Please consider merging this fix: https://github.com/jenkinsci/github-plugin/pull/41

Fix was merged.

Sorry, did not read all the comments there.

It looks like the fix wasn't a good fix, and the source of the problem is still unknown.

We've worked around the problem by no longer using the github plugin for polling/queueing builds, so if this doesn't affect anyone else, it's no longer critical.

Might I suggest though that a better implementation of the polling feature would be to do github polling per repo instead of per job? We have hundreds of jobs using the same repo, and at the least, generating many fewer github-polling.log files would cause the unclosed filehandles to build up much more slowly.

If you can reproduce the problem, you can use the File Leak Detector plugin to pinpoint the cause.

I confirmed (/file-handles) that job-specific github-polling.log files were not being closed. Running garbage-collection (/gc) and then revisiting open file handles (/file-handles) showed that github-polling.log files from e.g., 45 minutes earlier were still open. Not using the github plugin for polling solved the problem well enough for our needs, and I don't plan to reproduce the problem. If you would like to close as "Won't fix" or "Can't reproduce" that's totally fine by me.

I installed the File Leak Detector plugin and activated it, but could not reproduce. Various accesses to github-polling.log all reliably close the file. However I also did not manage to get a hook added, despite using a valid API token to connect to my own repo:

java.io.FileNotFoundException: https://api.github.com/repos/jglick/simple-maven-project-with-tests/hooks
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1624)
	at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
	at org.kohsuke.github.Requester.parse(Requester.java:383)
	at org.kohsuke.github.Requester._to(Requester.java:185)
	at org.kohsuke.github.Requester.to(Requester.java:160)
	at org.kohsuke.github.GHRepository.createHook(GHRepository.java:754)
	at com.cloudbees.jenkins.GitHubPushTrigger.createJenkinsHook(GitHubPushTrigger.java:161)

Possibly a side effect of JENKINS-27041.