use crate::cmp;
use crate::ffi::CStr;
use crate::io;
use crate::mem;
use crate::num::NonZeroUsize;
use crate::ptr;
use crate::sys::{os, stack_overflow};
use crate::time::Duration;

#[cfg(all(target_os = "linux", target_env = "gnu"))]
use crate::sys::weak::dlsym;
#[cfg(any(target_os = "solaris", target_os = "illumos", target_os = "nto"))]
use crate::sys::weak::weak;
#[cfg(not(any(target_os = "l4re", target_os = "vxworks", target_os = "espidf")))]
pub const DEFAULT_MIN_STACK_SIZE: usize = 2 * 1024 * 1024;
#[cfg(target_os = "l4re")]
pub const DEFAULT_MIN_STACK_SIZE: usize = 1024 * 1024;
#[cfg(target_os = "vxworks")]
pub const DEFAULT_MIN_STACK_SIZE: usize = 256 * 1024;
#[cfg(target_os = "espidf")]
pub const DEFAULT_MIN_STACK_SIZE: usize = 0; // 0 表示应使用 ESP-IDF menuconfig 系统中配置的栈大小

#[cfg(target_os = "fuchsia")]
mod zircon {
    type zx_handle_t = u32;
    type zx_status_t = i32;
    pub const ZX_PROP_NAME: u32 = 3;

    extern "C" {
        pub fn zx_object_set_property(
            handle: zx_handle_t,
            property: u32,
            value: *const libc::c_void,
            value_size: libc::size_t,
        ) -> zx_status_t;
        pub fn zx_thread_self() -> zx_handle_t;
    }
}

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

// 某些平台可能将 pthread_t 用作指针，在这种情况下，我们仍然希望线程为 Send/Sync
//
unsafe impl Send for Thread {}
unsafe impl Sync for Thread {}

impl Thread {
    // 不安全：有关安全要求，请参见 thread::Builder::spawn_unchecked
    pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
        let p = Box::into_raw(Box::new(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);

        #[cfg(target_os = "espidf")]
        if stack > 0 {
            // 仅在传递非零值时才设置栈
            // 0 用作指示应使用 ESP-IDF menuconfig 系统中配置的默认栈大小
            assert_eq!(
                libc::pthread_attr_setstacksize(&mut attr, cmp::max(stack, min_stack_size(&attr))),
                0
            );
        }

        #[cfg(not(target_os = "espidf"))]
        {
            let stack_size = cmp::max(stack, min_stack_size(&attr));

            match libc::pthread_attr_setstacksize(&mut attr, stack_size) {
                0 => {}
                n => {
                    assert_eq!(n, libc::EINVAL);
                    // EINVAL 表示 | stack_size | 太小或不是系统页面大小的倍数。
                    // 因为肯定是 >= PTHREAD_STACK_MIN，所以它一定是对齐问题。
                    // 向上舍入到最近的页面，然后重试。
                    //
                    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 *mut _);
        // Note: 如果线程创建失败并且该断言失败，则 p 将被泄漏。
        // 但是，替代设计可能会导致双重释放，这显然更糟。
        //
        assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);

        return if ret != 0 {
            // 线程无法启动，结果 p 没有被消费。
            // 因此，重建 box 使其被释放是安全的。
            drop(Box::from_raw(p));
            Err(io::Error::from_raw_os_error(ret))
        } else {
            Ok(Thread { id: native })
        };

        extern "C" fn thread_start(main: *mut libc::c_void) -> *mut libc::c_void {
            unsafe {
                // 接下来，设置我们的栈溢出处理程序，如果我们用完栈，可能会触发该处理程序。
                //
                let _handler = stack_overflow::Handler::new();
                // 最后，让我们运行一些代码。
                Box::from_raw(main as *mut Box<dyn FnOnce()>)();
            }
            ptr::null_mut()
        }
    }

