1 files changed, 127 insertions, 0 deletions
diff --git a/ctr-std/src/sys/horizon/rwlock.rs b/ctr-std/src/sys/horizon/rwlock.rs
new file mode 100644
index 0000000..4a802e9
--- /dev/null
+++ b/ctr-std/src/sys/horizon/rwlock.rs
@@ -0,0 +1,127 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use cell::UnsafeCell;
+use super::mutex::Mutex;
+use super::condvar::Condvar;
+
+// A simple read-preferring RWLock implementation that I found on wikipedia <.<
+pub struct RWLock {
+    mutex: Mutex,
+    cvar: Condvar,
+    reader_count: UnsafeCell<u32>, 
+    writer_active: UnsafeCell<bool>,
+}
+
+unsafe impl Send for RWLock {}
+unsafe impl Sync for RWLock {}
+
+impl RWLock {
+    pub const fn new() -> RWLock {
+        RWLock {
+            mutex: Mutex::new(),
+            cvar: Condvar::new(),
+            reader_count: UnsafeCell::new(0),
+            writer_active: UnsafeCell::new(false),
+        }
+    }
+
+    #[inline]
+    pub unsafe fn read(&self) {
+        self.mutex.lock();
+
+        while *self.writer_active.get() {
+            self.cvar.wait(&self.mutex);
+        }
+
+        assert!(*self.reader_count.get() != u32::max_value());
+        *self.reader_count.get() += 1;
+
+        self.mutex.unlock();
+    }
+
+    #[inline]
+    pub unsafe fn try_read(&self) -> bool {
+        if !self.mutex.try_lock() {
+            return false
+        }
+
+        while *self.writer_active.get() {
+            self.cvar.wait(&self.mutex);
+        }
+
+        assert!(*self.reader_count.get() != u32::max_value());
+        *self.reader_count.get() += 1;
+
+        self.mutex.unlock();
+        true
+    }
+
+    #[inline]
+    pub unsafe fn write(&self) {
+        self.mutex.lock();
+
+        while *self.writer_active.get() || *self.reader_count.get() > 0 {
+            self.cvar.wait(&self.mutex);
+        }
+
+        *self.writer_active.get() = true;
+
+        self.mutex.unlock();
+    }
+
+    #[inline]
+    pub unsafe fn try_write(&self) -> bool {
+        if !self.mutex.try_lock() {
+            return false;
+        }
+
+        while *self.writer_active.get() || *self.reader_count.get() > 0 {
+            self.cvar.wait(&self.mutex);
+        }
+
+        *self.writer_active.get() = true;
+
+        self.mutex.unlock();
+        true
+    }
+
+    #[inline]
+    pub unsafe fn read_unlock(&self) {
+        self.mutex.lock();
+
+        *self.reader_count.get() -= 1;
+
+        if *self.reader_count.get() == 0 {
+            self.cvar.notify_one()
+        }
+
+        self.mutex.unlock();
+    }
+
+    #[inline]
+    pub unsafe fn write_unlock(&self) {
+        self.mutex.lock();
+
+        *self.writer_active.get() = false;
+
+        self.cvar.notify_all();
+
+        self.mutex.unlock();
+    }
+
+    #[inline]
+    pub unsafe fn destroy(&self) {
+        self.mutex.destroy();
+        self.cvar.destroy();
+        *self.reader_count.get() = 0;
+        *self.writer_active.get() = false;
+    }
+}