Scala：如何捕獲子線程中的異常

Question

我曾經認爲Try捕獲了跨線程異常，如下例所示。我猜不是的：那麼如何在生成的子線程中捕獲異常呢？

// Simple class that throws error 
class Child extends Runnable { 
    def run { 
    val exception: Exception = new Exception("Foo") 
    val i = 1 
    Thread.sleep(1000) 
    val lines = scala.io.Source.fromFile("/tmp/filefoobar.txt").mkString 
    Thread.sleep(1000) 
    } 
} 
// spawn the class above 
def Parent() = { 
    val doit = Try { 
    val t = new Thread(new Child) 
    t.start 
    t.join() 
    } 

    doit match { 
    case Success(v) => println("uh oh did not capture error") 
    case Failure(v) => println("good we caught the error") 
    } 
} 

輸出 階>父（）

Exception in thread "Thread-35" java.io.FileNotFoundException: /tmp/filefoobar.txt (No such file or directory) 
    at java.io.FileInputStream.open0(Native Method) 
    at java.io.FileInputStream.open(FileInputStream.java:195) 
    at java.io.FileInputStream.<init>(FileInputStream.java:138) 
    at scala.io.Source$.fromFile(Source.scala:91) 
    at scala.io.Source$.fromFile(Source.scala:76) 
    at scala.io.Source$.fromFile(Source.scala:54) 
    at $line120.$read$$iw$$iw$Child.run(<console>:16) 
    at java.lang.Thread.run(Thread.java:745) 
uh oh did not capture error 

Answer 1

考慮使用期貨來處理異步任務的結果

import ExecutionContext.Implicits.global 
val resultFuture: Future[Unit] = Future { new Child.run } 
resultFuture.onComplete (result: Try[Unit] => ...) 

Answer 2

當兒童訪問該文件提出，其捕獲JRE並遵循默認行爲異常;打印堆棧跟蹤，然後將異常傳播到父進程，這會捕獲父級，如您在輸出中看到的那樣。

你可以做的是捕獲子進程中的異常並拋出異常，以便父進程可以處理它。

Answer 3

您可以使用Thread.setUncaughtExceptionHandler設置例外，然後從嘗試重新拋出：

import java.lang.Thread.UncaughtExceptionHandler 

def Parent() = { 

    @volatile 
    var maybeException: Option[Throwable] = None 

    val doit = Try { 
    val target = new Child 
    val t = new Thread(target) 
    t.setUncaughtExceptionHandler(new UncaughtExceptionHandler { 
     override def uncaughtException(t: Thread, th: Throwable): Unit = { 
     maybeException = Some(th) 
     } 
    }) 
    t.start() 
    t.join() 

    maybeException.foreach(th => throw th) 
    } 

    doit match { 
    case Success(v) => println("uh oh did not capture error") 
    case Failure(v) => println("good we caught the error") 
    } 
}