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

    #[cfg(target_os = "android")]
    pub fn set_name(name: &CStr) {
        const PR_SET_NAME: libc::c_int = 15;
        unsafe {
            libc::prctl(
                PR_SET_NAME,
                name.as_ptr(),
                0 as libc::c_ulong,
                0 as libc::c_ulong,
                0 as libc::c_ulong,
            );
        }
    }

    #[cfg(target_os = "linux")]
    pub fn set_name(name: &CStr) {
        const TASK_COMM_LEN: usize = 16;

        unsafe {
            // 从 glibc 2.12、musl 1.1.16 和 uClibc 1.0.20 开始可用。
            let name = truncate_cstr::<{ TASK_COMM_LEN }>(name);
            let res = libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
            // 我们没有在这里传播错误的好方法，但是在调试构建中，让我们检查一下这是否真的有效。
            debug_assert_eq!(res, 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", target_os = "watchos"))]
    pub fn set_name(name: &CStr) {
        unsafe {
            let name = truncate_cstr::<{ libc::MAXTHREADNAMESIZE }>(name);
            let res = libc::pthread_setname_np(name.as_ptr());
            // 我们没有在这里传播错误的好方法，但是在调试构建中，让我们检查一下这是否真的有效。
            debug_assert_eq!(res, 0);
        }
    }

    #[cfg(target_os = "netbsd")]
    pub fn set_name(name: &CStr) {
        unsafe {
            let cname = CStr::from_bytes_with_nul_unchecked(b"%s\0".as_slice());
            let res = libc::pthread_setname_np(
                libc::pthread_self(),
                cname.as_ptr(),
                name.as_ptr() as *mut libc::c_void,
            );
            debug_assert_eq!(res, 0);
        }
    }

    #[cfg(any(target_os = "solaris", target_os = "illumos", target_os = "nto"))]
    pub fn set_name(name: &CStr) {
        weak! {
            fn pthread_setname_np(
                libc::pthread_t, *const libc::c_char
            ) -> libc::c_int
        }

        if let Some(f) = pthread_setname_np.get() {
            let res = unsafe { f(libc::pthread_self(), name.as_ptr()) };
            debug_assert_eq!(res, 0);
        }
    }

    #[cfg(target_os = "fuchsia")]
    pub fn set_name(name: &CStr) {
        use self::zircon::*;
        unsafe {
            zx_object_set_property(
                zx_thread_self(),
                ZX_PROP_NAME,
                name.as_ptr() as *const libc::c_void,
                name.to_bytes().len(),
            );
        }
    }

    #[cfg(target_os = "haiku")]
    pub fn set_name(name: &CStr) {
        unsafe {
            let thread_self = libc::find_thread(ptr::null_mut());
            libc::rename_thread(thread_self, name.as_ptr());
        }
    }

    #[cfg(any(
        target_env = "newlib",
        target_os = "l4re",
        target_os = "emscripten",
        target_os = "redox",
        target_os = "vxworks"
    ))]
    pub fn set_name(_name: &CStr) {
        // Newlib、Emscripten 和 VxWorks 无法设置线程名称。
    }

    #[cfg(not(target_os = "espidf"))]
    pub fn sleep(dur: Duration) {
        let mut secs = dur.as_secs();
        let mut nsecs = dur.subsec_nanos() as _;

        // 如果我们被信号唤醒，则返回值为 -1，nanosleep 将使用剩余时间填充 `ts`。
        //
        unsafe {
            while secs > 0 || nsecs > 0 {
                let mut ts = libc::timespec {
                    tv_sec: cmp::min(libc::time_t::MAX as u64, secs) as libc::time_t,
                    tv_nsec: nsecs,
                };
                secs -= ts.tv_sec as u64;
                let ts_ptr = &mut ts as *mut _;
                if libc::nanosleep(ts_ptr, ts_ptr) == -1 {
                    assert_eq!(os::errno(), libc::EINTR);
                    secs += ts.tv_sec as u64;
                    nsecs = ts.tv_nsec;
                } else {
                    nsecs = 0;
                }
            }
        }
    }

