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//! File-locking support.
//!
//! This module defines the [`Filesystem`] type which is an abstraction over a
//! filesystem, ensuring that access to the filesystem is only done through
//! coordinated locks.
//!
//! The [`FileLock`] type represents a locked file, and provides access to the
//! file.
use std::fs::{File, OpenOptions};
use std::io;
use std::io::{Read, Seek, SeekFrom, Write};
use std::path::{Display, Path, PathBuf};
use crate::util::errors::CargoResult;
use crate::util::style;
use crate::util::GlobalContext;
use anyhow::Context as _;
use cargo_util::paths;
use sys::*;
/// A locked file.
///
/// This provides access to file while holding a lock on the file. This type
/// implements the [`Read`], [`Write`], and [`Seek`] traits to provide access
/// to the underlying file.
///
/// Locks are either shared (multiple processes can access the file) or
/// exclusive (only one process can access the file).
///
/// This type is created via methods on the [`Filesystem`] type.
///
/// When this value is dropped, the lock will be released.
#[derive(Debug)]
pub struct FileLock {
f: Option<File>,
path: PathBuf,
}
impl FileLock {
/// Returns the underlying file handle of this lock.
pub fn file(&self) -> &File {
self.f.as_ref().unwrap()
}
/// Returns the underlying path that this lock points to.
///
/// Note that special care must be taken to ensure that the path is not
/// referenced outside the lifetime of this lock.
pub fn path(&self) -> &Path {
&self.path
}
/// Returns the parent path containing this file
pub fn parent(&self) -> &Path {
self.path.parent().unwrap()
}
/// Removes all sibling files to this locked file.
///
/// This can be useful if a directory is locked with a sentinel file but it
/// needs to be cleared out as it may be corrupt.
pub fn remove_siblings(&self) -> CargoResult<()> {
let path = self.path();
for entry in path.parent().unwrap().read_dir()? {
let entry = entry?;
if Some(&entry.file_name()[..]) == path.file_name() {
continue;
}
let kind = entry.file_type()?;
if kind.is_dir() {
paths::remove_dir_all(entry.path())?;
} else {
paths::remove_file(entry.path())?;
}
}
Ok(())
}
}
impl Read for FileLock {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
self.file().read(buf)
}
}
impl Seek for FileLock {
fn seek(&mut self, to: SeekFrom) -> io::Result<u64> {
self.file().seek(to)
}
}
impl Write for FileLock {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
self.file().write(buf)
}
fn flush(&mut self) -> io::Result<()> {
self.file().flush()
}
}
impl Drop for FileLock {
fn drop(&mut self) {
if let Some(f) = self.f.take() {
if let Err(e) = unlock(&f) {
tracing::warn!("failed to release lock: {e:?}");
}
}
}
}
/// A "filesystem" is intended to be a globally shared, hence locked, resource
/// in Cargo.
///
/// The `Path` of a filesystem cannot be learned unless it's done in a locked
/// fashion, and otherwise functions on this structure are prepared to handle
/// concurrent invocations across multiple instances of Cargo.
///
/// The methods on `Filesystem` that open files return a [`FileLock`] which
/// holds the lock, and that type provides methods for accessing the
/// underlying file.
///
/// If the blocking methods (like [`Filesystem::open_ro_shared`]) detect that
/// they will block, then they will display a message to the user letting them
/// know it is blocked. There are non-blocking variants starting with the
/// `try_` prefix like [`Filesystem::try_open_ro_shared_create`].
///
/// The behavior of locks acquired by the `Filesystem` depend on the operating
/// system. On unix-like system, they are advisory using [`flock`], and thus
/// not enforced against processes which do not try to acquire the lock. On
/// Windows, they are mandatory using [`LockFileEx`], enforced against all
/// processes.
///
/// This **does not** guarantee that a lock is acquired. In some cases, for
/// example on filesystems that don't support locking, it will return a
/// [`FileLock`] even though the filesystem lock was not acquired. This is
/// intended to provide a graceful fallback instead of refusing to work.
/// Usually there aren't multiple processes accessing the same resource. In
/// that case, it is the user's responsibility to not run concurrent
/// processes.
///
/// [`flock`]: https://linux.die.net/man/2/flock
/// [`LockFileEx`]: https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-lockfileex
#[derive(Clone, Debug)]
pub struct Filesystem {
root: PathBuf,
}
impl Filesystem {
/// Creates a new filesystem to be rooted at the given path.
pub fn new(path: PathBuf) -> Filesystem {
Filesystem { root: path }
}
/// Like `Path::join`, creates a new filesystem rooted at this filesystem
/// joined with the given path.
pub fn join<T: AsRef<Path>>(&self, other: T) -> Filesystem {
Filesystem::new(self.root.join(other))
}
/// Like `Path::push`, pushes a new path component onto this filesystem.
pub fn push<T: AsRef<Path>>(&mut self, other: T) {
self.root.push(other);
}
/// Consumes this filesystem and returns the underlying `PathBuf`.
