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Mercurial > core / rust/lib/obj/src/object/meter.rs

changeset 698: 96958d3eb5b0
parent: c7165d93a9eb
author: Richard Westhaver <ellis@rwest.io>
date: Fri, 04 Oct 2024 22:04:59 -0400
permissions: -rw-r--r--
description: fixes 
     1 use std::borrow::Borrow;
     2 
     3 pub trait Meter<K, V> {
     4   /// The type used to store measurements.
     5   type Measure: Default + Copy;
     6   /// Calculate the size of `key` and `value`.
     7   fn measure<Q: ?Sized>(&self, key: &Q, value: &V) -> Self::Measure
     8   where
     9     K: Borrow<Q>;
    10 }
    11 
    12 /// Size limit based on a simple count of cache items.
    13 pub struct Count;
    14 
    15 impl<K, V> Meter<K, V> for Count {
    16   /// Don't store anything, the measurement can be derived from the map.
    17   type Measure = ();
    18 
    19   /// Don't actually count anything either.
    20   fn measure<Q: ?Sized>(&self, _: &Q, _: &V)
    21   where
    22     K: Borrow<Q>,
    23   {
    24   }
    25 }
    26 
    27 /// A trait to allow the default `Count` measurement to not store an
    28 /// extraneous counter.
    29 pub trait CountableMeter<K, V>: Meter<K, V> {
    30   /// Add `amount` to `current` and return the sum.
    31   fn add(&self, current: Self::Measure, amount: Self::Measure) -> Self::Measure;
    32   /// Subtract `amount` from `current` and return the difference.
    33   fn sub(&self, current: Self::Measure, amount: Self::Measure) -> Self::Measure;
    34   /// Return `current` as a `usize` if possible, otherwise return `None`.
    35   ///
    36   /// If this method returns `None` the cache will use the number of cache
    37   /// entries as its size.
    38   fn size(&self, current: Self::Measure) -> Option<u64>;
    39 }
    40 
    41 /// `Count` is all no-ops, the number of entries in the map is the size.
    42 impl<K, V, T: Meter<K, V>> CountableMeter<K, V> for T
    43 where
    44   T: CountableMeterWithMeasure<K, V, <T as Meter<K, V>>::Measure>,
    45 {
    46   fn add(&self, current: Self::Measure, amount: Self::Measure) -> Self::Measure {
    47     CountableMeterWithMeasure::meter_add(self, current, amount)
    48   }
    49   fn sub(&self, current: Self::Measure, amount: Self::Measure) -> Self::Measure {
    50     CountableMeterWithMeasure::meter_sub(self, current, amount)
    51   }
    52   fn size(&self, current: Self::Measure) -> Option<u64> {
    53     CountableMeterWithMeasure::meter_size(self, current)
    54   }
    55 }
    56 
    57 pub trait CountableMeterWithMeasure<K, V, M> {
    58   /// Add `amount` to `current` and return the sum.
    59   fn meter_add(&self, current: M, amount: M) -> M;
    60   /// Subtract `amount` from `current` and return the difference.
    61   fn meter_sub(&self, current: M, amount: M) -> M;
    62   /// Return `current` as a `usize` if possible, otherwise return `None`.
    63   ///
    64   /// If this method returns `None` the cache will use the number of cache
    65   /// entries as its size.
    66   fn meter_size(&self, current: M) -> Option<u64>;
    67 }
    68 
    69 /// For any other `Meter` with `Measure=usize`, just do the simple math.
    70 impl<K, V, T> CountableMeterWithMeasure<K, V, usize> for T
    71 where
    72   T: Meter<K, V>,
    73 {
    74   fn meter_add(&self, current: usize, amount: usize) -> usize {
    75     current + amount
    76   }
    77   fn meter_sub(&self, current: usize, amount: usize) -> usize {
    78     current - amount
    79   }
    80   fn meter_size(&self, current: usize) -> Option<u64> {
    81     Some(current as u64)
    82   }
    83 }
    84 
    85 impl<K, V> CountableMeterWithMeasure<K, V, ()> for Count {
    86   fn meter_add(&self, _current: (), _amount: ()) {}
    87   fn meter_sub(&self, _current: (), _amount: ()) {}
    88   fn meter_size(&self, _current: ()) -> Option<u64> {
    89     None
    90   }
    91 }