mutex.rs

// Copyright 2014 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 libc;
use mem;

pub struct Mutex { inner: UnsafeCell<libc::pthread_mutex_t> }

#[inline]
pub unsafe fn raw(m: &Mutex) -> *mut libc::pthread_mutex_t {
    m.inner.get()
}

unsafe impl Send for Mutex {}
unsafe impl Sync for Mutex {}

#[allow(dead_code)] // sys isn't exported yet
impl Mutex {
    pub const fn new() -> Mutex {
        // Might be moved to a different address, so it is better to avoid
        // initialization of potentially opaque OS data before it landed.
        // Be very careful using this newly constructed `Mutex`, reentrant
        // locking is undefined behavior until `init` is called!
        Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
    }
    #[inline]
    pub unsafe fn init(&mut self) {
        // Issue #33770
        //
        // A pthread mutex initialized with PTHREAD_MUTEX_INITIALIZER will have
        // a type of PTHREAD_MUTEX_DEFAULT, which has undefined behavior if you
        // try to re-lock it from the same thread when you already hold a lock.
        //
        // In practice, glibc takes advantage of this undefined behavior to
        // implement hardware lock elision, which uses hardware transactional
        // memory to avoid acquiring the lock. While a transaction is in
        // progress, the lock appears to be unlocked. This isn't a problem for
        // other threads since the transactional memory will abort if a conflict
        // is detected, however no abort is generated if re-locking from the
        // same thread.
        //
        // Since locking the same mutex twice will result in two aliasing &mut
        // references, we instead create the mutex with type
        // PTHREAD_MUTEX_NORMAL which is guaranteed to deadlock if we try to
        // re-lock it from the same thread, thus avoiding undefined behavior.
        let mut attr: libc::pthread_mutexattr_t = mem::uninitialized();
        let r = libc::pthread_mutexattr_init(&mut attr);
        debug_assert_eq!(r, 0);
        let r = libc::pthread_mutexattr_settype(&mut attr, libc::PTHREAD_MUTEX_NORMAL);
        debug_assert_eq!(r, 0);
        let r = libc::pthread_mutex_init(self.inner.get(), &attr);
        debug_assert_eq!(r, 0);
        let r = libc::pthread_mutexattr_destroy(&mut attr);
        debug_assert_eq!(r, 0);
    }
    #[inline]
    pub unsafe fn lock(&self) {
        let r = libc::pthread_mutex_lock(self.inner.get());
        debug_assert_eq!(r, 0);
    }
    #[inline]
    pub unsafe fn unlock(&self) {
        let r = libc::pthread_mutex_unlock(self.inner.get());
        debug_assert_eq!(r, 0);
    }
    #[inline]
    pub unsafe fn try_lock(&self) -> bool {
        libc::pthread_mutex_trylock(self.inner.get()) == 0
    }
    #[inline]
    #[cfg(not(target_os = "dragonfly"))]
    pub unsafe fn destroy(&self) {
        let r = libc::pthread_mutex_destroy(self.inner.get());
        debug_assert_eq!(r, 0);
    }
    #[inline]
    #[cfg(target_os = "dragonfly")]
    pub unsafe fn destroy(&self) {
        use libc;
        let r = libc::pthread_mutex_destroy(self.inner.get());
        // On DragonFly pthread_mutex_destroy() returns EINVAL if called on a
        // mutex that was just initialized with libc::PTHREAD_MUTEX_INITIALIZER.
        // Once it is used (locked/unlocked) or pthread_mutex_init() is called,
        // this behaviour no longer occurs.
        debug_assert!(r == 0 || r == libc::EINVAL);
    }
}

pub struct ReentrantMutex { inner: UnsafeCell<libc::pthread_mutex_t> }

unsafe impl Send for ReentrantMutex {}
unsafe impl Sync for ReentrantMutex {}

impl ReentrantMutex {
    pub unsafe fn uninitialized() -> ReentrantMutex {
        ReentrantMutex { inner: mem::uninitialized() }
    }

    pub unsafe fn init(&mut self) {
        let mut attr: libc::pthread_mutexattr_t = mem::uninitialized();
        let result = libc::pthread_mutexattr_init(&mut attr as *mut _);
        debug_assert_eq!(result, 0);
        let result = libc::pthread_mutexattr_settype(&mut attr as *mut _,
                                                    libc::PTHREAD_MUTEX_RECURSIVE);
        debug_assert_eq!(result, 0);
        let result = libc::pthread_mutex_init(self.inner.get(), &attr as *const _);
        debug_assert_eq!(result, 0);
        let result = libc::pthread_mutexattr_destroy(&mut attr as *mut _);
        debug_assert_eq!(result, 0);
    }

    pub unsafe fn lock(&self) {
        let result = libc::pthread_mutex_lock(self.inner.get());
        debug_assert_eq!(result, 0);
    }

    #[inline]
    pub unsafe fn try_lock(&self) -> bool {
        libc::pthread_mutex_trylock(self.inner.get()) == 0
    }

    pub unsafe fn unlock(&self) {
        let result = libc::pthread_mutex_unlock(self.inner.get());
        debug_assert_eq!(result, 0);
    }

    pub unsafe fn destroy(&self) {
        let result = libc::pthread_mutex_destroy(self.inner.get());
        debug_assert_eq!(result, 0);
    }
}