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
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License..

//! Native threads.

use sgx_types::{sgx_thread_t, sgx_thread_self};
use sgx_trts::enclave::*;
use core::any::Any;
use core::sync::atomic::AtomicUsize;
use core::sync::atomic::Ordering::SeqCst;
#[cfg(feature = "thread")]
use core::cell::UnsafeCell;
#[cfg(feature = "thread")]
use core::mem;
use core::fmt;
use core::num::NonZeroU64;
use alloc_crate::sync::Arc;
use alloc_crate::str;
use crate::panic;
use crate::panicking;
use crate::sys_common::thread_info;
use crate::sync::{SgxThreadMutex, SgxMutex, SgxCondvar};
use crate::time::Duration;
#[cfg(feature = "thread")]
use crate::sys::thread as imp;
#[cfg(feature = "thread")]
use crate::io;
use crate::ffi::{CStr, CString};
#[cfg(feature = "thread")]
use crate::sys_common::{AsInner, IntoInner};

#[macro_use] mod local;
pub use self::local::{LocalKey, AccessError};
pub use self::local::statik::Key as __StaticLocalKeyInner;
#[cfg(feature = "thread")]
pub use self::local::fast::Key as __FastLocalKeyInner;
#[cfg(feature = "thread")]
pub use self::local::os::Key as __OsLocalKeyInner;

////////////////////////////////////////////////////////////////////////////////
// Builder
////////////////////////////////////////////////////////////////////////////////

/// Thread factory, which can be used in order to configure the properties of
/// a new thread.
///
/// Methods can be chained on it in order to configure it.
///
/// The two configurations available are:
///
/// - [`name`]: specifies an [associated name for the thread][naming-threads]
/// - [`stack_size`]: specifies the [desired stack size for the thread][stack-size]
///
/// The [`spawn`] method will take ownership of the builder and create an
/// [`io::Result`] to the thread handle with the given configuration.
///
/// The [`thread::spawn`] free function uses a `Builder` with default
/// configuration and [`unwrap`]s its return value.
///
/// You may want to use [`spawn`] instead of [`thread::spawn`], when you want
/// to recover from a failure to launch a thread, indeed the free function will
/// panic where the `Builder` method will return a [`io::Result`].
///
#[cfg(feature = "thread")]
#[derive(Debug)]
pub struct Builder {
    // A name for the thread-to-be, for identification in panic messages
    name: Option<String>,
}

#[cfg(feature = "thread")]
impl Builder {
    /// Generates the base configuration for spawning a thread, from which
    /// configuration methods can be chained.
    ///
    pub fn new() -> Builder {
        if rsgx_get_thread_policy() != SgxThreadPolicy::Bound {
            panic!("The sgx thread policy must be Bound!");
        }
        Builder { name: None }
    }

    /// Names the thread-to-be. Currently the name is used for identification
    /// only in panic messages.
    ///
    /// The name must not contain null bytes (`\0`).
    ///
    /// For more information about named threads, see
    /// [this module-level documentation][naming-threads].
    ///
    pub fn name(mut self, name: String) -> Builder {
        self.name = Some(name);
        self
    }

    /// Spawns a new thread by taking ownership of the `Builder`, and returns an
    /// [`io::Result`] to its [`JoinHandle`].
    ///
    /// The spawned thread may outlive the caller (unless the caller thread
    /// is the main thread; the whole process is terminated when the main
    /// thread finishes). The join handle can be used to block on
    /// termination of the child thread, including recovering its panics.
    ///
    /// For a more complete documentation see [`thread::spawn`][`spawn`].
    ///
    /// # Errors
    ///
    /// Unlike the [`spawn`] free function, this method yields an
    /// [`io::Result`] to capture any failure to create the thread at
    /// the OS level.
    ///
    /// [`spawn`]: ../../std/thread/fn.spawn.html
    /// [`io::Result`]: ../../std/io/type.Result.html
    /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
    ///
    /// # Panics
    ///
    /// Panics if a thread name was set and it contained null bytes.
    ///
    pub fn spawn<F, T>(self, f: F) -> io::Result<JoinHandle<T>>
    where
        F: FnOnce() -> T,
        F: Send + 'static,
        T: Send + 'static,
    {
        unsafe { self.spawn_unchecked(f) }
    }

