Files
ab_glyph_rasterizer
addr2line
adler
andrew
approx
arrayvec
ash
atom
backtrace
bitflags
byteorder
calloop
cfg_if
colorful
conrod_core
conrod_derive
conrod_example_shared
conrod_gfx
conrod_glium
conrod_piston
conrod_rendy
conrod_vulkano
conrod_wgpu
conrod_winit
copyless
copypasta
crossbeam
crossbeam_channel
crossbeam_deque
crossbeam_epoch
crossbeam_queue
crossbeam_utils
daggy
dlib
downcast_rs
draw_state
either
fixedbitset
float
fnv
futures
futures_channel
futures_core
futures_executor
futures_io
futures_macro
futures_sink
futures_task
futures_util
async_await
future
io
lock
sink
stream
task
fxhash
getrandom
gfx
gfx_backend_empty
gfx_backend_vulkan
gfx_core
gfx_descriptor
gfx_hal
gfx_memory
gimli
glium
glutin
glutin_egl_sys
glutin_glx_sys
graphics
half
hibitset
inplace_it
input
instant
interpolation
iovec
itoa
lazy_static
lazycell
libc
libloading
line_drawing
linked_hash_map
lock_api
log
maybe_uninit
memchr
memmap
memoffset
miniz_oxide
mio
mio_extras
naga
net2
nix
nom
num
num_bigint
num_complex
num_cpus
num_integer
num_iter
num_rational
num_traits
object
once_cell
ordered_float
ordermap
osmesa_sys
owned_ttf_parser
parking_lot
parking_lot_core
percent_encoding
petgraph
pin_project
pin_project_internal
pin_project_lite
pin_utils
ppv_lite86
proc_macro2
proc_macro_hack
proc_macro_nested
quote
rand
rand_chacha
rand_core
raw_window_handle
read_color
relevant
rendy
rendy_chain
rendy_command
rendy_core
rendy_descriptor
rendy_factory
rendy_frame
rendy_graph
rendy_init
rendy_memory
rendy_mesh
rendy_resource
rendy_shader
rendy_texture
rendy_wsi
rustc_demangle
rustc_hash
rusttype
ryu
same_file
scoped_tls
scopeguard
serde
serde_derive
serde_json
shaderc
shaderc_sys
shared_library
slab
smallvec
smithay_client_toolkit
smithay_clipboard
spirv_headers
stb_truetype
syn
takeable_option
texture
thiserror
thiserror_impl
thread_profiler
time
tracing
tracing_core
ttf_parser
typed_arena
unicode_xid
vecmath
viewport
vk_sys
void
vulkano
buffer
command_buffer
descriptor
device
framebuffer
image
instance
memory
pipeline
query
swapchain
sync
vulkano_shaders
walkdir
wayland_client
wayland_commons
wayland_cursor
wayland_egl
wayland_protocols
wayland_sys
wgpu
wgpu_core
wgpu_types
winit
x11
x11_clipboard
x11_dl
xcb
xcursor
xdg
xml
 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
// Copyright 2016 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

use crate::thread_parker;
use std::sync::atomic::spin_loop_hint;

// Wastes some CPU time for the given number of iterations,
// using a hint to indicate to the CPU that we are spinning.
#[inline]
fn cpu_relax(iterations: u32) {
    for _ in 0..iterations {
        spin_loop_hint()
    }
}

/// A counter used to perform exponential backoff in spin loops.
#[derive(Default)]
pub struct SpinWait {
    counter: u32,
}

impl SpinWait {
    /// Creates a new `SpinWait`.
    #[inline]
    pub fn new() -> Self {
        Self::default()
    }

    /// Resets a `SpinWait` to its initial state.
    #[inline]
    pub fn reset(&mut self) {
        self.counter = 0;
    }

    /// Spins until the sleep threshold has been reached.
    ///
    /// This function returns whether the sleep threshold has been reached, at
    /// which point further spinning has diminishing returns and the thread
    /// should be parked instead.
    ///
    /// The spin strategy will initially use a CPU-bound loop but will fall back
    /// to yielding the CPU to the OS after a few iterations.
    #[inline]
    pub fn spin(&mut self) -> bool {
        if self.counter >= 10 {
            return false;
        }
        self.counter += 1;
        if self.counter <= 3 {
            cpu_relax(1 << self.counter);
        } else {
            thread_parker::thread_yield();
        }
        true
    }

    /// Spins without yielding the thread to the OS.
    ///
    /// Instead, the backoff is simply capped at a maximum value. This can be
    /// used to improve throughput in `compare_exchange` loops that have high
    /// contention.
    #[inline]
    pub fn spin_no_yield(&mut self) {
        self.counter += 1;
        if self.counter > 10 {
            self.counter = 10;
        }
        cpu_relax(1 << self.counter);
    }
}