///
/// Note that this is a relatively dangerous operation and should be used
/// with great caution!.
pub fn into_path_unlocked(self) -> PathBuf {
self.root
}
/// Returns the underlying `Path`.
///
/// Note that this is a relatively dangerous operation and should be used
/// with great caution!.
pub fn as_path_unlocked(&self) -> &Path {
&self.root
}
/// Creates the directory pointed to by this filesystem.
///
/// Handles errors where other Cargo processes are also attempting to
/// concurrently create this directory.
pub fn create_dir(&self) -> CargoResult<()> {
paths::create_dir_all(&self.root)
}
/// Returns an adaptor that can be used to print the path of this
/// filesystem.
pub fn display(&self) -> Display<'_> {
self.root.display()
}
/// Opens read-write exclusive access to a file, returning the locked
/// version of a file.
///
/// This function will create a file at `path` if it doesn't already exist
/// (including intermediate directories), and then it will acquire an
/// exclusive lock on `path`. If the process must block waiting for the
/// lock, the `msg` is printed to [`GlobalContext`].
///
/// The returned file can be accessed to look at the path and also has
/// read/write access to the underlying file.
pub fn open_rw_exclusive_create<P>(
&self,
path: P,
gctx: &GlobalContext,
msg: &str,
) -> CargoResult<FileLock>
where
P: AsRef<Path>,
{
let mut opts = OpenOptions::new();
opts.read(true).write(true).create(true);
let (path, f) = self.open(path.as_ref(), &opts, true)?;
acquire(gctx, msg, &path, &|| try_lock_exclusive(&f), &|| {
lock_exclusive(&f)
})?;
Ok(FileLock { f: Some(f), path })
}
/// A non-blocking version of [`Filesystem::open_rw_exclusive_create`].
///
/// Returns `None` if the operation would block due to another process
/// holding the lock.
pub fn try_open_rw_exclusive_create<P: AsRef<Path>>(
&self,
path: P,
) -> CargoResult<Option<FileLock>> {
let mut opts = OpenOptions::new();
opts.read(true).write(true).create(true);
let (path, f) = self.open(path.as_ref(), &opts, true)?;
if try_acquire(&path, &|| try_lock_exclusive(&f))? {
Ok(Some(FileLock { f: Some(f), path }))
} else {
Ok(None)
}
}
/// Opens read-only shared access to a file, returning the locked version of a file.
///
/// This function will fail if `path` doesn't already exist, but if it does
/// then it will acquire a shared lock on `path`. If the process must block
/// waiting for the lock, the `msg` is printed to [`GlobalContext`].
///
/// The returned file can be accessed to look at the path and also has read
/// access to the underlying file. Any writes to the file will return an
/// error.
pub fn open_ro_shared<P>(
&self,
path: P,
gctx: &GlobalContext,
msg: &str,
) -> CargoResult<FileLock>
where
P: AsRef<Path>,
{
let (path, f) = self.open(path.as_ref(), &OpenOptions::new().read(true), false)?;
acquire(gctx, msg, &path, &|| try_lock_shared(&f), &|| {
lock_shared(&f)
})?;
Ok(FileLock { f: Some(f), path })
}
/// Opens read-only shared access to a file, returning the locked version of a file.
///
/// Compared to [`Filesystem::open_ro_shared`], this will create the file
/// (and any directories in the parent) if the file does not already
/// exist.
pub fn open_ro_shared_create<P: AsRef<Path>>(
&self,
path: P,
gctx: &GlobalContext,
msg: &str,
) -> CargoResult<FileLock> {
let mut opts = OpenOptions::new();
opts.read(true).write(true).create(true);
let (path, f) = self.open(path.as_ref(), &opts, true)?;
acquire(gctx, msg, &path, &|| try_lock_shared(&f), &|| {
lock_shared(&f)
})?;
Ok(FileLock { f: Some(f), path })
}
/// A non-blocking version of [`Filesystem::open_ro_shared_create`].
