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Rollup merge of #136288 - joshtriplett:would-you-could-you-with-some-locks--would-you-could-you-in-some-docs, r=m-ou-se

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Improve documentation for file locking

Add notes to each method stating that locks get dropped on close.

Clarify the return values of the try methods: they're only defined if
the lock is held via a *different* file handle/descriptor. That goes
along with the documentation that calling them while holding a lock via
the *same* file handle/descriptor may deadlock.

Document the behavior of unlock if no lock is held.

r? `@m-ou-se`
(Documentation changes requested in https://github.com/rust-lang/rust/issues/130994 .)
This commit is contained in:
Matthias Krüger 2025-01-30 20:47:09 +01:00 • committed by GitHub
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1 changed files with 40 additions and 17 deletions
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57
library/std/src/fs.rs
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@ -629,9 +629,9 @@ impl File {
/// This acquires an exclusive advisory lock; no other file handle to this file may acquire
/// another lock.
///
/// If this file handle, or a clone of it, already holds an advisory lock the exact behavior is
/// unspecified and platform dependent, including the possibility that it will deadlock.
/// However, if this method returns, then an exclusive lock is held.
/// If this file handle/descriptor, or a clone of it, already holds an advisory lock the exact
/// behavior is unspecified and platform dependent, including the possibility that it will
/// deadlock. However, if this method returns, then an exclusive lock is held.
///
/// If the file not open for writing, it is unspecified whether this function returns an error.
///
@ -639,6 +639,9 @@ impl File {
/// [`try_lock_shared`], and [`unlock`]. Its interactions with other methods, such as [`read`]
/// and [`write`] are platform specific, and it may or may not cause non-lockholders to block.
///
/// The lock will be released when this file (along with any other file descriptors/handles
/// duplicated or inherited from it) is closed, or if the [`unlock`] method is called.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `flock` function on Unix with the `LOCK_EX` flag,
@ -671,19 +674,22 @@ impl File {
self.inner.lock()
}
/// Acquire a shared advisory lock on the file. Blocks until the lock can be acquired.
/// Acquire a shared (non-exclusive) advisory lock on the file. Blocks until the lock can be acquired.
///
/// This acquires a shared advisory lock; more than one file handle may hold a shared lock, but
/// none may hold an exclusive lock.
/// none may hold an exclusive lock at the same time.
///
/// If this file handle, or a clone of it, already holds an advisory lock, the exact behavior is
/// unspecified and platform dependent, including the possibility that it will deadlock.
/// However, if this method returns, then a shared lock is held.
/// If this file handle/descriptor, or a clone of it, already holds an advisory lock, the exact
/// behavior is unspecified and platform dependent, including the possibility that it will
/// deadlock. However, if this method returns, then a shared lock is held.
///
/// Note, this is an advisory lock meant to interact with [`lock`], [`try_lock`],
/// [`try_lock_shared`], and [`unlock`]. Its interactions with other methods, such as [`read`]
/// and [`write`] are platform specific, and it may or may not cause non-lockholders to block.
///
/// The lock will be released when this file (along with any other file descriptors/handles
/// duplicated or inherited from it) is closed, or if the [`unlock`] method is called.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `flock` function on Unix with the `LOCK_SH` flag,
@ -716,14 +722,18 @@ impl File {
self.inner.lock_shared()
}
/// Acquire an exclusive advisory lock on the file. Returns `Ok(false)` if the file is locked.
/// Try to acquire an exclusive advisory lock on the file.
///
/// Returns `Ok(false)` if a different lock is already held on this file (via another
/// handle/descriptor).
///
/// This acquires an exclusive advisory lock; no other file handle to this file may acquire
/// another lock.
///
/// If this file handle, or a clone of it, already holds an advisory lock, the exact behavior is
/// unspecified and platform dependent, including the possibility that it will deadlock.
/// However, if this method returns, then an exclusive lock is held.
/// If this file handle/descriptor, or a clone of it, already holds an advisory lock, the exact
/// behavior is unspecified and platform dependent, including the possibility that it will
/// deadlock. However, if this method returns `Ok(true)`, then it has acquired an exclusive
/// lock.
///
/// If the file not open for writing, it is unspecified whether this function returns an error.
///
@ -731,6 +741,9 @@ impl File {
/// [`try_lock_shared`], and [`unlock`]. Its interactions with other methods, such as [`read`]
/// and [`write`] are platform specific, and it may or may not cause non-lockholders to block.
///
/// The lock will be released when this file (along with any other file descriptors/handles
/// duplicated or inherited from it) is closed, or if the [`unlock`] method is called.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `flock` function on Unix with the `LOCK_EX` and
@ -764,20 +777,25 @@ impl File {
self.inner.try_lock()
}
/// Acquire a shared advisory lock on the file.
/// Returns `Ok(false)` if the file is exclusively locked.
/// Try to acquire a shared (non-exclusive) advisory lock on the file.
///
/// Returns `Ok(false)` if an exclusive lock is already held on this file (via another
/// handle/descriptor).
///
/// This acquires a shared advisory lock; more than one file handle may hold a shared lock, but
/// none may hold an exclusive lock.
/// none may hold an exclusive lock at the same time.
///
/// If this file handle, or a clone of it, already holds an advisory lock, the exact behavior is
/// unspecified and platform dependent, including the possibility that it will deadlock.
/// However, if this method returns, then a shared lock is held.
/// However, if this method returns `Ok(true)`, then it has acquired a shared lock.
///
/// Note, this is an advisory lock meant to interact with [`lock`], [`try_lock`],
/// [`try_lock`], and [`unlock`]. Its interactions with other methods, such as [`read`]
/// and [`write`] are platform specific, and it may or may not cause non-lockholders to block.
///
/// The lock will be released when this file (along with any other file descriptors/handles
/// duplicated or inherited from it) is closed, or if the [`unlock`] method is called.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `flock` function on Unix with the `LOCK_SH` and
@ -813,7 +831,12 @@ impl File {
/// Release all locks on the file.
///
/// All remaining locks are released when the file handle, and all clones of it, are dropped.
/// All locks are released when the file (along with any other file descriptors/handles
/// duplicated or inherited from it) is closed. This method allows releasing locks without
/// closing the file.
///
/// If no lock is currently held via this file descriptor/handle, this method may return an
/// error, or may return successfully without taking any action.
///
/// # Platform-specific behavior
///