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 | |
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 | |