--- runtime/vm/thread_pool.cc	(revision 0)
+++ runtime/vm/thread_pool.cc	(revision 0)
@@ -0,0 +1,281 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/thread_pool.h"
+
+namespace dart {
+
+DEFINE_FLAG(int, worker_timeout_millis, 5000,
+            "Free workers when they have been idle for this amount of time.");
+
+ThreadPool::ThreadPool()
+  : shutting_down_(false),
+    all_workers_(NULL),
+    idle_workers_(NULL),
+    count_started_(0),
+    count_stopped_(0),
+    count_running_(0),
+    count_idle_(0) {
+}
+
+
+ThreadPool::~ThreadPool() {
+  Shutdown();
+}
+
+
+void ThreadPool::Run(Task* task) {
+  Worker* worker = NULL;
+  {
+    MutexLocker ml(&mutex_);
+    if (shutting_down_) {
+      return;
+    }
+    worker = GetIdleWorker();
+  }
+  // Release ThreadPool::mutex_ before calling Worker functions.
+  worker->Run(task);
+}
+
+
+ThreadPool::Worker* ThreadPool::GetIdleWorker() {
+  // Lock is claimed in ThreadPool::Run.
+  ASSERT(!shutting_down_);
+  Worker* worker = NULL;
+  if (idle_workers_ == NULL) {
+    worker = new Worker(this);
+    ASSERT(worker != NULL);
+    count_started_++;
+
+    // Add worker to the all_workers_ list.
+    worker->all_next_ = all_workers_;
+    all_workers_ = worker;
+
+  } else {
+    // Get the first worker from the idle worker list.
+    worker = idle_workers_;
+    idle_workers_ = worker->idle_next_;
+    worker->idle_next_ = NULL;
+    count_idle_--;
+  }
+  worker->state_ = kRunning;
+  count_running_++;
+  return worker;
+}
+
+
+void ThreadPool::Shutdown() {
+  Worker* current = NULL;
+  {
+    MutexLocker ml(&mutex_);
+    shutting_down_ = true;
+    current = all_workers_;
+    all_workers_ = NULL;
+    idle_workers_ = NULL;
+    count_idle_ = 0;
+    count_running_ = 0;
+
+    while (current != NULL) {
+      Worker* next = current->all_next_;
+      current->all_next_ = NULL;
+      current->idle_next_ = NULL;
+      current->state_ = kDone;
+      current = next;
+    }
+  }
+  // Release ThreadPool::mutex_ before calling Worker functions.
+
+  while (current != NULL) {

[Ivan Posva, 2012/03/07 01:06:05]

Isn't current guaranteed to be NULL here?

[turnidge, 2012/03/07 18:02:20]

Oops, that broke in my most recent changes.  Fixed.

+    Worker* next = current->all_next_;
+    current->Shutdown();
+    current = next;
+  }
+}
+
+
+void ThreadPool::SetIdle(Worker* worker) {
+  MutexLocker ml(&mutex_);
+  if (shutting_down_) {
+    return;
+  }
+  ASSERT(worker->state_ == kRunning);
+  worker->idle_next_ = idle_workers_;
+  idle_workers_ = worker;
+  worker->state_ = kIdle;
+  count_idle_++;
+  count_running_--;
+}
+
+
+bool ThreadPool::RemoveWorkerFromAllList(Worker* worker) {
+  Worker* head = all_workers_;
+  ASSERT(worker != NULL && head != NULL);
+  ASSERT(worker->state_ != kDone);
+
+  // Special case head of list.
+  if (head == worker) {
+    head = worker->all_next_;
+    worker->all_next_ = NULL;
+    return true;
+  }
+
+  // We only want to remove a worker if it is idle.

[Ivan Posva, 2012/03/07 01:06:05]

Comment out of place?

[turnidge, 2012/03/07 18:02:20]

Comment removed, here and below.

+  for (Worker* current = head;
+       current->all_next_ != NULL;
+       current = current->all_next_) {
+    if (current->all_next_ == worker) {
+      // We found this worker in the idle list.  Remove it.

[Ivan Posva, 2012/03/07 01:06:05]

Comment seems out of place.

[turnidge, 2012/03/07 18:02:20]

Comment removed.

