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    use crate::cmp;
    use crate::ffi::CStr;
    use crate::io;
    use crate::mem;
    use crate::ptr;
    use crate::sys::os;
    use crate::time::Duration;

    use crate::sys_common::thread::*;

    #[cfg(not(target_os = "l4re"))]
    pub const DEFAULT_MIN_STACK_SIZE: usize = 2 * 1024 * 1024;
    #[cfg(target_os = "l4re")]
    pub const DEFAULT_MIN_STACK_SIZE: usize = 1024 * 1024;

    pub struct Thread {
        id: libc::pthread_t,
    }

    // Some platforms may have pthread_t as a pointer in which case we still want
    // a thread to be Send/Sync
    unsafe impl Send for Thread {}
    unsafe impl Sync for Thread {}

    // The pthread_attr_setstacksize symbol doesn't exist in the emscripten libc,
    // so we have to not link to it to satisfy emcc's ERROR_ON_UNDEFINED_SYMBOLS.
    #[cfg(not(target_os = "emscripten"))]
    unsafe fn pthread_attr_setstacksize(attr: *mut libc::pthread_attr_t,
                                        stack_size: libc::size_t) -> libc::c_int {
        libc::pthread_attr_setstacksize(attr, stack_size)
    }

    #[cfg(target_os = "emscripten")]
    unsafe fn pthread_attr_setstacksize(_attr: *mut libc::pthread_attr_t,
                                        _stack_size: libc::size_t) -> libc::c_int {
        panic!()
    }

    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 p = box p;
            let mut native: libc::pthread_t = mem::zeroed();
            let mut attr: libc::pthread_attr_t = mem::zeroed();
            assert_eq!(libc::pthread_attr_init(&mut attr), 0);

            let stack_size = cmp::max(stack, min_stack_size(&attr));

            match pthread_attr_setstacksize(&mut attr,
                                            stack_size) {
                0 => {}
                n => {
                    assert_eq!(n, libc::EINVAL);
                    // EINVAL means |stack_size| is either too small or not a
                    // multiple of the system page size.  Because it's definitely
                    // >= PTHREAD_STACK_MIN, it must be an alignment issue.
                    // Round up to the nearest page and try again.
                    let page_size = os::page_size();
                    let stack_size = (stack_size + page_size - 1) &
                                     (-(page_size as isize - 1) as usize - 1);
                    assert_eq!(libc::pthread_attr_setstacksize(&mut attr,
                                                               stack_size), 0);
                }
            };

            let ret = libc::pthread_create(&mut native, &attr, thread_start,
                                           &*p as *const _ as *mut _);
            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);

            return if ret != 0 {
                Err(io::Error::from_raw_os_error(ret))
            } else {
                mem::forget(p); // ownership passed to pthread_create
                Ok(Thread { id: native })
            };

            extern fn thread_start(main: *mut libc::c_void) -> *mut libc::c_void {
                unsafe { start_thread(main as *mut u8); }
                ptr::null_mut()
            }
        }

        pub fn yield_now() {
            let ret = unsafe { libc::sched_yield() };
            debug_assert_eq!(ret, 0);
        }

        #[cfg(any(target_os = "linux",
                  target_os = "android"))]
        pub fn set_name(name: &CStr) {
            const PR_SET_NAME: libc::c_int = 15;
            // pthread wrapper only appeared in glibc 2.12, so we use syscall
            // directly.
            unsafe {
                libc::prctl(PR_SET_NAME, name.as_ptr() as libc::c_ulong, 0, 0, 0);
            }
        }

        #[cfg(any(target_os = "freebsd",
                  target_os = "dragonfly",
                  target_os = "openbsd"))]
        pub fn set_name(name: &CStr) {
            unsafe {
                libc::pthread_set_name_np(libc::pthread_self(), name.as_ptr());
            }
        }

        #[cfg(any(target_os = "macos", target_os = "ios"))]
        pub fn set_name(name: &CStr) {
            unsafe {
                libc::pthread_setname_np(name.as_ptr());
            }
        }

