Remove the unstable and deprecated mpsc_select

This removes macro `select!` and `std::sync::mpsc::{Handle, Select}`,
which were all unstable and have been deprecated since 1.32.

1 files changed, 0 insertions, 352 deletions

diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
deleted file mode 100644
index d1b5f2deccc..00000000000
--- a/src/libstd/sync/mpsc/select.rs
+++ /dev/null
@@ -1,352 +0,0 @@
-//! Selection over an array of receivers
-//!
-//! This module contains the implementation machinery necessary for selecting
-//! over a number of receivers. One large goal of this module is to provide an
-//! efficient interface to selecting over any receiver of any type.
-//!
-//! This is achieved through an architecture of a "receiver set" in which
-//! receivers are added to a set and then the entire set is waited on at once.
-//! The set can be waited on multiple times to prevent re-adding each receiver
-//! to the set.
-//!
-//! Usage of this module is currently encouraged to go through the use of the
-//! `select!` macro. This macro allows naturally binding of variables to the
-//! received values of receivers in a much more natural syntax then usage of the
-//! `Select` structure directly.
-//!
-//! # Examples
-//!
-//! ```rust
-//! #![feature(mpsc_select)]
-//!
-//! use std::sync::mpsc::channel;
-//!
-//! let (tx1, rx1) = channel();
-//! let (tx2, rx2) = channel();
-//!
-//! tx1.send(1).unwrap();
-//! tx2.send(2).unwrap();
-//!
-//! select! {
-//!     val = rx1.recv() => {
-//!         assert_eq!(val.unwrap(), 1);
-//!     },
-//!     val = rx2.recv() => {
-//!         assert_eq!(val.unwrap(), 2);
-//!     }
-//! }
-//! ```
-
-#![allow(dead_code)]
-#![unstable(feature = "mpsc_select",
-            reason = "This implementation, while likely sufficient, is unsafe and \
-                      likely to be error prone. At some point in the future this \
-                      module will be removed.",
-            issue = "27800")]
-#![rustc_deprecated(since = "1.32.0",
-                    reason = "channel selection will be removed in a future release")]
-
-use core::cell::{Cell, UnsafeCell};
-use core::marker;
-use core::ptr;
-use core::usize;
-
-use crate::fmt;
-use crate::sync::mpsc::{Receiver, RecvError};
-use crate::sync::mpsc::blocking::{self, SignalToken};
-
-/// The "receiver set" of the select interface. This structure is used to manage
-/// a set of receivers which are being selected over.
-pub struct Select {
-    inner: UnsafeCell<SelectInner>,
-    next_id: Cell<usize>,
-}
-
-struct SelectInner {
-    head: *mut Handle<'static, ()>,
-    tail: *mut Handle<'static, ()>,
-}
-
-impl !marker::Send for Select {}
-
-/// A handle to a receiver which is currently a member of a `Select` set of
-/// receivers. This handle is used to keep the receiver in the set as well as
-/// interact with the underlying receiver.
-pub struct Handle<'rx, T:Send+'rx> {
-    /// The ID of this handle, used to compare against the return value of
-    /// `Select::wait()`.
-    id: usize,
-    selector: *mut SelectInner,
-    next: *mut Handle<'static, ()>,
-    prev: *mut Handle<'static, ()>,
-    added: bool,
-    packet: &'rx (dyn Packet+'rx),
-
-    // due to our fun transmutes, we be sure to place this at the end. (nothing
-    // previous relies on T)
-    rx: &'rx Receiver<T>,
-}
-
-struct Packets { cur: *mut Handle<'static, ()> }
-
-#[doc(hidden)]
-#[derive(PartialEq, Eq)]
-pub enum StartResult {
-    Installed,
-    Abort,
-}
-
-#[doc(hidden)]
-pub trait Packet {
-    fn can_recv(&self) -> bool;
-    fn start_selection(&self, token: SignalToken) -> StartResult;
-    fn abort_selection(&self) -> bool;
-}
-
-impl Select {
-    /// Creates a new selection structure. This set is initially empty.
