Struct FileHandleGuard 

pub struct FileHandleGuard<'a> { /* private fields */ }

RAII guard providing access to the file while the latch is held.

Implementations

impl<'a> FileHandleGuard<'a>

pub fn read_at(&mut self, offset: u64, buf: &mut [u8]) -> Result<usize>

Reads data from the file at the given offset.

Arguments

• offset - File offset to read from
• buf - Buffer to read into

Returns

Number of bytes read. Reads data from the file at the given offset.

Uses pread64 (one syscall) instead of lseek + read (two syscalls). The JVM lowers to pread64 on Linux.

pub fn read_exact_at(&mut self, offset: u64, buf: &mut [u8]) -> Result<()>

Reads exactly buf.len() bytes from the file at the given offset.

Uses pread64 in a retry loop. Returns an error if fewer bytes are available.

pub fn write_at(&mut self, offset: u64, buf: &[u8]) -> Result<usize>

Writes data to the file at the given offset.

Uses pwrite64 (one syscall) instead of lseek + write (two syscalls). FileChannel.write(ByteBuffer, position) which the JVM lowers to pwrite64 on Linux. This eliminates half the syscalls on the hot write path and removes the need to serialise seek+write under the guard (pwrite64 is inherently positional and thread-safe).

Arguments

• offset - File offset to write to (passed directly to pwrite64)
• buf - Data to write

Returns

Number of bytes written (always buf.len() on success).

pub fn sync(&mut self) -> Result<()>

Syncs all file data and metadata to disk (fsync).

Use this when the file’s metadata (size, mtime) must also be durable — typically for file-header writes. For log-data writes prefer sync_data() which is faster.

pub fn sync_data(&mut self) -> Result<()>

Syncs only the file data to disk (fdatasync).

Faster than sync() because it does not flush file metadata (mtime etc.). uses FileChannel.force(false) (= fdatasync) for all log-data writes and force(true) (= fsync) only for file-header writes.

/ FileChannel.force(false).

pub fn is_empty(&mut self) -> Result<bool>

Returns true if the file is empty.

pub fn len(&mut self) -> Result<u64>

Returns the file length.

pub fn truncate(&mut self, len: u64) -> Result<()>

Truncates the file to the given length.

pub fn file_num(&self) -> u32

Returns the file number.

pub fn log_version(&self) -> u32

Returns the log version.