std\sys\pal\windows/
thread.rs

1use core::ffi::c_void;
2
3use super::time::WaitableTimer;
4use super::to_u16s;
5use crate::ffi::CStr;
6use crate::num::NonZero;
7use crate::os::windows::io::{AsRawHandle, HandleOrNull};
8use crate::sys::handle::Handle;
9use crate::sys::{c, stack_overflow};
10use crate::sys_common::FromInner;
11use crate::time::{Duration, Instant};
12use crate::{io, ptr};
13
14pub const DEFAULT_MIN_STACK_SIZE: usize = 2 * 1024 * 1024;
15
16pub struct Thread {
17    handle: Handle,
18}
19
20impl Thread {
21    // unsafe: see thread::Builder::spawn_unchecked for safety requirements
22    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
23    pub unsafe fn new(
24        stack: usize,
25        _name: Option<&str>,
26        p: Box<dyn FnOnce()>,
27    ) -> io::Result<Thread> {
28        let p = Box::into_raw(Box::new(p));
29
30        // CreateThread rounds up values for the stack size to the nearest page size (at least 4kb).
31        // If a value of zero is given then the default stack size is used instead.
32        // SAFETY: `thread_start` has the right ABI for a thread's entry point.
33        // `p` is simply passed through to the new thread without being touched.
34        let ret = unsafe {
35            let ret = c::CreateThread(
36                ptr::null_mut(),
37                stack,
38                Some(thread_start),
39                p as *mut _,
40                c::STACK_SIZE_PARAM_IS_A_RESERVATION,
41                ptr::null_mut(),
42            );
43            HandleOrNull::from_raw_handle(ret)
44        };
45        return if let Ok(handle) = ret.try_into() {
46            Ok(Thread { handle: Handle::from_inner(handle) })
47        } else {
48            // The thread failed to start and as a result p was not consumed. Therefore, it is
49            // safe to reconstruct the box so that it gets deallocated.
50            unsafe { drop(Box::from_raw(p)) };
51            Err(io::Error::last_os_error())
52        };
53
54        unsafe extern "system" fn thread_start(main: *mut c_void) -> u32 {
55            // Next, reserve some stack space for if we otherwise run out of stack.
56            stack_overflow::reserve_stack();
57            // Finally, let's run some code.
58            // SAFETY: We are simply recreating the box that was leaked earlier.
59            // It's the responsibility of the one who call `Thread::new` to ensure this is safe to call here.
60            unsafe { Box::from_raw(main as *mut Box<dyn FnOnce()>)() };
61            0
62        }
63    }
64
65    pub fn set_name(name: &CStr) {
66        if let Ok(utf8) = name.to_str() {
67            if let Ok(utf16) = to_u16s(utf8) {
68                unsafe {
69                    // SAFETY: the vec returned by `to_u16s` ends with a zero value
70                    Self::set_name_wide(&utf16)
71                }
72            };
73        };
74    }
75
76    /// # Safety
77    ///
78    /// `name` must end with a zero value
79    pub unsafe fn set_name_wide(name: &[u16]) {
80        unsafe { c::SetThreadDescription(c::GetCurrentThread(), name.as_ptr()) };
81    }
82
83    pub fn join(self) {
84        let rc = unsafe { c::WaitForSingleObject(self.handle.as_raw_handle(), c::INFINITE) };
85        if rc == c::WAIT_FAILED {
86            panic!("failed to join on thread: {}", io::Error::last_os_error());
87        }
88    }
89
90    pub fn yield_now() {
91        // This function will return 0 if there are no other threads to execute,
92        // but this also means that the yield was useless so this isn't really a
93        // case that needs to be worried about.
94        unsafe {
95            c::SwitchToThread();
96        }
97    }
98
99    pub fn sleep(dur: Duration) {
100        fn high_precision_sleep(dur: Duration) -> Result<(), ()> {
101            let timer = WaitableTimer::high_resolution()?;
102            timer.set(dur)?;
103            timer.wait()
104        }
105        // Attempt to use high-precision sleep (Windows 10, version 1803+).
106        // On error fallback to the standard `Sleep` function.
107        // Also preserves the zero duration behavior of `Sleep`.
108        if dur.is_zero() || high_precision_sleep(dur).is_err() {
109            unsafe { c::Sleep(super::dur2timeout(dur)) }
110        }
111    }
112
113    pub fn sleep_until(deadline: Instant) {
114        let now = Instant::now();
115
116        if let Some(delay) = deadline.checked_duration_since(now) {
117            Self::sleep(delay);
118        }
119    }
120
121    pub fn handle(&self) -> &Handle {
122        &self.handle
123    }
124
125    pub fn into_handle(self) -> Handle {
126        self.handle
127    }
128}
129
130pub(crate) fn current_os_id() -> Option<u64> {
131    // SAFETY: FFI call with no preconditions.
132    let id: u32 = unsafe { c::GetCurrentThreadId() };
133
134    // A return value of 0 indicates failed lookup.
135    if id == 0 { None } else { Some(id.into()) }
136}
137
138pub fn available_parallelism() -> io::Result<NonZero<usize>> {
139    let res = unsafe {
140        let mut sysinfo: c::SYSTEM_INFO = crate::mem::zeroed();
141        c::GetSystemInfo(&mut sysinfo);
142        sysinfo.dwNumberOfProcessors as usize
143    };
144    match res {
145        0 => Err(io::Error::UNKNOWN_THREAD_COUNT),
146        cpus => Ok(unsafe { NonZero::new_unchecked(cpus) }),
147    }
148}
std\sys\pal\windows/thread.rs

std\sys\pal\windows/
thread.rs
