[SPARK-10001] [CORE] Interrupt tasks in repl with Ctrl+C

## What changes were proposed in this pull request?

Improve signal handling to allow interrupting running tasks from the REPL (with Ctrl+C).
If no tasks are running or Ctrl+C is pressed twice, the signal is forwarded to the default handler resulting in the usual termination of the application.

This PR is a rewrite of -- and therefore closes #8216 -- as per piaozhexiu's request

## How was this patch tested?
Signal handling is not easily testable therefore no unit tests were added. Nevertheless, the new functionality is implemented in a best-effort approach, soft-failing in case signals aren't available on a specific OS.

Author: Jakob Odersky <jakob@odersky.com>

Closes #12557 from jodersky/SPARK-10001-sigint.

core/src/main/scala/org/apache/spark/util/SignalLogger.scala

@@ -17,44 +17,20 @@
 
 package org.apache.spark.util
 
-import org.apache.commons.lang3.SystemUtils
 import org.slf4j.Logger
-import sun.misc.{Signal, SignalHandler}
 
 /**
  * Used to log signals received. This can be very useful in debugging crashes or kills.
- *
- * Inspired by Colin Patrick McCabe's similar class from Hadoop.
  */
 private[spark] object SignalLogger {
 
   private var registered = false
 
   /** Register a signal handler to log signals on UNIX-like systems. */
-  def register(log: Logger): Unit = synchronized {
-    if (SystemUtils.IS_OS_UNIX) {
-      require(!registered, "Can't re-install the signal handlers")
-      registered = true
-
-      val signals = Seq("TERM", "HUP", "INT")
-      for (signal <- signals) {
-        try {
-          new SignalLoggerHandler(signal, log)
-        } catch {
-          case e: Exception => log.warn("Failed to register signal handler " + signal, e)
-        }
-      }
-      log.info("Registered signal handlers for [" + signals.mkString(", ") + "]")
+  def register(log: Logger): Unit = Seq("TERM", "HUP", "INT").foreach{ sig =>
+    Signaling.register(sig) {
+      log.error("RECEIVED SIGNAL " + sig)
+      false
     }
   }
 }
-
-private sealed class SignalLoggerHandler(name: String, log: Logger) extends SignalHandler {
-
-  val prevHandler = Signal.handle(new Signal(name), this)
-
-  override def handle(signal: Signal): Unit = {
-    log.error("RECEIVED SIGNAL " + signal.getNumber() + ": SIG" + signal.getName())
-    prevHandler.handle(signal)
-  }
-}

core/src/main/scala/org/apache/spark/util/Signaling.scala

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.util
+
+import java.util.{Collections, LinkedList}
+
+import scala.collection.JavaConverters._
+import scala.collection.mutable.HashMap
+
+import org.apache.commons.lang3.SystemUtils
+import sun.misc.{Signal, SignalHandler}
+
+import org.apache.spark.internal.Logging
+
+
+/**
+ * Contains utilities for working with posix signals.
+ */
+private[spark] object Signaling extends Logging {
+
+  /**
+   * A handler for the given signal that runs a collection of actions.
+   */
+  private class ActionHandler(signal: Signal) extends SignalHandler {
+
+    private val actions = Collections.synchronizedList(new LinkedList[() => Boolean])
+
+    // original signal handler, before this handler was attached
+    private val prevHandler: SignalHandler = Signal.handle(signal, this)
+
+    /**
+     * Called when this handler's signal is received. Note that if the same signal is received
+     * before this method returns, it is escalated to the previous handler.
+     */
+    override def handle(sig: Signal): Unit = {
+      // register old handler, will receive incoming signals while this handler is running
+      Signal.handle(signal, prevHandler)
+
+      val escalate = actions.asScala forall { action =>
+        !action()
+      }
+
+      if(escalate) {
+        prevHandler.handle(sig)
+      }
+
+      // re-register this handler
+      Signal.handle(signal, this)
+    }
+
+    /**
+     * Add an action to be run by this handler.
+     * @param action An action to be run when a signal is received. Return true if the signal
+     * should be stopped with this handler, false if it should be escalated.
+     */
+    def register(action: => Boolean): Unit = actions.add(() => action)
+
+  }
+
+  // contains association of signals to their respective handlers
+  private val handlers = new HashMap[String, ActionHandler]
+
+  /**
+   * Adds an action to be run when a given signal is received by this process.
+   *
+   * Note that signals are only supported on unix-like operating systems and work on a best-effort
+   * basis: if a signal is not available or cannot be intercepted, only a warning is emitted.
+   *
+   * All actions for a given signal are run in a separate thread.
+   */
+  def register(signal: String)(action: => Boolean): Unit = synchronized {
+    if (SystemUtils.IS_OS_UNIX) try {
+      val handler = handlers.getOrElseUpdate(signal, {
+        val h = new ActionHandler(new Signal(signal))
+        logInfo("Registered signal handler for " + signal)
+        h
+      })
+      handler.register(action)
+    } catch {
+      case ex: Exception => logWarning(s"Failed to register signal handler for " + signal, ex)
+    }
+  }
+
+}

repl/scala-2.10/src/main/scala/org/apache/spark/repl/SparkILoop.scala

@@ -1022,6 +1022,7 @@ class SparkILoop(
     }
     sparkContext = new SparkContext(conf)
     logInfo("Created spark context..")
+    Signaling.cancelOnInterrupt(sparkContext)
     sparkContext
   }
 

repl/scala-2.11/src/main/scala/org/apache/spark/repl/Main.scala

@@ -88,6 +88,7 @@ object Main extends Logging {
     }
     sparkContext = new SparkContext(conf)
     logInfo("Created spark context..")
+    Signaling.cancelOnInterrupt(sparkContext)
     sparkContext
   }
 

repl/src/main/scala/org/apache/spark/repl/Signaling.scala

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.repl
+
+import org.apache.spark.SparkContext
+import org.apache.spark.internal.Logging
+import org.apache.spark.util.{Signaling => USignaling}
+
+private[repl] object Signaling extends Logging {
+
+  /**
+   * Register a SIGINT handler, that terminates all active spark jobs or terminates
+   * when no jobs are currently running.
+   * This makes it possible to interrupt a running shell job by pressing Ctrl+C.
+   */
+  def cancelOnInterrupt(ctx: SparkContext): Unit = USignaling.register("INT") {
+    if (!ctx.statusTracker.getActiveJobIds().isEmpty) {
+      logWarning("Cancelling all active jobs, this can take a while. " +
+        "Press Ctrl+C again to exit now.")
+      ctx.cancelAllJobs()
+      true
+    } else {
+      false
+    }
+  }
+
+}