如何使用“fcntl()”locking和解锁pid文件

我在网上进行研究,甚至在stackoverflow中find一个使用fcntl()来locking和解锁PID文件"/var/run/myapp.pid"例子,但我没有find一个明确的例子。

你能指点我一个例子使用fcntl()来locking和解锁PID文件?

不应该locking锁(如果文件被locking)

正如你在Linux上标记的,逐字形式的man lockf (由我强调):

在Linux上, lockf () 只是fcntl (2)锁定的一个接口 。 许多其他系统以这种方式实现lockf (),但是请注意,POSIX.1-2001保留未指定的lockf ()和fcntl (2)锁之间的关系。 一个便携式应用程序可能应该避免混合调用这些接口。

因此,查找当前glibc源( eglibc-2.11.3/io/lockf.cfcntl()来实现锁定的可能用法如下所示:

 /* 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); } 

首先进行编译需要几个mod:

  • fcntl替换__fcntl
  • errno = <errno-define>替换__set_errno(<errno-define>)

其次,它成为异步信号保存:

  • 用对struct fcntl变量的适当分配来替换对memset()的调用。