metriken 0.3.4

A fast and lightweight metrics library
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101

// Copyright 2021 Twitter, Inc.
// Licensed under the Apache License, Version 2.0
// http://www.apache.org/licenses/LICENSE-2.0

use crate::Metric;
use once_cell::sync::OnceCell;
use std::cell::Cell;
use std::ops::{Deref, DerefMut};

// Note: This implementation is mostly copied from the Lazy implementation
//       within once_cell. It only adds the `get` option to try to access
//       the value without initializing the Lazy instance.
//
//       This should be replaced with the new primitives in std::lazy once
//       those stabilize.

/// A value which is initialized on the first access.
///
/// This type is thread-safe and can be used in statics.
pub struct Lazy<T, F = fn() -> T> {
    cell: OnceCell<T>,
    func: Cell<Option<F>>,
}

unsafe impl<T, F: Send> Sync for Lazy<T, F> where OnceCell<T>: Sync {}

impl<T, F> Lazy<T, F> {
    /// Create a new lazy value with the given initializing function.
    pub const fn new(func: F) -> Self {
        Self {
            cell: OnceCell::new(),
            func: Cell::new(Some(func)),
        }
    }

    /// If this lazy has been initialized, then return a reference to the
    /// contained value.
    pub fn get(this: &Self) -> Option<&T> {
        this.cell.get()
    }

    /// If this lazy has been initialized, then return a reference to the
    /// contained value.
    pub fn get_mut(this: &mut Self) -> Option<&mut T> {
        this.cell.get_mut()
    }
}

impl<T, F: FnOnce() -> T> Lazy<T, F> {
    /// Force the evaluation of this lazy value and return a reference to
    /// the result. This is equivalent to the `Deref` impl.
    pub fn force(this: &Self) -> &T {
        this.cell.get_or_init(|| {
            let func = this
                .func
                .take()
                .unwrap_or_else(|| panic!("Lazy instance has previously been poisoned"));

            func()
        })
    }
}

impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        Self::force(self)
    }
}

impl<T, F: FnOnce() -> T> DerefMut for Lazy<T, F> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        Self::force(self);
        self.cell.get_mut().unwrap_or_else(|| unreachable!())
    }
}

impl<T: Default> Default for Lazy<T> {
    /// Create a new lazy value using `default` as the initializing function.
    fn default() -> Self {
        Self::new(T::default)
    }
}

impl<T: Metric, F: Send + 'static> Metric for Lazy<T, F> {
    fn is_enabled(&self) -> bool {
        Lazy::get(self).is_some()
    }

    fn as_any(&self) -> Option<&dyn std::any::Any> {
        match Lazy::get(self) {
            Some(metric) => Some(metric),
            None => None,
        }
    }

    fn value(&self) -> Option<crate::Value> {
        Lazy::get(self).and_then(|metric| metric.value())
    }
}