What happens to an instance of ServerSocket blocked inside accept(), when I drop all references to i
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by Hanno Fietz
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or by Hanno Fietz
Published on 2010-04-01T19:19:47Z
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2010/04/01
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In a multithreaded Java application, I just tracked down a strange-looking bug, realizing that what seemed to be happening was this:
- one of my objects was storing a reference to an instance of
ServerSocket - on startup, one thread would, in its main loop in
run(), callaccept()on the socket - while the socket was still waiting for a connection, another thread would try to restart the component
- under some conditions, the restart process missed the cleanup sequence before it reached the initialization sequence
- as a result, the reference to the socket was overwritten with a new instance, which then wasn't able to
bind()anymore - the socket which was blocking inside the
accept()wasn't accessible anymore, leaving a complete shutdown and restart of the application as the only way to get rid of it.
Which leaves me wondering: with no references left to the ServerSocket instance, what would free the socket for a new connection? At what point would the ServerSocket become garbage collected? In general, what are good practices I can follow to avoid this type of bug?
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