[SPARK-2313] Use socket to communicate GatewayServer port back to Python driver
This patch changes PySpark so that the GatewayServer's port is communicated back to the Python process that launches it over a local socket instead of a pipe. The old pipe-based approach was brittle and could fail if `spark-submit` printed unexpected to stdout. To accomplish this, I wrote a custom `PythonGatewayServer.main()` function to use in place of Py4J's `GatewayServer.main()`. Closes #3424. Author: Josh Rosen <joshrosen@databricks.com> Closes #4603 from JoshRosen/SPARK-2313 and squashes the following commits: 6a7740b [Josh Rosen] Remove EchoOutputThread since it's no longer needed 0db501f [Josh Rosen] Use select() so that we don't block if GatewayServer dies. 9bdb4b6 [Josh Rosen] Handle case where getListeningPort returns -1 3fb7ed1 [Josh Rosen] Remove stdout=PIPE 2458934 [Josh Rosen] Use underscore to mark env var. as private d12c95d [Josh Rosen] Use Logging and Utils.tryOrExit() e5f9730 [Josh Rosen] Wrap everything in a giant try-block 2f70689 [Josh Rosen] Use stdin PIPE to share fate with driver 8bf956e [Josh Rosen] Initial cut at passing Py4J gateway port back to driver via socket
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Josh Rosen
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.spark.api.python
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import java.io.DataOutputStream
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import java.net.Socket
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import py4j.GatewayServer
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import org.apache.spark.Logging
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import org.apache.spark.util.Utils
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/**
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* Process that starts a Py4J GatewayServer on an ephemeral port and communicates the bound port
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* back to its caller via a callback port specified by the caller.
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*
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* This process is launched (via SparkSubmit) by the PySpark driver (see java_gateway.py).
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*/
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private[spark] object PythonGatewayServer extends Logging {
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def main(args: Array[String]): Unit = Utils.tryOrExit {
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// Start a GatewayServer on an ephemeral port
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val gatewayServer: GatewayServer = new GatewayServer(null, 0)
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gatewayServer.start()
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val boundPort: Int = gatewayServer.getListeningPort
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if (boundPort == -1) {
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logError("GatewayServer failed to bind; exiting")
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System.exit(1)
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} else {
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logDebug(s"Started PythonGatewayServer on port $boundPort")
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}
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// Communicate the bound port back to the caller via the caller-specified callback port
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val callbackHost = sys.env("_PYSPARK_DRIVER_CALLBACK_HOST")
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val callbackPort = sys.env("_PYSPARK_DRIVER_CALLBACK_PORT").toInt
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logDebug(s"Communicating GatewayServer port to Python driver at $callbackHost:$callbackPort")
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val callbackSocket = new Socket(callbackHost, callbackPort)
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val dos = new DataOutputStream(callbackSocket.getOutputStream)
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dos.writeInt(boundPort)
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dos.close()
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callbackSocket.close()
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// Exit on EOF or broken pipe to ensure that this process dies when the Python driver dies:
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while (System.in.read() != -1) {
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// Do nothing
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}
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logDebug("Exiting due to broken pipe from Python driver")
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System.exit(0)
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}
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}
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@ -39,7 +39,6 @@ import org.apache.ivy.plugins.resolver.{ChainResolver, IBiblioResolver}
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import org.apache.spark.SPARK_VERSION
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import org.apache.spark.deploy.rest._
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import org.apache.spark.executor._
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import org.apache.spark.util.{ChildFirstURLClassLoader, MutableURLClassLoader, Utils}
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/**
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@ -284,8 +283,7 @@ object SparkSubmit {
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// If we're running a python app, set the main class to our specific python runner
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if (args.isPython && deployMode == CLIENT) {
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if (args.primaryResource == PYSPARK_SHELL) {
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args.mainClass = "py4j.GatewayServer"
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args.childArgs = ArrayBuffer("--die-on-broken-pipe", "0")
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args.mainClass = "org.apache.spark.api.python.PythonGatewayServer"
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} else {
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// If a python file is provided, add it to the child arguments and list of files to deploy.