        #[cfg(target_os = "netbsd")]
        pub fn set_name(name: &CStr) {
            use crate::ffi::CString;
            let cname = CString::new(&b"%s"[..]).unwrap();
            unsafe {
                libc::pthread_setname_np(libc::pthread_self(), cname.as_ptr(),
                                         name.as_ptr() as *mut libc::c_void);
            }
        }
        #[cfg(any(target_env = "newlib",
                  target_os = "solaris",
                  target_os = "haiku",
                  target_os = "l4re",
                  target_os = "emscripten",
                  target_os = "hermit"))]
        pub fn set_name(_name: &CStr) {
            // Newlib, Illumos, Haiku, and Emscripten have no way to set a thread name.
        }
        #[cfg(target_os = "fuchsia")]
        pub fn set_name(_name: &CStr) {
            // FIXME: determine whether Fuchsia has a way to set a thread name.
        }

        pub fn sleep(dur: Duration) {
            let mut secs = dur.as_secs();
            let mut nsecs = dur.subsec_nanos() as _;

            // If we're awoken with a signal then the return value will be -1 and
            // nanosleep will fill in `ts` with the remaining time.
            unsafe {
                while secs > 0 || nsecs > 0 {
                    let mut ts = libc::timespec {
                        tv_sec: cmp::min(libc::time_t::max_value() as u64, secs) as libc::time_t,
                        tv_nsec: nsecs,
                    };
                    secs -= ts.tv_sec as u64;
                    if libc::nanosleep(&ts, &mut ts) == -1 {
                        assert_eq!(os::errno(), libc::EINTR);
                        secs += ts.tv_sec as u64;
                        nsecs = ts.tv_nsec;
                    } else {
                        nsecs = 0;
                    }
                }
            }
        }

        pub fn join(self) {
            unsafe {
                let ret = libc::pthread_join(self.id, ptr::null_mut());
                mem::forget(self);
                assert!(ret == 0,
                        "failed to join thread: {}", io::Error::from_raw_os_error(ret));
            }
        }

        pub fn id(&self) -> libc::pthread_t { self.id }

        pub fn into_id(self) -> libc::pthread_t {
            let id = self.id;
            mem::forget(self);
            id
        }
    }

    impl Drop for Thread {
        fn drop(&mut self) {
            let ret = unsafe { libc::pthread_detach(self.id) };
            debug_assert_eq!(ret, 0);
        }
    }

    #[cfg(all(not(all(target_os = "linux", not(target_env = "musl"))),
              not(target_os = "freebsd"),
              not(target_os = "macos"),
              not(all(target_os = "netbsd", not(target_vendor = "rumprun"))),
              not(target_os = "openbsd"),
              not(target_os = "solaris")))]
    #[cfg_attr(test, allow(dead_code))]
    pub mod guard {
        use crate::ops::Range;
        pub type Guard = Range<usize>;
        pub unsafe fn current() -> Option<Guard> { None }
        pub unsafe fn init() -> Option<Guard> { None }
    }

    #[cfg(any(all(target_os = "linux", not(target_env = "musl")),
              target_os = "freebsd",
              target_os = "macos",
              all(target_os = "netbsd", not(target_vendor = "rumprun")),
              target_os = "openbsd",
              target_os = "solaris"))]
    #[cfg_attr(test, allow(dead_code))]
    pub mod guard {
        use libc::{mmap, mprotect};
        use libc::{PROT_NONE, PROT_READ, PROT_WRITE, MAP_PRIVATE, MAP_ANON, MAP_FAILED, MAP_FIXED};

        use crate::ops::Range;
        use crate::sys::os;

        // This is initialized in init() and only read from after
        static mut PAGE_SIZE: usize = 0;

        pub type Guard = Range<usize>;