    pub unsafe fn spawn_unchecked<'a, F, T>(self, f: F) -> io::Result<JoinHandle<T>>
    where
        F: FnOnce() -> T,
        F: Send + 'a,
        T: Send + 'a,
    {
        let Builder { name } = self;

        let my_thread = SgxThread::new(name);
        let their_thread = my_thread.clone();

        let my_packet : Arc<UnsafeCell<Option<Result<T>>>>
            = Arc::new(UnsafeCell::new(None));
        let their_packet = my_packet.clone();

        let main = move || {
            if let Some(name) = their_thread.cname() {
                imp::Thread::set_name(name);
            }
            thread_info::set(their_thread);
            #[cfg(feature = "backtrace")]
            let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
                crate::sys_common::backtrace::__rust_begin_short_backtrace(f)
            }));
            #[cfg(not(feature = "backtrace"))]
            let try_result = panic::catch_unwind(panic::AssertUnwindSafe(f));
            *their_packet.get() = Some(try_result);
        };

        Ok(JoinHandle(JoinInner {
            // `imp::Thread::new` takes a closure with a `'static` lifetime, since it's passed
            // through FFI or otherwise used with low-level threading primitives that have no
            // notion of or way to enforce lifetimes.
            //
            // As mentioned in the `Safety` section of this function's documentation, the caller of
            // this function needs to guarantee that the passed-in lifetime is sufficiently long
            // for the lifetime of the thread.
            //
            // Similarly, the `sys` implementation must guarantee that no references to the closure
            // exist after the thread has terminated, which is signaled by `Thread::join`
            // returning.
            native: Some(imp::Thread::new(
                mem::transmute::<Box<dyn FnOnce() + 'a>, Box<dyn FnOnce() + 'static>>(Box::new(
                    main,
                )),
            )?),
            thread: my_thread,
            packet: Packet(my_packet),
        }))
    }
}

////////////////////////////////////////////////////////////////////////////////
// Free functions
////////////////////////////////////////////////////////////////////////////////

/// Spawns a new thread, returning a [`JoinHandle`] for it.
///
/// The join handle will implicitly *detach* the child thread upon being
/// dropped. In this case, the child thread may outlive the parent (unless
/// the parent thread is the main thread; the whole process is terminated when
/// the main thread finishes). Additionally, the join handle provides a [`join`]
/// method that can be used to join the child thread. If the child thread
/// panics, [`join`] will return an [`Err`] containing the argument given to
/// [`panic`].
///
/// This will create a thread using default parameters of [`Builder`], if you
/// want to specify the stack size or the name of the thread, use this API
/// instead.
///
/// As you can see in the signature of `spawn` there are two constraints on
/// both the closure given to `spawn` and its return value, let's explain them:
///
/// - The `'static` constraint means that the closure and its return value
///   must have a lifetime of the whole program execution. The reason for this
///   is that threads can `detach` and outlive the lifetime they have been
///   created in.
///   Indeed if the thread, and by extension its return value, can outlive their
///   caller, we need to make sure that they will be valid afterwards, and since
///   we *can't* know when it will return we need to have them valid as long as
///   possible, that is until the end of the program, hence the `'static`
///   lifetime.
/// - The [`Send`] constraint is because the closure will need to be passed
///   *by value* from the thread where it is spawned to the new thread. Its
///   return value will need to be passed from the new thread to the thread
///   where it is `join`ed.
///   As a reminder, the [`Send`] marker trait expresses that it is safe to be
///   passed from thread to thread. [`Sync`] expresses that it is safe to have a
///   reference be passed from thread to thread.
///
/// # Panics
///
/// Panics if the OS fails to create a thread; use [`Builder::spawn`]
/// to recover from such errors.
///
#[cfg(feature = "thread")]
pub fn spawn<F, T>(f: F) -> JoinHandle<T>
where
    F: FnOnce() -> T,
    F: Send + 'static,
    T: Send + 'static,
{
    Builder::new().spawn(f).expect("failed to spawn thread")
}