-    ///
-    /// Usage of this struct directly can sometimes be burdensome, and usage is much easier through
-    /// the `select!` macro.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(mpsc_select)]
-    ///
-    /// use std::sync::mpsc::Select;
-    ///
-    /// let select = Select::new();
-    /// ```
-    pub fn new() -> Select {
-        Select {
-            inner: UnsafeCell::new(SelectInner {
-                head: ptr::null_mut(),
-                tail: ptr::null_mut(),
-            }),
-            next_id: Cell::new(1),
-        }
-    }
-
-    /// Creates a new handle into this receiver set for a new receiver. Note
-    /// that this does *not* add the receiver to the receiver set, for that you
-    /// must call the `add` method on the handle itself.
-    pub fn handle<'a, T: Send>(&'a self, rx: &'a Receiver<T>) -> Handle<'a, T> {
-        let id = self.next_id.get();
-        self.next_id.set(id + 1);
-        Handle {
-            id,
-            selector: self.inner.get(),
-            next: ptr::null_mut(),
-            prev: ptr::null_mut(),
-            added: false,
-            rx,
-            packet: rx,
-        }
-    }
-
-    /// Waits for an event on this receiver set. The returned value is *not* an
-    /// index, but rather an ID. This ID can be queried against any active
-    /// `Handle` structures (each one has an `id` method). The handle with
-    /// the matching `id` will have some sort of event available on it. The
-    /// event could either be that data is available or the corresponding
-    /// channel has been closed.
-    pub fn wait(&self) -> usize {
-        self.wait2(true)
-    }
-
-    /// Helper method for skipping the preflight checks during testing
-    pub(super) fn wait2(&self, do_preflight_checks: bool) -> usize {
-        // Note that this is currently an inefficient implementation. We in
-        // theory have knowledge about all receivers in the set ahead of time,
-        // so this method shouldn't really have to iterate over all of them yet
-        // again. The idea with this "receiver set" interface is to get the
-        // interface right this time around, and later this implementation can
-        // be optimized.
-        //
-        // This implementation can be summarized by:
-        //
-        //      fn select(receivers) {
-        //          if any receiver ready { return ready index }
-        //          deschedule {
-        //              block on all receivers
-        //          }
-        //          unblock on all receivers
-        //          return ready index
-        //      }
-        //
-        // Most notably, the iterations over all of the receivers shouldn't be
-        // necessary.
-        unsafe {
-            // Stage 1: preflight checks. Look for any packets ready to receive
-            if do_preflight_checks {
-                for handle in self.iter() {
-                    if (*handle).packet.can_recv() {
-                        return (*handle).id();
-                    }
-                }
-            }
-
-            // Stage 2: begin the blocking process
-            //
-            // Create a number of signal tokens, and install each one
-            // sequentially until one fails. If one fails, then abort the
-            // selection on the already-installed tokens.
-            let (wait_token, signal_token) = blocking::tokens();
-            for (i, handle) in self.iter().enumerate() {
-                match (*handle).packet.start_selection(signal_token.clone()) {
-                    StartResult::Installed => {}
-                    StartResult::Abort => {
-                        // Go back and abort the already-begun selections
-                        for handle in self.iter().take(i) {
-                            (*handle).packet.abort_selection();
-                        }
-                        return (*handle).id;
-                    }
-                }
-            }
-
-            // Stage 3: no messages available, actually block
-            wait_token.wait();
-
-            // Stage 4: there *must* be message available; find it.
-            //
-            // Abort the selection process on each receiver. If the abort
-            // process returns `true`, then that means that the receiver is
-            // ready to receive some data. Note that this also means that the
-            // receiver may have yet to have fully read the `to_wake` field and
-            // woken us up (although the wakeup is guaranteed to fail).
-            //
-            // This situation happens in the window of where a sender invokes
-            // increment(), sees -1, and then decides to wake up the thread. After
-            // all this is done, the sending thread will set `selecting` to
-            // `false`. Until this is done, we cannot return. If we were to
-            // return, then a sender could wake up a receiver which has gone
-            // back to sleep after this call to `select`.
