Closed cberner closed 2 months ago
We discussed this in the libs-api meeting today. We agree that file locking should be supporting in the standard library. However these should be directly exposed on File
rather than in OS-specific traits. This makes the API more useful for users who need simple file locking support and OSes without such support can just return ErrorKind::Unsupported
.
Here's an API overview:
impl File {
fn lock(&self) -> io::Result<()>;
fn lock_shared(&self) -> io::Result<()>;
fn try_lock(&self) -> io::Result<bool>;
fn try_lock_shared(&self) -> io::Result<bool>;
fn unlock(&self) -> io::Result<()>;
}
These should be carefully documented to ensure they work on all platforms. For example:
dup
or DuplicateHandle
) keeps the file open.Feel free to open a tracking issue and open a PR to rust-lang/rust to add it as an unstable feature.
Sounds good. Thanks for the feedback!
Proposal
Problem statement
Provide an API to lock files (i.e. flock)
Motivating examples or use cases
redb contains unsafe code and requires a dependency on libc to lock and unlock files, as well as implementations for both Linux and Windows.
It looks like Cargo similarly has its own file locking code.
Having a file lock API for each platform, similar to the existing support for raw fds and API likes
read_exact_at
, would allow std to be used instead of unsafe invocations of libc.Solution sketch
I have two ideas, but would be happy to implement any API that's desired: 1) A trait like
std::os::unix::fs::FileExt
that containslock()
andunlock()
APIs. 2) ALockedFile
struct, which own aFile
object and ensure that the lock was released with aDrop
implementation, and provide accessors to the file.Alternatives
I've worked around it by using the
libc
crateLinks and related work
What happens now?
This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.
Possible responses
The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):
Second, if there's a concrete solution: