Java Socket Close Detection, Late FINs
This is a wierd problem I have been facing.
I understand that the only way that you can detect a remote client socket close(graceful only, NOT reset) in java is through reading (or writing )on a socket and detect IOException. For the final FIN/ACK the server should close the socket in the Exception handling.
I have a server that currently does this in two ways. I read on the socket for a message on the socket.
1. Using a DataInputStream (reads 2Bytes)
2. Using a BufferedReader (reads a line)
I have a client that opens n connections and closes them after 20 sec. I am doing 'netstat -al' to grep on the port to determine the status of connections on the server.
Problem 1.
When I am using BufferedReader, and open 100 connections to the server and close them (after 20 sec), I see that all the connections are closed in a matter of ms. (netstat -al| grep <portnum> shows no connections in CLOSE_WAIT). But on the other hand when I use DataInputStream some connections are lingering in CLOSE_WAIT for more than 20 seconds (this time increases with the number of connections).
Why is this?
Problem 2.
The DataInputStream.read(2bytearray) does not throw IOException when I close the socket on the client side. It blocks till I close the connection on the client side. When the connection is closed the read succeeds. This to me is really wierd. Is this not a bug?
I tried DataInputStream.readFully(2bytearray) and this works. This throws an Exception when the Client socket is closed.
Any light on these issues is extremely appreciated.
Thanks
Subu
Thanks for the response. That was a good point. I tried the BufferedInputStream also. This also does not seem really fast. For 100 connections it takes about 5 - 10 seconds. But even that is high. I dont think the server is a processing bottleneck. This is a production machine I am testing with. In any case I will do a top next to see that. (If 100 connections are high for the server, both the versions of the server should perform the sameway right)
Thanks
Subu
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