author | Pierre-Yves David <pierre-yves.david@octobus.net> |
Thu, 16 Mar 2023 20:37:11 +0100 | |
branch | stable |
changeset 50311 | e2ba2234bf1c |
parent 49930 | e98fd81bb151 |
child 51868 | db7dbe6f7bb2 |
permissions | -rw-r--r-- |
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//! Filesystem-based locks for local repositories |
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|
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use crate::errors::HgError; |
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use crate::errors::HgResultExt; |
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use crate::vfs::Vfs; |
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use std::io; |
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use std::io::ErrorKind; |
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|
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#[derive(derive_more::From)] |
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pub enum LockError { |
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AlreadyHeld, |
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#[from] |
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Other(HgError), |
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} |
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/// Try to call `f` with the lock acquired, without waiting. |
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/// |
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/// If the lock is aready held, `f` is not called and `LockError::AlreadyHeld` |
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/// is returned. `LockError::Io` is returned for any unexpected I/O error |
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/// accessing the lock file, including for removing it after `f` was called. |
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/// The return value of `f` is dropped in that case. If all is successful, the |
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/// return value of `f` is forwarded. |
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pub fn try_with_lock_no_wait<R>( |
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hg_vfs: Vfs, |
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lock_filename: &str, |
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f: impl FnOnce() -> R, |
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) -> Result<R, LockError> { |
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let our_lock_data = &*OUR_LOCK_DATA; |
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for _retry in 0..5 { |
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match make_lock(hg_vfs, lock_filename, our_lock_data) { |
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Ok(()) => { |
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let result = f(); |
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unlock(hg_vfs, lock_filename)?; |
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return Ok(result); |
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} |
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Err(HgError::IoError { error, .. }) |
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if error.kind() == ErrorKind::AlreadyExists => |
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{ |
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let lock_data = read_lock(hg_vfs, lock_filename)?; |
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if lock_data.is_none() { |
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// Lock was apparently just released, retry acquiring it |
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continue; |
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} |
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if !lock_should_be_broken(&lock_data) { |
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return Err(LockError::AlreadyHeld); |
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} |
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// The lock file is left over from a process not running |
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// anymore. Break it, but with another lock to |
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// avoid a race. |
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break_lock(hg_vfs, lock_filename)?; |
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|
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// Retry acquiring |
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} |
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Err(error) => Err(error)?, |
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} |
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} |
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Err(LockError::AlreadyHeld) |
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} |
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fn break_lock(hg_vfs: Vfs, lock_filename: &str) -> Result<(), LockError> { |
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try_with_lock_no_wait(hg_vfs, &format!("{}.break", lock_filename), || { |
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// Check again in case some other process broke and |
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// acquired the lock in the meantime |
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let lock_data = read_lock(hg_vfs, lock_filename)?; |
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if !lock_should_be_broken(&lock_data) { |
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return Err(LockError::AlreadyHeld); |
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} |
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Ok(hg_vfs.remove_file(lock_filename)?) |
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})? |
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} |
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|
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#[cfg(unix)] |
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fn make_lock( |
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hg_vfs: Vfs, |
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lock_filename: &str, |
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data: &str, |
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) -> Result<(), HgError> { |
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// Use a symbolic link because creating it is atomic. |
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// The link’s "target" contains data not representing any path. |
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let fake_symlink_target = data; |
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hg_vfs.create_symlink(lock_filename, fake_symlink_target) |
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} |
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|
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fn read_lock( |
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hg_vfs: Vfs, |
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lock_filename: &str, |
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) -> Result<Option<String>, HgError> { |
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let link_target = |
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hg_vfs.read_link(lock_filename).io_not_found_as_none()?; |
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if let Some(target) = link_target { |
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let data = target |
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.into_os_string() |
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.into_string() |
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.map_err(|_| HgError::corrupted("non-UTF-8 lock data"))?; |
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Ok(Some(data)) |