        #[cfg(target_os = "solaris")]
        unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
            let mut current_stack: libc::stack_t = crate::mem::zeroed();
            assert_eq!(libc::stack_getbounds(&mut current_stack), 0);
            Some(current_stack.ss_sp)
        }

        #[cfg(target_os = "macos")]
        unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
            let stackaddr = libc::pthread_get_stackaddr_np(libc::pthread_self()) as usize -
                 libc::pthread_get_stacksize_np(libc::pthread_self());
            Some(stackaddr as *mut libc::c_void)
        }

        #[cfg(target_os = "openbsd")]
        unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
            let mut current_stack: libc::stack_t = crate::mem::zeroed();
            assert_eq!(libc::pthread_stackseg_np(libc::pthread_self(),
                                                 &mut current_stack), 0);

            let stackaddr = if libc::pthread_main_np() == 1 {
                // main thread
                current_stack.ss_sp as usize - current_stack.ss_size + PAGE_SIZE
            } else {
                // new thread
                current_stack.ss_sp as usize - current_stack.ss_size
            };
            Some(stackaddr as *mut libc::c_void)
        }

        #[cfg(any(target_os = "android", target_os = "freebsd",
                  target_os = "linux", target_os = "netbsd", target_os = "l4re"))]
        unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
            let mut ret = None;
            let mut attr: libc::pthread_attr_t = crate::mem::zeroed();
            assert_eq!(libc::pthread_attr_init(&mut attr), 0);
            #[cfg(target_os = "freebsd")]
                let e = libc::pthread_attr_get_np(libc::pthread_self(), &mut attr);
            #[cfg(not(target_os = "freebsd"))]
                let e = libc::pthread_getattr_np(libc::pthread_self(), &mut attr);
            if e == 0 {
                let mut stackaddr = crate::ptr::null_mut();
                let mut stacksize = 0;
                assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackaddr,
                                                       &mut stacksize), 0);
                ret = Some(stackaddr);
            }
            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
            ret
        }

        // Precondition: PAGE_SIZE is initialized.
        unsafe fn get_stack_start_aligned() -> Option<*mut libc::c_void> {
            assert!(PAGE_SIZE != 0);
            let stackaddr = get_stack_start()?;

            // Ensure stackaddr is page aligned! A parent process might
            // have reset RLIMIT_STACK to be non-page aligned. The
            // pthread_attr_getstack() reports the usable stack area
            // stackaddr < stackaddr + stacksize, so if stackaddr is not
            // page-aligned, calculate the fix such that stackaddr <
            // new_page_aligned_stackaddr < stackaddr + stacksize
            let remainder = (stackaddr as usize) % PAGE_SIZE;
            Some(if remainder == 0 {
                stackaddr
            } else {
                ((stackaddr as usize) + PAGE_SIZE - remainder) as *mut libc::c_void
            })
        }

        pub unsafe fn init() -> Option<Guard> {
            PAGE_SIZE = os::page_size();

            let stackaddr = get_stack_start_aligned()?;

            if cfg!(target_os = "linux") {
                // Linux doesn't allocate the whole stack right away, and
                // the kernel has its own stack-guard mechanism to fault
                // when growing too close to an existing mapping.  If we map
                // our own guard, then the kernel starts enforcing a rather
                // large gap above that, rendering much of the possible
                // stack space useless.  See #43052.
                //
                // Instead, we'll just note where we expect rlimit to start
                // faulting, so our handler can report "stack overflow", and
                // trust that the kernel's own stack guard will work.
                let stackaddr = stackaddr as usize;
                Some(stackaddr - PAGE_SIZE..stackaddr)
            } else {
                // Reallocate the last page of the stack.
                // This ensures SIGBUS will be raised on
                // stack overflow.
                // Systems which enforce strict PAX MPROTECT do not allow
                // to mprotect() a mapping with less restrictive permissions
                // than the initial mmap() used, so we mmap() here with
                // read/write permissions and only then mprotect() it to
                // no permissions at all. See issue #50313.
                let result = mmap(stackaddr, PAGE_SIZE, PROT_READ | PROT_WRITE,
                                  MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
                if result != stackaddr || result == MAP_FAILED {
                    panic!("failed to allocate a guard page");
                }

                let result = mprotect(stackaddr, PAGE_SIZE, PROT_NONE);
                if result != 0 {
                    panic!("failed to protect the guard page");
                }

                let guardaddr = stackaddr as usize;
                let offset = if cfg!(target_os = "freebsd") {
                    2
                } else {
                    1
                };

