java.lang.NullPointerException: Attempt to invoke virtual method 'void java.net.Socket.close()' on a null object reference #957

wengbiancheng · 2019-12-09T14:58:53Z

Describe the bug
java.lang.NullPointerException: Attempt to invoke virtual method 'void java.net.Socket.close()' on a null object reference
I have encountered this error many times, but I cannot reproduce it because I found that the error seems to be caused by multi-threaded concurrency.
I found that socket.close () appears in two different threads.
One is the reconnect() and it will call the reset():

private void reset() {

	Thread current = Thread.currentThread();
	if (current == writeThread || current == connectReadThread) {
		throw new IllegalStateException("You cannot initialize a reconnect out of the websocket thread. Use reconnect in another thread to insure a successful cleanup.");
	}
	try {
		closeBlocking();
		if( writeThread != null ) {
			this.writeThread.interrupt();
			this.writeThread = null;
		}
		if( connectReadThread != null ) {
			this.connectReadThread.interrupt();
			this.connectReadThread = null;
		}
		this.draft.reset();
		if( this.socket != null ) {
			this.socket.close();
			this.socket = null;
		}
	} catch ( Exception e ) {
		onError( e );
		engine.closeConnection( CloseFrame.ABNORMAL_CLOSE, e.getMessage() );
		return;
	}
	connectLatch = new CountDownLatch( 1 );
	closeLatch = new CountDownLatch( 1 );
	this.engine = new WebSocketImpl( this, this.draft );
}

One is in the WebsocketWriteThread:

private class WebsocketWriteThread implements Runnable {


	@Override
	public void run() {
		Thread.currentThread().setName( "WebSocketWriteThread-" + Thread.currentThread().getId() );
		try {
			runWriteData();
		} catch ( IOException e ) {
			handleIOException( e );
		} finally {
			closeSocket();
			writeThread = null;
		}
	}

	/**
	 * Closing the socket
	 */
	private void closeSocket() {
		try {
			if( socket != null ) {
				socket.close();
			}
		} catch ( IOException ex ) {
			onWebsocketError( webSocketClient, ex );
		}
	}
}

Obviously the reconnect thread and the write thread are not the same thread.This reminds me of a piece of code I saw elsewhere.

public class GcsTest {

private static String mStr = null;

private static void printStrLength() {
    if (null != mStr) {
        int len = mStr.length();
        System.out.println("length = " + len);
    }
}

public static void main(String[] args) {
    GThreadA threadA = new GThreadA();
    GThreadB threadB = new GThreadB();
    threadA.start();
    threadB.start();
}

static class GThreadA extends Thread {
    @Override
    public void run() {
        while (true) {
            if (null == mStr) {
                mStr = "Gcs";
            } else {
                mStr = null;
            }
        }
    }
}

static class GThreadB extends Thread {
    @Override
    public void run() {
        while (true) {
            printStrLength();
        }
    }
}}

It will have a null pointer error.It may take some time to run before the error occurs.After threadB just judged if (null! = mStr), it switched to threadA. At this time, threadA also judged that mStr was not null, so it set mStr to null, and then switched to threadB. When threadB gets the length A null pointer exception occurred.

So when reconnect () happens, is it possible that there are some conditions that triggered closeSocket in writeThread.And when reconnectThread sets the socket to null, just writeThread switches to socket.close().So it happened a null pointer exception and WebsocketWriteThread does not catch null pointer exception,it only catches IOException,so the entire application crashed.

Environment(please complete the following information):

Version used:1.4.0
Java version:1.8.0_131
Operating System and version: Android 9

The text was updated successfully, but these errors were encountered:

StellaSong12 · 2020-01-10T08:21:57Z

same situation, there may should be thread locked
if( socket != null ) {
socket.close();
}

pawankgupta-se · 2020-05-11T15:22:43Z

Hi @marci4
I am also facing this issue, while client wants to disconnects sever getting this java.lang.NullPointerException. Find the below log. Let me know if you need more information