-            //
-            // Note that it is a "fairly small window" in which an increment()
-            // views that it should wake a thread up until the `selecting` bit
-            // is set to false. For now, the implementation currently just spins
-            // in a yield loop. This is very distasteful, but this
-            // implementation is already nowhere near what it should ideally be.
-            // A rewrite should focus on avoiding a yield loop, and for now this
-            // implementation is tying us over to a more efficient "don't
-            // iterate over everything every time" implementation.
-            let mut ready_id = usize::MAX;
-            for handle in self.iter() {
-                if (*handle).packet.abort_selection() {
-                    ready_id = (*handle).id;
-                }
-            }
-
-            // We must have found a ready receiver
-            assert!(ready_id != usize::MAX);
-            return ready_id;
-        }
-    }
-
-    fn iter(&self) -> Packets { Packets { cur: unsafe { &*self.inner.get() }.head } }
-}
-
-impl<'rx, T: Send> Handle<'rx, T> {
-    /// Retrieves the ID of this handle.
-    #[inline]
-    pub fn id(&self) -> usize { self.id }
-
-    /// Blocks to receive a value on the underlying receiver, returning `Some` on
-    /// success or `None` if the channel disconnects. This function has the same
-    /// semantics as `Receiver.recv`
-    pub fn recv(&mut self) -> Result<T, RecvError> { self.rx.recv() }
-
-    /// Adds this handle to the receiver set that the handle was created from. This
-    /// method can be called multiple times, but it has no effect if `add` was
-    /// called previously.
-    ///
-    /// This method is unsafe because it requires that the `Handle` is not moved
-    /// while it is added to the `Select` set.
-    pub unsafe fn add(&mut self) {
-        if self.added { return }
-        let selector = &mut *self.selector;
-        let me = self as *mut Handle<'rx, T> as *mut Handle<'static, ()>;
-
-        if selector.head.is_null() {
-            selector.head = me;
-            selector.tail = me;
-        } else {
-            (*me).prev = selector.tail;
-            assert!((*me).next.is_null());
-            (*selector.tail).next = me;
-            selector.tail = me;
-        }
-        self.added = true;
-    }
-
-    /// Removes this handle from the `Select` set. This method is unsafe because
-    /// it has no guarantee that the `Handle` was not moved since `add` was
-    /// called.
-    pub unsafe fn remove(&mut self) {
-        if !self.added { return }
-
-        let selector = &mut *self.selector;
-        let me = self as *mut Handle<'rx, T> as *mut Handle<'static, ()>;
-
-        if self.prev.is_null() {
-            assert_eq!(selector.head, me);
-            selector.head = self.next;
-        } else {
-            (*self.prev).next = self.next;
-        }
-        if self.next.is_null() {
-            assert_eq!(selector.tail, me);
-            selector.tail = self.prev;
-        } else {
-            (*self.next).prev = self.prev;
-        }
-
-        self.next = ptr::null_mut();
-        self.prev = ptr::null_mut();
-
-        self.added = false;
-    }
-}
-
-impl Drop for Select {
-    fn drop(&mut self) {
-        unsafe {
-            assert!((&*self.inner.get()).head.is_null());
-            assert!((&*self.inner.get()).tail.is_null());
-        }
-    }
-}
-
-impl<T: Send> Drop for Handle<'_, T> {
-    fn drop(&mut self) {
-        unsafe { self.remove() }
-    }
-}
-
-impl Iterator for Packets {
-    type Item = *mut Handle<'static, ()>;
-
-    fn next(&mut self) -> Option<*mut Handle<'static, ()>> {
-        if self.cur.is_null() {
-            None
-        } else {
-            let ret = Some(self.cur);
-            unsafe { self.cur = (*self.cur).next; }
-            ret
-        }
-    }
-}
-
-impl fmt::Debug for Select {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Select").finish()
-    }
-}
-
-impl<T: Send> fmt::Debug for Handle<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Handle").finish()
-    }
-}