library/std/src/sys/sgx/mutex.rs

   1 use super::waitqueue::{try_lock_or_false, SpinMutex, WaitQueue, WaitVariable};
   2 use crate::sys_common::lazy_box::{LazyBox, LazyInit};
   3
   4 pub struct Mutex {
   5     inner: SpinMutex<WaitVariable<bool>>,
   6 }
   7
   8 // not movable: see UnsafeList implementation
   9 pub(crate) type MovableMutex = LazyBox<Mutex>;
  10
  11 impl LazyInit for Mutex {
  12     fn init() -> Box<Self> {
  13         Box::new(Self::new())
  14     }
  15 }
  16
  17 // Implementation according to “Operating Systems: Three Easy Pieces”, chapter 28
  18 impl Mutex {
  19     pub const fn new() -> Mutex {
  20         Mutex { inner: SpinMutex::new(WaitVariable::new(false)) }
  21     }
  22
  23     #[inline]
  24     pub unsafe fn lock(&self) {
  25         let mut guard = self.inner.lock();
  26         if *guard.lock_var() {
  27             // Another thread has the lock, wait
  28             WaitQueue::wait(guard, || {})
  29         // Another thread has passed the lock to us
  30         } else {
  31             // We are just now obtaining the lock
  32             *guard.lock_var_mut() = true;
  33         }
  34     }
  35
  36     #[inline]
  37     pub unsafe fn unlock(&self) {
  38         let guard = self.inner.lock();
  39         if let Err(mut guard) = WaitQueue::notify_one(guard) {
  40             // No other waiters, unlock
  41             *guard.lock_var_mut() = false;
  42         } else {
  43             // There was a thread waiting, just pass the lock
  44         }
  45     }
  46
  47     #[inline]
  48     pub unsafe fn try_lock(&self) -> bool {
  49         let mut guard = try_lock_or_false!(self.inner);
  50         if *guard.lock_var() {
  51             // Another thread has the lock
  52             false
  53         } else {
  54             // We are just now obtaining the lock
  55             *guard.lock_var_mut() = true;
  56             true
  57         }
  58     }
  59 }