2020-05-11 20:45:56.998 18418-18701/com.example.websocket.receiver E/org.java_websocket.server.WebSocketServer: [WebSocketSelector-120593] WebSocketServer::handleFatal Shutdown due to fatal errorjava.lang.NullPointerException: ssl == null
        at com.android.org.conscrypt.NativeCrypto.SSL_set_timeout(Native Method)
        at com.android.org.conscrypt.SslWrapper.setTimeout(SslWrapper.java:101)
        at com.android.org.conscrypt.ActiveSession.invalidate(ActiveSession.java:147)
        at com.android.org.conscrypt.DelegatingExtendedSSLSession.invalidate(DelegatingExtendedSSLSession.java:120)
        at org.java_websocket.SSLSocketChannel2.close(SSLSocketChannel2.java:354)
        at org.java_websocket.WebSocketImpl.closeConnection(WebSocketImpl.java:511)
        at org.java_websocket.WebSocketImpl.closeConnection(WebSocketImpl.java:545)
        at org.java_websocket.server.WebSocketServer.handleIOException(WebSocketServer.java:608)
        at org.java_websocket.server.WebSocketServer.run(WebSocketServer.java:361)
        at java.lang.Thread.run(Thread.java:764)
2020-05-11 20:45:56.999 18418-18701/com.example.websocket.receiver W/System.err: java.lang.NullPointerException: ssl == null
2020-05-11 20:45:57.000 18418-18701/com.example.websocket.receiver W/System.err:     at com.android.org.conscrypt.NativeCrypto.SSL_set_timeout(Native Method)
2020-05-11 20:45:57.000 18418-18701/com.example.websocket.receiver W/System.err:     at com.android.org.conscrypt.SslWrapper.setTimeout(SslWrapper.java:101)
2020-05-11 20:45:57.000 18418-18701/com.example.websocket.receiver W/System.err:     at com.android.org.conscrypt.ActiveSession.invalidate(ActiveSession.java:147)
2020-05-11 20:45:57.001 18418-18701/com.example.websocket.receiver W/System.err:     at com.android.org.conscrypt.DelegatingExtendedSSLSession.invalidate(DelegatingExtendedSSLSession.java:120)
2020-05-11 20:45:57.001 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.SSLSocketChannel2.close(SSLSocketChannel2.java:354)
2020-05-11 20:45:57.001 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.WebSocketImpl.closeConnection(WebSocketImpl.java:511)
2020-05-11 20:45:57.002 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.WebSocketImpl.closeConnection(WebSocketImpl.java:545)
2020-05-11 20:45:57.002 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.server.WebSocketServer.handleIOException(WebSocketServer.java:608)
2020-05-11 20:45:57.002 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.server.WebSocketServer.run(WebSocketServer.java:361)
2020-05-11 20:45:57.003 18418-18701/com.example.websocket.receiver W/System.err:     at java.lang.Thread.run(Thread.java:764)
2020-05-11 20:45:57.004 18418-18701/com.example.websocket.receiver E/WebSocketReceiver: <1d711>  ssl == null
2020-05-11 20:45:57.014 18418-18701/com.example.websocket.receiver E/org.java_websocket.server.WebSocketServer: [WebSocketSelector-120593] WebSocketServer::handleFatal Interrupt during stopjava.lang.NullPointerException: ssl == null
        at com.android.org.conscrypt.NativeCrypto.SSL_set_timeout(Native Method)
        at com.android.org.conscrypt.SslWrapper.setTimeout(SslWrapper.java:101)
        at com.android.org.conscrypt.ActiveSession.invalidate(ActiveSession.java:147)
        at com.android.org.conscrypt.DelegatingExtendedSSLSession.invalidate(DelegatingExtendedSSLSession.java:120)
        at org.java_websocket.SSLSocketChannel2.close(SSLSocketChannel2.java:354)
        at org.java_websocket.WebSocketImpl.closeConnection(WebSocketImpl.java:511)
        at org.java_websocket.WebSocketImpl.closeConnection(WebSocketImpl.java:545)
        at org.java_websocket.server.WebSocketServer.handleIOException(WebSocketServer.java:608)
        at org.java_websocket.server.WebSocketServer.run(WebSocketServer.java:361)
        at java.lang.Thread.run(Thread.java:764)
2020-05-11 20:45:57.014 18418-18701/com.example.websocket.receiver W/System.err: java.lang.InterruptedException
2020-05-11 20:45:57.014 18418-18701/com.example.websocket.receiver W/System.err:     at java.lang.Object.wait(Native Method)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at java.lang.Object.wait(Object.java:422)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at java.lang.Thread.join(Thread.java:1262)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.server.WebSocketServer.stop(WebSocketServer.java:265)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.server.WebSocketServer.stop(WebSocketServer.java:270)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.server.WebSocketServer.handleFatal(WebSocketServer.java:635)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at org.java_websocket.server.WebSocketServer.run(WebSocketServer.java:371)
2020-05-11 20:45:57.015 18418-18701/com.example.websocket.receiver W/System.err:     at java.lang.Thread.run(Thread.java:764)
2020-05-11 20:45:57.016 18418-18701/com.example.websocket.receiver E/WebSocketReceiver: <1d711>  null
2020-05-11 20:45:57.017 18418-18701/com.example.websocket.receiver V/org.java_websocket.AbstractWebSocket: [WebSocketSelector-120593] AbstractWebSocket::stopConnectionLostTimer Connection lost timer stopped
a