/// Gets a handle to the thread that invokes it.
///
pub fn current() -> SgxThread {
    thread_info::current_thread().expect("use of thread::current() need TCS policy is Bound")
}

/// Cooperatively gives up a timeslice to the OS scheduler.
///
/// This is used when the programmer knows that the thread will have nothing
/// to do for some time, and thus avoid wasting computing time.
///
/// For example when polling on a resource, it is common to check that it is
/// available, and if not to yield in order to avoid busy waiting.
///
/// Thus the pattern of `yield`ing after a failed poll is rather common when
/// implementing low-level shared resources or synchronization primitives.
///
/// However programmers will usually prefer to use [`channel`]s, [`Condvar`]s,
/// [`Mutex`]es or [`join`] for their synchronization routines, as they avoid
/// thinking about thread scheduling.
///
/// Note that [`channel`]s for example are implemented using this primitive.
/// Indeed when you call `send` or `recv`, which are blocking, they will yield
/// if the channel is not available.
///
#[cfg(feature = "thread")]
pub fn yield_now() {
    imp::Thread::yield_now()
}

/// Determines whether the current thread is unwinding because of panic.
///
/// A common use of this feature is to poison shared resources when writing
/// unsafe code, by checking `panicking` when the `drop` is called.
///
/// This is usually not needed when writing safe code, as [`Mutex`es][Mutex]
/// already poison themselves when a thread panics while holding the lock.
///
/// This can also be used in multithreaded applications, in order to send a
/// message to other threads warning that a thread has panicked (e.g., for
/// monitoring purposes).
///
pub fn panicking() -> bool {
    panicking::panicking()
}

/// Puts the current thread to sleep for at least the specified amount of time.
///
/// The thread may sleep longer than the duration specified due to scheduling
/// specifics or platform-dependent functionality. It will never sleep less.
///
/// # Platform-specific behavior
///
/// On Unix platforms, the underlying syscall may be interrupted by a
/// spurious wakeup or signal handler. To ensure the sleep occurs for at least
/// the specified duration, this function may invoke that system call multiple
/// times.
///
#[cfg(feature = "thread")]
pub fn sleep_ms(ms: u32) {
    sleep(Duration::from_millis(ms as u64))
}

/// Puts the current thread to sleep for at least the specified amount of time.
///
/// The thread may sleep longer than the duration specified due to scheduling
/// specifics or platform-dependent functionality. It will never sleep less.
///
/// # Platform-specific behavior
///
/// On Unix platforms, the underlying syscall may be interrupted by a
/// spurious wakeup or signal handler. To ensure the sleep occurs for at least
/// the specified duration, this function may invoke that system call multiple
/// times.
/// Platforms which do not support nanosecond precision for sleeping will
/// have `dur` rounded up to the nearest granularity of time they can sleep for.
///
#[cfg(feature = "thread")]
pub fn sleep(dur: Duration) {
    imp::Thread::sleep(dur)
}

///
/// The rsgx_thread_self function returns the unique thread identification.
///
/// # Description
///
/// The function is a simple wrap of get_thread_data() provided in the tRTS,
/// which provides a trusted thread unique identifier.
///
/// # Requirements
///
/// Library: libsgx_tstdc.a
///
/// # Return value
///
/// The return value cannot be NULL and is always valid as long as it is invoked by a thread inside the enclave.
///
pub fn rsgx_thread_self() -> sgx_thread_t {
    unsafe { sgx_thread_self() }
}

