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       1                 :             : /* File locking.
       2                 :             :    Copyright (C) 2023-2024 Free Software Foundation, Inc.
       3                 :             : 
       4                 :             : This file is part of GCC.
       5                 :             : 
       6                 :             : GCC is free software; you can redistribute it and/or modify it under
       7                 :             : the terms of the GNU General Public License as published by the Free
       8                 :             : Software Foundation; either version 3, or (at your option) any later
       9                 :             : version.
      10                 :             : 
      11                 :             : GCC is distributed in the hope that it will be useful, but WITHOUT ANY
      12                 :             : WARRANTY; without even the implied warranty of MERCHANTABILITY or
      13                 :             : FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      14                 :             : for more details.
      15                 :             : 
      16                 :             : You should have received a copy of the GNU General Public License
      17                 :             : along with GCC; see the file COPYING3.  If not see
      18                 :             : <http://www.gnu.org/licenses/>.  */
      19                 :             : 
      20                 :             : #ifndef LOCKFILE_H
      21                 :             : #define LOCKFILE_H
      22                 :             : 
      23                 :             : /* Used to synchronize across multiple processes.  */
      24                 :        8833 : class lockfile {
      25                 :             : public:
      26                 :             :   /* Default constructor.  */
      27                 :        8833 :   lockfile (): fd (-1)
      28                 :             :   {}
      29                 :             :   /* Intended constructor for use.  Filename should not be used for anything
      30                 :             :      other than locking to prevent unintentional unlock.  */
      31                 :           0 :   lockfile (std::string filename): lockfile ()
      32                 :             :   {
      33                 :           0 :     this->filename = std::move (filename);
      34                 :             :   }
      35                 :             :   lockfile (lockfile const& o): lockfile (o.filename)
      36                 :             :   {}
      37                 :             : 
      38                 :           0 :   void operator=(lockfile o)
      39                 :             :   {
      40                 :           0 :     unlock ();
      41                 :           0 :     this->filename = o.filename;
      42                 :           0 :     this->fd = o.fd;
      43                 :           0 :     o.fd = -1;
      44                 :           0 :   }
      45                 :             : 
      46                 :             :   /* Unique write lock.  No other lock can be held on this lockfile.
      47                 :             :      Blocking call.  */
      48                 :             :   int lock_write ();
      49                 :             : 
      50                 :             :   /* Unique write lock.  No other lock can be held on this lockfile.
      51                 :             :      Only locks if this filelock is not locked by any other process.
      52                 :             :      Return whether locking was successful.  */
      53                 :             :   int try_lock_write ();
      54                 :             : 
      55                 :             :   /* Shared read lock.  Only read lock can be held concurrently.
      56                 :             :      If write lock is already held by this process, it will be
      57                 :             :      changed to read lock.
      58                 :             :      Blocking call.  */
      59                 :             :   int lock_read ();
      60                 :             : 
      61                 :             :   /* Unlock all previously placed locks.  */
      62                 :             :   void unlock ();
      63                 :             : 
      64                 :             :   /* Returns whether any lock is held.  */
      65                 :             :   bool
      66                 :             :   locked ()
      67                 :             :   {
      68                 :             :     return fd < 0;
      69                 :             :   }
      70                 :             : 
      71                 :             :   /* Are lockfiles supported?  */
      72                 :             :   static bool lockfile_supported ();
      73                 :             : private:
      74                 :             :   std::string filename;
      75                 :             :   int fd;
      76                 :             : };
      77                 :             : 
      78                 :             : #endif