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

#![cfg_attr(test, allow(dead_code))] // why is this necessary?
use super::unsupported;
use crate::ffi::CStr;
use crate::io;
use crate::num::NonZeroUsize;
use crate::time::Duration;

use super::abi::usercalls;

pub struct Thread(task_queue::JoinHandle);

pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;

pub use self::task_queue::JoinNotifier;

mod task_queue {
    use super::wait_notify;
    use crate::sync::{Mutex, MutexGuard, Once};

    pub type JoinHandle = wait_notify::Waiter;

    pub struct JoinNotifier(Option<wait_notify::Notifier>);

    impl Drop for JoinNotifier {
        fn drop(&mut self) {
            self.0.take().unwrap().notify();
        }
    }

    pub(super) struct Task {
        p: Box<dyn FnOnce()>,
        done: JoinNotifier,
    }

    impl Task {
        pub(super) fn new(p: Box<dyn FnOnce()>) -> (Task, JoinHandle) {
            let (done, recv) = wait_notify::new();
            let done = JoinNotifier(Some(done));
            (Task { p, done }, recv)
        }

        pub(super) fn run(self) -> JoinNotifier {
            (self.p)();
            self.done
        }
    }

    #[cfg_attr(test, linkage = "available_externally")]
    #[export_name = "_ZN16__rust_internals3std3sys3sgx6thread15TASK_QUEUE_INITE"]
    static TASK_QUEUE_INIT: Once = Once::new();
    #[cfg_attr(test, linkage = "available_externally")]
    #[export_name = "_ZN16__rust_internals3std3sys3sgx6thread10TASK_QUEUEE"]
    static mut TASK_QUEUE: Option<Mutex<Vec<Task>>> = None;

    pub(super) fn lock() -> MutexGuard<'static, Vec<Task>> {
        unsafe {
            TASK_QUEUE_INIT.call_once(|| TASK_QUEUE = Some(Default::default()));
            TASK_QUEUE.as_ref().unwrap().lock().unwrap()
        }
    }
}

/// This module provides a synchronization primitive that does not use thread
/// local variables. This is needed for signaling that a thread has finished
/// execution. The signal is sent once all TLS destructors have finished at
/// which point no new thread locals should be created.
pub mod wait_notify {
    use super::super::waitqueue::{SpinMutex, WaitQueue, WaitVariable};
    use crate::sync::Arc;

    pub struct Notifier(Arc<SpinMutex<WaitVariable<bool>>>);

    impl Notifier {
        /// Notify the waiter. The waiter is either notified right away (if
        /// currently blocked in `Waiter::wait()`) or later when it calls the
        /// `Waiter::wait()` method.
        pub fn notify(self) {
            let mut guard = self.0.lock();
            *guard.lock_var_mut() = true;
            let _ = WaitQueue::notify_one(guard);
        }
    }

    pub struct Waiter(Arc<SpinMutex<WaitVariable<bool>>>);

    impl Waiter {
        /// Wait for a notification. If `Notifier::notify()` has already been
        /// called, this will return immediately, otherwise the current thread
        /// is blocked until notified.
        pub fn wait(self) {
            let guard = self.0.lock();
            if *guard.lock_var() {
                return;
            }
            WaitQueue::wait(guard, || {});
        }
    }

    pub fn new() -> (Notifier, Waiter) {
        let inner = Arc::new(SpinMutex::new(WaitVariable::new(false)));
        (Notifier(inner.clone()), Waiter(inner))
    }
}

impl Thread {
    // unsafe: see thread::Builder::spawn_unchecked for safety requirements
    pub unsafe fn new(_stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
        let mut queue_lock = task_queue::lock();
        unsafe { usercalls::launch_thread()? };
        let (task, handle) = task_queue::Task::new(p);
        queue_lock.push(task);
        Ok(Thread(handle))
    }

    pub(super) fn entry() -> JoinNotifier {
        let mut pending_tasks = task_queue::lock();
        let task = rtunwrap!(Some, pending_tasks.pop());
        drop(pending_tasks); // make sure to not hold the task queue lock longer than necessary
        task.run()
    }

    pub fn yield_now() {
        let wait_error = rtunwrap!(Err, usercalls::wait(0, usercalls::raw::WAIT_NO));
        rtassert!(wait_error.kind() == io::ErrorKind::WouldBlock);
    }

    pub fn set_name(_name: &CStr) {
        // FIXME: could store this pointer in TLS somewhere
    }

    pub fn sleep(dur: Duration) {
        usercalls::wait_timeout(0, dur, || true);
    }

    pub fn join(self) {
        self.0.wait();
    }
}

pub fn available_concurrency() -> io::Result<NonZeroUsize> {
    unsupported()
}

pub mod guard {
    pub type Guard = !;
    pub unsafe fn current() -> Option<Guard> {
        None
    }
    pub unsafe fn init() -> Option<Guard> {
        None
    }
}