///
/// Returns `None` if the operation would block due to another process
/// holding the lock.
pub fn try_open_ro_shared_create<P: AsRef<Path>>(
&self,
path: P,
) -> CargoResult<Option<FileLock>> {
let mut opts = OpenOptions::new();
opts.read(true).write(true).create(true);
let (path, f) = self.open(path.as_ref(), &opts, true)?;
if try_acquire(&path, &|| try_lock_shared(&f))? {
Ok(Some(FileLock { f: Some(f), path }))
} else {
Ok(None)
}
}
fn open(&self, path: &Path, opts: &OpenOptions, create: bool) -> CargoResult<(PathBuf, File)> {
let path = self.root.join(path);
let f = opts
.open(&path)
.or_else(|e| {
// If we were requested to create this file, and there was a
// NotFound error, then that was likely due to missing
// intermediate directories. Try creating them and try again.
if e.kind() == io::ErrorKind::NotFound && create {
paths::create_dir_all(path.parent().unwrap())?;
Ok(opts.open(&path)?)
} else {
Err(anyhow::Error::from(e))
}
})
.with_context(|| format!("failed to open: {}", path.display()))?;
Ok((path, f))
}
}
impl PartialEq<Path> for Filesystem {
fn eq(&self, other: &Path) -> bool {
self.root == other
}
}
impl PartialEq<Filesystem> for Path {
fn eq(&self, other: &Filesystem) -> bool {
self == other.root
}
}
fn try_acquire(path: &Path, lock_try: &dyn Fn() -> io::Result<()>) -> CargoResult<bool> {
// File locking on Unix is currently implemented via `flock`, which is known
// to be broken on NFS. We could in theory just ignore errors that happen on
// NFS, but apparently the failure mode [1] for `flock` on NFS is **blocking
// forever**, even if the "non-blocking" flag is passed!
//
// As a result, we just skip all file locks entirely on NFS mounts. That
// should avoid calling any `flock` functions at all, and it wouldn't work
// there anyway.
//
// [1]: https://github.com/rust-lang/cargo/issues/2615
if is_on_nfs_mount(path) {
tracing::debug!("{path:?} appears to be an NFS mount, not trying to lock");
return Ok(true);
}
match lock_try() {
Ok(()) => return Ok(true),
// In addition to ignoring NFS which is commonly not working we also
// just ignore locking on filesystems that look like they don't
// implement file locking.
Err(e) if error_unsupported(&e) => return Ok(true),
Err(e) => {
if !error_contended(&e) {
let e = anyhow::Error::from(e);
let cx = format!("failed to lock file: {}", path.display());
return Err(e.context(cx));
}
}
}
Ok(false)
}
/// Acquires a lock on a file in a "nice" manner.
///
/// Almost all long-running blocking actions in Cargo have a status message
/// associated with them as we're not sure how long they'll take. Whenever a
/// conflicted file lock happens, this is the case (we're not sure when the lock
/// will be released).
///
/// This function will acquire the lock on a `path`, printing out a nice message
/// to the console if we have to wait for it. It will first attempt to use `try`
/// to acquire a lock on the crate, and in the case of contention it will emit a
/// status message based on `msg` to [`GlobalContext`]'s shell, and then use `block` to
/// block waiting to acquire a lock.
///
/// Returns an error if the lock could not be acquired or if any error other
/// than a contention error happens.
fn acquire(
gctx: &GlobalContext,
msg: &str,
path: &Path,
lock_try: &dyn Fn() -> io::Result<()>,
lock_block: &dyn Fn() -> io::Result<()>,
) -> CargoResult<()> {
if cfg!(debug_assertions) {
// Force borrow to catch invalid borrows outside of contention situations
gctx.shell().verbosity();
}
if try_acquire(path, lock_try)? {
return Ok(());
}
let msg = format!("waiting for file lock on {}", msg);
gctx.shell()
.status_with_color("Blocking", &msg, &style::NOTE)?;
lock_block().with_context(|| format!("failed to lock file: {}", path.display()))?;
Ok(())
}
#[cfg(all(target_os = "linux", not(target_env = "musl")))]
fn is_on_nfs_mount(path: &Path) -> bool {
use std::ffi::CString;
use std::mem;
use std::os::unix::prelude::*;
let Ok(path) = CString::new(path.as_os_str().as_bytes()) else {
return false;
};
unsafe {
let mut buf: libc::statfs = mem::zeroed();
let r = libc::statfs(path.as_ptr(), &mut buf);
r == 0 && buf.f_type as u32 == libc::NFS_SUPER_MAGIC as u32
}
}
#[cfg(any(not(target_os = "linux"), target_env = "musl"))]
fn is_on_nfs_mount(_path: &Path) -> bool {
false
}
#[cfg(unix)]
mod sys {
use std::fs::File;
use std::io::{Error, Result};
use std::os::unix::io::AsRawFd;
pub(super) fn lock_shared(file: &File) -> Result<()> {
flock(file, libc::LOCK_SH)
}
pub(super) fn lock_exclusive(file: &File) -> Result<()> {
flock(file, libc::LOCK_EX)
}
pub(super) fn try_lock_shared(file: &File) -> Result<()> {
flock(file, libc::LOCK_SH | libc::LOCK_NB)
}
pub(super) fn try_lock_exclusive(file: &File) -> Result<()> {
flock(file, libc::LOCK_EX | libc::LOCK_NB)
}
pub(super) fn unlock(file: &File) -> Result<()> {
flock(file, libc::LOCK_UN)
}
pub(super) fn error_contended(err: &Error) -> bool {
err.raw_os_error().map_or(false, |x| x == libc::EWOULDBLOCK)
}
pub(super) fn error_unsupported(err: &Error) -> bool {
match err.raw_os_error() {
// Unfortunately, depending on the target, these may or may not be the same.
