Socket.setSoTimeOut() i dont get it

Question

setSoTimeout
public void setSoTimeout(int timeout)
throws SocketExceptionEnable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a read() call on the InputStream associated with this Socket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the Socket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.
i dont get what it means when it says block? stop? And when it says it must be vailid prior to entering the block operation where abouts is that?
Thanks

Answer 1

Some Socket methods are designed to read a known number of bytes from an input stream. If those methods read less than the specified number of bytes, they will "block", which means that Socket is incapable of performing any other task until the read method completes. This can tie up system resources by keeping connections open, and might not be something desired. To avoid this, you would set the Socket's timeout value, and after the specified interval, if the Socket is still "blocked", it will timeout. When it times out, it throws an exception, but does not close the Socket or perform any Socket-related shutdown routines; it has not been "stopped". In order to shut down the Socket, you would have to write code to catch the appropriate exception, and explicitly close the Socket in that catch block. The explanation of the Socket's behavior is intended to let you know that the timeout process that happens when you set a timeout value greater than 0 is not designed to perform any resource deallocation or Socket close actions - that responsibility is left up to the programmer to handle or delegate as they see fit.
So basically, a Socket, when attempting to read from an input stream, will not be able to do anything else until that read completes - it "blocks" waiting for the read to complete. If the read does not complete, a method is needed to free up resources that may be associated with that Socket after a certain amount of time has passed (maybe the code is being run in an environment where system thread or connectivity resources are at a premium). By setting a timeout value on a Socket you can achieve this goal, but the responsibility for stopping or closing the Socket so that the appropriate resources are released lies with the programmer using the Socket.
Hope this isn't too incomprehensible; I recommend looking at Sun's tutorials and documentation related to Sockets for somewhat clearer explanations and code examples.
-dSn