java - 如何在 Android 中创建锁 (concurrent.locks.Lock)？

Question

这一定很明显，但我找不到答案。我需要锁定一个变量，以确保避免几个竞争危险情况。根据 android 文档，据我所知，使用 Lock 存在一个非常简单的解决方案：

Lock l = ...;
l.lock();
try {
    // access the resource protected by this lock
 }
 finally {
     l.unlock();
 }

到目前为止，一切都很好。但是，我无法使第一行工作。似乎是这样的：

Lock l = new Lock();

可能是正确的，但 Eclipse 报告“无法实例化类型锁定” - 仅此而已。

有什么建议么？

Answer 1

If you're very keen on using a Lock, you need to choose a Lock implementation as you cannot instantiate interfaces. As per the docs You have 3 choices:

• ReentrantLock
• Condition This isn't a Lock itself but rather a helper class since Conditions are bound to Locks.
• ReadWriteLock

You're probably looking for the ReentrantLock possibly with some Conditions

This means that instead of Lock l = new Lock(); you would do:

ReentrantLock lock = new ReentrantLock();

However, if all you're needing to lock is a small part, a synchronized block/method is cleaner (as suggested by @Leonidos & @assylias).

If you have a method that sets the value, you can do:

public synchronized void setValue (var newValue)
{
  value = newValue;
}

or if this is a part of a larger method:

public void doInfinite ()
{
  //code
  synchronized (this)
  { 
    value = aValue;
  }
}

Answer 2

Just because Lock is an interface and can't be instantiated. Use its subclasses.