Method runGnuplot

src/tsd/GraphHandler.java:862–900

Runs Gnuplot in a subprocess to generate the graph. This function will block while Gnuplot is running. @param query The query being handled (for logging purposes). @param basepath The base path used for the Gnuplot files. @param plot The plot object to generate Gnuplot's input files

(final HttpQuery query,
                        final String basepath,
                        final Plot plot)

   * @throws GnuplotException if Gnuplot returns non-zero.
   */
  static int runGnuplot(final HttpQuery query,
                        final String basepath,
                        final Plot plot) throws IOException {
    final int nplotted = plot.dumpToFiles(basepath);
    final long start_time = System.nanoTime();
    final Process gnuplot = new ProcessBuilder(GNUPLOT,
      basepath + ".out", basepath + ".err", basepath + ".gnuplot").start();
    final int rv;
    try {
      rv = gnuplot.waitFor();  // Couldn't find how to do this asynchronously.
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();  // Restore the interrupted status.
      throw new IOException("interrupted", e);  // I hate checked exceptions.
    } finally {
      // We need to always destroy() the Process, otherwise we "leak" file
      // descriptors and pipes.  Unless I'm blind, this isn't actually
      // documented in the Javadoc of the !@#$%^ JDK, and in Java 6 there's no
      // way to ask the stupid-ass ProcessBuilder to not create fucking pipes.
      // I think when the GC kicks in the JVM may run some kind of a finalizer
      // that closes the pipes, because I've never seen this issue on long
      // running TSDs, except where ulimit -n was low (the default, 1024).
      gnuplot.destroy();
    }
    gnuplotlatency.add((int) ((System.nanoTime() - start_time) / 1000000));
    if (rv != 0) {
      final byte[] stderr = readFile(query, new File(basepath + ".err"),
                                     4096);
      // Sometimes Gnuplot will error out but still create the file.
      new File(basepath + ".png").delete();
      if (stderr == null) {
        throw new GnuplotException(rv);
      }
      throw new GnuplotException(new String(stderr));
    }
    // Remove the files for stderr/stdout if they're empty.
    deleteFileIfEmpty(basepath + ".out");
    deleteFileIfEmpty(basepath + ".err");
    return nplotted;
  }

  private static void deleteFileIfEmpty(final String path) {
    final File file = new File(path);