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/* flint_lock.cc: database locking for flint backend.
*
* Copyright (C) 2005,2006,2007 Olly Betts
*
* This program 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 2 of the
* License, or (at your option) any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
* USA
*/
#include <config.h>
#include "flint_lock.h"
#ifndef __WIN32__
#include "safeerrno.h"
#include "safefcntl.h"
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
// FIXME:1.1: It's unclear why this workaround is needed here, yet not needed
// in configure or the other files which include sys/socket.h and use
// SOCKLEN_T. The commit comment doesn't help, and there's no obvious related
// email thread. I think the way forward is to drop this in 1.1.0, and if it
// is required, we can work out why this file is different and either fix that
// or add a "safesyssocket.h" header to replace <sys/socket.h> uses with.
#ifdef _NEWLIB_VERSION
// Workaround bug in newlib (at least some versions) - socklen_t doesn't
// get defined if you just "#include <sys/socket.h>".
#include <netinet/in.h>
#endif
#include <sys/socket.h>
#include <sys/wait.h>
#include <signal.h>
#endif
#include "omassert.h"
#ifdef __CYGWIN__
#include <sys/cygwin.h>
#endif
FlintLock::reason
FlintLock::lock(bool exclusive) {
// Currently we only support exclusive locks.
(void)exclusive;
Assert(exclusive);
#if defined __CYGWIN__ || defined __WIN32__
Assert(hFile == INVALID_HANDLE_VALUE);
#ifdef __CYGWIN__
char fnm[MAX_PATH];
cygwin_conv_to_win32_path(filename.c_str(), fnm);
#else
const char *fnm = filename.c_str();
#endif
hFile = CreateFile(fnm, GENERIC_WRITE, FILE_SHARE_READ,
NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile != INVALID_HANDLE_VALUE) return SUCCESS;
if (GetLastError() == ERROR_ALREADY_EXISTS) return INUSE;
return UNKNOWN;
#elif defined __EMX__
APIRET rc;
ULONG ulAction;
rc = DosOpen((PCSZ)filename.c_str(), &hFile, &ulAction, 0, FILE_NORMAL,
OPEN_ACTION_OPEN_IF_EXISTS | OPEN_ACTION_CREATE_IF_NEW,
OPEN_SHARE_DENYWRITE | OPEN_ACCESS_WRITEONLY,
NULL);
if (rc == NO_ERROR) return SUCCESS;
if (rc == ERROR_ACCESS_DENIED) return INUSE;
return UNKNOWN;
#else
Assert(fd == -1);
int lockfd = open(filename.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0600);
if (lockfd < 0) return UNKNOWN; // Couldn't open lockfile.
int fds[2];
if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, fds) < 0) {
// Couldn't create socketpair.
close(lockfd);
return UNKNOWN;
}
pid_t child = fork();
if (child == 0) {
// Child process.
close(fds[0]);
reason why = SUCCESS;
{
struct flock fl;
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 1;
while (fcntl(lockfd, F_SETLK, &fl) == -1) {
if (errno != EINTR) {
// Lock failed - translate known errno values into a reason
// code.
if (errno == EACCES || errno == EAGAIN) {
why = INUSE;
} else if (errno == ENOLCK) {
why = UNSUPPORTED;
} else {
_exit(0);
}
break;
}
}
}
{
// Tell the parent if we got the lock, and if not, why not.
char ch = static_cast<char>(why);
while (write(fds[1], &ch, 1) < 0) {
// EINTR means a signal interrupted us, so retry.
// Otherwise we're DOOMED! The best we can do is just exit
// and the parent process should get EOF and know the lock
// failed.
if (errno != EINTR) _exit(1);
}
if (why != SUCCESS) _exit(0);
}
//shutdown(fds[1], 1); // Disable further sends.
// Connect pipe to stdin.
dup2(fds[1], 0);
// FIXME: use special statically linked helper instead of cat.
execl("/bin/cat", "/bin/cat", (void*)NULL);
// Emulate cat ourselves (we try to avoid this to reduce VM overhead).
char ch;
while (read(0, &ch, 1) != 0) { /* Do nothing */ }
_exit(0);
}
close(lockfd);
if (child == -1) {
// Couldn't fork.
close(fds[0]);
close(fds[1]);
return UNKNOWN;
}
// Parent process.
close(fds[1]);
while (true) {
char ch;
int n = read(fds[0], &ch, 1);
if (n == 1) {
reason why = static_cast<reason>(ch);
if (why == SUCCESS) break; // Got the lock.
close(fds[0]);
return why;
}
if (n == 0 || errno != EINTR) {
// EOF means the lock failed; we also treat unexpected errors from
// read() the same way.
close(fds[0]);
return UNKNOWN;
}
}
//shutdown(fds[0], 0); // Disable further receives.
fd = fds[0];
pid = child;
return SUCCESS;
#endif
}
void
FlintLock::release() {
#if defined __CYGWIN__ || defined __WIN32__
if (hFile == INVALID_HANDLE_VALUE) return;
CloseHandle(hFile);
hFile = INVALID_HANDLE_VALUE;
#elif defined __EMX__
if (hFile == NULLHANDLE) return;
DosClose(hFile);
hFile = NULLHANDLE;
#else
if (fd < 0) return;
close(fd);
fd = -1;
// The only likely error from kill is ESRCH. The other possibilities
// (according to the Linux man page) are EINVAL (invalid signal) and EPERM
// (don't have permission to SIGHUP the process) but in none of the cases
// does calling waitpid do us any good!
if (kill(pid, SIGHUP) == 0) {
int status;
while (waitpid(pid, &status, 0) < 0) {
if (errno != EINTR) break;
}
}
#endif
}
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