include/llvm/Support/LockFileManager.h

   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   WaitForUnlockResult waitForUnlock();
  81
  82   /// Remove the lock file.  This may delete a different lock file than
  83   /// the one previously read if there is a race.
  84   std::error_code unsafeRemoveLockFile();
  85
  86   /// Get error message, or "" if there is no error.
  87   std::string getErrorMessage() const;
  88
  89   /// Set error and error message
  90   void setError(const std::error_code &EC, StringRef ErrorMsg = "") {
  91     ErrorCode = EC;
  92     ErrorDiagMsg = ErrorMsg.str();
  93   }
  94 };
  95
  96 } // end namespace llvm
  97
  98 #endif // LLVM_SUPPORT_LOCKFILEMANAGER_H