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1 //===--- 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 <system_error>
15 #include <utility> // for std::pair
16 
17 namespace llvm {
18 class StringRef;
19 
20 /// \brief Class that manages the creation of a lock file to aid
21 /// implicit coordination between different processes.
22 ///
23 /// The implicit coordination works by creating a ".lock" file alongside
24 /// the file that we're coordinating for, using the atomicity of the file
25 /// system to ensure that only a single process can create that ".lock" file.
26 /// When the lock file is removed, the owning process has finished the
27 /// operation.
28 class LockFileManager {
29 public:
30   /// \brief Describes the state of a lock file.
31   enum LockFileState {
32     /// \brief The lock file has been created and is owned by this instance
33     /// of the object.
34     LFS_Owned,
35     /// \brief The lock file already exists and is owned by some other
36     /// instance.
37     LFS_Shared,
38     /// \brief An error occurred while trying to create or find the lock
39     /// file.
40     LFS_Error
41   };
42 
43   /// \brief Describes the result of waiting for the owner to release the lock.
44   enum WaitForUnlockResult {
45     /// \brief The lock was released successfully.
46     Res_Success,
47     /// \brief Owner died while holding the lock.
48     Res_OwnerDied,
49     /// \brief Reached timeout while waiting for the owner to release the lock.
50     Res_Timeout
51   };
52 
53 private:
54   SmallString<128> FileName;
55   SmallString<128> LockFileName;
56   SmallString<128> UniqueLockFileName;
57 
58   Optional<std::pair<std::string, int> > Owner;
59   Optional<std::error_code> Error;
60   std::string ErrorDiagMsg;
61 
62   LockFileManager(const LockFileManager &) = delete;
63   LockFileManager &operator=(const LockFileManager &) = delete;
64 
65   static Optional<std::pair<std::string, int> >
66   readLockFile(StringRef LockFileName);
67 
68   static bool processStillExecuting(StringRef Hostname, int PID);
69 
70 public:
71 
72   LockFileManager(StringRef FileName);
73   ~LockFileManager();
74 
75   /// \brief Determine the state of the lock file.
76   LockFileState getState() const;
77 
LockFileState()78   operator LockFileState() const { return getState(); }
79 
80   /// \brief For a shared lock, wait until the owner releases the lock.
81   WaitForUnlockResult waitForUnlock();
82 
83   /// \brief Remove the lock file.  This may delete a different lock file than
84   /// the one previously read if there is a race.
85   std::error_code unsafeRemoveLockFile();
86 
87   /// \brief Get error message, or "" if there is no error.
88   std::string getErrorMessage() const;
89 
90   /// \brief Set error and error message
91   void setError(std::error_code &EC, StringRef ErrorMsg = "") {
92     Error = EC;
93     ErrorDiagMsg = ErrorMsg.str();
94   }
95 };
96 
97 } // end namespace llvm
98 
99 #endif // LLVM_SUPPORT_LOCKFILEMANAGER_H
100