Introduce a basic shared task pool, and use it for image decoding.

components/util/lib.rs

@@ -50,6 +50,7 @@ pub mod str;
 pub mod task;
 pub mod tid;
 pub mod time;
+pub mod taskpool;
 pub mod vec;
 pub mod workqueue;
 

components/util/taskpool.rs

@@ -0,0 +1,53 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! A load-balancing task pool.
+//!
+//! This differs in implementation from std::sync::TaskPool in that each job is
+//! up for grabs by any of the child tasks in the pool.
+//!
+
+//
+// This is based on the cargo task pool.
+// https://github.com/rust-lang/cargo/blob/master/src/cargo/util/pool.rs
+//
+// The only difference is that a normal channel is used instead of a sync_channel.
+//
+
+use std::sync::{Arc, Mutex};
+
+pub struct TaskPool {
+    tx: Sender<proc():Send>,
+}
+
+impl TaskPool {
+    pub fn new(tasks: uint) -> TaskPool {
+        assert!(tasks > 0);
+        let (tx, rx) = channel();
+
+        let state = Arc::new(Mutex::new(rx));
+
+        for _ in range(0, tasks) {
+            let state = state.clone();
+            spawn(proc() worker(&*state));
+        }
+
+        return TaskPool { tx: tx };
+
+        fn worker(rx: &Mutex<Receiver<proc():Send>>) {
+            loop {
+                let job = rx.lock().recv_opt();
+                match job {
+                    Ok(job) => job(),
+                    Err(..) => break,
+                }
+            }
+        }
+    }
+
+    pub fn execute(&self, job: proc():Send) {
+        self.tx.send(job);
+    }
+}
+