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/* Copyright (c) 2000, 2025, Oracle and/or its affiliates.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is designed to work with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have either included with
the program or referenced in the documentation.
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, version 2.0, 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 "my_config.h"
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#include "my_compiler.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_io.h"
#include "my_sys.h"
#include "my_thread_local.h"
#include "mysys_err.h"
#include "storage/myisam/myisam_sys.h"
#ifndef _WIN32
#include <signal.h>
extern "C" {
typedef void (*sig_return)(int); /* Returns type from signal */
static int volatile my_have_got_alarm = 0;
static uint my_time_to_wait_for_lock = 2; /* In seconds */
static void my_set_alarm_variable(int signo [[maybe_unused]]) {
my_have_got_alarm = 1; /* Tell program that time expired */
}
} // extern C
#endif /* !_WIN32 */
#ifdef _WIN32
#define WIN_LOCK_INFINITE -1
#define WIN_LOCK_SLEEP_MILLIS 100
static int win_lock(File fd, int locktype, my_off_t start, my_off_t length,
int timeout_sec) {
LARGE_INTEGER liOffset, liLength;
DWORD dwFlags;
OVERLAPPED ov{};
HANDLE hFile = (HANDLE)my_get_osfhandle(fd);
int i;
int timeout_millis = timeout_sec * 1000;
DBUG_TRACE;
liOffset.QuadPart = start;
liLength.QuadPart = length;
ov.Offset = liOffset.LowPart;
ov.OffsetHigh = liOffset.HighPart;
if (locktype == F_UNLCK) {
if (UnlockFileEx(hFile, 0, liLength.LowPart, liLength.HighPart, &ov))
return 0;
/*
For compatibility with fcntl implementation, ignore error,
if region was not locked
*/
if (GetLastError() == ERROR_NOT_LOCKED) {
SetLastError(0);
return 0;
}
goto error;
} else if (locktype == F_RDLCK)
/* read lock is mapped to a shared lock. */
dwFlags = 0;
else
/* write lock is mapped to an exclusive lock. */
dwFlags = LOCKFILE_EXCLUSIVE_LOCK;
/*
Drop old lock first to avoid double locking.
During analyze of Bug#38133 (Myisamlog test fails on Windows)
I met the situation that the program myisamlog locked the file
exclusively, then additionally shared, then did one unlock, and
then blocked on an attempt to lock it exclusively again.
Unlocking before every lock fixed the problem.
Note that this introduces a race condition. When the application
wants to convert an exclusive lock into a shared one, it will now
first unlock the file and then lock it shared. A waiting exclusive
lock could step in here. For reasons described in Bug#38133 and
Bug#41124 (Server hangs on Windows with --external-locking after
INSERT...SELECT) and in the review thread at
http://lists.mysql.com/commits/60721 it seems to be the better
option than not to unlock here.
If one day someone notices a way how to do file lock type changes
on Windows without unlocking before taking the new lock, please
change this code accordingly to fix the race condition.
*/
if (!UnlockFileEx(hFile, 0, liLength.LowPart, liLength.HighPart, &ov) &&
(GetLastError() != ERROR_NOT_LOCKED))
goto error;
if (timeout_sec == WIN_LOCK_INFINITE) {
if (LockFileEx(hFile, dwFlags, 0, liLength.LowPart, liLength.HighPart, &ov))
return 0;
goto error;
}
dwFlags |= LOCKFILE_FAIL_IMMEDIATELY;
timeout_millis = timeout_sec * 1000;
/* Try lock in a loop, until the lock is acquired or timeout happens */
for (i = 0;; i += WIN_LOCK_SLEEP_MILLIS) {
if (LockFileEx(hFile, dwFlags, 0, liLength.LowPart, liLength.HighPart, &ov))
return 0;
if (GetLastError() != ERROR_LOCK_VIOLATION) goto error;
if (i >= timeout_millis) break;
Sleep(WIN_LOCK_SLEEP_MILLIS);
}
/* timeout */
errno = EAGAIN;
return -1;
error:
my_osmaperr(GetLastError());
return -1;
}
#endif
/*
Lock a part of a file
RETURN VALUE
0 Success
-1 An error has occurred and 'my_errno' is set
to indicate the actual error code.
*/
int my_lock(File fd, int locktype, myf MyFlags) {
DBUG_TRACE;
DBUG_PRINT("my", ("fd: %d Op: %d MyFlags: %d", fd, locktype, MyFlags));
if (my_disable_locking) return 0;
#if defined(_WIN32)
{
int timeout_sec;
if (MyFlags & MY_DONT_WAIT)
timeout_sec = 0;
else
timeout_sec = WIN_LOCK_INFINITE;
if (win_lock(fd, locktype, 0, 0x3FFFFFFF, timeout_sec) == 0) return 0;
}
#else
{
struct flock lock;
lock.l_type = (short)locktype;
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0; // End of file.
if (MyFlags & MY_DONT_WAIT) {
int value;
uint alarm_old;
sig_return alarm_signal;
if (fcntl(fd, F_SETLK, &lock) != -1) /* Check if we can lock */
return 0; /* Ok, file locked */
DBUG_PRINT("info", ("Was locked, trying with alarm"));
my_have_got_alarm = 0;
alarm_old = alarm(my_time_to_wait_for_lock);
alarm_signal = signal(SIGALRM, my_set_alarm_variable);
while ((value = fcntl(fd, F_SETLKW, &lock)) && !my_have_got_alarm &&
errno == EINTR) { /* Setup again so we don`t miss it */
(void)alarm(my_time_to_wait_for_lock);
my_have_got_alarm = 0;
}
(void)signal(SIGALRM, alarm_signal);
(void)alarm(alarm_old);
if (value != -1) return 0;
if (errno == EINTR) errno = EAGAIN;
} else if (fcntl(fd, F_SETLKW, &lock) != -1) /* Wait until a lock */
return 0;
}
#endif /* _WIN32 */
/* We got an error. We don't want EACCES errors */
set_my_errno((errno == EACCES) ? EAGAIN : errno ? errno : -1);
if (MyFlags & MY_WME) {
char errbuf[MYSYS_STRERROR_SIZE];
if (locktype == F_UNLCK)
my_error(EE_CANTUNLOCK, MYF(0), my_errno(),
my_strerror(errbuf, sizeof(errbuf), my_errno()));
else
my_error(EE_CANTLOCK, MYF(0), my_errno(),
my_strerror(errbuf, sizeof(errbuf), my_errno()));
}
DBUG_PRINT("error", ("my_errno: %d (%d)", my_errno(), errno));
return -1;
} /* my_lock */
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