/rust/registry/src/github.com-1ecc6299db9ec823/crossbeam-epoch-0.9.3/src/epoch.rs

Source (jump to first uncovered line)
//! The global epoch
//!
//! The last bit in this number is unused and is always zero. Every so often the global epoch is
//! incremented, i.e. we say it "advances". A pinned participant may advance the global epoch only
//! if all currently pinned participants have been pinned in the current epoch.
//!
//! If an object became garbage in some epoch, then we can be sure that after two advancements no
//! participant will hold a reference to it. That is the crux of safe memory reclamation.

use crate::primitive::sync::atomic::AtomicUsize;
use core::sync::atomic::Ordering;

/// An epoch that can be marked as pinned or unpinned.
///
/// Internally, the epoch is represented as an integer that wraps around at some unspecified point
/// and a flag that represents whether it is pinned or unpinned.
#[derive(Copy, Clone, Default, Debug, Eq, PartialEq)]
pub(crate) struct Epoch {
    /// The least significant bit is set if pinned. The rest of the bits hold the epoch.
    data: usize,
}

impl Epoch {
    /// Returns the starting epoch in unpinned state.
    #[inline]
    pub(crate) fn starting() -> Self {
        Self::default()
    }

    /// Returns the number of epochs `self` is ahead of `rhs`.
    ///
    /// Internally, epochs are represented as numbers in the range `(isize::MIN / 2) .. (isize::MAX
    /// / 2)`, so the returned distance will be in the same interval.
    pub(crate) fn wrapping_sub(self, rhs: Self) -> isize {
        // The result is the same with `(self.data & !1).wrapping_sub(rhs.data & !1) as isize >> 1`,
        // because the possible difference of LSB in `(self.data & !1).wrapping_sub(rhs.data & !1)`
        // will be ignored in the shift operation.
        self.data.wrapping_sub(rhs.data & !1) as isize >> 1
    }

    /// Returns `true` if the epoch is marked as pinned.
    #[inline]
    pub(crate) fn is_pinned(self) -> bool {
        (self.data & 1) == 1
    }

    /// Returns the same epoch, but marked as pinned.
    #[inline]
    pub(crate) fn pinned(self) -> Epoch {
        Epoch {
            data: self.data | 1,
        }
    }

    /// Returns the same epoch, but marked as unpinned.
    #[inline]
    pub(crate) fn unpinned(self) -> Epoch {
        Epoch {
            data: self.data & !1,
        }
    }

    /// Returns the successor epoch.
    ///
    /// The returned epoch will be marked as pinned only if the previous one was as well.
    #[inline]
    pub(crate) fn successor(self) -> Epoch {
        Epoch {
            data: self.data.wrapping_add(2),
        }
    }
}

/// An atomic value that holds an `Epoch`.
#[derive(Default, Debug)]
pub(crate) struct AtomicEpoch {
    /// Since `Epoch` is just a wrapper around `usize`, an `AtomicEpoch` is similarly represented
    /// using an `AtomicUsize`.
    data: AtomicUsize,
}

impl AtomicEpoch {
    /// Creates a new atomic epoch.
    #[inline]
    pub(crate) fn new(epoch: Epoch) -> Self {
        let data = AtomicUsize::new(epoch.data);
        AtomicEpoch { data }
    }

    /// Loads a value from the atomic epoch.
    #[inline]
    pub(crate) fn load(&self, ord: Ordering) -> Epoch {
        Epoch {
            data: self.data.load(ord),
        }
    }

    /// Stores a value into the atomic epoch.
    #[inline]
    pub(crate) fn store(&self, epoch: Epoch, ord: Ordering) {
        self.data.store(epoch.data, ord);
    }

    /// Stores a value into the atomic epoch if the current value is the same as `current`.
    ///
    /// The return value is a result indicating whether the new value was written and containing
    /// the previous value. On success this value is guaranteed to be equal to `current`.
    ///
    /// This method takes two `Ordering` arguments to describe the memory
    /// ordering of this operation. `success` describes the required ordering for the
    /// read-modify-write operation that takes place if the comparison with `current` succeeds.
    /// `failure` describes the required ordering for the load operation that takes place when
    /// the comparison fails. Using `Acquire` as success ordering makes the store part
    /// of this operation `Relaxed`, and using `Release` makes the successful load
    /// `Relaxed`. The failure ordering can only be `SeqCst`, `Acquire` or `Relaxed`
    /// and must be equivalent to or weaker than the success ordering.
    #[inline]
    pub(crate) fn compare_exchange(
        &self,
        current: Epoch,
        new: Epoch,
        success: Ordering,
        failure: Ordering,
    ) -> Result<Epoch, Epoch> {
        match self
            .data
            .compare_exchange(current.data, new.data, success, failure)
        {
            Ok(data) => Ok(Epoch { data }),
            Err(data) => Err(Epoch { data }),
        }
    }
}

