llvm/Support/LockFileManager.h

0001 //===--- LockFileManager.h - File-level locking utility ---------*- C++ -*-===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008 #ifndef LLVM_SUPPORT_LOCKFILEMANAGER_H
0009 #define LLVM_SUPPORT_LOCKFILEMANAGER_H
0010
0011 #include "llvm/ADT/SmallString.h"
0012 #include <optional>
0013 #include <system_error>
0014 #include <utility> // for std::pair
0015
0016 namespace llvm {
0017 class StringRef;
0018
0019 /// Class that manages the creation of a lock file to aid
0020 /// implicit coordination between different processes.
0021 ///
0022 /// The implicit coordination works by creating a ".lock" file alongside
0023 /// the file that we're coordinating for, using the atomicity of the file
0024 /// system to ensure that only a single process can create that ".lock" file.
0025 /// When the lock file is removed, the owning process has finished the
0026 /// operation.
0027 class LockFileManager {
0028 public:
0029   /// Describes the state of a lock file.
0030   enum LockFileState {
0031     /// The lock file has been created and is owned by this instance
0032     /// of the object.
0033     LFS_Owned,
0034     /// The lock file already exists and is owned by some other
0035     /// instance.
0036     LFS_Shared,
0037     /// An error occurred while trying to create or find the lock
0038     /// file.
0039     LFS_Error
0040   };
0041
0042   /// Describes the result of waiting for the owner to release the lock.
0043   enum WaitForUnlockResult {
0044     /// The lock was released successfully.
0045     Res_Success,
0046     /// Owner died while holding the lock.
0047     Res_OwnerDied,
0048     /// Reached timeout while waiting for the owner to release the lock.
0049     Res_Timeout
0050   };
0051
0052 private:
0053   SmallString<128> FileName;
0054   SmallString<128> LockFileName;
0055   SmallString<128> UniqueLockFileName;
0056
0057   std::optional<std::pair<std::string, int>> Owner;
0058   std::error_code ErrorCode;
0059   std::string ErrorDiagMsg;
0060
0061   LockFileManager(const LockFileManager &) = delete;
0062   LockFileManager &operator=(const LockFileManager &) = delete;
0063
0064   static std::optional<std::pair<std::string, int>>
0065   readLockFile(StringRef LockFileName);
0066
0067   static bool processStillExecuting(StringRef Hostname, int PID);
0068
0069 public:
0070
0071   LockFileManager(StringRef FileName);
0072   ~LockFileManager();
0073
0074   /// Determine the state of the lock file.
0075   LockFileState getState() const;
0076
0077   operator LockFileState() const { return getState(); }
0078
0079   /// For a shared lock, wait until the owner releases the lock.
0080   /// Total timeout for the file to appear is ~1.5 minutes.
0081   /// \param MaxSeconds the maximum total wait time in seconds.
0082   WaitForUnlockResult waitForUnlock(const unsigned MaxSeconds = 90);
0083
0084   /// Remove the lock file.  This may delete a different lock file than
0085   /// the one previously read if there is a race.
0086   std::error_code unsafeRemoveLockFile();
0087
0088   /// Get error message, or "" if there is no error.
0089   std::string getErrorMessage() const;
0090
0091   /// Set error and error message
0092   void setError(const std::error_code &EC, StringRef ErrorMsg = "") {
0093     ErrorCode = EC;
0094     ErrorDiagMsg = ErrorMsg.str();
0095   }
0096 };
0097
0098 } // end namespace llvm
0099
0100 #endif // LLVM_SUPPORT_LOCKFILEMANAGER_H