    #[cfg(target_os = "espidf")]
    pub fn sleep(dur: Duration) {
        let mut micros = dur.as_micros();
        unsafe {
            while micros > 0 {
                let st = if micros > u32::MAX as u128 { u32::MAX } else { micros as u32 };
                libc::usleep(st);

                micros -= st as u128;
            }
        }
    }

    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(any(target_os = "linux", target_os = "macos", target_os = "ios", target_os = "watchos"))]
fn truncate_cstr<const MAX_WITH_NUL: usize>(cstr: &CStr) -> [libc::c_char; MAX_WITH_NUL] {
    let mut result = [0; MAX_WITH_NUL];
    for (src, dst) in cstr.to_bytes().iter().zip(&mut result[..MAX_WITH_NUL - 1]) {
        *dst = *src as libc::c_char;
    }
    result
}

pub fn available_parallelism() -> io::Result<NonZeroUsize> {
    cfg_if::cfg_if! {
        if #[cfg(any(
            target_os = "android",
            target_os = "emscripten",
            target_os = "fuchsia",
            target_os = "ios",
            target_os = "linux",
            target_os = "macos",
            target_os = "solaris",
            target_os = "illumos",
        ))] {
            #[cfg(any(target_os = "android", target_os = "linux"))]
            {
                let quota = cgroups::quota().max(1);
                let mut set: libc::cpu_set_t = unsafe { mem::zeroed() };
                unsafe {
                    if libc::sched_getaffinity(0, mem::size_of::<libc::cpu_set_t>(), &mut set) == 0 {
                        let count = libc::CPU_COUNT(&set) as usize;
                        let count = count.min(quota);
                        // SAFETY: 关联掩码不能为空，并且配额被限制为至少 1
                        return Ok(NonZeroUsize::new_unchecked(count));
                    }
                }
            }
            match unsafe { libc::sysconf(libc::_SC_NPROCESSORS_ONLN) } {
                -1 => Err(io::Error::last_os_error()),
                0 => Err(io::const_io_error!(io::ErrorKind::NotFound, "The number of hardware threads is not known for the target platform")),
                cpus => Ok(unsafe { NonZeroUsize::new_unchecked(cpus as usize) }),
            }
        } else if #[cfg(any(target_os = "freebsd", target_os = "dragonfly", target_os = "netbsd"))] {
            use crate::ptr;

            #[cfg(target_os = "freebsd")]
            {
                let mut set: libc::cpuset_t = unsafe { mem::zeroed() };
                unsafe {
                    if libc::cpuset_getaffinity(
                        libc::CPU_LEVEL_WHICH,
                        libc::CPU_WHICH_PID,
                        -1,
                        mem::size_of::<libc::cpuset_t>(),
                        &mut set,
                    ) == 0 {
                        let count = libc::CPU_COUNT(&set) as usize;
                        if count > 0 {
                            return Ok(NonZeroUsize::new_unchecked(count));
                        }
                    }
                }
            }

            let mut cpus: libc::c_uint = 0;
            let mut cpus_size = crate::mem::size_of_val(&cpus);

            unsafe {
                cpus = libc::sysconf(libc::_SC_NPROCESSORS_ONLN) as libc::c_uint;
            }

            // 在出现错误或没有硬件线程的情况下的后备方法。
            if cpus < 1 {
                let mut mib = [libc::CTL_HW, libc::HW_NCPU, 0, 0];
                let res = unsafe {
                    libc::sysctl(
                        mib.as_mut_ptr(),
                        2,
                        &mut cpus as *mut _ as *mut _,
                        &mut cpus_size as *mut _ as *mut _,
                        ptr::null_mut(),
                        0,
                    )
                };

