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 "llvm/ADT/StringRef.h"
15 #include <system_error>
16 #include <utility> // for std::pair
17 
18 namespace llvm {
19 /// \brief 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   /// \brief Describes the state of a lock file.
30   enum LockFileState {
31     /// \brief The lock file has been created and is owned by this instance
32     /// of the object.
33     LFS_Owned,
34     /// \brief The lock file already exists and is owned by some other
35     /// instance.
36     LFS_Shared,
37     /// \brief An error occurred while trying to create or find the lock
38     /// file.
39     LFS_Error
40   };
41 
42   /// \brief Describes the result of waiting for the owner to release the lock.
43   enum WaitForUnlockResult {
44     /// \brief The lock was released successfully.
45     Res_Success,
46     /// \brief Owner died while holding the lock.
47     Res_OwnerDied,
48     /// \brief 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   Optional<std::pair<std::string, int> > Owner;
58   Optional<std::error_code> Error;
59 
60   LockFileManager(const LockFileManager &) = delete;
61   LockFileManager &operator=(const LockFileManager &) = delete;
62 
63   static Optional<std::pair<std::string, int> >
64   readLockFile(StringRef LockFileName);
65 
66   static bool processStillExecuting(StringRef Hostname, int PID);
67 
68 public:
69 
70   LockFileManager(StringRef FileName);
71   ~LockFileManager();
72 
73   /// \brief Determine the state of the lock file.
74   LockFileState getState() const;
75 
LockFileState()76   operator LockFileState() const { return getState(); }
77 
78   /// \brief For a shared lock, wait until the owner releases the lock.
79   WaitForUnlockResult waitForUnlock();
80 
81   /// \brief Remove the lock file.  This may delete a different lock file than
82   /// the one previously read if there is a race.
83   std::error_code unsafeRemoveLockFile();
84 };
85 
86 } // end namespace llvm
87 
88 #endif // LLVM_SUPPORT_LOCKFILEMANAGER_H
89