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This article mainly shows you "how to ensure the uniqueness of the application in the script". The content is simple and clear, hoping to help you solve your doubts. Let the editor lead you to study and learn the article "how to ensure the uniqueness of the application in the script".

A solution to shell script

Creating an existing file directory using the features of mkdir will fail. The first time the program runs, you can create a / tmp/lock folder that indicates that a program is currently running, and when you start the second program, mkdir / tmp/lock will fail.

#! / bin/bash

Mkdir / tmp/lock

If [$?-ne 0]; then

Echo "there is tr script running..."

Exit 1

Fi

Trap "rm-fr / tmp/lock" SIGINT SIGTERM

Sleep 50

If [- d / tmp/lock]; then

Rm-fr / tmp/lock

Echo "rm-fr / tmp/lock"

Fi

Note that the trap command in linux prevents the script from terminating abnormally: by kill (not kill-9), crtl+c interrupts more detailed information about "trap of the Linux command-processing signals in the script" http://codingstandards.iteye.com/blog/836588

Second, the solution of python script

When you search the Internet for python locked files, you will be prompted by the fcntl module. Python's file locks currently use the fcntl library, which actually provides an interface for ioctl,flock and fcntl functions on Unix.

Fcntl module function flock (file_handle, operation)

Where file_handle represents a file descriptor and operation refers to the lock operation to be performed, there are several types:

Fcntl.LOCK_UN unlock: delete the lock created by the floc () function

Fcntl.LOCK_EX exclusive lock: processes other than locked processes do not have read and write access to locked files.

Fcntl.LOCK_SH shared locks: all processes do not have write access, even locked processes. All processes have read access.

Fcntl.LOCK_NB non-blocking lock: this parameter means that the function will return immediately if it cannot acquire the file lock, otherwise, if the lock is not successfully requested using LOCK_EX/LOCK_SH, the current process will wait for the file lock to be obtained. Using LOCK_NB can not block the process while acquiring this exclusive lock, and LOCK_NB can also perform bitwise or (|) operations with LOCK_SH or LOCK_NB, such as fcnt.flock (file_handle,fcntl.LOCK_EX | fcntl.LOCK_NB), so that the system will not block the current process.

Note:

1. The f.close () operation on the file will invalidate the file lock

two。 The file lock fails after the end of the main process

3. The LOCK_EX of flock () is an "advice lock". The kernel does not force the state of the lock to be checked, but needs to be explicitly checked where the file is manipulated in the code to take effect.

Test script

In the script, the is_running function is used to lock the file, and time.sleep (10) simulates the program that has been executed for a long time, successfully locking the lock.py for the first time, and running lock.py again during the run of the program, which will fail to acquire the lock and exit the program in time.

#! / usr/bin/python2.6

# coding:utf8

Import time

Import fcntl

Import sys

Def is_running (file):

Lock_file=open (file, "w")

Try:

Fcntl.lockf (lock_file,fcntl.LOCK_EX | fcntl.LOCK_NB)

Print "lock the file, please wait for 10s."

Except:

The print 'file is locked and cannot be executed. Please run it later.'

Return None

Return lock_file

If _ name__ = = "_ _ main__":

Lockfile= "/ tmp/rsync_is_running"

A=is_running (lockfile)

If an is None:

Print "lock file failed, rsync is running."

Sys.exit (0)

Else:

Print "lock file successed!!"

Time.sleep (10)

Test examples:

Conversation one

Conversation two

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