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
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156

// 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 core::{
    ptr,
    sync::atomic::{AtomicI32, Ordering},
};
use libc;
use std::thread;
use std::time::Instant;

// x32 Linux uses a non-standard type for tv_nsec in timespec.
// See https://sourceware.org/bugzilla/show_bug.cgi?id=16437
#[cfg(all(target_arch = "x86_64", target_pointer_width = "32"))]
#[allow(non_camel_case_types)]
type tv_nsec_t = i64;
#[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
#[allow(non_camel_case_types)]
type tv_nsec_t = libc::c_long;

fn errno() -> libc::c_int {
    #[cfg(target_os = "linux")]
    unsafe {
        *libc::__errno_location()
    }
    #[cfg(target_os = "android")]
    unsafe {
        *libc::__errno()
    }
}

// Helper type for putting a thread to sleep until some other thread wakes it up
pub struct ThreadParker {
    futex: AtomicI32,
}

impl super::ThreadParkerT for ThreadParker {
    type UnparkHandle = UnparkHandle;

    const IS_CHEAP_TO_CONSTRUCT: bool = true;

    #[inline]
    fn new() -> ThreadParker {
        ThreadParker {
            futex: AtomicI32::new(0),
        }
    }

    #[inline]
    unsafe fn prepare_park(&self) {
        self.futex.store(1, Ordering::Relaxed);
    }

    #[inline]
    unsafe fn timed_out(&self) -> bool {
        self.futex.load(Ordering::Relaxed) != 0
    }

    #[inline]
    unsafe fn park(&self) {
        while self.futex.load(Ordering::Acquire) != 0 {
            self.futex_wait(None);
        }
    }

    #[inline]
    unsafe fn park_until(&self, timeout: Instant) -> bool {
        while self.futex.load(Ordering::Acquire) != 0 {
            let now = Instant::now();
            if timeout <= now {
                return false;
            }
            let diff = timeout - now;
            if diff.as_secs() as libc::time_t as u64 != diff.as_secs() {
                // Timeout overflowed, just sleep indefinitely
                self.park();
                return true;
            }
            // SAFETY: libc::timespec is zero initializable.
            let mut ts: libc::timespec = std::mem::zeroed();
            ts.tv_sec = diff.as_secs() as libc::time_t;
            ts.tv_nsec = diff.subsec_nanos() as tv_nsec_t;
            self.futex_wait(Some(ts));
        }
        true
    }

    // Locks the parker to prevent the target thread from exiting. This is
    // necessary to ensure that thread-local ThreadData objects remain valid.
    // This should be called while holding the queue lock.
    #[inline]
    unsafe fn unpark_lock(&self) -> UnparkHandle {
        // We don't need to lock anything, just clear the state
        self.futex.store(0, Ordering::Release);

        UnparkHandle { futex: &self.futex }
    }
}

impl ThreadParker {
    #[inline]
    fn futex_wait(&self, ts: Option<libc::timespec>) {
        let ts_ptr = ts
            .as_ref()
            .map(|ts_ref| ts_ref as *const _)
            .unwrap_or(ptr::null());
        let r = unsafe {
            libc::syscall(
                libc::SYS_futex,
                &self.futex,
                libc::FUTEX_WAIT | libc::FUTEX_PRIVATE_FLAG,
                1,
                ts_ptr,
            )
        };
        debug_assert!(r == 0 || r == -1);
        if r == -1 {
            debug_assert!(
                errno() == libc::EINTR
                    || errno() == libc::EAGAIN
                    || (ts.is_some() && errno() == libc::ETIMEDOUT)
            );
        }
    }
}

pub struct UnparkHandle {
    futex: *const AtomicI32,
}

impl super::UnparkHandleT for UnparkHandle {
    #[inline]
    unsafe fn unpark(self) {
        // The thread data may have been freed at this point, but it doesn't
        // matter since the syscall will just return EFAULT in that case.
        let r = libc::syscall(
            libc::SYS_futex,
            self.futex,
            libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
            1,
        );
        debug_assert!(r == 0 || r == 1 || r == -1);
        if r == -1 {
            debug_assert_eq!(errno(), libc::EFAULT);
        }
    }
}

#[inline]
pub fn thread_yield() {
    thread::yield_now();
}