parallel-search.rs

use std::comm::*;

use std::libc::funcs::posix88::unistd;

// this simulates a processing-intesive task.
fn test(x: bool) -> bool {
  unsafe {
    unistd::sleep(1);
  }

  x
}

// search through the given vec sequentially
fn search_seq(haystack: &[bool]) {
  for haystack.iter().advance |&x| {
    if test(x) {
      println("Found it!");
      return;
    } else {
      println("Not it.");
    }
  }
}

// search through the given vec in parallel
fn search_par(haystack: &[bool]) {
  // we'll use 4 tasks.

  // break our vector into 4 chunks
  // each tasks will operate on one of these chunks.
  let chunks = [
    haystack.slice(0,  12),
    haystack.slice(12, 24),
    haystack.slice(24, 36),
    haystack.slice(36, 48),
  ];

  // set up intertask communication
  let (port, chan) = stream();
  let chan = SharedChan::new(chan);

  // spawn the search subtasks
  for chunks.iter().advance |&chunk| {
    // this needs to be owned so that it can be passed into our closure.
    let chunk: ~[bool] = chunk.to_owned();

    let child_chan     = chan.clone();

    do spawn {
      // do a sequential search through this subtask's chunk
      for chunk.iter().advance |&x| {
        child_chan.send(test(x));

        // this seems to be necessary to wake up the main task
        std::task::yield();
      }
    }
  }

  // look at the results coming coming from each subtask
  loop {
    let result = port.recv();

    if result {
      // we're done. my hope is that exiting this function will kill the
      // subtasks.
      println("Found it!");
      return;
    } else {
      println("Not it.");
    }
  }
}

fn main() {
  let haystack = [
    false, false, false, false, false, false, false, false, false, false, false, false,
    false, false, false, false, false, false, false, false, false, false, false, false,
    false, false, false, false, false, false, false, false, false, false, false, false,
    false, false, false, false, true,  false, false, false, false, false, false, false
  ];

  //search_seq(haystack);

  search_par(haystack);
}