Wednesday, June 25, 2014

One strange memory leak

I am working with some PDF processing library on a server side application. For some time now I have seen quite a huge memory leak and I started to investigate.
Apart from the obvious streams not closed I could see nothing wrong in the code.
However I decided to have a deeper look and i issued the following command

ltrace -fCS -p `pidof tomcat` 2>leak.out 1>&2

To my surprise I have seen lots of SYS_fork() in the output meaning that the library forked the entire appserver :) - WOW. It was not an disaster because fork() is COW so the memory is duplicated only when the children write something - but as this is an appserver it is kind of a heavy operation to fork it every time.

This also explained why the system seemed to leak memory. During the execution of the children processes new buffers are allocated and as the new processes have their own lifecycle it consumes quite a lot of memory.


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