diff options
Diffstat (limited to '')
| -rw-r--r-- | library/std/src/sync/mpsc/oneshot.rs | 315 |
1 files changed, 0 insertions, 315 deletions
diff --git a/library/std/src/sync/mpsc/oneshot.rs b/library/std/src/sync/mpsc/oneshot.rs deleted file mode 100644 index 0e259b8ae..000000000 --- a/library/std/src/sync/mpsc/oneshot.rs +++ /dev/null @@ -1,315 +0,0 @@ -/// Oneshot channels/ports -/// -/// This is the initial flavor of channels/ports used for comm module. This is -/// an optimization for the one-use case of a channel. The major optimization of -/// this type is to have one and exactly one allocation when the chan/port pair -/// is created. -/// -/// Another possible optimization would be to not use an Arc box because -/// in theory we know when the shared packet can be deallocated (no real need -/// for the atomic reference counting), but I was having trouble how to destroy -/// the data early in a drop of a Port. -/// -/// # Implementation -/// -/// Oneshots are implemented around one atomic usize variable. This variable -/// indicates both the state of the port/chan but also contains any threads -/// blocked on the port. All atomic operations happen on this one word. -/// -/// In order to upgrade a oneshot channel, an upgrade is considered a disconnect -/// on behalf of the channel side of things (it can be mentally thought of as -/// consuming the port). This upgrade is then also stored in the shared packet. -/// The one caveat to consider is that when a port sees a disconnected channel -/// it must check for data because there is no "data plus upgrade" state. -pub use self::Failure::*; -use self::MyUpgrade::*; -pub use self::UpgradeResult::*; - -use crate::cell::UnsafeCell; -use crate::ptr; -use crate::sync::atomic::{AtomicPtr, Ordering}; -use crate::sync::mpsc::blocking::{self, SignalToken}; -use crate::sync::mpsc::Receiver; -use crate::time::Instant; - -// Various states you can find a port in. -const EMPTY: *mut u8 = ptr::invalid_mut::<u8>(0); // initial state: no data, no blocked receiver -const DATA: *mut u8 = ptr::invalid_mut::<u8>(1); // data ready for receiver to take -const DISCONNECTED: *mut u8 = ptr::invalid_mut::<u8>(2); // channel is disconnected OR upgraded -// Any other value represents a pointer to a SignalToken value. The -// protocol ensures that when the state moves *to* a pointer, -// ownership of the token is given to the packet, and when the state -// moves *from* a pointer, ownership of the token is transferred to -// whoever changed the state. - -pub struct Packet<T> { - // Internal state of the chan/port pair (stores the blocked thread as well) - state: AtomicPtr<u8>, - // One-shot data slot location - data: UnsafeCell<Option<T>>, - // when used for the second time, a oneshot channel must be upgraded, and - // this contains the slot for the upgrade - upgrade: UnsafeCell<MyUpgrade<T>>, -} - -pub enum Failure<T> { - Empty, - Disconnected, - Upgraded(Receiver<T>), -} - -pub enum UpgradeResult { - UpSuccess, - UpDisconnected, - UpWoke(SignalToken), -} - -enum MyUpgrade<T> { - NothingSent, - SendUsed, - GoUp(Receiver<T>), -} - -impl<T> Packet<T> { - pub fn new() -> Packet<T> { - Packet { - data: UnsafeCell::new(None), - upgrade: UnsafeCell::new(NothingSent), - state: AtomicPtr::new(EMPTY), - } - } - - pub fn send(&self, t: T) -> Result<(), T> { - unsafe { - // Sanity check - match *self.upgrade.get() { - NothingSent => {} - _ => panic!("sending on a oneshot that's already sent on "), - } - assert!((*self.data.get()).is_none()); - ptr::write(self.data.get(), Some(t)); - ptr::write(self.upgrade.get(), SendUsed); - - match self.state.swap(DATA, Ordering::SeqCst) { - // Sent the data, no one was waiting - EMPTY => Ok(()), - - // Couldn't send the data, the port hung up first. Return the data - // back up the stack. - DISCONNECTED => { - self.state.swap(DISCONNECTED, Ordering::SeqCst); - ptr::write(self.upgrade.get(), NothingSent); - Err((&mut *self.data.get()).take().unwrap()) - } - - // Not possible, these are one-use channels - DATA => unreachable!(), - - // There is a thread waiting on the other end. We leave the 'DATA' - // state inside so it'll pick it up on the other end. - ptr => { - SignalToken::from_raw(ptr).signal(); - Ok(()) - } - } - } - } - - // Just tests whether this channel has been sent on or not, this is only - // safe to use from the sender. - pub fn sent(&self) -> bool { - unsafe { !matches!(*self.upgrade.get(), NothingSent) } - } - - pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure<T>> { - // Attempt to not block the thread (it's a little expensive). If it looks - // like we're not empty, then immediately go through to `try_recv`. - if self.state.load(Ordering::SeqCst) == EMPTY { - let (wait_token, signal_token) = blocking::tokens(); - let ptr = unsafe { signal_token.to_raw() }; - - // race with senders to enter the blocking state - if self.state.compare_exchange(EMPTY, ptr, Ordering::SeqCst, Ordering::SeqCst).is_ok() { - if let Some(deadline) = deadline { - let timed_out = !wait_token.wait_max_until(deadline); - // Try to reset the state - if timed_out { - self.abort_selection().map_err(Upgraded)?; - } - } else { - wait_token.wait(); - debug_assert!