1 files changed, 68 insertions, 0 deletions
diff --git a/ctr-std/src/io/lazy.rs b/ctr-std/src/io/lazy.rs
new file mode 100644
index 0000000..ce205c3
--- /dev/null
+++ b/ctr-std/src/io/lazy.rs
@@ -0,0 +1,68 @@
+// Copyright 2015 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::Cell;
+use ptr;
+use sync::Arc;
+use sys_common;
+use sys_common::mutex::Mutex;
+
+pub struct Lazy<T> {
+    lock: Mutex,
+    ptr: Cell<*mut Arc<T>>,
+    init: fn() -> Arc<T>,
+}
+
+unsafe impl<T> Sync for Lazy<T> {}
+
+impl<T: Send + Sync + 'static> Lazy<T> {
+    pub const fn new(init: fn() -> Arc<T>) -> Lazy<T> {
+        Lazy {
+            lock: Mutex::new(),
+            ptr: Cell::new(ptr::null_mut()),
+            init: init
+        }
+    }
+
+    pub fn get(&'static self) -> Option<Arc<T>> {
+        unsafe {
+            self.lock.lock();
+            let ptr = self.ptr.get();
+            let ret = if ptr.is_null() {
+                Some(self.init())
+            } else if ptr as usize == 1 {
+                None
+            } else {
+                Some((*ptr).clone())
+            };
+            self.lock.unlock();
+            return ret
+        }
+    }
+
+    unsafe fn init(&'static self) -> Arc<T> {
+        // If we successfully register an at exit handler, then we cache the
+        // `Arc` allocation in our own internal box (it will get deallocated by
+        // the at exit handler). Otherwise we just return the freshly allocated
+        // `Arc`.
+        let registered = sys_common::at_exit(move || {
+            self.lock.lock();
+            let ptr = self.ptr.get();
+            self.ptr.set(1 as *mut _);
+            self.lock.unlock();
+            drop(Box::from_raw(ptr))
+        });
+        let ret = (self.init)();
+        if registered.is_ok() {
+            self.ptr.set(Box::into_raw(Box::new(ret.clone())));
+        }
+        ret
+    }
+}