gcc/lockfile.h

   1 /* File locking.
   2    Copyright (C) 2023-2025 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 class lockfile {
  25 public:
  26   /* Default constructor.  */
  27   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   lockfile (std::string filename): lockfile ()
  32   {
  33     this->filename = std::move (filename);
  34   }
  35   lockfile (lockfile const& o): lockfile (o.filename)
  36   {}
  37
  38   void operator=(lockfile o)
  39   {
  40     unlock ();
  41     this->filename = o.filename;
  42     this->fd = o.fd;
  43     o.fd = -1;
  44   }
  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