pub fn hashmap_random_keys() -> (u64, u64) {
    const KEY_LEN: usize = core::mem::size_of::<u64>();

    let mut v = [0u8; KEY_LEN * 2];
    imp::fill_bytes(&mut v);

    let key1 = v[0..KEY_LEN].try_into().unwrap();
    let key2 = v[KEY_LEN..].try_into().unwrap();

    (u64::from_ne_bytes(key1), u64::from_ne_bytes(key2))
}

#[cfg(all(
    unix,
    not(target_os = "macos"),
    not(target_os = "ios"),
    not(target_os = "watchos"),
    not(target_os = "openbsd"),
    not(target_os = "freebsd"),
    not(target_os = "netbsd"),
    not(target_os = "fuchsia"),
    not(target_os = "redox"),
    not(target_os = "vxworks"),
    not(target_os = "emscripten"),
    not(target_os = "vita"),
))]
mod imp {
    use crate::fs::File;
    use crate::io::Read;

    #[cfg(any(target_os = "linux", target_os = "android"))]
    use crate::sys::weak::syscall;

    #[cfg(any(target_os = "linux", target_os = "android"))]
    fn getrandom(buf: &mut [u8]) -> libc::ssize_t {
        use crate::sync::atomic::{AtomicBool, Ordering};
        use crate::sys::os::errno;

        // 弱符号允许插入，例如用于想要禁用一致性随机性的性能测量。
        // 否则，我们将尝试原始的 syscall。
        // (在 glibc 2.25，Musl 1.1.20，android API 级别 28 中添加了 `getrandom`)
        syscall! {
            fn getrandom(
                buffer: *mut libc::c_void,
                length: libc::size_t,
                flags: libc::c_uint
            ) -> libc::ssize_t
        }

        // 这提供了在给定时刻可用的最佳质量随机数，而不会阻塞，并且比回退到 /dev/urandom 更可取。
        //
        static GRND_INSECURE_AVAILABLE: AtomicBool = AtomicBool::new(true);
        if GRND_INSECURE_AVAILABLE.load(Ordering::Relaxed) {
            let ret = unsafe { getrandom(buf.as_mut_ptr().cast(), buf.len(), libc::GRND_INSECURE) };
            if ret == -1 && errno() as libc::c_int == libc::EINVAL {
                GRND_INSECURE_AVAILABLE.store(false, Ordering::Relaxed);
            } else {
                return ret;
            }
        }

        unsafe { getrandom(buf.as_mut_ptr().cast(), buf.len(), libc::GRND_NONBLOCK) }
    }

    #[cfg(any(target_os = "espidf", target_os = "horizon"))]
    fn getrandom(buf: &mut [u8]) -> libc::ssize_t {
        unsafe { libc::getrandom(buf.as_mut_ptr().cast(), buf.len(), 0) }
    }

    #[cfg(not(any(
        target_os = "linux",
        target_os = "android",
        target_os = "espidf",
        target_os = "horizon"
    )))]
    fn getrandom_fill_bytes(_buf: &mut [u8]) -> bool {
        false
    }

    #[cfg(any(
        target_os = "linux",
        target_os = "android",
        target_os = "espidf",
        target_os = "horizon"
    ))]
    fn getrandom_fill_bytes(v: &mut [u8]) -> bool {
        use crate::sync::atomic::{AtomicBool, Ordering};
        use crate::sys::os::errno;

        static GETRANDOM_UNAVAILABLE: AtomicBool = AtomicBool::new(false);
        if GETRANDOM_UNAVAILABLE.load(Ordering::Relaxed) {
            return false;
        }

        let mut read = 0;
        while read < v.len() {
            let result = getrandom(&mut v[read..]);
            if result == -1 {
                let err = errno() as libc::c_int;
                if err == libc::EINTR {
                    continue;
                } else if err == libc::ENOSYS || err == libc::EPERM {
                    // 如果当前内核不支持 `getrandom`，则回退到读取 /dev/urandom。
                    //
                    // 如果使用 seccomp 之类的功能或在虚拟机内部将其禁用，也请回退。
                    //
                    //
                    GETRANDOM_UNAVAILABLE.store(true, Ordering::Relaxed);
                    return false;
                } else if err == libc::EAGAIN {
                    return false;
                } else {
                    panic!("unexpected getrandom error: {err}");
                }
            } else {
                read += result as usize;
            }
        }
        true
    }

    pub fn fill_bytes(v: &mut [u8]) {
        // 如果 getrandom() 返回 EAGAIN，则 getrandom_fill_bytes 可能失败，这意味着它会被阻塞，因为非阻塞池 (urandom) 由于缺少熵而尚未在内核中初始化。
        // 我们这样做的后盾是避免阻塞可能依赖于此调用的应用程序，而无需知道它们是否起作用。
        // /dev/urandom 的 PRNG 仍将使用，但要在可能可预测的熵池上使用。
        //
        //
        //
        //
        if getrandom_fill_bytes(v) {
            return;
        }

        // getrandom 失败，因为它永久或暂时 (由于缺少熵) 不可用。
        //
        // 打开 /dev/urandom，从中读取，然后再次将其关闭。
        let mut file = File::open("/dev/urandom").expect("failed to open /dev/urandom");
        file.read_exact(v).expect("failed to read /dev/urandom")
    }
}