                // 处理错误 (如果有)。
                if res == -1 {
                    return Err(io::Error::last_os_error());
                } else if cpus == 0 {
                    return Err(io::const_io_error!(io::ErrorKind::NotFound, "The number of hardware threads is not known for the target platform"));
                }
            }
            Ok(unsafe { NonZeroUsize::new_unchecked(cpus as usize) })
        } else if #[cfg(target_os = "openbsd")] {
            use crate::ptr;

            let mut cpus: libc::c_uint = 0;
            let mut cpus_size = crate::mem::size_of_val(&cpus);
            let mut mib = [libc::CTL_HW, libc::HW_NCPU, 0, 0];

            let res = unsafe {
                libc::sysctl(
                    mib.as_mut_ptr(),
                    2,
                    &mut cpus as *mut _ as *mut _,
                    &mut cpus_size as *mut _ as *mut _,
                    ptr::null_mut(),
                    0,
                )
            };

            // 处理错误 (如果有)。
            if res == -1 {
                return Err(io::Error::last_os_error());
            } else if cpus == 0 {
                return Err(io::const_io_error!(io::ErrorKind::NotFound, "The number of hardware threads is not known for the target platform"));
            }

            Ok(unsafe { NonZeroUsize::new_unchecked(cpus as usize) })
        } else if #[cfg(target_os = "nto")] {
            unsafe {
                use libc::_syspage_ptr;
                if _syspage_ptr.is_null() {
                    Err(io::const_io_error!(io::ErrorKind::NotFound, "No syspage available"))
                } else {
                    let cpus = (*_syspage_ptr).num_cpu;
                    NonZeroUsize::new(cpus as usize)
                        .ok_or(io::const_io_error!(io::ErrorKind::NotFound, "The number of hardware threads is not known for the target platform"))
                }
            }
        } else if #[cfg(target_os = "haiku")] {
            // system_info cpu_count 字段在启动时使用 `smp_set_num_cpus` `get_system_info` 调用然后 `smp_get_num_cpus` 获取静态数据集
            //
            unsafe {
                let mut sinfo: libc::system_info = crate::mem::zeroed();
                let res = libc::get_system_info(&mut sinfo);

                if res != libc::B_OK {
                    return Err(io::const_io_error!(io::ErrorKind::NotFound, "The number of hardware threads is not known for the target platform"));
                }

                Ok(NonZeroUsize::new_unchecked(sinfo.cpu_count as usize))
            }
        } else {
            // FIXME: 在 vxWorks、Redox、l4re 上实现
            Err(io::const_io_error!(io::ErrorKind::Unsupported, "Getting the number of hardware threads is not supported on the target platform"))
        }
    }
}

#[cfg(any(target_os = "android", target_os = "linux"))]
mod cgroups {
    //! 目前没有被覆盖
    //! * 非标准挂载点中的 cgroup v2
    //! * 包含控制字符或空格的路径，因为它们会在 procfs 输出中转义，我们不会取消转义
    //!
    use crate::borrow::Cow;
    use crate::ffi::OsString;
    use crate::fs::{try_exists, File};
    use crate::io::Read;
    use crate::io::{BufRead, BufReader};
    use crate::os::unix::ffi::OsStringExt;
    use crate::path::Path;
    use crate::path::PathBuf;
    use crate::str::from_utf8;

    #[derive(PartialEq)]
    enum Cgroup {
        V1,
        V2,
    }

    /// 如果配额无法确定或未设置，则以核心等价物返回 cgroup CPU 配额，向下舍入或 usize::MAX。
    ///
    pub(super) fn quota() -> usize {
        let mut quota = usize::MAX;
        if cfg!(miri) {
            // 由于隔离，在默认标志下尝试打开文件会失败。
            // 而且 Miri 无论如何都没有并行性。
            return quota;
        }

