Slick 3.0-RC3失败，返回java.util.concurrent.RejectedExecutionException [英] Slick 3.0-RC3 fails with java.util.concurrent.RejectedExecutionException

问题描述

我想要熟悉Slick 3.0和Futures（使用Scala 2.11.6）。我使用基于 Slick的Multi-DB Cake Pattern示例的简单代码。为什么以下代码以异常终止并如何解决它？

I'm trying to get familiar with Slick 3.0 and Futures (using Scala 2.11.6). I use simple code based on Slick's Multi-DB Cake Pattern example. Why does the following code terminate with an exception and how to fix it?

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)

推荐答案

不正确的是你想要做什么：Slick的运行方法不返回 Unit 一个异常 - 像以前的版本中一样。 run 现在返回 Future ，因此如果要按顺序运行操作，您需要 flatMap 的步骤，或使用for-comprehension：

I think that something is not correct in what you are trying to do: Slick's run method doesn't return Unit and doesn't fail with an exception - as it used to in previous versions. run now returns a Future, so if you want to run actions in sequence you need to flatMap the steps, or use a for-comprehension:

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
}

我不确定你真的需要使用 db.close 什么可能导致错误（即，数据库与运行实际查询的未来关闭，因此执行不会发生）。

I am not sure that you really need to use db.close that way: that is actually what may be causing the error (i.e. the db is closed in concurrence with the future that runs the actual queries so the execution can't happen).

如果您想句柄错误使用未来的功能，例如：

If you want to handle errors use Future's capabilities, e.g.:

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

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