1 //===--- LockFileManager.h - File-level locking utility ---------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 #ifndef LLVM_SUPPORT_LOCKFILEMANAGER_H 9 #define LLVM_SUPPORT_LOCKFILEMANAGER_H 10 11 #include "llvm/ADT/SmallString.h" 12 #include <optional> 13 #include <system_error> 14 #include <utility> // for std::pair 15 16 namespace llvm { 17 class StringRef; 18 19 /// Class that manages the creation of a lock file to aid 20 /// implicit coordination between different processes. 21 /// 22 /// The implicit coordination works by creating a ".lock" file alongside 23 /// the file that we're coordinating for, using the atomicity of the file 24 /// system to ensure that only a single process can create that ".lock" file. 25 /// When the lock file is removed, the owning process has finished the 26 /// operation. 27 class LockFileManager { 28 public: 29 /// Describes the state of a lock file. 30 enum LockFileState { 31 /// The lock file has been created and is owned by this instance 32 /// of the object. 33 LFS_Owned, 34 /// The lock file already exists and is owned by some other 35 /// instance. 36 LFS_Shared, 37 /// An error occurred while trying to create or find the lock 38 /// file. 39 LFS_Error 40 }; 41 42 /// Describes the result of waiting for the owner to release the lock. 43 enum WaitForUnlockResult { 44 /// The lock was released successfully. 45 Res_Success, 46 /// Owner died while holding the lock. 47 Res_OwnerDied, 48 /// Reached timeout while waiting for the owner to release the lock. 49 Res_Timeout 50 }; 51 52 private: 53 SmallString<128> FileName; 54 SmallString<128> LockFileName; 55 SmallString<128> UniqueLockFileName; 56 57 std::optional<std::pair<std::string, int>> Owner; 58 std::error_code ErrorCode; 59 std::string ErrorDiagMsg; 60 61 LockFileManager(const LockFileManager &) = delete; 62 LockFileManager &operator=(const LockFileManager &) = delete; 63 64 static std::optional<std::pair<std::string, int>> 65 readLockFile(StringRef LockFileName); 66 67 static bool processStillExecuting(StringRef Hostname, int PID); 68 69 public: 70 71 LockFileManager(StringRef FileName); 72 ~LockFileManager(); 73 74 /// Determine the state of the lock file. 75 LockFileState getState() const; 76 LockFileState()77 operator LockFileState() const { return getState(); } 78 79 /// For a shared lock, wait until the owner releases the lock. 80 /// Total timeout for the file to appear is ~1.5 minutes. 81 /// \param MaxSeconds the maximum total wait time in seconds. 82 WaitForUnlockResult waitForUnlock(const unsigned MaxSeconds = 90); 83 84 /// Remove the lock file. This may delete a different lock file than 85 /// the one previously read if there is a race. 86 std::error_code unsafeRemoveLockFile(); 87 88 /// Get error message, or "" if there is no error. 89 std::string getErrorMessage() const; 90 91 /// Set error and error message 92 void setError(const std::error_code &EC, StringRef ErrorMsg = "") { 93 ErrorCode = EC; 94 ErrorDiagMsg = ErrorMsg.str(); 95 } 96 }; 97 98 } // end namespace llvm 99 100 #endif // LLVM_SUPPORT_LOCKFILEMANAGER_H 101