        let _: Option<()> = try {
            let mut buf = Vec::with_capacity(128);
            // 在 cgroup 层次结构中找到我们的位置
            File::open("/proc/self/cgroup").ok()?.read_to_end(&mut buf).ok()?;
            let (cgroup_path, version) =
                buf.split(|&c| c == b'\n').fold(None, |previous, line| {
                    let mut fields = line.splitn(3, |&c| c == b':');
                    // 第二个字段是 v1 的控制器列表或 v2 为空
                    let version = match fields.nth(1) {
                        Some(b"") => Cgroup::V2,
                        Some(controllers)
                            if from_utf8(controllers)
                                .is_ok_and(|c| c.split(',').any(|c| c == "cpu")) =>
                        {
                            Cgroup::V1
                        }
                        _ => return previous,
                    };

                    // 已经找到的 v1 胜过 v2，因为它明确指定了它的控制器
                    if previous.is_some() && version == Cgroup::V2 {
                        return previous;
                    }

                    let path = fields.last()?;
                    // 跳过前导斜杠
                    Some((path[1..].to_owned(), version))
                })?;
            let cgroup_path = PathBuf::from(OsString::from_vec(cgroup_path));

            quota = match version {
                Cgroup::V1 => quota_v1(cgroup_path),
                Cgroup::V2 => quota_v2(cgroup_path),
            };
        };

        quota
    }

    fn quota_v2(group_path: PathBuf) -> usize {
        let mut quota = usize::MAX;

        let mut path = PathBuf::with_capacity(128);
        let mut read_buf = String::with_capacity(20);

        // file-hierarchy(7) 手册页中定义的标准挂载位置
        let cgroup_mount = "/sys/fs/cgroup";

        path.push(cgroup_mount);
        path.push(&group_path);

        path.push("cgroup.controllers");

        // 如果我们没有看到 cgroup2，请跳过
        if matches!(try_exists(&path), Err(_) | Ok(false)) {
            return usize::MAX;
        };

        path.pop();

        let _: Option<()> = try {
            while path.starts_with(cgroup_mount) {
                path.push("cpu.max");

                read_buf.clear();

                if File::open(&path).and_then(|mut f| f.read_to_string(&mut read_buf)).is_ok() {
                    let raw_quota = read_buf.lines().next()?;
                    let mut raw_quota = raw_quota.split(' ');
                    let limit = raw_quota.next()?;
                    let period = raw_quota.next()?;
                    match (limit.parse::<usize>(), period.parse::<usize>()) {
                        (Ok(limit), Ok(period)) if period > 0 => {
                            quota = quota.min(limit / period);
                        }
                        _ => {}
                    }
                }

                path.pop(); // 弹出文件名
                path.pop(); // 弹出目录
            }
        };

        quota
    }

    fn quota_v1(group_path: PathBuf) -> usize {
        let mut quota = usize::MAX;
        let mut path = PathBuf::with_capacity(128);
        let mut read_buf = String::with_capacity(20);

        // 如果硬编码 cgroups(7) 手册页中提到的常用位置不起作用，请扫描 mountinfo 并为绑定挂载调整 `group_path`
        //
        let mounts: &[fn(&Path) -> Option<(_, &Path)>] = &[
            |p| Some((Cow::Borrowed("/sys/fs/cgroup/cpu"), p)),
            |p| Some((Cow::Borrowed("/sys/fs/cgroup/cpu,cpuacct"), p)),
            // 在具有大量挂载点的系统上，这可能是很昂贵的，但我们只有在 /proc/self/cgroups 明确指出该进程属于 cpu-controller cgroup v1 并且默认值不起作用时，才能达到这一点
            //
            //
            find_mountpoint,
        ];

        for mount in mounts {
            let Some((mount, group_path)) = mount(&group_path) else { continue };

            path.clear();
            path.push(mount.as_ref());
            path.push(&group_path);

