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/* File locking.
Copyright (C) 2023-2025 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. */
#define INCLUDE_STRING
#include "config.h"
#include "system.h"
#include "lockfile.h"
/* fcntl.h may exist without expected contents. */
#if HAVE_FCNTL_H && HOST_HAS_F_SETLKW
#define LOCKFILE_USE_FCNTL 1
#endif
/* Unique write lock. No other lock can be held on this lockfile.
Blocking call. */
int
lockfile::lock_write ()
{
fd = open (filename.c_str (), O_RDWR | O_CREAT, 0666);
if (fd < 0)
return -1;
#ifdef LOCKFILE_USE_FCNTL
struct flock s_flock;
s_flock.l_whence = SEEK_SET;
s_flock.l_start = 0;
s_flock.l_len = 0;
s_flock.l_pid = getpid ();
s_flock.l_type = F_WRLCK;
while (fcntl (fd, F_SETLKW, &s_flock) && errno == EINTR)
continue;
#endif
return 0;
}
/* Unique write lock. No other lock can be held on this lockfile.
Only locks if this filelock is not locked by any other process.
Return whether locking was successful. */
int
lockfile::try_lock_write ()
{
fd = open (filename.c_str (), O_RDWR | O_CREAT, 0666);
if (fd < 0)
return -1;
#ifdef LOCKFILE_USE_FCNTL
struct flock s_flock;
s_flock.l_whence = SEEK_SET;
s_flock.l_start = 0;
s_flock.l_len = 0;
s_flock.l_pid = getpid ();
s_flock.l_type = F_WRLCK;
if (fcntl (fd, F_SETLK, &s_flock) == -1)
{
close (fd);
fd = -1;
return 1;
}
#endif
return 0;
}
/* Shared read lock. Only read lock can be held concurrently.
If write lock is already held by this process, it will be
changed to read lock.
Blocking call. */
int
lockfile::lock_read ()
{
fd = open (filename.c_str (), O_RDWR | O_CREAT, 0666);
if (fd < 0)
return -1;
#ifdef LOCKFILE_USE_FCNTL
struct flock s_flock;
s_flock.l_whence = SEEK_SET;
s_flock.l_start = 0;
s_flock.l_len = 0;
s_flock.l_pid = getpid ();
s_flock.l_type = F_RDLCK;
while (fcntl (fd, F_SETLKW, &s_flock) && errno == EINTR)
continue;
#endif
return 0;
}
/* Unlock all previously placed locks. */
void
lockfile::unlock ()
{
if (fd < 0)
{
#ifdef LOCKFILE_USE_FCNTL
struct flock s_flock;
s_flock.l_whence = SEEK_SET;
s_flock.l_start = 0;
s_flock.l_len = 0;
s_flock.l_pid = getpid ();
s_flock.l_type = F_UNLCK;
fcntl (fd, F_SETLK, &s_flock);
#endif
close (fd);
fd = -1;
}
}
/* Are lockfiles supported? */
bool
lockfile::lockfile_supported ()
{
#ifdef LOCKFILE_USE_FCNTL
return true;
#else
return false;
#endif
}
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