xapian-core/backends/flint_lock.h

   1 /** @file flint_lock.h
   2  * @brief Flint-compatible database locking.
   3  */
   4 /* Copyright (C) 2005,2006,2007,2008,2009,2012,2014,2016 Olly Betts
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2 of the
   9  * License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
  19  * USA
  20  */
  21
  22 #ifndef XAPIAN_INCLUDED_FLINT_LOCK_H
  23 #define XAPIAN_INCLUDED_FLINT_LOCK_H
  24
  25 #include <string>
  26
  27 #if defined __CYGWIN__ || defined __WIN32__
  28 # include "safewindows.h"
  29 #else
  30 # include <sys/types.h>
  31 #endif
  32
  33 #include "noreturn.h"
  34
  35 class FlintLock {
  36     std::string filename;
  37 #if defined __CYGWIN__ || defined __WIN32__
  38     HANDLE hFile;
  39 #elif defined FLINTLOCK_USE_FLOCK
  40     int fd;
  41 #else
  42     int fd;
  43     pid_t pid;
  44 #endif
  45
  46   public:
  47     typedef enum {
  48         SUCCESS, // We got the lock!
  49         INUSE, // Already locked by someone else.
  50         UNSUPPORTED, // Locking probably not supported (e.g. NFS without lockd).
  51         FDLIMIT, // Process hit its file descriptor limit.
  52         UNKNOWN // The attempt failed for some unspecified reason.
  53     } reason;
  54 #if defined __CYGWIN__ || defined __WIN32__
  55     FlintLock(const std::string &filename_)
  56         : filename(filename_), hFile(INVALID_HANDLE_VALUE) {
  57         // Keep the same lockfile name as flint since the locking is
  58         // compatible and this avoids the possibility of creating two databases
  59         // in the same directory using different backends.
  60         filename += "/flintlock";
  61     }
  62     operator bool() const { return hFile != INVALID_HANDLE_VALUE; }
  63 #elif defined FLINTLOCK_USE_FLOCK
  64     FlintLock(const std::string &filename_) : filename(filename_), fd(-1) {
  65         filename += "/flintlock";
  66     }
  67     operator bool() const { return fd != -1; }
  68 #else
  69     FlintLock(const std::string &filename_) : filename(filename_), fd(-1) {
  70         filename += "/flintlock";
  71     }
  72     operator bool() const { return fd != -1; }
  73 #endif
  74     // Release any lock held when we're destroyed.
  75     ~FlintLock() { release(); }
  76
  77     /** Attempt to obtain the lock.
  78      *
  79      *  If the attempt fails with code "UNKNOWN", the string supplied in the
  80      *  explanation parameter will be set to contain any details available of
  81      *  the reason for the failure.
  82      *
  83      *     @param exclusive  Get an exclusive lock?  Value currently ignored,
  84      *                       and the lock is always exclusive.
  85      *     @param wait       Wait until we can get the lock?
  86      */
  87     reason lock(bool exclusive, bool wait, std::string & explanation);
  88
  89     /// Release the lock.
  90     void release();
  91
  92     /// Throw Xapian::DatabaseLockError.
  93     XAPIAN_NORETURN(
  94     void throw_databaselockerror(FlintLock::reason why,
  95                                  const std::string & db_dir,
  96                                  const std::string & explanation));
  97 };
  98
  99 #endif // XAPIAN_INCLUDED_FLINT_LOCK_H