I wrote a small piece of code which basically listens to JMS queue and receives messages. The following 3 code snips shows what I wanted to do.
The snip on left is the improved and refactored code and the one on the right is the bad code.
In this following snip I tried to create a queue and receive messages in it.
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The mistake I did here, as can be seen in the right hand side is, I create the queue and also receive messages in it, both in the same method.
In the following snip, I am calling the method to receive messags in the queue but what I overlooked is that I am also creating the queue in it. This is the where the disaster is lurking.
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So even if I close session and connection in the following snip, it just closes the last connection.
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Whereas I have created hell lot of connections in snip-2, ( Notice the while loop, which was churning umpteen number of queue connections )
I am only closing the last connection in snip-3 which leaves thousands of connections opened in memory. This triggered garbage collection which took about 12-13% of CPU consistently even if nothing was processing in the system.
This demonstrates the side effects of trying to do too many things in a single method. Also it is very important to handle connections, whether databse / JMS / sockets very very carefully. This made me sleepless for a night.
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