Line	Count	Source (jump to first uncovered line)
1		//! The global epoch
2		//!
3		//! The last bit in this number is unused and is always zero. Every so often the global epoch is
4		//! incremented, i.e. we say it "advances". A pinned participant may advance the global epoch only
5		//! if all currently pinned participants have been pinned in the current epoch.
6		//!
7		//! If an object became garbage in some epoch, then we can be sure that after two advancements no
8		//! participant will hold a reference to it. That is the crux of safe memory reclamation.
9
10		use crate::primitive::sync::atomic::AtomicUsize;
11		use core::sync::atomic::Ordering;
12
13		/// An epoch that can be marked as pinned or unpinned.
14		///
15		/// Internally, the epoch is represented as an integer that wraps around at some unspecified point
16		/// and a flag that represents whether it is pinned or unpinned.
17	0	#[derive(Copy, Clone, Default, Debug, Eq, PartialEq)]
18		pub(crate) struct Epoch {
19		/// The least significant bit is set if pinned. The rest of the bits hold the epoch.
20		data: usize,
21		}
22
23		impl Epoch {
24		/// Returns the starting epoch in unpinned state.
25		#[inline]
26		pub(crate) fn starting() -> Self {
27		Self::default()
28		}
29
30		/// Returns the number of epochs `self` is ahead of `rhs`.
31		///
32		/// Internally, epochs are represented as numbers in the range `(isize::MIN / 2) .. (isize::MAX
33		/// / 2)`, so the returned distance will be in the same interval.
34		pub(crate) fn wrapping_sub(self, rhs: Self) -> isize {
35		// The result is the same with `(self.data & !1).wrapping_sub(rhs.data & !1) as isize >> 1`,
36		// because the possible difference of LSB in `(self.data & !1).wrapping_sub(rhs.data & !1)`
37		// will be ignored in the shift operation.
38		self.data.wrapping_sub(rhs.data & !1) as isize >> 1
39		}
40
41		/// Returns `true` if the epoch is marked as pinned.
42		#[inline]
43		pub(crate) fn is_pinned(self) -> bool {
44		(self.data & 1) == 1
45		}
46
47		/// Returns the same epoch, but marked as pinned.
48		#[inline]
49		pub(crate) fn pinned(self) -> Epoch {
50		Epoch {
51		data: self.data \| 1,
52		}
53		}
54
55		/// Returns the same epoch, but marked as unpinned.
56		#[inline]
57		pub(crate) fn unpinned(self) -> Epoch {
58		Epoch {
59		data: self.data & !1,
60		}
61		}
62
63		/// Returns the successor epoch.
64		///
65		/// The returned epoch will be marked as pinned only if the previous one was as well.
66		#[inline]
67		pub(crate) fn successor(self) -> Epoch {
68		Epoch {
69		data: self.data.wrapping_add(2),
70		}
71		}
72		}
73
74		/// An atomic value that holds an `Epoch`.
75	0	#[derive(Default, Debug)]
76		pub(crate) struct AtomicEpoch {
77		/// Since `Epoch` is just a wrapper around `usize`, an `AtomicEpoch` is similarly represented
78		/// using an `AtomicUsize`.
79		data: AtomicUsize,
80		}
81
82		impl AtomicEpoch {
83		/// Creates a new atomic epoch.
84		#[inline]
85		pub(crate) fn new(epoch: Epoch) -> Self {
86		let data = AtomicUsize::new(epoch.data);
87		AtomicEpoch { data }
88		}
89
90		/// Loads a value from the atomic epoch.
91		#[inline]
92		pub(crate) fn load(&self, ord: Ordering) -> Epoch {
93		Epoch {
94		data: self.data.load(ord),
95		}
96		}
97
98		/// Stores a value into the atomic epoch.
99		#[inline]
100		pub(crate) fn store(&self, epoch: Epoch, ord: Ordering) {
101		self.data.store(epoch.data, ord);
102		}
103
104		/// Stores a value into the atomic epoch if the current value is the same as `current`.
105		///
106		/// The return value is a result indicating whether the new value was written and containing
107		/// the previous value. On success this value is guaranteed to be equal to `current`.
108		///
109		/// This method takes two `Ordering` arguments to describe the memory
110		/// ordering of this operation. `success` describes the required ordering for the
111		/// read-modify-write operation that takes place if the comparison with `current` succeeds.
112		/// `failure` describes the required ordering for the load operation that takes place when
113		/// the comparison fails. Using `Acquire` as success ordering makes the store part
114		/// of this operation `Relaxed`, and using `Release` makes the successful load
115		/// `Relaxed`. The failure ordering can only be `SeqCst`, `Acquire` or `Relaxed`
116		/// and must be equivalent to or weaker than the success ordering.
117		#[inline]
118	0	pub(crate) fn compare_exchange(
119	0	&self,
120	0	current: Epoch,
121	0	new: Epoch,
122	0	success: Ordering,
123	0	failure: Ordering,
124	0	) -> Result<Epoch, Epoch> {
125	0	match self
126	0	.data
127	0	.compare_exchange(current.data, new.data, success, failure)
128		{
129	0	Ok(data) => Ok(Epoch { data }),
130	0	Err(data) => Err(Epoch { data }),
131		}
132	0	} Unexecuted instantiation: <crossbeam_epoch::epoch::AtomicEpoch>::compare_exchange Unexecuted instantiation: <crossbeam_epoch::epoch::AtomicEpoch>::compare_exchange
133		}

Coverage Report

Created: 2021-03-22 08:29