lazy.rs.html -- source
Description: Source to the Rust file `src/libstd/io/lazy.rs`.
Keywords: rust, rustlang, rust-lang

     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62
    63
    64
    65
    66
    67
    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,
            }
        }

        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
        }
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result
+
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)