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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 
     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