            // 如果我们猜错了挂载，请跳过
            if matches!(try_exists(&path), Err(_) | Ok(false)) {
                continue;
            }

            while path.starts_with(mount.as_ref()) {
                let mut parse_file = |name| {
                    path.push(name);
                    read_buf.clear();

                    let f = File::open(&path);
                    path.pop(); // 在任何提前返回之前恢复缓冲区
                    f.ok()?.read_to_string(&mut read_buf).ok()?;
                    let parsed = read_buf.trim().parse::<usize>().ok()?;

                    Some(parsed)
                };

                let limit = parse_file("cpu.cfs_quota_us");
                let period = parse_file("cpu.cfs_period_us");

                match (limit, period) {
                    (Some(limit), Some(period)) if period > 0 => quota = quota.min(limit / period),
                    _ => {}
                }

                path.pop();
            }

            // 我们通过了上面的 try_exists，所以我们应该在到达这一行时遍历了正确的层次结构
            //
            break;
        }

        quota
    }

    /// 使用 cpu 控制器扫描 cgroup v1 挂载点的 mountinfo
    ///
    /// 如果 cgroupfs 是绑定挂载，则调整 `group_path` 以跳过已包含的前缀
    ///
    fn find_mountpoint(group_path: &Path) -> Option<(Cow<'static, str>, &Path)> {
        let mut reader = BufReader::new(File::open("/proc/self/mountinfo").ok()?);
        let mut line = String::with_capacity(256);
        loop {
            line.clear();
            if reader.read_line(&mut line).ok()? == 0 {
                break;
            }

            let line = line.trim();
            let mut items = line.split(' ');

            let sub_path = items.nth(3)?;
            let mount_point = items.next()?;
            let mount_opts = items.next_back()?;
            let filesystem_type = items.nth_back(1)?;

            if filesystem_type != "cgroup" || !mount_opts.split(',').any(|opt| opt == "cpu") {
                // 不是 cgroup / 不是 cpu 控制器
                continue;
            }

            let sub_path = Path::new(sub_path).strip_prefix("/").ok()?;

            if !group_path.starts_with(sub_path) {
                // 这是一个绑定挂载，绑定的子目录不包含该进程所属的 cgroup
                //
                continue;
            }

            let trimmed_group_path = group_path.strip_prefix(sub_path).ok()?;

            return Some((Cow::Owned(mount_point.to_owned()), trimmed_group_path));
        }

        None
    }
}

#[cfg(all(
    not(target_os = "linux"),
    not(target_os = "freebsd"),
    not(target_os = "macos"),
    not(target_os = "netbsd"),
    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(
    target_os = "linux",
    target_os = "freebsd",
    target_os = "macos",
    target_os = "netbsd",
    target_os = "openbsd",
    target_os = "solaris"
))]
#[cfg_attr(test, allow(dead_code))]
pub mod guard {
    #[cfg(not(all(target_os = "linux", target_env = "gnu")))]
    use libc::{mmap as mmap64, mprotect};
    #[cfg(all(target_os = "linux", target_env = "gnu"))]
    use libc::{mmap64, mprotect};
    use libc::{MAP_ANON, MAP_FAILED, MAP_FIXED, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE};

    use crate::io;
    use crate::ops::Range;
    use crate::sync::atomic::{AtomicUsize, Ordering};
    use crate::sys::os;

    // 这是在 init() 中初始化的，只能在之后读取
    static PAGE_SIZE: AtomicUsize = AtomicUsize::new(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 th = libc::pthread_self();
        let stackptr = libc::pthread_get_stackaddr_np(th);
        Some(stackptr.map_addr(|addr| addr - libc::pthread_get_stacksize_np(th)))
    }

    #[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 stack_ptr = current_stack.ss_sp;
        let stackaddr = if libc::pthread_main_np() == 1 {
            // 主线程
            stack_ptr.addr() - current_stack.ss_size + PAGE_SIZE.load(Ordering::Relaxed)
        } else {
            // 新线程
            stack_ptr.addr() - current_stack.ss_size
        };
        Some(stack_ptr.with_addr(stackaddr))
    }

