我在网上甚至在stackoverflow上做了一个研究，以便找到一个使用fcntl()锁定和解锁pid文件"/var/run/myapp.pid"的例子，但我没有找到一个明确的例子。
你能给我一个例子，使用fcntl()锁定和解锁pid文件?
锁不应该被阻塞(如果文件已经被锁定)
当您标记Linux时，逐字逐句地形成man lockf(我强调):
在Linux上，lockf() 只是fcntl(2) locking之上的一个接口。许多其他系统以这种方式实现lockf()，但是请注意POSIX.1-2001没有指明lockf()和fcntl(2)锁之间的关系。可移植应用程序应该避免混合调用这些接口。
所以查找当前的glibc源代码(eglibc-2.11.3/io/lockf.c) fcntl()实现锁定的可能用法如下:
/* Copyright (C) 1994,1996,1997,1998,2000,2003 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
/* lockf is a simplified interface to fcntl's locking facilities. */
int
lockf (int fd, int cmd, off_t len)
{
struct flock fl;
memset ((char *) &fl, ' ', sizeof (fl));
/* lockf is always relative to the current file position. */
fl.l_whence = SEEK_CUR;
fl.l_start = 0;
fl.l_len = len;
switch (cmd)
{
case F_TEST:
/* Test the lock: return 0 if FD is unlocked or locked by this process;
return -1, set errno to EACCES, if another process holds the lock. */
fl.l_type = F_RDLCK;
if (__fcntl (fd, F_GETLK, &fl) < 0)
return -1;
if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
return 0;
__set_errno (EACCES);
return -1;
case F_ULOCK:
fl.l_type = F_UNLCK;
cmd = F_SETLK;
break;
case F_LOCK:
fl.l_type = F_WRLCK;
cmd = F_SETLKW;
break;
case F_TLOCK:
fl.l_type = F_WRLCK;
cmd = F_SETLK;
break;
default:
__set_errno (EINVAL);
return -1;
}
/* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
used. Therefore we don't have to care about cancellation here,
the fcntl() function will take care of it. */
return __fcntl (fd, cmd, &fl);
}
需要一些mod来完成编译:
- 用
fcntl代替__fcntl - 用
errno = <errno-define>代替__set_errno(<errno-define>)
. .其次是async-signal-save:
- 用对
struct fcntl变量的适当赋值替换对memset()的调用。