marci4 · 2020-05-11T16:20:23Z

@pawankgupta-se looks like this issue is caused by the OS?

pawankgupta-se · 2020-05-11T17:09:03Z

@marci4 Not sure, but something related to Thread. But I have very simple code as of now. Not introducing any other thread from my side. And this issue is consistent.

marci4 · 2020-05-11T17:36:31Z

@pawankgupta-se there are a few other issues which you can find with a quick google e.g. square/okhttp#4260

runfengai · 2020-05-31T17:52:10Z

I hava the same problem. There are two solutions for me.

use UncaughtExceptionHandler to catch the exception.
Customize a class similar to WebSocketClient,and rewrite two methods: reset() & closeSocket() in WebsocketWriteThread

`

    //in custom WebSocketClient
    private final Object obj = new Object();
    private void reset() {
        //...
        synchronized (obj) {
            if (this.socket != null) {
                this.socket.close();
                this.socket = null;
            }
        }
        //...
    }

`

    //in WebsocketWriteThread,we rewrite
    private void closeSocket() {
        try {
            synchronized (obj) {
                if (socket != null) {
                    socket.close();
                }
            }
        } catch (IOException ex) {
            onWebsocketError(webSocketClient, ex);
        }
    }

`

hhyq520 · 2020-12-28T02:25:58Z

This problem has broken down a lot,I hope the author can solve this problem in the next version。

marci4 added the missing-information label Dec 24, 2019

marci4 added the up-for-grabs label Dec 28, 2020

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java.lang.NullPointerException: Attempt to invoke virtual method 'void java.net.Socket.close()' on a null object reference #957

java.lang.NullPointerException: Attempt to invoke virtual method 'void java.net.Socket.close()' on a null object reference #957

wengbiancheng commented Dec 9, 2019

StellaSong12 commented Jan 10, 2020

pawankgupta-se commented May 11, 2020 •

edited

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marci4 commented May 11, 2020

pawankgupta-se commented May 11, 2020 •

edited

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marci4 commented May 11, 2020

runfengai commented May 31, 2020 •

edited

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hhyq520 commented Dec 28, 2020

java.lang.NullPointerException: Attempt to invoke virtual method 'void java.net.Socket.close()' on a null object reference #957

java.lang.NullPointerException: Attempt to invoke virtual method 'void java.net.Socket.close()' on a null object reference #957

Comments

wengbiancheng commented Dec 9, 2019

StellaSong12 commented Jan 10, 2020

pawankgupta-se commented May 11, 2020 • edited Loading

marci4 commented May 11, 2020

pawankgupta-se commented May 11, 2020 • edited Loading

marci4 commented May 11, 2020

runfengai commented May 31, 2020 • edited Loading

hhyq520 commented Dec 28, 2020

pawankgupta-se commented May 11, 2020 •

edited

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pawankgupta-se commented May 11, 2020 •

edited

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runfengai commented May 31, 2020 •

edited

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