    #[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();
        #[cfg(target_os = "freebsd")]
        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);
        }
        if e == 0 || cfg!(target_os = "freebsd") {
            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
        }
        ret
    }

    // 前提条件: PAGE_SIZE 已初始化。
    unsafe fn get_stack_start_aligned() -> Option<*mut libc::c_void> {
        let page_size = PAGE_SIZE.load(Ordering::Relaxed);
        assert!(page_size != 0);
        let stackptr = get_stack_start()?;
        let stackaddr = stackptr.addr();

        // 确保 stackaddr 是页对齐的！ 父进程可能已将 RLIMIT_STACK 重置为非页面对齐。
        // pthread_attr_getstack() 报告可用的栈区域 stackaddr <stackaddr + stacksize，因此，如果 stackaddr 不是页面对齐的，则计算修正值，使 stackaddr <new_page_aligned_stackaddr <stackaddr + stacksize
        //
        //
        //
        //
        let remainder = stackaddr % page_size;
        Some(if remainder == 0 {
            stackptr
        } else {
            stackptr.with_addr(stackaddr + page_size - remainder)
        })
    }

    pub unsafe fn init() -> Option<Guard> {
        let page_size = os::page_size();
        PAGE_SIZE.store(page_size, Ordering::Relaxed);

        if cfg!(all(target_os = "linux", not(target_env = "musl"))) {
            // Linux 不会立即分配整个栈，并且内核具有自己的栈保护机制，以便在与现有映射太接近时发生故障。
            // 如果我们使用自己的保护程序 map，则内核将开始在此之上强制执行一个较大的间隙，从而使很多可能的栈空间变得无用。
            // 请参见 #43052。
            //
            // 取而代之的是，我们只需要注意 rlimit 会在哪里开始出错，以便我们的处理程序可以报告 "栈溢出"，并相信内核自己的栈保护会起作用。
            //
            //
            //
            //
            //
            let stackptr = get_stack_start_aligned()?;
            let stackaddr = stackptr.addr();
            Some(stackaddr - page_size..stackaddr)
        } else if cfg!(all(target_os = "linux", target_env = "musl")) {
            // 对于主线程，musl 的 pthread_attr_getstack 返回当前的栈大小，而不是其最终可以增长到的最大大小。
            // 它不能用于确定内核的栈保护的位置。
            //
            //
            None
        } else if cfg!(target_os = "freebsd") {
            // FreeBSD 的栈会自动增长，并且可以选择在底部包含一个保护页面。
            // 如果我们自己尝试重新映射栈底，FreeBSD 的保护页面就会向上移动。
            //
            // 所以我们将只使用内置的保护页面。
            let stackptr = get_stack_start_aligned()?;
            let guardaddr = stackptr.addr();
            // 从技术上讲，保护页面的数量是由 security.bsd.stack_guard_page sysctl 可调和控制的，但几乎没有理由将其从默认值更改。
            // 自 FreeBSD 11.1 和 10.4 以来，默认值一直为 1。
            //
            //
            const GUARD_PAGES: usize = 1;
            let guard = guardaddr..guardaddr + GUARD_PAGES * page_size;
            Some(guard)
        } else if cfg!(target_os = "openbsd") {
            // OpenBSD 栈已经包含一个保护页面，并且栈是不无效的。
            //
            // 我们只需要注意我们期望 rlimit 从哪里开始出错，因此我们的处理程序可以报告 "stack overflow"，并相信内核自己的栈保护将起作用。
            //
            //
            //
            let stackptr = get_stack_start_aligned()?;
            let stackaddr = stackptr.addr();
            Some(stackaddr - page_size..stackaddr)
        } else {
            // 重新分配栈的最后一页。
            // 这样可以确保在栈溢出时引发 SIGBUS。
            // 强制执行严格 PAX MPROTECT 的系统不允许 mprotect() 具有比使用的初始 mmap() 少的限制性权限的映射，因此我们这里的 mmap() 具有 read/write 权限，然后只有 mprotect() 完全没有权限。
            // 请参见 issue #50313。
            //
            //
            //
            //
            let stackptr = get_stack_start_aligned()?;
            let result = mmap64(
                stackptr,
                page_size,
                PROT_READ | PROT_WRITE,
                MAP_PRIVATE | MAP_ANON | MAP_FIXED,
                -1,
                0,
            );
            if result != stackptr || result == MAP_FAILED {
                panic!("failed to allocate a guard page: {}", io::Error::last_os_error());
            }

