src/cancelable-task.cc

// Copyright 2015 the V8 project 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 "src/cancelable-task.h"

#include "src/base/platform/platform.h"
#include "src/isolate.h"

namespace v8 {
namespace internal {


Cancelable::Cancelable(CancelableTaskManager* parent)
    : parent_(parent), status_(kWaiting), id_(0), cancel_counter_(0) {
  id_ = parent->Register(this);
}


Cancelable::~Cancelable() {
  // The following check is needed to avoid calling an already terminated
  // manager object. This happens when the manager cancels all pending tasks
  // in {CancelAndWait} only before destroying the manager object.
  if (TryRun() || IsRunning()) {
    parent_->RemoveFinishedTask(id_);
  }
}

CancelableTaskManager::CancelableTaskManager() : task_id_counter_(0) {}

uint32_t CancelableTaskManager::Register(Cancelable* task) {
  base::LockGuard<base::Mutex> guard(&mutex_);
  uint32_t id = ++task_id_counter_;
  // The loop below is just used when task_id_counter_ overflows.
  while (cancelable_tasks_.count(id) > 0) ++id;
  cancelable_tasks_[id] = task;
  return id;
}


void CancelableTaskManager::RemoveFinishedTask(uint32_t id) {
  base::LockGuard<base::Mutex> guard(&mutex_);
  size_t removed = cancelable_tasks_.erase(id);
  USE(removed);
  DCHECK_NE(0, removed);
  cancelable_tasks_barrier_.NotifyOne();
}


bool CancelableTaskManager::TryAbort(uint32_t id) {
  base::LockGuard<base::Mutex> guard(&mutex_);
  auto entry = cancelable_tasks_.find(id);
  if (entry != cancelable_tasks_.end()) {
    Cancelable* value = entry->second;
    if (value->Cancel()) {
      // Cannot call RemoveFinishedTask here because of recursive locking.
      cancelable_tasks_.erase(entry);
      cancelable_tasks_barrier_.NotifyOne();
      return true;
    }
  }
  return false;
}


void CancelableTaskManager::CancelAndWait() {
  // Clean up all cancelable fore- and background tasks. Tasks are canceled on
  // the way if possible, i.e., if they have not started yet.  After each round
  // of canceling we wait for the background tasks that have already been
  // started.
  base::LockGuard<base::Mutex> guard(&mutex_);

  // Cancelable tasks could be running or could potentially register new
  // tasks, requiring a loop here.
  while (!cancelable_tasks_.empty()) {
    for (auto it = cancelable_tasks_.begin(); it != cancelable_tasks_.end();) {
      auto current = it;
      // We need to get to the next element before erasing the current.
      ++it;
      if (current->second->Cancel()) {
        cancelable_tasks_.erase(current);
      }
    }
    // Wait for already running background tasks.
    if (!cancelable_tasks_.empty()) {
      cancelable_tasks_barrier_.Wait(&mutex_);
    }
  }
}


CancelableTask::CancelableTask(Isolate* isolate)
    : Cancelable(isolate->cancelable_task_manager()), isolate_(isolate) {}


CancelableIdleTask::CancelableIdleTask(Isolate* isolate)
    : Cancelable(isolate->cancelable_task_manager()), isolate_(isolate) {}

}  // namespace internal
}  // namespace v8