                Some(guardaddr..guardaddr + offset * PAGE_SIZE)
            }
        }

        #[cfg(any(target_os = "macos",
                  target_os = "openbsd",
                  target_os = "solaris"))]
        pub unsafe fn current() -> Option<Guard> {
            let stackaddr = get_stack_start()? as usize;
            Some(stackaddr - PAGE_SIZE..stackaddr)
        }

        #[cfg(any(target_os = "android", target_os = "freebsd",
                  target_os = "linux", target_os = "netbsd", target_os = "l4re"))]
        pub unsafe fn current() -> Option<Guard> {
            let mut ret = None;
            let mut attr: libc::pthread_attr_t = crate::mem::zeroed();
            assert_eq!(libc::pthread_attr_init(&mut attr), 0);
            #[cfg(target_os = "freebsd")]
                let e = libc::pthread_attr_get_np(libc::pthread_self(), &mut attr);
            #[cfg(not(target_os = "freebsd"))]
                let e = libc::pthread_getattr_np(libc::pthread_self(), &mut attr);
            if e == 0 {
                let mut guardsize = 0;
                assert_eq!(libc::pthread_attr_getguardsize(&attr, &mut guardsize), 0);
                if guardsize == 0 {
                    panic!("there is no guard page");
                }
                let mut stackaddr = crate::ptr::null_mut();
                let mut size = 0;
                assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackaddr,
                                                       &mut size), 0);

                let stackaddr = stackaddr as usize;
                ret = if cfg!(target_os = "freebsd") {
                    // FIXME does freebsd really fault *below* the guard addr?
                    let guardaddr = stackaddr - guardsize;
                    Some(guardaddr - PAGE_SIZE..guardaddr)
                } else if cfg!(target_os = "netbsd") {
                    Some(stackaddr - guardsize..stackaddr)
                } else if cfg!(all(target_os = "linux", target_env = "gnu")) {
                    // glibc used to include the guard area within the stack, as noted in the BUGS
                    // section of `man pthread_attr_getguardsize`.  This has been corrected starting
                    // with glibc 2.27, and in some distro backports, so the guard is now placed at the
                    // end (below) the stack.  There's no easy way for us to know which we have at
                    // runtime, so we'll just match any fault in the range right above or below the
                    // stack base to call that fault a stack overflow.
                    Some(stackaddr - guardsize..stackaddr + guardsize)
                } else {
                    Some(stackaddr..stackaddr + guardsize)
                };
            }
            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
            ret
        }
    }

    // glibc >= 2.15 has a __pthread_get_minstack() function that returns
    // PTHREAD_STACK_MIN plus however many bytes are needed for thread-local
    // storage.  We need that information to avoid blowing up when a small stack
    // is created in an application with big thread-local storage requirements.
    // See #6233 for rationale and details.
    #[cfg(target_os = "linux")]
    #[allow(deprecated)]
    fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
        weak!(fn __pthread_get_minstack(*const libc::pthread_attr_t) -> libc::size_t);

        match __pthread_get_minstack.get() {
            None => libc::PTHREAD_STACK_MIN,
            Some(f) => unsafe { f(attr) },
        }
    }

    // No point in looking up __pthread_get_minstack() on non-glibc
    // platforms.
    #[cfg(all(not(target_os = "linux"),
              not(target_os = "netbsd")))]
    fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
        libc::PTHREAD_STACK_MIN
    }

    #[cfg(target_os = "netbsd")]
    fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
        2048 // just a guess
    }

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