我在网络和Stack Overflow上进行了研究,以寻找使用fcntl()
锁定和解锁pid文件“/ var / run / myapp.pid”
的示例,但我没有找到清晰的示例。
您能否提供一个使用fcntl()
锁定和解锁pid文件的示例?
如果文件已被锁定,则不应阻止锁定。
man lockf
(我强调)可以得知:lockf()在Linux上只是在fcntl(2)锁定之上的接口。许多其他系统也是这样实现lockf()的,但请注意,POSIX.1-2001未指定lockf()和fcntl(2)锁定之间的关系。便携式应用程序可能应避免混合调用这些接口。eglibc-2.11.3/io/lockf.c
)时,使用fcntl()
实现锁定的可能方法如下:/* 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, '\0', 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);
}
首先需要进行一些修改才能使其编译:
__fcntl
替换为fcntl
__set_errno(<errno-define>)
替换为errno = <errno-define>
... 其次,需要使其变得异步信号安全:
memset()
的调用替换为对struct fcntl
变量的适当赋值。
lockf()
函数,例如它的名称为async_lockf()
。然后我将上述函数的内容复制到这个函数中,并进行您指定的更改。那么新的async_lockf()
函数将是异步信号安全的函数,然后我可以在sigaction处理程序中使用它。这是正确的吗? - MOHAMEDmemset()
,我会将其更改为:struct flock fl = {0}
。 - MOHAMEDflock()
的调用混淆。 - alk