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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 "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 
     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