// For targets in which they are the same, the duplicate pattern causes a warning.
#[allow(unreachable_patterns)]
Some(libc::ENOTSUP | libc::EOPNOTSUPP) => true,
Some(libc::ENOSYS) => true,
_ => false,
}
}
#[cfg(not(target_os = "solaris"))]
fn flock(file: &File, flag: libc::c_int) -> Result<()> {
let ret = unsafe { libc::flock(file.as_raw_fd(), flag) };
if ret < 0 {
Err(Error::last_os_error())
} else {
Ok(())
}
}
#[cfg(target_os = "solaris")]
fn flock(file: &File, flag: libc::c_int) -> Result<()> {
// Solaris lacks flock(), so try to emulate using fcntl()
let mut flock = libc::flock {
l_type: 0,
l_whence: 0,
l_start: 0,
l_len: 0,
l_sysid: 0,
l_pid: 0,
l_pad: [0, 0, 0, 0],
};
flock.l_type = if flag & libc::LOCK_UN != 0 {
libc::F_UNLCK
} else if flag & libc::LOCK_EX != 0 {
libc::F_WRLCK
} else if flag & libc::LOCK_SH != 0 {
libc::F_RDLCK
} else {
panic!("unexpected flock() operation")
};
let mut cmd = libc::F_SETLKW;
if (flag & libc::LOCK_NB) != 0 {
cmd = libc::F_SETLK;
}
let ret = unsafe { libc::fcntl(file.as_raw_fd(), cmd, &flock) };
if ret < 0 {
Err(Error::last_os_error())
} else {
Ok(())
}
}
}
#[cfg(windows)]
mod sys {
use std::fs::File;
use std::io::{Error, Result};
use std::mem;
use std::os::windows::io::AsRawHandle;
use windows_sys::Win32::Foundation::HANDLE;
use windows_sys::Win32::Foundation::{ERROR_INVALID_FUNCTION, ERROR_LOCK_VIOLATION};
use windows_sys::Win32::Storage::FileSystem::{
LockFileEx, UnlockFile, LOCKFILE_EXCLUSIVE_LOCK, LOCKFILE_FAIL_IMMEDIATELY,
};
pub(super) fn lock_shared(file: &File) -> Result<()> {
lock_file(file, 0)
}
pub(super) fn lock_exclusive(file: &File) -> Result<()> {
lock_file(file, LOCKFILE_EXCLUSIVE_LOCK)
}
pub(super) fn try_lock_shared(file: &File) -> Result<()> {
lock_file(file, LOCKFILE_FAIL_IMMEDIATELY)
}
pub(super) fn try_lock_exclusive(file: &File) -> Result<()> {
lock_file(file, LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY)
}
pub(super) fn error_contended(err: &Error) -> bool {
err.raw_os_error()
.map_or(false, |x| x == ERROR_LOCK_VIOLATION as i32)
}
pub(super) fn error_unsupported(err: &Error) -> bool {
err.raw_os_error()
.map_or(false, |x| x == ERROR_INVALID_FUNCTION as i32)
}
pub(super) fn unlock(file: &File) -> Result<()> {
unsafe {
let ret = UnlockFile(file.as_raw_handle() as HANDLE, 0, 0, !0, !0);
if ret == 0 {
Err(Error::last_os_error())
} else {
Ok(())
}
}
}
fn lock_file(file: &File, flags: u32) -> Result<()> {
unsafe {
let mut overlapped = mem::zeroed();
let ret = LockFileEx(
file.as_raw_handle() as HANDLE,
flags,
0,
!0,
!0,
&mut overlapped,
);
if ret == 0 {
Err(Error::last_os_error())
} else {
Ok(())
}
}
}
}