Struct FileLock 

pub struct FileLock { /* private fields */ }

File lock state machine. Wraps a raw fd and tracks the current lock level.

All transitions follow the legal state progression:

• UNLOCKED → SHARED (only valid transition from UNLOCKED)
• SHARED → RESERVED
• RESERVED → EXCLUSIVE (via PENDING internally)
• EXCLUSIVE/RESERVED → SHARED (downgrade)
• SHARED → UNLOCKED

Implementations

impl FileLock

pub fn new(file: &File) -> Self

Create a new lock state for the given file. Starts UNLOCKED.

pub fn level(&self) -> LockLevel

Current lock level.

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

Acquire SHARED lock (for readers and initial open).

Multiple processes can hold SHARED simultaneously. Blocks if another process holds PENDING or EXCLUSIVE.

pub fn lock_reserved(&mut self, timeout: Duration) -> Result<()>

Acquire RESERVED lock (write intent — one at a time).

Signals that this process intends to write. Readers continue unimpeded. Only one RESERVED lock can exist at a time.

Retries with exponential backoff until the timeout expires, then returns WriterLocked.

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

Escalate from RESERVED to EXCLUSIVE.

First acquires PENDING (blocks new readers), then waits for existing readers to drain, then acquires EXCLUSIVE.

This is a blocking operation — it waits until all existing SHARED locks are released.

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

Downgrade from EXCLUSIVE or RESERVED to SHARED.

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

Release all locks (SHARED → UNLOCKED).

Trait Implementations

impl Drop for FileLock

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

🔬This is a nightly-only experimental API. (pin_ergonomics)

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.