+      current->all_next_ = current->all_next_->all_next_;
+      worker->all_next_ = NULL;
+      return true;
+    }
+  }
+}
+
+
+bool ThreadPool::RemoveWorkerFromIdleList(Worker* worker) {
+  Worker* head = idle_workers_;
+  ASSERT(worker != NULL && head != NULL);
+  ASSERT(worker->state_ == kIdle);
+
+  // Special case head of list.
+  if (head == worker) {
+    head = worker->idle_next_;
+    worker->idle_next_ = NULL;
+    return true;
+  }
+
+  // We only want to remove a worker if it is idle.
+  for (Worker* current = head;
+       current->idle_next_ != NULL;
+       current = current->idle_next_) {
+    if (current->idle_next_ == worker) {
+      // We found this worker in the idle list.  Remove it.
+      current->idle_next_ = current->idle_next_->idle_next_;
+      worker->idle_next_ = NULL;
+      return true;
+    }
+  }
+}
+
+
+bool ThreadPool::ReleaseIdleWorker(Worker* worker) {
+  MutexLocker ml(&mutex_);
+  if (shutting_down_) {
+    return false;
+  }
+  if (worker->state_ != kIdle) {
+    return false;
+  }
+
+  // Remove from idle list.
+  bool found = RemoveWorkerFromIdleList(worker);
+  ASSERT(found);
+
+  // Remove from all list.
+  found = RemoveWorkerFromAllList(worker);
+  ASSERT(found);
+
+  worker->state_ = kDone;
+  count_stopped_++;
+  count_idle_--;
+  return true;
+}
+
+
+ThreadPool::Task::Task() {
+}
+
+
+ThreadPool::Task::~Task() {
+}
+
+
+ThreadPool::Worker::Worker(ThreadPool* pool)
+  : pool_(pool),
+    task_(NULL),
+    started_(false),
+    done_(false),
+    state_(kInvalid),
+    all_next_(NULL),
+    idle_next_(NULL) {
+}
+
+
+void ThreadPool::Worker::Run(Task* task) {
+  MonitorLocker ml(&monitor_);
+  ASSERT(task_ == NULL);
+  if (!started_) {
+    Thread::Start(&Worker::Main, reinterpret_cast<uword>(this));
+    started_ = true;
+  }
+  task_ = task;
+  ml.Notify();
+}
+
+
+void ThreadPool::Worker::Loop() {
+  MonitorLocker ml(&monitor_);
+  if (done_) {
+    return;
+  }
+
+  ASSERT(started_ && task_ != NULL);
+  int64_t idle_start = 0;
+  while (true) {
+    Task* task = task_;
+    task_ = NULL;
+
+    // Release monitor while handling the task.
+    monitor_.Exit();
+    task->Run();
+    delete task;
+    monitor_.Enter();
+
+    if (done_) {
+      return;
+    }
+    ASSERT(task_ == NULL);
+
+    pool_->SetIdle(this);
+    idle_start = OS::GetCurrentTimeMillis();
+    do {
+      Monitor::WaitResult result = ml.Wait(FLAG_worker_timeout_millis);
+      if (done_) {
+        return;
+      }
+      if (task_ == NULL &&
+          result == Monitor::kTimedOut &&
+          FLAG_worker_timeout_millis > 0) {
+        bool timeout =
+            (OS::GetCurrentTimeMillis() - idle_start) >
+            FLAG_worker_timeout_millis;
+        if (timeout && pool_->ReleaseIdleWorker(this)) {
+          return;
+        }
+      }
+    } while (task_ == NULL);
+  }
+  UNREACHABLE();
+}
+
+
+void ThreadPool::Worker::Shutdown() {
+  MonitorLocker ml(&monitor_);
+  done_ = true;
+  ml.Notify();
+}
+
+
+// static
+void ThreadPool::Worker::Main(uword args) {
+  Worker* worker = reinterpret_cast<Worker*>(args);
+  worker->Loop();
+
+  // It should be okay to access these unlocked here in this assert.
+  ASSERT(worker->state_ == kDone && worker->idle_next_ == NULL);
+  delete worker;
+}
+
+}  // namespace dart