Maven says "Too many open files in system" and fails

I’m trying to run PIT on my code base, but lately I’ve been getting a “Too many open files in system” error. I used to be able to avoid this by calling ulimit -n 2048 (see this StackOverflow question), but lately PIT wil simply hang after a while if I do that.

I’m running PIT from Maven on a 2015 MacBook. The problem occurs with PIT 1.1.4, 1.1.5 and 1.1.6 (haven’t tried any older versions).

Any ideas?

Here’s my Maven output when using 1.1.5:

~/workspaces/equalsverifier/equalsverifier (static-analysis)$ mvn org.pitest:pitest-maven:mutationCoverage
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=128m; support was removed in 8.0
[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building EqualsVerifier 1.7.4-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- pitest-maven:1.1.5:mutationCoverage (default-cli) @ equalsverifier ---
[INFO] Found plugin : Default csv report plugin
[INFO] Found plugin : Default xml report plugin
[INFO] Found plugin : Default html report plugin
[INFO] Found plugin : Default limit mutations plugin
[INFO] Found shared classpath plugin : Default mutation engine
[INFO] Adding org.pitest:pitest to SUT classpath
[INFO] Mutating from /Users/jqno/workspaces/equalsverifier/equalsverifier/target/classes
2:13:59 PM PIT >> INFO : Verbose logging is disabled. If you encounter an problem please enable it before reporting an issue.
2:13:59 PM PIT >> INFO : SLAVE : objc[53294]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/bin/java and /Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/lib/libinstrument.dylib. One of the two will be 
2:13:59 PM PIT >> INFO : SLAVE : used. Which one is undefined.

2:13:59 PM PIT >> INFO : Sending 293 test classes to slave
2:13:59 PM PIT >> INFO : Sent tests to slave
2:13:59 PM PIT >> INFO : SLAVE : 2:13:59 PM PIT >> INFO : Checking environment

2:14:00 PM PIT >> INFO : SLAVE : 2:14:00 PM PIT >> INFO : Found  632 tests

2:14:00 PM PIT >> INFO : SLAVE : 2:14:00 PM PIT >> INFO : Dependency analysis reduced number of potential tests by 0

2:14:00 PM PIT >> INFO : SLAVE : 2:14:00 PM PIT >> INFO : 632 tests received

|2:14:05 PM PIT >> INFO : Calculated coverage in 5 seconds.
2:14:05 PM PIT >> INFO : Created  56 mutation test units
stderr  : objc[53295]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/bin/java and /Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/lib/libinstrument.dylib. One of the two will be stderr  : used. Which one is undefined.
stderr  : 2:14:26 PM PIT >> WARNING : Error during mutation test
java.lang.UnsupportedOperationException: Tried to retrieve value but had None.
    at org.pitest.functional.Option$None.value(Option.java:89)
    at org.pitest.mutationtest.engine.gregor.GregorMutater.getMutstderr  : ation(GregorMutater.java:120)
    at org.pitest.mutationtest.execute.MutationTestWorker.processMutation(MutationTestWorker.java:91)
    at org.pitest.mutationtest.execute.MutationTestWorker.run(MutationTestWorker.java:77)
    at org.pitest.mutationtest.execute.Mutastderr  : tionTestSlave.run(MutationTestSlave.java:84)
    at org.pitest.mutationtest.execute.MutationTestSlave.main(MutationTestSlave.java:113)
2:14:26 PM PIT >> WARNING : Slave exited abnormally due to RUN_ERROR
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 28.433 s
[INFO] Finished at: 2015-09-14T14:14:26+02:00
[INFO] Final Memory: 12M/278M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.pitest:pitest-maven:1.1.5:mutationCoverage (default-cli) on project equalsverifier: Execution default-cli of goal org.pitest:pitest-maven:1.1.5:mutationCoverage failed: java.io.IOException: Cannot run program "/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/bin/java" (in directory "/Users/jqno/workspaces/equalsverifier/equalsverifier"): error=23, Too many open files in system
[ERROR] 
[ERROR] Please copy and paste the information and the complete stacktrace below when reporting an issue
[ERROR] VM : Java HotSpot(TM) 64-Bit Server VM
[ERROR] Vendor : Oracle Corporation
[ERROR] Version : 25.45-b02
[ERROR] Uptime : 29327
[ERROR] Input ->
[ERROR] 1 : -Xmx512m
[ERROR] 2 : -XX:MaxPermSize=128m
[ERROR] 3 : -Dclassworlds.conf=/usr/local/Cellar/maven/3.3.3/libexec/bin/m2.conf
[ERROR] 4 : -Dmaven.home=/usr/local/Cellar/maven/3.3.3/libexec
[ERROR] 5 : -Dmaven.multiModuleProjectDirectory=/Users/jqno/workspaces/equalsverifier/equalsverifier
[ERROR] BootClassPathSupported : true
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException

[hcoles]

@jqno Now reproduced - by running

mvn clean test

On that branch without invoking pitest.

Closing the stream seems to fix the issue.

[hcoles]

@jqno Glad I could help - think I made exactly the same mistake with classloader resources a while ago.