在Scala actor中访问共享资源的正确方法

Question

在Java中,可以同步访问多线程环境中所需的共享资源的方法或块.

我想知道"Scala Actors"这样做的方式是如何工作的.

假设我有一个java.sql.Connection对象的连接池,我希望提供对它的线程安全访问.我将它实现为接收消息并向发送者发回连接的actor.

似乎有三种方法可以做到这一点:

1. 使用未来
2. 使用 !?
3. 有需要的班级Connection也是演员

码:

sealed abstract class ConnectionPoolMessage
case class NewConnection extends ConnectionPoolMessage
case class CloseConnection(c:Connection) extends ConnectionPoolMessage

class ConnectionPool extends Actor {
  def act() {
    while (true) {
      receive() {
        case NewConnection => sender ! getConnectionFromPool
        case CloseConnection(conn) => returnConnection(conn)
      }
    }
  }
}

// Here, my "do stuff" method is all in one place, and I block waiting
// on the Future from the pool; however this could take forever and cause trouble
class UsingFuture {
  val pool = new ConnectionPool
  def doSomething() {
    val connectionFuture = pool !! NewConnection
    val connection = connectionFuture() // concerned that we can't timeout here
    // do stuff with my Connection instance
    pool ! CloseConnection(connection)  
  }
}


// here, I wait and just use a timeout
// Seems clean to me, I guess.
class UsingBangQuestion {
  val pool = new ConnectionPool
  def doSomething() {
    pool !?(TIMEOUT,NewConnection) match {
      case Some(conn) => {
        // do something with connection
        pool ! CloseConnection(conn)
      }
      case None => throw new RuntimeException("timed out")
    }
  }
}

// here, I don't worry about timeouts, cause I only use the
// the connection when I receive a message back with it.  
// The problem is that I now have to split my logic up
// with two methods
class AsAnActor extends Actor {
  val pool = new ConnectionPool
  def startSomething() {
    start
    pool ! NewConnection
  }
  def act() {
    receive() {
      case conn:Connection => finishSomething(conn)
    }
  }
  def finishSomething(conn:Connection) {
    // do stuff with my Connection
    pool ! CloseConnection(conn)
  }
}

未来的版本似乎最干净,除了我可以永远阻止的事实.

有什么想法,或者是我对这个错误的全部概念？

Answer 1

这可能是不好的风格，但一种方法是通过让您的参与者（需要连接）直接插入连接池并使用同步来获取Connection. 老实说，我真的不明白这种方法有什么问题。我更喜欢它而不是!!or !?，后者只会尖叫死锁（甚至活锁）！

我想另一种方法是向您的池发送一条消息，该消息表示需要通过连接完成的工作以及结果的可能目标：

class DbWork(f: Connection => Unit)
class DbWorkWithResult[T](f:Connection => T, target: OutputChannel[Any])

然后你可以这样使用它：

pool ! new DbWork( { (conn: Connection) => //do something 
                 })

或者：

pool ! new DbWorkWithResult[Int]( (conn: Connection) => //return int
                 }, self)