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/Optional.h"
12#include "llvm/ADT/SmallString.h"
13#include <system_error>
14#include <utility> // for std::pair
15
16namespace llvm {
17class 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.
27class LockFileManager {
28public:
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
52private:
53  SmallString<128> FileName;
54  SmallString<128> LockFileName;
55  SmallString<128> UniqueLockFileName;
56
57  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 Optional<std::pair<std::string, int> >
65  readLockFile(StringRef LockFileName);
66
67  static bool processStillExecuting(StringRef Hostname, int PID);
68
69public:
70
71  LockFileManager(StringRef FileName);
72  ~LockFileManager();
73
74  /// Determine the state of the lock file.
75  LockFileState getState() const;
76
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 wait time per iteration in seconds.
82  WaitForUnlockResult waitForUnlock(const unsigned MaxSeconds = 40);
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