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use libc;
use {Errno, Result};

#[cfg(any(target_os = "android", target_os = "linux"))]
pub use self::sched_linux_like::*;

#[cfg(any(target_os = "android", target_os = "linux"))]
mod sched_linux_like {
    use errno::Errno;
    use libc::{self, c_int, c_void};
    use std::mem;
    use std::option::Option;
    use std::os::unix::io::RawFd;
    use unistd::Pid;
    use {Error, Result};

    // For some functions taking with a parameter of type CloneFlags,
    // only a subset of these flags have an effect.
    libc_bitflags! {
        pub struct CloneFlags: c_int {
            CLONE_VM;
            CLONE_FS;
            CLONE_FILES;
            CLONE_SIGHAND;
            CLONE_PTRACE;
            CLONE_VFORK;
            CLONE_PARENT;
            CLONE_THREAD;
            CLONE_NEWNS;
            CLONE_SYSVSEM;
            CLONE_SETTLS;
            CLONE_PARENT_SETTID;
            CLONE_CHILD_CLEARTID;
            CLONE_DETACHED;
            CLONE_UNTRACED;
            CLONE_CHILD_SETTID;
            CLONE_NEWCGROUP;
            CLONE_NEWUTS;
            CLONE_NEWIPC;
            CLONE_NEWUSER;
            CLONE_NEWPID;
            CLONE_NEWNET;
            CLONE_IO;
        }
    }

    pub type CloneCb<'a> = Box<dyn FnMut() -> isize + 'a>;

    #[repr(C)]
    #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
    pub struct CpuSet {
        cpu_set: libc::cpu_set_t,
    }

    impl CpuSet {
        pub fn new() -> CpuSet {
            CpuSet {
                cpu_set: unsafe { mem::zeroed() },
            }
        }

        pub fn is_set(&self, field: usize) -> Result<bool> {
            if field >= 8 * mem::size_of::<libc::cpu_set_t>() {
                Err(Error::Sys(Errno::EINVAL))
            } else {
                Ok(unsafe { libc::CPU_ISSET(field, &self.cpu_set) })
            }
        }

        pub fn set(&mut self, field: usize) -> Result<()> {
            if field >= 8 * mem::size_of::<libc::cpu_set_t>() {
                Err(Error::Sys(Errno::EINVAL))
            } else {
                Ok(unsafe { libc::CPU_SET(field, &mut self.cpu_set) })
            }
        }

        pub fn unset(&mut self, field: usize) -> Result<()> {
            if field >= 8 * mem::size_of::<libc::cpu_set_t>() {
                Err(Error::Sys(Errno::EINVAL))
            } else {
                Ok(unsafe { libc::CPU_CLR(field, &mut self.cpu_set) })
            }
        }
    }

    pub fn sched_setaffinity(pid: Pid, cpuset: &CpuSet) -> Result<()> {
        let res = unsafe {
            libc::sched_setaffinity(
                pid.into(),
                mem::size_of::<CpuSet>() as libc::size_t,
                &cpuset.cpu_set,
            )
        };

        Errno::result(res).map(drop)
    }

    pub fn clone(
        mut cb: CloneCb,
        stack: &mut [u8],
        flags: CloneFlags,
        signal: Option<c_int>,
    ) -> Result<Pid> {
        extern "C" fn callback(data: *mut CloneCb) -> c_int {
            let cb: &mut CloneCb = unsafe { &mut *data };
            (*cb)() as c_int
        }

        let res = unsafe {
            let combined = flags.bits() | signal.unwrap_or(0);
            let ptr = stack.as_mut_ptr().offset(stack.len() as isize);
            let ptr_aligned = ptr.offset((ptr as usize % 16) as isize * -1);
            libc::clone(
                mem::transmute(
                    callback as extern "C" fn(*mut Box<dyn FnMut() -> isize>) -> i32,
                ),
                ptr_aligned as *mut c_void,
                combined,
                &mut cb as *mut _ as *mut c_void,
            )
        };

        Errno::result(res).map(Pid::from_raw)
    }

    pub fn unshare(flags: CloneFlags) -> Result<()> {
        let res = unsafe { libc::unshare(flags.bits()) };

        Errno::result(res).map(drop)
    }

    pub fn setns(fd: RawFd, nstype: CloneFlags) -> Result<()> {
        let res = unsafe { libc::setns(fd, nstype.bits()) };

        Errno::result(res).map(drop)
    }
}

/// Explicitly yield the processor to other threads.
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/sched_yield.html)
pub fn sched_yield() -> Result<()> {
    let res = unsafe { libc::sched_yield() };

    Errno::result(res).map(drop)
}