///
/// The rsgx_thread_equal function compares two thread identifiers.
///
/// # Description
///
/// The function compares two thread identifiers provided by sgx_thread_
/// self to determine if the IDs refer to the same trusted thread.
///
/// # Requirements
///
/// Library: libsgx_tstdc.a
///
/// # Return value
///
/// **true**
///
/// The two thread IDs are equal.
///
pub fn rsgx_thread_equal(a: sgx_thread_t, b: sgx_thread_t) -> bool {
    a == b
}

pub fn current_td() -> SgxThreadData {
    unsafe {
        SgxThreadData::from_raw(rsgx_thread_self())
    }
}

// constants for park/unpark
const EMPTY: usize = 0;
const PARKED: usize = 1;
const NOTIFIED: usize = 2;

/// Blocks unless or until the current thread's token is made available.
///
/// A call to `park` does not guarantee that the thread will remain parked
/// forever, and callers should be prepared for this possibility.
///
/// # park and unpark
///
/// Every thread is equipped with some basic low-level blocking support, via the
/// [`thread::park`][`park`] function and [`thread::Thread::unpark`][`unpark`]
/// method. [`park`] blocks the current thread, which can then be resumed from
/// another thread by calling the [`unpark`] method on the blocked thread's
/// handle.
///
/// Conceptually, each [`Thread`] handle has an associated token, which is
/// initially not present:
///
/// * The [`thread::park`][`park`] function blocks the current thread unless or
///   until the token is available for its thread handle, at which point it
///   atomically consumes the token. It may also return *spuriously*, without
///   consuming the token. [`thread::park_timeout`] does the same, but allows
///   specifying a maximum time to block the thread for.
///
/// * The [`unpark`] method on a [`Thread`] atomically makes the token available
///   if it wasn't already. Because the token is initially absent, [`unpark`]
///   followed by [`park`] will result in the second call returning immediately.
///
/// In other words, each [`Thread`] acts a bit like a spinlock that can be
/// locked and unlocked using `park` and `unpark`.
///
/// Notice that being unblocked does not imply any synchronization with someone
/// that unparked this thread, it could also be spurious.
/// For example, it would be a valid, but inefficient, implementation to make both [`park`] and
/// [`unpark`] return immediately without doing anything.
///
/// The API is typically used by acquiring a handle to the current thread,
/// placing that handle in a shared data structure so that other threads can
/// find it, and then `park`ing in a loop. When some desired condition is met, another
/// thread calls [`unpark`] on the handle.
///
/// The motivation for this design is twofold:
///
/// * It avoids the need to allocate mutexes and condvars when building new
///   synchronization primitives; the threads already provide basic
///   blocking/signaling.
///
/// * It can be implemented very efficiently on many platforms.
///
pub fn park() {
    let thread = current();

    // If we were previously notified then we consume this notification and
    // return quickly.
    if thread.inner.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst).is_ok() {
        return;
    }

    // Otherwise we need to coordinate going to sleep
    let mut m = thread.inner.lock.lock().unwrap();
    match thread.inner.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
        Ok(_) => {}
        Err(NOTIFIED) => {
            // We must read here, even though we know it will be `NOTIFIED`.
            // This is because `unpark` may have been called again since we read
            // `NOTIFIED` in the `compare_exchange` above. We must perform an
            // acquire operation that synchronizes with that `unpark` to observe
            // any writes it made before the call to unpark. To do that we must
            // read from the write it made to `state`.
            let old = thread.inner.state.swap(EMPTY, SeqCst);
            assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
            return;
        } // should consume this notification, so prohibit spurious wakeups in next park.
        Err(_) => panic!("inconsistent park state"),
    }
    loop {
        m = thread.inner.cvar.wait(m).unwrap();
        match thread.inner.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst) {
            Ok(_) => return, // got a notification
            Err(_) => {}     // spurious wakeup, go back to sleep
        }
    }
}

