extra: Add an intrusive MPSC to be used soon

2 files changed, 140 insertions, 0 deletions

diff --git a/src/etc/licenseck.py b/src/etc/licenseck.py
index b5a721c03ff..afbf34d0753 100644
--- a/src/etc/licenseck.py
+++ b/src/etc/licenseck.py
@@ -41,6 +41,7 @@ exceptions = [
     "libstd/sync/mpsc_queue.rs", # BSD
     "libstd/sync/spsc_queue.rs", # BSD
     "libstd/sync/mpmc_bounded_queue.rs", # BSD
+    "libextra/sync/mpsc_intrusive.rs", # BSD
 ]
 
 def check_license(name, contents):
diff --git a/src/libextra/sync/mpsc_intrusive.rs b/src/libextra/sync/mpsc_intrusive.rs
new file mode 100644
index 00000000000..0f13a4980d9
--- /dev/null
+++ b/src/libextra/sync/mpsc_intrusive.rs
@@ -0,0 +1,139 @@
+/* Copyright (c) 2010-2011 Dmitry Vyukov. All rights reserved.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *    1. Redistributions of source code must retain the above copyright notice,
+ *       this list of conditions and the following disclaimer.
+ *
+ *    2. Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY DMITRY VYUKOV "AS IS" AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+ * EVENT SHALL DMITRY VYUKOV OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
+ * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * The views and conclusions contained in the software and documentation are
+ * those of the authors and should not be interpreted as representing official
+ * policies, either expressed or implied, of Dmitry Vyukov.
+ */
+
+//! A mostly lock-free multi-producer, single consumer queue.
+//!
+//! This module implements an intrusive MPSC queue. This queue is incredibly
+//! unsafe (due to use of unsafe pointers for nodes), and hence is not public.
+
+// http://www.1024cores.net/home/lock-free-algorithms
+//                         /queues/intrusive-mpsc-node-based-queue
+
+use std::cast;
+use std::sync::atomics;
+
+// NB: all links are done as AtomicUint instead of AtomicPtr to allow for static
+// initialization.
+
+pub struct Node<T> {
+    next: atomics::AtomicUint,
+    data: T,
+}
+
+pub struct DummyNode {
+    next: atomics::AtomicUint,
+}
+
+pub struct Queue<T> {
+    head: atomics::AtomicUint,
+    tail: *mut Node<T>,
+    stub: DummyNode,
+}
+
+impl<T: Send> Queue<T> {
+    pub fn new() -> Queue<T> {
+        Queue {
+            head: atomics::AtomicUint::new(0),
+            tail: 0 as *mut Node<T>,
+            stub: DummyNode {
+                next: atomics::AtomicUint::new(0),
+            },
+        }
+    }
+
+    pub unsafe fn push(&mut self, node: *mut Node<T>) {
+        (*node).next.store(0, atomics::Release);
+        let prev = self.head.swap(node as uint, atomics::AcqRel);
+
+        // Note that this code is slightly modified to allow static
+        // initialization of these queues with rust's flavor of static
+        // initialization.
+        if prev == 0 {
+            self.stub.next.store(node as uint, atomics::Release);
+        } else {
+            let prev = prev as *mut Node<T>;
+            (*prev).next.store(node as uint, atomics::Release);
+        }
+    }
+
+    /// You'll note that the other MPSC queue in std::sync is non-intrusive and
+    /// returns a `PopResult` here to indicate when the queue is inconsistent.
+    /// An "inconsistent state" in the other queue means that a pusher has
+    /// pushed, but it hasn't finished linking the rest of the chain.
+    ///
+    /// This queue also suffers from this problem, but I currently haven't been
+    /// able to detangle when this actually happens. This code is translated
+    /// verbatim from the website above, and is more complicated than the
+    /// non-intrusive version.
+    ///
+    /// Right now consumers of this queue must be ready for this fact. Just
+    /// because `pop` returns `None` does not mean that there is not data
+    /// on the queue.
+    pub unsafe fn pop(&mut self) -> Option<*mut Node<T>> {
+        let tail = self.tail;
+        let mut tail = if !tail.is_null() {tail} else {
+            cast::transmute(&self.stub)
+        };
+        let mut next = (*tail).next(atomics::Relaxed);
+        if tail as uint == &self.stub as *DummyNode as uint {
+            if next.is_null() {
+                return None;
+            }
+            self.tail = next;
+            tail = next;
+            next = (*next).next(atomics::Relaxed);
+        }
+        if !next.is_null() {
+            self.tail = next;
+            return Some(tail);
+        }
+        let head = self.head.load(atomics::Acquire) as *mut Node<T>;
+        if tail != head {
+            return None;
+        }
+        let stub = cast::transmute(&self.stub);
+        self.push(stub);
+        next = (*tail).next(atomics::Relaxed);
+        if !next.is_null() {
+            self.tail = next;
+            return Some(tail);
+        }
+        return None
+    }
+}
+
+impl<T: Send> Node<T> {
+    pub fn new(t: T) -> Node<T> {
+        Node {
+            data: t,
+            next: atomics::AtomicUint::new(0),
+        }
+    }
+    pub unsafe fn next(&mut self, ord: atomics::Ordering) -> *mut Node<T> {
+        cast::transmute::<uint, *mut Node<T>>(self.next.load(ord))
+    }
+}