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} else { |
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Ok(None) |
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} |
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} |
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|
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fn unlock(hg_vfs: Vfs, lock_filename: &str) -> Result<(), HgError> { |
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hg_vfs.remove_file(lock_filename) |
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} |
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104 |
|
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/// Return whether the process that is/was holding the lock is known not to be |
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/// running anymore. |
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fn lock_should_be_broken(data: &Option<String>) -> bool { |
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(|| -> Option<bool> { |
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let (prefix, pid) = data.as_ref()?.split_once(':')?; |
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if prefix != *LOCK_PREFIX { |
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return Some(false); |
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} |
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let process_is_running; |
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|
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#[cfg(unix)] |
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{ |
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let pid: libc::pid_t = pid.parse().ok()?; |
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unsafe { |
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let signal = 0; // Test if we could send a signal, without sending |
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let result = libc::kill(pid, signal); |
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if result == 0 { |
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process_is_running = true |
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} else { |
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let errno = |
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io::Error::last_os_error().raw_os_error().unwrap(); |
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process_is_running = errno != libc::ESRCH |
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} |
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} |
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129 |
} |
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130 |
|
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131 |
Some(!process_is_running) |
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})() |
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.unwrap_or(false) |
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134 |
} |
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135 |
|
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136 |
lazy_static::lazy_static! { |
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/// A string which is used to differentiate pid namespaces |
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138 |
/// |
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/// It's useful to detect "dead" processes and remove stale locks with |
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/// confidence. Typically it's just hostname. On modern linux, we include an |
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/// extra Linux-specific pid namespace identifier. |
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142 |
static ref LOCK_PREFIX: String = { |
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143 |
// Note: this must match the behavior of `_getlockprefix` in `mercurial/lock.py` |
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144 |
|
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/// Same as https://github.com/python/cpython/blob/v3.10.0/Modules/socketmodule.c#L5414 |
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const BUFFER_SIZE: usize = 1024; |
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// This cast is *needed* for platforms with signed chars |
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#[allow(clippy::unnecessary_cast)] |
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let mut buffer = [0 as libc::c_char; BUFFER_SIZE]; |
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let hostname_bytes = unsafe { |
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let result = libc::gethostname(buffer.as_mut_ptr(), BUFFER_SIZE); |
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152 |
if result != 0 { |
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panic!("gethostname: {}", io::Error::last_os_error()) |
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154 |
} |
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155 |
std::ffi::CStr::from_ptr(buffer.as_mut_ptr()).to_bytes() |
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156 |
}; |
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157 |
let hostname = |
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158 |
std::str::from_utf8(hostname_bytes).expect("non-UTF-8 hostname"); |
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159 |
|
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160 |
#[cfg(target_os = "linux")] |
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161 |
{ |
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162 |
use std::os::linux::fs::MetadataExt; |
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163 |
match std::fs::metadata("/proc/self/ns/pid") { |
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164 |
Ok(meta) => { |
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return format!("{}/{:x}", hostname, meta.st_ino()) |
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166 |
} |
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167 |
Err(error) => { |
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168 |
// TODO: match on `error.kind()` when `NotADirectory` |
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169 |
// is available on all supported Rust versions: |
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170 |
// https://github.com/rust-lang/rust/issues/86442 |
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171 |
use libc::{ |
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172 |
ENOENT, // ErrorKind::NotFound |
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173 |
ENOTDIR, // ErrorKind::NotADirectory |
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174 |
EACCES, // ErrorKind::PermissionDenied |
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175 |
}; |
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176 |
match error.raw_os_error() { |
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177 |
Some(ENOENT) | Some(ENOTDIR) | Some(EACCES) => {} |
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178 |
_ => panic!("stat /proc/self/ns/pid: {}", error), |
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179 |
} |
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180 |
} |
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181 |
} |
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182 |
} |
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183 |
|
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184 |
hostname.to_owned() |
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185 |
}; |
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186 |
|
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187 |
static ref OUR_LOCK_DATA: String = format!("{}:{}", &*LOCK_PREFIX, std::process::id()); |
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188 |
} |