/// Use [`park_timeout`].
///
/// Blocks unless or until the current thread's token is made available or
/// the specified duration has been reached (may wake spuriously).
///
/// The semantics of this function are equivalent to [`park`] except
/// that the thread will be blocked for roughly no longer than `dur`. This
/// method should not be used for precise timing due to anomalies such as
/// preemption or platform differences that may not cause the maximum
/// amount of time waited to be precisely `ms` long.
///
/// See the [park documentation][`park`] for more detail.
///
/// [`park_timeout`]: fn.park_timeout.html
/// [`park`]: ../../std/thread/fn.park.html
pub fn park_timeout_ms(ms: u32) {
    park_timeout(Duration::from_millis(ms as u64))
}

/// Blocks unless or until the current thread's token is made available or
/// the specified duration has been reached (may wake spuriously).
///
/// The semantics of this function are equivalent to [`park`][park] except
/// that the thread will be blocked for roughly no longer than `dur`. This
/// method should not be used for precise timing due to anomalies such as
/// preemption or platform differences that may not cause the maximum
/// amount of time waited to be precisely `dur` long.
///
/// See the [park documentation][park] for more details.
///
/// # Platform-specific behavior
///
/// Platforms which do not support nanosecond precision for sleeping will have
/// `dur` rounded up to the nearest granularity of time they can sleep for.
///
/// # Examples
///
/// Waiting for the complete expiration of the timeout:
///
/// ```rust,no_run
/// use std::thread::park_timeout;
/// use std::time::{Instant, Duration};
///
/// let timeout = Duration::from_secs(2);
/// let beginning_park = Instant::now();
///
/// let mut timeout_remaining = timeout;
/// loop {
///     park_timeout(timeout_remaining);
///     let elapsed = beginning_park.elapsed();
///     if elapsed >= timeout {
///         break;
///     }
///     println!("restarting park_timeout after {:?}", elapsed);
///     timeout_remaining = timeout - elapsed;
/// }
/// ```
///
/// [park]: fn.park.html
pub fn park_timeout(dur: Duration) {
    let thread = current();

    // Like `park` above we have a fast path for an already-notified thread, and
    // afterwards we start coordinating for a sleep.
    // return quickly.
    if thread.inner.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst).is_ok() {
        return;
    }
    let m = thread.inner.lock.lock().unwrap();
    match thread.inner.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
        Ok(_) => {}
        Err(NOTIFIED) => {
            // We must read again here, see `park`.
            let old = thread.inner.state.swap(EMPTY, SeqCst);
            assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
            return;
        } // should consume this notification, so prohibit spurious wakeups in next park.
        Err(_) => panic!("inconsistent park_timeout state"),
    }

    // Wait with a timeout, and if we spuriously wake up or otherwise wake up
    // from a notification we just want to unconditionally set the state back to
    // empty, either consuming a notification or un-flagging ourselves as
    // parked.
    let (_m, _result) = thread.inner.cvar.wait_timeout(m, dur).unwrap();
    match thread.inner.state.swap(EMPTY, SeqCst) {
        NOTIFIED => {} // got a notification, hurray!
        PARKED => {}   // no notification, alas
        n => panic!("inconsistent park_timeout state: {}", n),
    }
}

////////////////////////////////////////////////////////////////////////////////
// ThreadId
////////////////////////////////////////////////////////////////////////////////

