CODEWITHSUNDEEP
javasockets
altair211
altair211

Reputation: 97

thread hangs in socketRead0 Java

Basically I am trying to download a HTML content of a webpage. The method is very simple

        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
        BufferReader in = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
        String line;
        StringBuilder pageBuilder = new StringBuilder();
        while ((line = in.readLine()) != null) {
            pageBuilder.append(line + "\n");
        }

But sometimes the program just hangs. I tried to debug and the thread stack trace tells me that it hangs when calling to method SocketRead0. I tried to set readtimeout for the connection but it does not work. Any ideas on how can I detect and get through the block of SocketRead0 ?

Edit: It seems that the problem I actually have is that getReponseCode implicitly calls some getInputStream and some read() methods and then hangs at readSocket0(). Is there anyway I can make sure that the call to getReponseCode() will be safe ? Here is the stack trace of one thread hanging: Level 0 is the most recent call

thread 24stacktrace
        At 0level
        at method socketRead0
        at line -2
        At 1level
        at method read
        at line 129
        At 2level
        at method fill
        at line 218
        At 3level
        at method read1
        at line 258
        At 4level
        at method read
        at line 317
        At 5level
        at method parseHTTPHeader
        at line 687
        At 6level
        at method parseHTTP
        at line 632
        At 7level
        at method getInputStream
        at line 1200
        At 8level
        at method getResponseCode
        at line 379
        At 9level
        at method pushFinalRedirectedURL
        at line 132
        At 10level
        at method process
        at line 134
        At 11level
        at method run
        at line 40

Upvotes: 1

Views: 6654

Answers (4)

Renato Dinhani
Renato Dinhani

Reputation: 36746

I have this error too and solved it. This problem occurs because sometimes the software try to open a connection to a server that don't send an response, but don't give a error too.

The software still waiting the server answer, but it never comes.

To avoid this, you need to use the setConnectTimeout() method, so if the server don't send a answer in determined time, the connection will be aborted.

setConnectTimeout() reference

Upvotes: 2

DaveFar
DaveFar

Reputation: 7467

Just an addition to the previous answers about socket read being blocking: if method private native int socketRead0(FileDescriptor fd, byte b[], int off, int len, int timeout) throws IOException gets the timeout 0 (the default), no timeout is used. Hence it can block instead of throwing an IOException.

Upvotes: 1

Russell Durham
Russell Durham

Reputation: 624

You need to make sure your buffer has data to be read before you call the readline function. As Peter mentioned, SocketRead is a blocking function which means when it is called it will sit and wait until data is placed on the stream.

Try this:

while (in.ready()) {
    line = in.readLine();
    pageBuilder.append(line + "\n");
}

Here is the link to the BufferedReader API.

Upvotes: 2

Peter Lawrey
Peter Lawrey

Reputation: 533820

socket read is a blocking operation. It will block until there is more data, the end of stream is reached or the connection is closed.

Upvotes: 2

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