Java同步方法问题

发布于 2024-11-16 22:23:09 字数 197 浏览 0 评论 0原文

我的类有两个同步方法：

class Service {

 public synchronized void calc1();

 public synchronized void calc2();

}

两者都需要相当长的时间来执行。问题是这些方法的执行是否会互相阻塞。即这两个方法可以在不同线程中并行执行吗？

原文

I have class with 2 synchronized methods:

class Service {

 public synchronized void calc1();

 public synchronized void calc2();

}

Both takes considerable time to execute. The question is would execution of these methods blocks each other. I.e. can both methods be executed in parallel in different threads?

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心不设防 2024-11-23 22:23:09

不它们不能在同一个服务上并行执行 - 两个方法共享同一个监视器（即 this），因此如果线程 A 正在执行 calc1，线程 B 将无法获取监视器，因此无法运行 calc2。（请注意，线程 B 可以在 Service 的不同实例上调用任一方法，因为它将尝试获取不同的、未持有的监视器，因为 this 所讨论的会有所不同。）

最简单的解决方案（假设您希望它们独立运行）是使用显式监视器执行类似以下操作：

class Service {
   private final Object calc1Lock = new Object();
   private final Object calc2Lock = new Object();

   public void calc1() {
       synchronized(calc1Lock) {
           // ... method body
       }
   }

   public void calc2() {
       synchronized(calc2Lock) {
           // ... method body
       }
   }

}

所讨论的“锁”不需要具有任何特殊功能不仅仅是对象，因此具有特定的监视器。如果您有更复杂的要求，可能涉及尝试立即锁定并回退，或查询谁拥有锁定，您可以使用实际的锁定对象，但对于基本情况，这些简单的 Object 锁都很好。

No they can't be executed in parallel on the same service - both methods share the same monitor (i.e. this), and so if thread A is executing calc1, thread B won't be able to obtain the monitor and so won't be able to run calc2. (Note that thread B could call either method on a different instance of Service though, as it will be trying to acquire a different, unheld monitor, since the this in question would be different.)

The simplest solution (assuming you want them to run independently) would be to do something like the following using explicit monitors:

class Service {
   private final Object calc1Lock = new Object();
   private final Object calc2Lock = new Object();

   public void calc1() {
       synchronized(calc1Lock) {
           // ... method body
       }
   }

   public void calc2() {
       synchronized(calc2Lock) {
           // ... method body
       }
   }

}

The "locks" in question don't need to have any special abilities other than being Objects, and thus having a specific monitor. If you have more complex requirements that might involve trying to lock and falling back immediately, or querying who holds a lock, you can use the actual Lock objects, but for the basic case these simple Object locks are fine.

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