/// A unique identifier for a running thread.
///
/// A `ThreadId` is an opaque object that has a unique value for each thread
/// that creates one. `ThreadId`s are not guaranteed to correspond to a thread's
/// system-designated identifier. A `ThreadId` can be retrieved from the [`id`]
/// method on a [`Thread`].
///
/// # Examples
///
/// ```
/// use std::thread;
///
/// let other_thread = thread::spawn(|| {
///     thread::current().id()
/// });
///
/// let other_thread_id = other_thread.join().unwrap();
/// assert!(thread::current().id() != other_thread_id);
/// ```
///
/// [`id`]: ../../std/thread/struct.Thread.html#method.id
/// [`Thread`]: ../../std/thread/struct.Thread.html
#[derive(Eq, PartialEq, Clone, Copy, Hash, Debug)]
pub struct ThreadId(NonZeroU64);

impl ThreadId {
    // Generate a new unique thread ID.
    fn new() -> ThreadId {
        // We never call `GUARD.init()`, so it is UB to attempt to
        // acquire this mutex reentrantly!

        static GUARD: SgxThreadMutex = SgxThreadMutex::new();
        static mut COUNTER: u64 = 1;

        unsafe {
            let _ = GUARD.lock();

            // If we somehow use up all our bits, panic so that we're not
            // covering up subtle bugs of IDs being reused.
            if COUNTER == crate::u64::MAX {
                panic!("failed to generate unique thread ID: bitspace exhausted");
            }

            let id = COUNTER;
            COUNTER += 1;

            GUARD.unlock();

            ThreadId(NonZeroU64::new(id).unwrap())
        }
    }

    /// This returns a numeric identifier for the thread identified by this
    /// `ThreadId`.
    ///
    /// As noted in the documentation for the type itself, it is essentially an
    /// opaque ID, but is guaranteed to be unique for each thread. The returned
    /// value is entirely opaque -- only equality testing is stable. Note that
    /// it is not guaranteed which values new threads will return, and this may
    /// change across Rust versions.
    pub fn as_u64(&self) -> NonZeroU64 {
        self.0
    }
}

////////////////////////////////////////////////////////////////////////////////
// Thread
////////////////////////////////////////////////////////////////////////////////

/// The internal representation of a `Thread` handle
struct Inner {
    name: Option<CString>, // Guaranteed to be UTF-8
    id: ThreadId,

    // state for thread park/unpark
    state: AtomicUsize,
    lock: SgxMutex<()>,
    cvar: SgxCondvar,
}

/// A handle to a thread.
///
#[derive(Clone)]
pub struct SgxThread {
    inner: Arc<Inner>,
}

impl SgxThread {

    // Used only internally to construct a thread object without spawning
    // Panics if the name contains nuls.
    pub(crate) fn new(name: Option<String>) -> SgxThread {
        let cname =
            name.map(|n| CString::new(n).expect("thread name may not contain interior null bytes"));
        SgxThread {
            inner: Arc::new(Inner {
                name: cname,
                id: ThreadId::new(),
                state: AtomicUsize::new(EMPTY),
                lock: SgxMutex::new(()),
                cvar: SgxCondvar::new(),
            }),
        }
    }

    /// Atomically makes the handle's token available if it is not already.
    ///
    /// Every thread is equipped with some basic low-level blocking support, via
    /// the [`park`][park] function and the `unpark()` method. These can be
    /// used as a more CPU-efficient implementation of a spinlock.
    ///
    pub fn unpark(&self) {
        // To ensure the unparked thread will observe any writes we made
        // before this call, we must perform a release operation that `park`
        // can synchronize with. To do that we must write `NOTIFIED` even if
        // `state` is already `NOTIFIED`. That is why this must be a swap
        // rather than a compare-and-swap that returns if it reads `NOTIFIED`
        // on failure.
        match self.inner.state.swap(NOTIFIED, SeqCst) {
            EMPTY => return,    // no one was waiting
            NOTIFIED => return, // already unparked
            PARKED => {}        // gotta go wake someone up
            _ => panic!("inconsistent state in unpark"),
        }