(self.state.load(Ordering::SeqCst) != EMPTY); - } - } else { - // drop the signal token, since we never blocked - drop(unsafe { SignalToken::from_raw(ptr) }); - } - } - - self.try_recv() - } - - pub fn try_recv(&self) -> Result<T, Failure<T>> { - unsafe { - match self.state.load(Ordering::SeqCst) { - EMPTY => Err(Empty), - - // We saw some data on the channel, but the channel can be used - // again to send us an upgrade. As a result, we need to re-insert - // into the channel that there's no data available (otherwise we'll - // just see DATA next time). This is done as a cmpxchg because if - // the state changes under our feet we'd rather just see that state - // change. - DATA => { - let _ = self.state.compare_exchange( - DATA, - EMPTY, - Ordering::SeqCst, - Ordering::SeqCst, - ); - match (&mut *self.data.get()).take() { - Some(data) => Ok(data), - None => unreachable!(), - } - } - - // There's no guarantee that we receive before an upgrade happens, - // and an upgrade flags the channel as disconnected, so when we see - // this we first need to check if there's data available and *then* - // we go through and process the upgrade. - DISCONNECTED => match (&mut *self.data.get()).take() { - Some(data) => Ok(data), - None => match ptr::replace(self.upgrade.get(), SendUsed) { - SendUsed | NothingSent => Err(Disconnected), - GoUp(upgrade) => Err(Upgraded(upgrade)), - }, - }, - - // We are the sole receiver; there cannot be a blocking - // receiver already. - _ => unreachable!(), - } - } - } - - // Returns whether the upgrade was completed. If the upgrade wasn't - // completed, then the port couldn't get sent to the other half (it will - // never receive it). - pub fn upgrade(&self, up: Receiver<T>) -> UpgradeResult { - unsafe { - let prev = match *self.upgrade.get() { - NothingSent => NothingSent, - SendUsed => SendUsed, - _ => panic!("upgrading again"), - }; - ptr::write(self.upgrade.get(), GoUp(up)); - - match self.state.swap(DISCONNECTED, Ordering::SeqCst) { - // If the channel is empty or has data on it, then we're good to go. - // Senders will check the data before the upgrade (in case we - // plastered over the DATA state). - DATA | EMPTY => UpSuccess, - - // If the other end is already disconnected, then we failed the - // upgrade. Be sure to trash the port we were given. - DISCONNECTED => { - ptr::replace(self.upgrade.get(), prev); - UpDisconnected - } - - // If someone's waiting, we gotta wake them up - ptr => UpWoke(SignalToken::from_raw(ptr)), - } - } - } - - pub fn drop_chan(&self) { - match self.state.swap(DISCONNECTED, Ordering::SeqCst) { - DATA | DISCONNECTED | EMPTY => {} - - // If someone's waiting, we gotta wake them up - ptr => unsafe { - SignalToken::from_raw(ptr).signal(); - }, - } - } - - pub fn drop_port(&self) { - match self.state.swap(DISCONNECTED, Ordering::SeqCst) { - // An empty channel has nothing to do, and a remotely disconnected - // channel also has nothing to do b/c we're about to run the drop - // glue - DISCONNECTED | EMPTY => {} - - // There's data on the channel, so make sure we destroy it promptly. - // This is why not using an arc is a little difficult (need the box - // to stay valid while we take the data). - DATA => unsafe { - (&mut *self.data.get()).take().unwrap(); - }, - - // We're the only ones that can block on this port - _ => unreachable!(), - } - } - - //////////////////////////////////////////////////////////////////////////// - // select implementation - //////////////////////////////////////////////////////////////////////////// - - // Remove a previous selecting thread from this port. This ensures that the - // blocked thread will no longer be visible to any other threads. - // - // The return value indicates whether there's data on this port. - pub fn abort_selection(&self) -> Result<bool, Receiver<T>> { - let state = match self.state.load(Ordering::SeqCst) { - // Each of these states means that no further activity will happen - // with regard to abortion selection - s @ (EMPTY | DATA | DISCONNECTED) => s, - - // If we've got a blocked thread, then use an atomic to gain ownership - // of it (may fail) - ptr => self - .state - .compare_exchange(ptr, EMPTY, Ordering::SeqCst, Ordering::SeqCst) - .unwrap_or_else(|x| x), - }; - - // Now that we've got ownership of our state, figure out what to do - // about it. - match state { - EMPTY => unreachable!(), - // our thread used for select was stolen - DATA => Ok(true), - - // If the other end has hung up, then we have complete ownership - // of the port. First, check if there was data waiting for us. This - // is possible if the other end sent something and then hung up. - // - // We then need to check to see if there was an upgrade requested, - // and if so, the upgraded port needs to have its selection aborted. - DISCONNECTED => unsafe { - if (*self.data.get()).is_some() { - Ok(true) - } else { - match ptr::replace(self.upgrade.get(), SendUsed) { - GoUp(port) => Err(port), - _ => Ok(true), - } - } - }, - - // We woke ourselves up from select. - ptr => unsafe { - drop(SignalToken::from_raw(ptr)); - Ok(false) - }, - } - } -} - -impl<T> Drop for Packet<T> { - fn drop(&mut self) { - assert_eq!(self.state.load(Ordering::SeqCst), DISCONNECTED); - } -} |