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POBlocking read from an input TCP socket
 

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    <p>I am currently working on a project for a distributed systems course where we have to implement a small sensor network in java. The sensors send the temperature every x seconds to an admin node (that is also a sensor), that records them. Upon request, an user node connects to the admin node and receives the mean of the detected temperatures. One of the issues is that the admin node can "fail". Before failing it actually sends a message to the user node, that needs to send a special packet to one of the other regular nodes that will become the new admin. The user node communicates with the admin with a TCP connection trough which it sends a "request" packet and receives a packet containing the temperature. I am currently using java.net.socket to implement this. </p> <p>The problem comes when the admin fails. In normal condition, could create a new thread that waits for this "fail" message from the server and then creates a new socket with the newly selected admin node. But, if the admin fails before it sends a message in response to a user request, the user node will be indefinitely waiting, because it is reading from an input stream.</p> <p>In particular, I am using the following lines to create the socket and the input stream:</p> <pre><code> this.socket = new Socket(this.serverAddress,this.serverPort); this.in = new DataInputStream(socket.getInputStream()); </code></pre> <p>and the following line in an while loop to read the response temperature.</p> <pre><code> String data = in.readUTF(); </code></pre> <p>How would you suggest to handle this situation?</p> <p>Also, I was thinking to use the same TCP connection for receiving the "fail" message from the admin node. How can I support this?</p>
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    1. CODoes the `Stream` not die when the admin node fails?
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    2. COAre you using a separate thread for the user node input stream? ; Add a timeout to the handler on the thread running the user node input stream.
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    3. CO@bmorris591 Yes, the stream dies when the TCP connection is over, so an exception is thrown. So I was thinking that, when I receive this exception I could start the procedure for electing the new admin. But, in normal cases, it is another thread that takes care of this, when it receives the "fail" message. So it could happen that the exception is thrown and it starts the procedure, then the "fail" is received and the procedure is started again
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