        // There is a period between when the parked thread sets `state` to
        // `PARKED` (or last checked `state` in the case of a spurious wake
        // up) and when it actually waits on `cvar`. If we were to notify
        // during this period it would be ignored and then when the parked
        // thread went to sleep it would never wake up. Fortunately, it has
        // `lock` locked at this stage so we can acquire `lock` to wait until
        // it is ready to receive the notification.
        //
        // Releasing `lock` before the call to `notify_one` means that when the
        // parked thread wakes it doesn't get woken only to have to wait for us
        // to release `lock`.
        drop(self.inner.lock.lock().unwrap());
        self.inner.cvar.notify_one()
    }

    /// Gets the thread's unique identifier.
    ///
    pub fn id(&self) -> ThreadId {
        self.inner.id
    }

    /// Gets the thread's name.
    ///
    /// For more information about named threads, see
    /// [this module-level documentation][naming-threads].
    ///
    pub fn name(&self) -> Option<&str> {
        self.cname().map(|s| unsafe { str::from_utf8_unchecked(s.to_bytes()) })
    }

    fn cname(&self) -> Option<&CStr> {
        self.inner.name.as_ref().map(|s| &**s)
    }
}

impl fmt::Debug for SgxThread {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("SgxThread").field("id", &self.id()).field("name", &self.name()).finish()
    }
}

////////////////////////////////////////////////////////////////////////////////
// JoinHandle
////////////////////////////////////////////////////////////////////////////////

/// A specialized [`Result`] type for threads.
///
/// Indicates the manner in which a thread exited.
///
/// The value contained in the `Result::Err` variant
/// is the value the thread panicked with;
/// that is, the argument the `panic!` macro was called with.
/// Unlike with normal errors, this value doesn't implement
/// the [`Error`](crate::error::Error) trait.
///
/// Thus, a sensible way to handle a thread panic is to either:
/// 1. `unwrap` the `Result<T>`, propagating the panic
/// 2. or in case the thread is intended to be a subsystem boundary
/// that is supposed to isolate system-level failures,
/// match on the `Err` variant and handle the panic in an appropriate way.
///
/// A thread that completes without panicking is considered to exit successfully.
///
pub type Result<T> = crate::result::Result<T, Box<dyn Any + Send + 'static>>;

// This packet is used to communicate the return value between the child thread
// and the parent thread. Memory is shared through the `Arc` within and there's
// no need for a mutex here because synchronization happens with `join()` (the
// parent thread never reads this packet until the child has exited).
//
// This packet itself is then stored into a `JoinInner` which in turns is placed
// in `JoinHandle` and `JoinGuard`. Due to the usage of `UnsafeCell` we need to
// manually worry about impls like Send and Sync. The type `T` should
// already always be Send (otherwise the thread could not have been created) and
// this type is inherently Sync because no methods take &self. Regardless,
// however, we add inheriting impls for Send/Sync to this type to ensure it's
// Send/Sync and that future modifications will still appropriately classify it.
#[cfg(feature = "thread")]
struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);

#[cfg(feature = "thread")]
unsafe impl<T: Send> Send for Packet<T> {}
#[cfg(feature = "thread")]
unsafe impl<T: Sync> Sync for Packet<T> {}

/// Inner representation for JoinHandle
#[cfg(feature = "thread")]
struct JoinInner<T> {
    native: Option<imp::Thread>,
    thread: SgxThread,
    packet: Packet<T>,
}

#[cfg(feature = "thread")]
impl<T> JoinInner<T> {
    fn join(&mut self) -> Result<T> {
        self.native.take().unwrap().join();
        unsafe { (*self.packet.0.get()).take().unwrap() }
    }
}

