From b0d16462ff4e214ade8357b1a9e40b943a74ae5b Mon Sep 17 00:00:00 2001
From: LalehB <laghabab@uci.edu>
Date: Sat, 27 Sep 2014 15:12:22 -0700
Subject: [PATCH 1/2] Adding back-off instead of busy-spinning

Also changed the total number of spinning similar to Cilk
---
 components/util/workqueue.rs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/components/util/workqueue.rs b/components/util/workqueue.rs
index 3a0b3e32f915..c2b81741e0c9 100644
--- a/components/util/workqueue.rs
+++ b/components/util/workqueue.rs
@@ -16,6 +16,7 @@ use std::rand::weak_rng;
 use std::sync::atomics::{AtomicUint, SeqCst};
 use std::sync::deque::{Abort, BufferPool, Data, Empty, Stealer, Worker};
 use std::task::TaskBuilder;
+use libc::funcs::posix88::unistd::usleep;
 
 /// A unit of work.
 ///
@@ -70,7 +71,7 @@ struct WorkerThread<QueueData, WorkData> {
     rng: XorShiftRng,
 }
 
-static SPIN_COUNT: uint = 1000;
+static SPIN_COUNT: uint = 128;
 
 impl<QueueData: Send, WorkData: Send> WorkerThread<QueueData, WorkData> {
     /// The main logic. This function starts up the worker and listens for
@@ -87,6 +88,7 @@ impl<QueueData: Send, WorkData: Send> WorkerThread<QueueData, WorkData> {
             // We're off!
             //
             // FIXME(pcwalton): Can't use labeled break or continue cross-crate due to a Rust bug.
+            let mut back_off_sleep = 0 as u32;
             loop {
                 // FIXME(pcwalton): Nasty workaround for the lack of labeled break/continue
                 // cross-crate.
@@ -107,10 +109,15 @@ impl<QueueData: Send, WorkData: Send> WorkerThread<QueueData, WorkData> {
                                 }
                                 Data(work) => {
                                     work_unit = work;
+                                    back_off_sleep = 0 as u32;
                                     break
                                 }
                             }
 
+                            if (i>100) {
+                                unsafe {usleep(back_off_sleep as u32)};
+                                back_off_sleep = back_off_sleep + 5;
+                            }
                             if i == SPIN_COUNT {
                                 match self.port.try_recv() {
                                     Ok(StopMsg) => {

From 293969cb7d0a97ad61f580d2e3f5f73b39740f71 Mon Sep 17 00:00:00 2001
From: Clark Gaebel <cgaebel@mozilla.com>
Date: Mon, 27 Oct 2014 14:19:44 -0700
Subject: [PATCH 2/2] Addressed code review comments.

---
 components/util/workqueue.rs | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/components/util/workqueue.rs b/components/util/workqueue.rs
index c2b81741e0c9..8708d8585a6c 100644
--- a/components/util/workqueue.rs
+++ b/components/util/workqueue.rs
@@ -71,7 +71,9 @@ struct WorkerThread<QueueData, WorkData> {
     rng: XorShiftRng,
 }
 
-static SPIN_COUNT: uint = 128;
+static SPIN_COUNT: u32 = 128;
+static SPINS_UNTIL_BACKOFF: u32 = 100;
+static BACKOFF_INCREMENT_IN_US: u32 = 5;
 
 impl<QueueData: Send, WorkData: Send> WorkerThread<QueueData, WorkData> {
     /// The main logic. This function starts up the worker and listens for
@@ -85,10 +87,11 @@ impl<QueueData: Send, WorkData: Send> WorkerThread<QueueData, WorkData> {
                 ExitMsg => return,
             };
 
+            let mut back_off_sleep = 0 as u32;
+
             // We're off!
             //
             // FIXME(pcwalton): Can't use labeled break or continue cross-crate due to a Rust bug.
-            let mut back_off_sleep = 0 as u32;
             loop {
                 // FIXME(pcwalton): Nasty workaround for the lack of labeled break/continue
                 // cross-crate.
@@ -114,10 +117,13 @@ impl<QueueData: Send, WorkData: Send> WorkerThread<QueueData, WorkData> {
                                 }
                             }
 
-                            if (i>100) {
-                                unsafe {usleep(back_off_sleep as u32)};
-                                back_off_sleep = back_off_sleep + 5;
+                            if i > SPINS_UNTIL_BACKOFF {
+                                unsafe {
+                                    usleep(back_off_sleep as u32);
+                                }
+                                back_off_sleep += BACKOFF_INCREMENT_IN_US;
                             }
+
                             if i == SPIN_COUNT {
                                 match self.port.try_recv() {
                                     Ok(StopMsg) => {