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