Question

I find myself having to explicitly call System.gc() in my Groovy scripts to prevent errors like the one below. Why doesn’t the garbage collector do this for me? Is there something I can do to cause it to garbage collect to prevent these errors (maybe JAVA_OPTS)?

Caught: java.util.concurrent.ExecutionException: org.codehaus.groovy.runtime.InvokerInvocationException: java.io.IOException: Cannot run program "ls": java.io.IOException: error=24, Too many open files
    at groovyx.gpars.GParsPool.runForkJoin(GParsPool.groovy:305)
    at UsageAnalyzer$_run_closure2_closure6.doCall(UsageAnalyzer.groovy:36)
    at groovyx.gpars.GParsPool$_withExistingPool_closure1.doCall(GParsPool.groovy:170)
    at groovyx.gpars.GParsPool$_withExistingPool_closure1.doCall(GParsPool.groovy)
    at groovyx.gpars.GParsPool.withExistingPool(GParsPool.groovy:169)
    at groovyx.gpars.GParsPool.withPool(GParsPool.groovy:141)
    at groovyx.gpars.GParsPool.withPool(GParsPool.groovy:117)
    at groovyx.gpars.GParsPool.withPool(GParsPool.groovy:96)
    at UsageAnalyzer$_run_closure2.doCall(<removed>)
    at UsageAnalyzer.run(<removed>)

This stack trace is from a parallel program but it happens in sequential programs as well.

Answer 1

As you’re using groovy, you can use the convenient methods such as File.withReader(), File.withWriter(), File.withInputStream(), InputStream.withStream() to ensure resources get closed cleanly. This is less cumbersome than using Java’s try .. finally idiom, as there’s not need to explicitly call close(), or declare a variable outside the try block.

e.g. to read from a file.

File f = new File('/mumble/mumble/')
f.withReader{ r -> 
   // do stuff with reader here
}