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I'm using a library called PyBoof that makes use of py4j.

I'm trying to install it on a Centos 7 server but I'm getting an error when starting the Gateway Server. I know there're a lot of issues created for the same problem, but none of the solutions worked for me.

Reproducible code and the error I'm receiving is the following:

from py4j.java_gateway import JavaGateway
gateway = JavaGateway()
gateway.start()

Traceback (most recent call last):
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 982, in _get_connection
    connection = self.deque.pop()
IndexError: pop from an empty deque

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 1132, in start
    self.socket.connect((self.address, self.port))
ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/root/project/py4j_java_gateway.py", line 3, in <module>
    gateway.start()
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 1320, in __call__
    answer = self.gateway_client.send_command(command)
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 1036, in send_command
    connection = self._get_connection()
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 984, in _get_connection
    connection = self._create_connection()
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 990, in _create_connection
    connection.start()
  File "/root/project/venv/lib/python3.9/site-packages/py4j/java_gateway.py", line 1144, in start
    raise Py4JNetworkError(msg, e)
py4j.protocol.Py4JNetworkError: An error occurred while trying to connect to the Java server (127.0.0.1:25333)

Below are the software versions I'm running:

$ cat /etc/redhat-release
CentOS Linux release 7.9.2009 (Core)

$ python --version
Python 3.9.13

$ pip show py4j
Name: py4j
Version: 0.10.9.5
Summary: Enables Python programs to dynamically access arbitrary Java objects
Home-page: https://www.py4j.org/
Author: Barthelemy Dagenais
Author-email: barthelemy@infobart.com
License: BSD License
Location: /root/clab-services-api/venv/lib/python3.9/site-packages
Requires:
Required-by: PyBoof

$ java -version
java version "17.0.3.1" 2022-04-22 LTS
Java(TM) SE Runtime Environment (build 17.0.3.1+2-LTS-6)
Java HotSpot(TM) 64-Bit Server VM (build 17.0.3.1+2-LTS-6, mixed mode, sharing)

I don't know if it helps, but I've tried to build py4j jar, and there were additional errors when running the build tests:

$ /opt/apache-maven-3.8.6/bin/mvn install -X

...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  12.907 s
[INFO] Finished at: 2022-06-28T04:34:53+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test (default-test) on project py4j: There are test failures.
[ERROR]
[ERROR] Please refer to /root/py4j/py4j-java/target/surefire-reports for the individual test results.
[ERROR] -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test (default-test) on project py4j: There are test failures.

Please refer to /root/py4j/py4j-java/target/surefire-reports for the individual test results.
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:375)
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:351)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:171)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:163)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:294)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:960)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:293)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:196)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:568)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: org.apache.maven.plugin.MojoFailureException: There are test failures.

Please refer to /root/py4j/py4j-java/target/surefire-reports for the individual test results.
    at org.apache.maven.plugin.surefire.SurefireHelper.reportExecution (SurefireHelper.java:83)
    at org.apache.maven.plugin.surefire.SurefirePlugin.writeSummary (SurefirePlugin.java:176)
    at org.apache.maven.plugin.surefire.SurefirePlugin.handleSummary (SurefirePlugin.java:150)
    at org.apache.maven.plugin.surefire.AbstractSurefireMojo.executeAfterPreconditionsChecked (AbstractSurefireMojo.java:650)
    at org.apache.maven.plugin.surefire.AbstractSurefireMojo.execute (AbstractSurefireMojo.java:586)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:370)
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:351)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:171)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:163)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:294)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:960)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:293)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:196)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:568)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
[ERROR]
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

I've also tried to start the Gateway Server throw Java from this answer, but my Java knowledge is limited and I was unable to compile a jar for it.

import py4j.GatewayServer;

public class myTest {

    public static void main(String[] args) {
        myTest app = new myTest();
        // app is now the gateway.entry_point
        GatewayServer server = new GatewayServer(app);
        server.start();
    }
}

I've also tried installing the package py4j-java but was unable to run py4j.jar:

$ yum -y install py4j-java

$ java -jar /usr/share/java/py4j/py4j.jar
no main manifest attribute, in /usr/share/java/py4j/py4j.jar
CIRCLE
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  • So is your java server running? Of course you can not connect to it if it is not running. If you think that it is running, try to telnet to `127.0.0.1:25333` – Scary Wombat Jun 28 '22 at 03:59
  • @ScaryWombat It’s py4j who’s responsible for starting the server. Running telnet on 25333 doesn’t return anything – CIRCLE Jun 28 '22 at 04:15
  • so why does it say *py4j.protocol.Py4JNetworkError: An error occurred while trying to connect to the Java server (127.0.0.1:25333)* ? Anyway make sure that selinux is OK? – Scary Wombat Jun 28 '22 at 04:19
  • @ScaryWombat running `sestatus` says my SELinux is disabled. What do you mean by OK? Should it be enabled? If so, why? – CIRCLE Jun 28 '22 at 20:47
  • well if selinux is disabled then it will not be affecting it, so it should be OK. My opinion is that your java gateway server should be running before python, but that is the limit of my knowledge. – Scary Wombat Jun 28 '22 at 23:45

1 Answers1

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This problem was happening because the Java 17 version is incompatible with the implementation of Py4j in the project PyBoof.
See this issue for more information.

Installing Java 15 fixed the issue.

CIRCLE
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