sccache on Jenkins

When using sccache on Jenkins one has to know about how to deal with the sccache server process. Unless specified otherwise, sccache uses port 4226. On invocation, sccache tries to connect to a sccache server instance on this port. If no server is running, a new instance is spawned. Jenkins tries to kill all spawned processes once a job is finished. This results in broken builds when two run in parallel and the first one who spawned the server is finished and the server is killed. The other job way be in contact with the server (e.g waiting for a cache response) and fail.

One option to solve this problem is to spawn a always running sccache server process by setting SCCACHE_IDLE_TIMEOUT to 0 and start the server beside Jenkins as a system service. This implies that all jobs use the same sccache configuration and share the statistics.

If a per-jobs sccache configuration is needed or preferred (e.g place a local disc cache in $WORKSPACE) the Port allocator plugin does a good job. It assigns a free and unique port number to a job by exporting a variable. Naming this variable SCCACHE_SERVER_PORT is enough to make the job spawn it's own sccache server that is save to terminate upon job termination. This approach has the advantage that each job (with a dedicated server instance) maintains it's own statistics that might be interesting upon job finalization.