scala - Slick 3.0-RC3 失败并出现 java.util.concurrent.RejectedExecutionException

Question

我正在尝试熟悉 Slick 3.0 和 Futures(使用 Scala 2.11.6)。我使用基于 Slick's Multi-DB Cake Pattern example 的简单代码。为什么以下代码会因异常而终止以及如何修复它？

import scala.concurrent.Await
import scala.concurrent.duration._
import slick.jdbc.JdbcBackend.Database
import scala.concurrent.ExecutionContext.Implicits.global

class Dispatcher(db: Database, dal: DAL) {
  import dal.driver.api._

  def init() = {
    db.run(dal.create)
    try db.run(dal.stuffTable += Stuff(23,"hi"))
    finally db.close

    val x = {
      try db.run(dal.stuffTable.filter(_.serial === 23).result)
      finally db.close
    }
    // This crashes:
    val result = Await.result(x, 2 seconds)
  }
}

执行失败:

java.util.concurrent.RejectedExecutionException: Task slick.backend.DatabaseComponent$DatabaseDef$$anon$2@5c73f637 rejected from java.util.concurrent.ThreadPoolExecutor@4129c44c[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 2]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
    at scala.concurrent.impl.ExecutionContextImpl$$anon$1.execute(ExecutionContextImpl.scala:136)
    at slick.backend.DatabaseComponent$DatabaseDef$class.runSynchronousDatabaseAction(DatabaseComponent.scala:224)
    at slick.jdbc.JdbcBackend$DatabaseDef.runSynchronousDatabaseAction(JdbcBackend.scala:38)
    at slick.backend.DatabaseComponent$DatabaseDef$class.runInContext(DatabaseComponent.scala:201)
    at slick.jdbc.JdbcBackend$DatabaseDef.runInContext(JdbcBackend.scala:38)
    at slick.backend.DatabaseComponent$DatabaseDef$class.runInternal(DatabaseComponent.scala:75)
    at slick.jdbc.JdbcBackend$DatabaseDef.runInternal(JdbcBackend.scala:38)
    at slick.backend.DatabaseComponent$DatabaseDef$class.run(DatabaseComponent.scala:72)
    at slick.jdbc.JdbcBackend$DatabaseDef.run(JdbcBackend.scala:38)
    at Dispatcher.init(Dispatcher.scala:15)
    at SlickDemo$.main(SlickDemo.scala:16)
    at SlickDemo.main(SlickDemo.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)

Answer 1

我认为您尝试执行的操作不正确:Slick 的 run 方法不会返回 Unit 并且不会因异常而失败 - 如它在以前的版本中曾经使用过。 run 现在返回一个 Future，因此，如果您想按顺序运行操作，则需要 flatMap 这些步骤，或使用 for 理解:

def init() = {
  val = results for {
    _ <- db.run(dal.create)
    _ <- db.run(dal.stuffTable += Stuff(23, "hi"))
    r <- db.run(dal.stuffTable.filter(_.serial === 23).result)
  } yield r
}

我不确定您是否真的需要这样使用db.close:这实际上可能是导致错误的原因(即数据库与运行实际的 future 同时关闭)查询，因此执行无法发生)。

如果您想处理错误，请使用 Future 的功能，例如:

result.onFailure { case NonFatal(ex) => // do something with the exception }