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// Usage: PythonAppRunner <main python file> <extra python files> [app arguments]
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@ -17,19 +17,20 @@
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import atexit
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import os
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import sys
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import select
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import signal
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import shlex
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import socket
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import platform
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from subprocess import Popen, PIPE
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from threading import Thread
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from py4j.java_gateway import java_import, JavaGateway, GatewayClient
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from pyspark.serializers import read_int
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def launch_gateway():
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SPARK_HOME = os.environ["SPARK_HOME"]
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gateway_port = -1
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if "PYSPARK_GATEWAY_PORT" in os.environ:
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gateway_port = int(os.environ["PYSPARK_GATEWAY_PORT"])
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else:
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@ -41,36 +42,42 @@ def launch_gateway():
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submit_args = submit_args if submit_args is not None else ""
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submit_args = shlex.split(submit_args)
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command = [os.path.join(SPARK_HOME, script)] + submit_args + ["pyspark-shell"]
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# Start a socket that will be used by PythonGatewayServer to communicate its port to us
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callback_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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callback_socket.bind(('127.0.0.1', 0))
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callback_socket.listen(1)
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callback_host, callback_port = callback_socket.getsockname()
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env = dict(os.environ)
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env['_PYSPARK_DRIVER_CALLBACK_HOST'] = callback_host
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env['_PYSPARK_DRIVER_CALLBACK_PORT'] = str(callback_port)
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# Launch the Java gateway.
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# We open a pipe to stdin so that the Java gateway can die when the pipe is broken
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if not on_windows:
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# Don't send ctrl-c / SIGINT to the Java gateway:
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def preexec_func():
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signal.signal(signal.SIGINT, signal.SIG_IGN)
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env = dict(os.environ)
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env["IS_SUBPROCESS"] = "1" # tell JVM to exit after python exits
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proc = Popen(command, stdout=PIPE, stdin=PIPE, preexec_fn=preexec_func, env=env)
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proc = Popen(command, stdin=PIPE, preexec_fn=preexec_func, env=env)
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else:
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# preexec_fn not supported on Windows
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proc = Popen(command, stdout=PIPE, stdin=PIPE)
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proc = Popen(command, stdin=PIPE, env=env)
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try:
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# Determine which ephemeral port the server started on:
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gateway_port = proc.stdout.readline()
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gateway_port = int(gateway_port)
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except ValueError:
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# Grab the remaining lines of stdout
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(stdout, _) = proc.communicate()
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exit_code = proc.poll()
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error_msg = "Launching GatewayServer failed"
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error_msg += " with exit code %d!\n" % exit_code if exit_code else "!\n"
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error_msg += "Warning: Expected GatewayServer to output a port, but found "
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if gateway_port == "" and stdout == "":
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error_msg += "no output.\n"
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else:
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error_msg += "the following:\n\n"
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error_msg += "--------------------------------------------------------------\n"
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error_msg += gateway_port + stdout
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error_msg += "--------------------------------------------------------------\n"
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raise Exception(error_msg)
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gateway_port = None
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# We use select() here in order to avoid blocking indefinitely if the subprocess dies
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# before connecting
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while gateway_port is None and proc.poll() is None:
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timeout = 1 # (seconds)
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readable, _, _ = select.select([callback_socket], [], [], timeout)
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if callback_socket in readable:
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gateway_connection = callback_socket.accept()[0]
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# Determine which ephemeral port the server started on:
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gateway_port = read_int(gateway_connection.makefile())
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gateway_connection.close()
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callback_socket.close()
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if gateway_port is None:
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raise Exception("Java gateway process exited before sending the driver its port number")
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# In Windows, ensure the Java child processes do not linger after Python has exited.
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# In UNIX-based systems, the child process can kill itself on broken pipe (i.e. when
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@ -88,21 +95,6 @@ def launch_gateway():
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Popen(["cmd", "/c", "taskkill", "/f", "/t", "/pid", str(proc.pid)])
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atexit.register(killChild)
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# Create a thread to echo output from the GatewayServer, which is required
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# for Java log output to show up:
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class EchoOutputThread(Thread):
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def __init__(self, stream):
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Thread.__init__(self)
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self.daemon = True
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self.stream = stream
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def run(self):
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while True:
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line = self.stream.readline()
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sys.stderr.write(line)
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EchoOutputThread(proc.stdout).start()
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# Connect to the gateway
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gateway = JavaGateway(GatewayClient(port=gateway_port), auto_convert=False)
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