[SPARK-31946][CORE] Make worker/executor decommission signal configur…

…able

### What changes were proposed in this pull request?

This PR proposed to make worker/executor decommission signal configurable.

* Added confs: `spark.worker.decommission.signal` / `spark.executor.decommission.signal`
* Rename `WorkerSigPWRReceived`/ `ExecutorSigPWRReceived` to `WorkerDecomSigReceived`/ `ExecutorDecomSigReceived`

### Why are the changes needed?

The current signal `PWR` can't work on macOS since it's not compliant with POSIX while macOS does.  So the developers currently can't do end-to-end decommission test on their macOS environment.

Besides, the configuration becomes more flexible for users in case the default signal (`PWR`) gets conflicted with their own applications/environment.

### Does this PR introduce _any_ user-facing change?

No (it's a new API for 3.2)

### How was this patch tested?

Manually tested.

Closes #30968 from Ngone51/configurable-decom-signal.

Authored-by: yi.wu <yi.wu@databricks.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

core/src/main/scala/org/apache/spark/deploy/DeployMessage.scala

@@ -77,10 +77,10 @@ private[deploy] object DeployMessages {
   object DecommissionWorker extends DeployMessage
 
   /**
-   * A message that sent by the Worker to itself when it receives PWR signal,
+   * A message that sent by the Worker to itself when it receives a signal,
    * indicating the Worker starts to decommission.
    */
-  object WorkerSigPWRReceived extends DeployMessage
+  object WorkerDecommissionSigReceived extends DeployMessage
 
   /**
    * A message sent from Worker to Master to tell Master that the Worker has started

core/src/main/scala/org/apache/spark/deploy/worker/Worker.scala

@@ -66,16 +66,17 @@ private[deploy] class Worker(
   Utils.checkHost(host)
   assert (port > 0)
 
-  // If worker decommissioning is enabled register a handler on PWR to shutdown.
+  // If worker decommissioning is enabled register a handler on the configured signal to shutdown.
   if (conf.get(config.DECOMMISSION_ENABLED)) {
-    logInfo("Registering SIGPWR handler to trigger decommissioning.")
-    SignalUtils.register("PWR", "Failed to register SIGPWR handler - " +
+    val signal = conf.get(config.Worker.WORKER_DECOMMISSION_SIGNAL)
+    logInfo(s"Registering SIG$signal handler to trigger decommissioning.")
+    SignalUtils.register(signal, s"Failed to register SIG$signal handler - " +
       "disabling worker decommission feature.") {
-       self.send(WorkerSigPWRReceived)
+       self.send(WorkerDecommissionSigReceived)
        true
     }
   } else {
-    logInfo("Worker decommissioning not enabled, SIGPWR will result in exiting.")
+    logInfo("Worker decommissioning not enabled.")
   }
 
   // A scheduled executor used to send messages at the specified time.
@@ -682,7 +683,7 @@ private[deploy] class Worker(
     case DecommissionWorker =>
       decommissionSelf()
 
-    case WorkerSigPWRReceived =>
+    case WorkerDecommissionSigReceived =>
       decommissionSelf()
       // Tell the Master that we are starting decommissioning
       // so it stops trying to launch executor/driver on us

core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala

@@ -82,9 +82,10 @@ private[spark] class CoarseGrainedExecutorBackend(
 
   override def onStart(): Unit = {
     if (env.conf.get(DECOMMISSION_ENABLED)) {
-      logInfo("Registering PWR handler to trigger decommissioning.")
-      SignalUtils.register("PWR", "Failed to register SIGPWR handler - " +
-        "disabling executor decommission feature.") (self.askSync[Boolean](ExecutorSigPWRReceived))
+      val signal = env.conf.get(EXECUTOR_DECOMMISSION_SIGNAL)
+      logInfo(s"Registering SIG$signal handler to trigger decommissioning.")
+      SignalUtils.register(signal, s"Failed to register SIG$signal handler - disabling" +
+        s" executor decommission feature.") (self.askSync[Boolean](ExecutorDecommissionSigReceived))
     }
 
     logInfo("Connecting to driver: " + driverUrl)
@@ -208,7 +209,7 @@ private[spark] class CoarseGrainedExecutorBackend(
   }
 
   override def receiveAndReply(context: RpcCallContext): PartialFunction[Any, Unit] = {
-    case ExecutorSigPWRReceived =>
+    case ExecutorDecommissionSigReceived =>
       var driverNotified = false
       try {
         driver.foreach { driverRef =>

core/src/main/scala/org/apache/spark/internal/config/Worker.scala

@@ -82,4 +82,11 @@ private[spark] object Worker {
       .version("2.0.2")
       .intConf
       .createWithDefault(100)
+
+  val WORKER_DECOMMISSION_SIGNAL =
+    ConfigBuilder("spark.worker.decommission.signal")
+      .doc("The signal that used to trigger the worker to start decommission.")
+      .version("3.2.0")
+      .stringConf
+      .createWithDefaultString("PWR")
 }

core/src/main/scala/org/apache/spark/internal/config/package.scala

@@ -1927,6 +1927,13 @@ package object config {
       .timeConf(TimeUnit.SECONDS)
       .createOptional
 
+  private[spark] val EXECUTOR_DECOMMISSION_SIGNAL =
+    ConfigBuilder("spark.executor.decommission.signal")
+      .doc("The signal that used to trigger the executor to start decommission.")
+      .version("3.2.0")
+      .stringConf
+      .createWithDefaultString("PWR")
+
   private[spark] val STAGING_DIR = ConfigBuilder("spark.yarn.stagingDir")
     .doc("Staging directory used while submitting applications.")
     .version("2.0.0")

core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedClusterMessage.scala

@@ -102,9 +102,9 @@ private[spark] object CoarseGrainedClusterMessages {
   // It's used for Standalone's cases, where decommission is triggered at MasterWebUI or Worker.
   object DecommissionExecutor extends CoarseGrainedClusterMessage
 
-  // A message that sent to the executor itself when it receives PWR signal,
+  // A message that sent to the executor itself when it receives a signal,
   // indicating the executor starts to decommission.
-  object ExecutorSigPWRReceived extends CoarseGrainedClusterMessage
+  object ExecutorDecommissionSigReceived extends CoarseGrainedClusterMessage
 
   case class RemoveWorker(workerId: String, host: String, message: String)
     extends CoarseGrainedClusterMessage