#[cfg(target_os = "macos")]
mod imp {
    use crate::fs::File;
    use crate::io::Read;
    use crate::sys::os::errno;
    use crate::sys::weak::weak;
    use libc::{c_int, c_void, size_t};

    fn getentropy_fill_bytes(v: &mut [u8]) -> bool {
        weak!(fn getentropy(*mut c_void, size_t) -> c_int);

        getentropy
            .get()
            .map(|f| {
                // getentropy(2) 允许最大缓冲区大小为 256 字节
                for s in v.chunks_mut(256) {
                    let ret = unsafe { f(s.as_mut_ptr() as *mut c_void, s.len()) };
                    if ret == -1 {
                        panic!("unexpected getentropy error: {}", errno());
                    }
                }
                true
            })
            .unwrap_or(false)
    }

    pub fn fill_bytes(v: &mut [u8]) {
        if getentropy_fill_bytes(v) {
            return;
        }

        // 对于不支持熵的较旧 macos
        let mut file = File::open("/dev/urandom").expect("failed to open /dev/urandom");
        file.read_exact(v).expect("failed to read /dev/urandom")
    }
}

#[cfg(any(target_os = "openbsd", target_os = "emscripten", target_os = "vita"))]
mod imp {
    use crate::sys::os::errno;

    pub fn fill_bytes(v: &mut [u8]) {
        // getentropy(2) 允许最大缓冲区大小为 256 字节
        for s in v.chunks_mut(256) {
            let ret = unsafe { libc::getentropy(s.as_mut_ptr() as *mut libc::c_void, s.len()) };
            if ret == -1 {
                panic!("unexpected getentropy error: {}", errno());
            }
        }
    }
}

// 在 iOS 和 MacOS 上，`SecRandomCopyBytes` 用 `kCCRandomDefault` 调用 `CCRandomCopyBytes`。
// `CCRandomCopyBytes` 管理一个 CSPRNG，它是从 `/dev/random` 中植入的，它运行在通过 GCD 访问的自己的线程上。
//
// 为了在 `hashmap_random_keys` 中每个线程一次生成两个 u64，这似乎不必要。
// 因此，`SecRandomCopyBytes` 仅在沙箱阻止直接访问 `/dev/urandom` 的 iOS 上使用。
//
//
#[cfg(any(target_os = "ios", target_os = "watchos"))]
mod imp {
    use crate::io;
    use crate::ptr;
    use libc::{c_int, size_t};

    enum SecRandom {}

    #[allow(non_upper_case_globals)]
    const kSecRandomDefault: *const SecRandom = ptr::null();

    extern "C" {
        fn SecRandomCopyBytes(rnd: *const SecRandom, count: size_t, bytes: *mut u8) -> c_int;
    }

    pub fn fill_bytes(v: &mut [u8]) {
        let ret = unsafe { SecRandomCopyBytes(kSecRandomDefault, v.len(), v.as_mut_ptr()) };
        if ret == -1 {
            panic!("couldn't generate random bytes: {}", io::Error::last_os_error());
        }
    }
}

#[cfg(any(target_os = "freebsd", target_os = "netbsd"))]
mod imp {
    use crate::ptr;

    pub fn fill_bytes(v: &mut [u8]) {
        let mib = [libc::CTL_KERN, libc::KERN_ARND];
        // kern.arandom 允许最大缓冲区大小为 256 字节
        for s in v.chunks_mut(256) {
            let mut s_len = s.len();
            let ret = unsafe {
                libc::sysctl(
                    mib.as_ptr(),
                    mib.len() as libc::c_uint,
                    s.as_mut_ptr() as *mut _,
                    &mut s_len,
                    ptr::null(),
                    0,
                )
            };
            if ret == -1 || s_len != s.len() {
                panic!(
                    "kern.arandom sysctl failed! (returned {}, s.len() {}, oldlenp {})",
                    ret,
                    s.len(),
                    s_len
                );
            }
        }
    }
}

#[cfg(target_os = "fuchsia")]
mod imp {
    #[link(name = "zircon")]
    extern "C" {
        fn zx_cprng_draw(buffer: *mut u8, len: usize);
    }

    pub fn fill_bytes(v: &mut [u8]) {
        unsafe { zx_cprng_draw(v.as_mut_ptr(), v.len()) }
    }
}

#[cfg(target_os = "redox")]
mod imp {
    use crate::fs::File;
    use crate::io::Read;

    pub fn fill_bytes(v: &mut [u8]) {
        // 打开兰特:，从中读取，然后再次将其关闭。
        let mut file = File::open("rand:").expect("failed to open rand:");
        file.read_exact(v).expect("failed to read rand:")
    }
}

#[cfg(target_os = "vxworks")]
mod imp {
    use crate::io;
    use core::sync::atomic::{AtomicBool, Ordering::Relaxed};

    pub fn fill_bytes(v: &mut [u8]) {
        static RNG_INIT: AtomicBool = AtomicBool::new(false);
        while !RNG_INIT.load(Relaxed) {
            let ret = unsafe { libc::randSecure() };
            if ret < 0 {
                panic!("couldn't generate random bytes: {}", io::Error::last_os_error());
            } else if ret > 0 {
                RNG_INIT.store(true, Relaxed);
                break;
            }
            unsafe { libc::usleep(10) };
        }
        let ret = unsafe {
            libc::randABytes(v.as_mut_ptr() as *mut libc::c_uchar, v.len() as libc::c_int)
        };
        if ret < 0 {
            panic!("couldn't generate random bytes: {}", io::Error::last_os_error());
        }
    }
}