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//===--- LockFileManager.h - File-level locking utility ---------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_LOCKFILEMANAGER_H
#define LLVM_SUPPORT_LOCKFILEMANAGER_H
#include "llvm/ADT/SmallString.h"
#include <optional>
#include <system_error>
#include <utility> // for std::pair
namespace llvm {
class StringRef;
/// Class that manages the creation of a lock file to aid
/// implicit coordination between different processes.
///
/// The implicit coordination works by creating a ".lock" file alongside
/// the file that we're coordinating for, using the atomicity of the file
/// system to ensure that only a single process can create that ".lock" file.
/// When the lock file is removed, the owning process has finished the
/// operation.
class LockFileManager {
public:
/// Describes the state of a lock file.
enum LockFileState {
/// The lock file has been created and is owned by this instance
/// of the object.
LFS_Owned,
/// The lock file already exists and is owned by some other
/// instance.
LFS_Shared,
/// An error occurred while trying to create or find the lock
/// file.
LFS_Error
};
/// Describes the result of waiting for the owner to release the lock.
enum WaitForUnlockResult {
/// The lock was released successfully.
Res_Success,
/// Owner died while holding the lock.
Res_OwnerDied,
/// Reached timeout while waiting for the owner to release the lock.
Res_Timeout
};
private:
SmallString<128> FileName;
SmallString<128> LockFileName;
SmallString<128> UniqueLockFileName;
std::optional<std::pair<std::string, int>> Owner;
std::error_code ErrorCode;
std::string ErrorDiagMsg;
LockFileManager(const LockFileManager &) = delete;
LockFileManager &operator=(const LockFileManager &) = delete;
static std::optional<std::pair<std::string, int>>
readLockFile(StringRef LockFileName);
static bool processStillExecuting(StringRef Hostname, int PID);
public:
LockFileManager(StringRef FileName);
~LockFileManager();
/// Determine the state of the lock file.
LockFileState getState() const;
operator LockFileState() const { return getState(); }
/// For a shared lock, wait until the owner releases the lock.
/// Total timeout for the file to appear is ~1.5 minutes.
/// \param MaxSeconds the maximum total wait time in seconds.
WaitForUnlockResult waitForUnlock(const unsigned MaxSeconds = 90);
/// Remove the lock file. This may delete a different lock file than
/// the one previously read if there is a race.
std::error_code unsafeRemoveLockFile();
/// Get error message, or "" if there is no error.
std::string getErrorMessage() const;
/// Set error and error message
void setError(const std::error_code &EC, StringRef ErrorMsg = "") {
ErrorCode = EC;
ErrorDiagMsg = ErrorMsg.str();
}
};
} // end namespace llvm
#endif // LLVM_SUPPORT_LOCKFILEMANAGER_H
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