demuxins streams

gistfile1.java

  // demuxing multithreaded sysout calls? why not ;)

  static class PerThreadOutputStream extends OutputStream {
    ThreadLocal<ByteArrayOutputStream> baos = new ThreadLocal<ByteArrayOutputStream>();
    private PrintStream sink;

    public PerThreadOutputStream(PrintStream sink) {
      this.sink = sink;
    }

    @Override
    public void write(int b) throws IOException {
      ByteArrayOutputStream os = baos.get();
      if (os == null) {
        os = new ByteArrayOutputStream();
        baos.set(os);
      }
      os.write(b);

      if (b == '\n') {
        flushToSink();
      }
    }

    private void flushToSink() throws IOException {
      synchronized (sink) {
        ByteArrayOutputStream os = baos.get();
        if (os != null) {
          sink.write(os.toByteArray());
          os.reset();
        }
      }
    }
  }

  public static void main(String[] args) {
    System.setOut(new PrintStream(new PerThreadOutputStream(System.out)));

    final CountDownLatch latch = new CountDownLatch(1);
    for (int i = 0; i < 10; i++) {
      final int j = i;
      Thread t = new Thread() {
        @Override
        public void run() {
          try {
            latch.await();
            for (int k = 0; k < 10; k++) {
              Thread.sleep(50);
              System.out.print(j);
            }
            System.out.println();
          } catch (Exception e) {
          }
        }
      };
      t.start();
    }
    latch.countDown();
  }