            let result = mprotect(stackptr, page_size, PROT_NONE);
            if result != 0 {
                panic!("failed to protect the guard page: {}", io::Error::last_os_error());
            }

            let guardaddr = stackptr.addr();

            Some(guardaddr..guardaddr + page_size)
        }
    }

    #[cfg(any(target_os = "macos", target_os = "openbsd", target_os = "solaris"))]
    pub unsafe fn current() -> Option<Guard> {
        let stackptr = get_stack_start()?;
        let stackaddr = stackptr.addr();
        Some(stackaddr - PAGE_SIZE.load(Ordering::Relaxed)..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();
        #[cfg(target_os = "freebsd")]
        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 {
                if cfg!(all(target_os = "linux", target_env = "musl")) {
                    // 1.1.19 之前的 musl 版本始终将从 pthread_attr_get_np 获得的防护大小报告为零。
                    //
                    // 使用页面大小作为后备。
                    guardsize = PAGE_SIZE.load(Ordering::Relaxed);
                } else {
                    panic!("there is no guard page");
                }
            }
            let mut stackptr = crate::ptr::null_mut::<libc::c_void>();
            let mut size = 0;
            assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackptr, &mut size), 0);

            let stackaddr = stackptr.addr();
            ret = if cfg!(any(target_os = "freebsd", target_os = "netbsd")) {
                Some(stackaddr - guardsize..stackaddr)
            } else if cfg!(all(target_os = "linux", target_env = "musl")) {
                Some(stackaddr - guardsize..stackaddr)
            } else if cfg!(all(target_os = "linux", any(target_env = "gnu", target_env = "uclibc")))
            {
                // 如 `man pthread_attr_getguardsize` 的 `BUGS` 部分所述，glibc 曾经将保护区包括在栈内。
                // 从 glibc 2.27 开始，并且在某些发行版本的反向移植中，此问题已得到纠正，因此现在将保护放置在栈的 (below) 的末尾。
                // 没有简单的方法让我们知道在运行时有哪些故障，因此我们只匹配栈基础上方或下方范围内的任何故障，以调用导致栈溢出的故障。
                //
                //
                //
                Some(stackaddr - guardsize..stackaddr + guardsize)
            } else {
                Some(stackaddr..stackaddr + guardsize)
            };
        }
        if e == 0 || cfg!(target_os = "freebsd") {
            assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
        }
        ret
    }
}

// glibc>= 2.15 具有一个 __pthread_get_minstack() 函数，该函数返回 PTHREAD_STACK_MIN 以及线程本地存储所需的字节。
// 我们需要这些信息，以避免在具有大量线程本地存储需求的应用程序中创建一个小的栈时发生崩溃。
//
// 有关原理和详细信息，请参见 #6233。
//
#[cfg(all(target_os = "linux", target_env = "gnu"))]
fn min_stack_size(attr: *const libc::pthread_attr_t) -> usize {
    // 我们使用 dlsym 来避免 ELF 版本对 GLIBC_PRIVATE 的依赖。
    // (#23628) 我们真的不应该使用这样的内部符号，但目前没有其他方法可以解释 TLS 大小。
    //
    dlsym!(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) },
    }
}

// 在非 glibc 平台上查找 __pthread_get_minstack() 毫无意义。
#[cfg(all(not(all(target_os = "linux", target_env = "gnu")), 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 // 只是一个猜测
}