/// An owned permission to join on a thread (block on its termination).
///
/// A `JoinHandle` *detaches* the associated thread when it is dropped, which
/// means that there is no longer any handle to thread and no way to `join`
/// on it.
///
/// Due to platform restrictions, it is not possible to [`Clone`] this
/// handle: the ability to join a thread is a uniquely-owned permission.
///
/// This `struct` is created by the [`thread::spawn`] function and the
/// [`thread::Builder::spawn`] method.
///
/// # Examples
///
/// Creation from [`thread::spawn`]:
///
/// ```
/// use std::thread;
///
/// let join_handle: thread::JoinHandle<_> = thread::spawn(|| {
///     // some work here
/// });
/// ```
///
/// Creation from [`thread::Builder::spawn`]:
///
/// ```
/// use std::thread;
///
/// let builder = thread::Builder::new();
///
/// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
///     // some work here
/// }).unwrap();
/// ```
///
/// Child being detached and outliving its parent:
///
/// ```no_run
/// use std::thread;
/// use std::time::Duration;
///
/// let original_thread = thread::spawn(|| {
///     let _detached_thread = thread::spawn(|| {
///         // Here we sleep to make sure that the first thread returns before.
///         thread::sleep(Duration::from_millis(10));
///         // This will be called, even though the JoinHandle is dropped.
///         println!("♫ Still alive ♫");
///     });
/// });
///
/// original_thread.join().expect("The thread being joined has panicked");
/// println!("Original thread is joined.");
///
/// // We make sure that the new thread has time to run, before the main
/// // thread returns.
///
/// thread::sleep(Duration::from_millis(1000));
/// ```
///
/// [`Clone`]: ../../std/clone/trait.Clone.html
/// [`thread::spawn`]: fn.spawn.html
/// [`thread::Builder::spawn`]: struct.Builder.html#method.spawn

#[cfg(feature = "thread")]
pub struct JoinHandle<T>(JoinInner<T>);
#[cfg(feature = "thread")]
unsafe impl<T> Send for JoinHandle<T> {}
#[cfg(feature = "thread")]
unsafe impl<T> Sync for JoinHandle<T> {}
#[cfg(feature = "thread")]
impl<T> JoinHandle<T> {
    /// Extracts a handle to the underlying thread.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::thread;
    ///
    /// let builder = thread::Builder::new();
    ///
    /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
    ///     // some work here
    /// }).unwrap();
    ///
    /// let thread = join_handle.thread();
    /// println!("thread id: {:?}", thread.id());
    /// ```
    pub fn thread(&self) -> &SgxThread {
        &self.0.thread
    }

    /// Waits for the associated thread to finish.
    ///
    /// In terms of [atomic memory orderings],  the completion of the associated
    /// thread synchronizes with this function returning. In other words, all
    /// operations performed by that thread are ordered before all
    /// operations that happen after `join` returns.
    ///
    /// If the child thread panics, [`Err`] is returned with the parameter given
    /// to [`panic`].
    ///
    /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
    /// [`panic`]: ../../std/macro.panic.html
    /// [atomic memory orderings]: ../../std/sync/atomic/index.html
    ///
    /// # Panics
    ///
    /// This function may panic on some platforms if a thread attempts to join
    /// itself or otherwise may create a deadlock with joining threads.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::thread;
    ///
    /// let builder = thread::Builder::new();
    ///
    /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
    ///     // some work here
    /// }).unwrap();
    /// join_handle.join().expect("Couldn't join on the associated thread");
    /// ```
    pub fn join(mut self) -> Result<T> {
        self.0.join()
    }
}

#[cfg(feature = "thread")]
impl<T> AsInner<imp::Thread> for JoinHandle<T> {
    fn as_inner(&self) -> &imp::Thread {
        self.0.native.as_ref().unwrap()
    }
}

#[cfg(feature = "thread")]
impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
    fn into_inner(self) -> imp::Thread {
        self.0.native.unwrap()
    }
}

#[cfg(feature = "thread")]
impl<T> fmt::Debug for JoinHandle<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.pad("JoinHandle { .. }")
    }
}

#[cfg(feature = "thread")]
fn _assert_sync_and_send() {
    fn _assert_both<T: Send + Sync>() {}
    _assert_both::<JoinHandle<()>>();
    _assert_both::<SgxThread>();
}