code: private boolean check(File fingerprintFile, TaskListener listener) {
          try {
              Fingerprint fp = loadFingerprint(fingerprintFile);
              if (fp == null || !fp.isAlive()) {
                  listener.getLogger().println("deleting obsolete " + fingerprintFile);
                  fingerprintFile.delete();
                  return true;
              } else {
                  // get the fingerprint in the official map so have the changes visible to Jenkins
                  // otherwise the mutation made in FingerprintMap can override our trimming.
                  fp = getFingerprint(fp);
                  return fp.trim();
              }
          } catch (IOException e) {
              Functions.printStackTrace(e, listener.error("Failed to process " + fingerprintFile));
              return false;
          }
      }
docs: Examines the file and returns true if a file was deleted.