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      1 //===--- LockFileManager.h - File-level locking utility ---------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 #ifndef LLVM_SUPPORT_LOCKFILEMANAGER_H
      9 #define LLVM_SUPPORT_LOCKFILEMANAGER_H
     10 
     11 #include "llvm/ADT/Optional.h"
     12 #include "llvm/ADT/SmallString.h"
     13 #include <system_error>
     14 #include <utility> // for std::pair
     15 
     16 namespace llvm {
     17 class StringRef;
     18 
     19 /// 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   /// Describes the state of a lock file.
     30   enum LockFileState {
     31     /// The lock file has been created and is owned by this instance
     32     /// of the object.
     33     LFS_Owned,
     34     /// The lock file already exists and is owned by some other
     35     /// instance.
     36     LFS_Shared,
     37     /// An error occurred while trying to create or find the lock
     38     /// file.
     39     LFS_Error
     40   };
     41 
     42   /// Describes the result of waiting for the owner to release the lock.
     43   enum WaitForUnlockResult {
     44     /// The lock was released successfully.
     45     Res_Success,
     46     /// Owner died while holding the lock.
     47     Res_OwnerDied,
     48     /// 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   std::error_code ErrorCode;
     59   std::string ErrorDiagMsg;
     60 
     61   LockFileManager(const LockFileManager &) = delete;
     62   LockFileManager &operator=(const LockFileManager &) = delete;
     63 
     64   static Optional<std::pair<std::string, int> >
     65   readLockFile(StringRef LockFileName);
     66 
     67   static bool processStillExecuting(StringRef Hostname, int PID);
     68 
     69 public:
     70 
     71   LockFileManager(StringRef FileName);
     72   ~LockFileManager();
     73 
     74   /// Determine the state of the lock file.
     75   LockFileState getState() const;
     76 
     77   operator LockFileState() const { return getState(); }
     78 
     79   /// For a shared lock, wait until the owner releases the lock.
     80   /// Total timeout for the file to appear is ~1.5 minutes.
     81   /// \param MaxSeconds the maximum total wait time in seconds.
     82   WaitForUnlockResult waitForUnlock(const unsigned MaxSeconds = 90);
     83 
     84   /// 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   /// Get error message, or "" if there is no error.
     89   std::string getErrorMessage() const;
     90 
     91   /// 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
    101