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Andrew Scull5e1ddfa2018-08-14 10:06:54 +01001//===--- LockFileManager.h - File-level locking utility ---------*- C++ -*-===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9#ifndef LLVM_SUPPORT_LOCKFILEMANAGER_H
10#define LLVM_SUPPORT_LOCKFILEMANAGER_H
11
12#include "llvm/ADT/Optional.h"
13#include "llvm/ADT/SmallString.h"
14#include "llvm/Support/FileSystem.h"
15#include <system_error>
16#include <utility> // for std::pair
17
18namespace llvm {
19class StringRef;
20
21/// \brief Class that manages the creation of a lock file to aid
22/// implicit coordination between different processes.
23///
24/// The implicit coordination works by creating a ".lock" file alongside
25/// the file that we're coordinating for, using the atomicity of the file
26/// system to ensure that only a single process can create that ".lock" file.
27/// When the lock file is removed, the owning process has finished the
28/// operation.
29class LockFileManager {
30public:
31 /// \brief Describes the state of a lock file.
32 enum LockFileState {
33 /// \brief The lock file has been created and is owned by this instance
34 /// of the object.
35 LFS_Owned,
36 /// \brief The lock file already exists and is owned by some other
37 /// instance.
38 LFS_Shared,
39 /// \brief An error occurred while trying to create or find the lock
40 /// file.
41 LFS_Error
42 };
43
44 /// \brief Describes the result of waiting for the owner to release the lock.
45 enum WaitForUnlockResult {
46 /// \brief The lock was released successfully.
47 Res_Success,
48 /// \brief Owner died while holding the lock.
49 Res_OwnerDied,
50 /// \brief Reached timeout while waiting for the owner to release the lock.
51 Res_Timeout
52 };
53
54private:
55 SmallString<128> FileName;
56 SmallString<128> LockFileName;
57 Optional<sys::fs::TempFile> UniqueLockFile;
58
59 Optional<std::pair<std::string, int> > Owner;
60 std::error_code ErrorCode;
61 std::string ErrorDiagMsg;
62
63 LockFileManager(const LockFileManager &) = delete;
64 LockFileManager &operator=(const LockFileManager &) = delete;
65
66 static Optional<std::pair<std::string, int> >
67 readLockFile(StringRef LockFileName);
68
69 static bool processStillExecuting(StringRef Hostname, int PID);
70
71public:
72
73 LockFileManager(StringRef FileName);
74 ~LockFileManager();
75
76 /// \brief Determine the state of the lock file.
77 LockFileState getState() const;
78
79 operator LockFileState() const { return getState(); }
80
81 /// \brief For a shared lock, wait until the owner releases the lock.
82 WaitForUnlockResult waitForUnlock();
83
84 /// \brief 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 /// \brief Get error message, or "" if there is no error.
89 std::string getErrorMessage() const;
90
91 /// \brief 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