fd-lock 1.1.1

Advisory cross-platform lock on a file using a file descriptor to it.
Documentation 
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use std::io::{Error, ErrorKind};
use std::ops;
use std::os::windows::io::AsRawHandle;

use winapi::um::fileapi::{LockFile, UnlockFile};

// /// Lock a file descriptor.
// #[inline]
// pub fn lock(handle: RawHandle) -> Result<FdLockGuard<'_, T>, Error> {
//     if unsafe { LockFile(handle.clone(), 0, 0, 1, 0) } {
//         Ok(FdLockGuard { handle })
//     } else {
//         Err(ErrorKind::Locked.into())
//     }
// }

// /// Unlock a file descriptor.
// #[inline]
// fn unlock(handle: HANDLE) -> Result<(), Error> {
//     if unsafe { UnlockFile(handle, 0, 0, 1, 0) } {
//         Ok(())
//     } else {
//         Err(ErrorKind::Locked.into())
//     }
// }

/// A guard that unlocks the file descriptor when it goes out of scope.
#[derive(Debug)]
pub struct FdLockGuard<'fdlock, T: AsRawHandle> {
    lock: &'fdlock mut FdLock<T>,
}

impl<T: AsRawHandle> ops::Deref for FdLockGuard<'_, T> {
    type Target = T;

    #[inline]
    fn deref(&self) -> &Self::Target {
        &self.lock.t
    }
}

impl<T: AsRawHandle> ops::DerefMut for FdLockGuard<'_, T> {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.lock.t
    }
}

impl<T: AsRawHandle> Drop for FdLockGuard<'_, T> {
    #[inline]
    fn drop(&mut self) {
        let handle = self.lock.t.as_raw_handle();
        if unsafe { !UnlockFile(handle, 0, 0, 1, 0) } == 0 {
            panic!("Could not unlock the file descriptor");
        }
    }
}

/// A file descriptor lock.
#[derive(Debug)]
pub struct FdLock<T: AsRawHandle> {
    t: T,
}

impl<T: AsRawHandle> FdLock<T> {
    /// Create a new instance.
    #[inline]
    pub fn new(t: T) -> Self {
        FdLock { t }
    }

    // /// Acquires a new lock, blocking the current thread until it's able to do so.
    // ///
    // /// This function will block the local thread until it is available to acquire the lock. Upon
    // /// returning, the thread is the only thread with the lock held. An RAII guard is returned to allow
    // /// scoped unlock of the lock. When the guard goes out of scope, the lock will be unlocked.
    // #[inline]
    // pub fn lock(&mut self) -> Result<FdLockGuard<'_, T>, Error> {
    //     let handle = self.t.as_raw_handle();
    //     let overlapped = ptr::null_mut()
    //     if unsafe { LockFile(handle, 0, 0, 1, 0) } {
    //         Ok(FdLockGuard { lock: self })
    //     } else {
    //         Err(ErrorKind::Other.into())
    //     }
    // }

    /// Attempts to acquire this lock.
    ///
    /// If the lock could not be acquired at this time, then `Err` is returned. Otherwise, an RAII
    /// guard is returned. The lock will be unlocked when the guard is dropped.
    ///
    /// This function does not block.
    #[inline]
    pub fn try_lock(&mut self) -> Result<FdLockGuard<'_, T>, Error> {
        let handle = self.t.as_raw_handle();
        if unsafe { LockFile(handle, 0, 0, 1, 0) } == 0 {
            Err(ErrorKind::Other.into())
        } else {
            Ok(FdLockGuard { lock: self })
        }
    }
}