对Python多线程读写文件加锁的实例详解

import fcntl
import threading
import time
 
 
def writetoTxt(txtFile):
 id = threading.currentThread().getName()
 with open(txtFile, 'a') as f:
  fcntl.flock(f.fileno(), fcntl.LOCK_EX) #加锁
  print "{0} acquire lock".format(id)
  f.write("write from {0} \r\n".format(id))
  time.sleep(3)
 # 在with块外，文件关闭，自动解锁
 print "{0} exit".format(id)
 
 
for i in range(5):
 myThread = threading.Thread(target=writetoTxt, args=("test.txt",))
 myThread.start()

Thread-1 acquire lock
Thread-1 exit
Thread-2 acquire lock
Thread-2 exit
Thread-3 acquire lock
Thread-3 exit
Thread-5 acquire lock
Thread-5 exit
Thread-4 acquire lock
Thread-4 exit

fcntl.flock(f.fileno(), fcntl.LOCK_EX)

fcntl.flock(f.fileno(),fcntl.LOCK_UN)

线程同步能够保证多个线程安全访问竞争资源，最简单的同步机制是引入互斥锁。

互斥锁为资源引入一个状态：锁定/非锁定。

某个线程要更改共享数据时，先将其锁定，此时资源的状态为“锁定”，其他线程不能更改；

直到该线程释放资源，将资源的状态变成“非锁定”，其他的线程才能再次锁定该资源。

互斥锁保证了每次只有一个线程进行写入操作，从而保证了多线程情况下数据的正确性。

#创建锁
mutex = threading.Lock()
#锁定
mutex.acquire([timeout])
#解锁
mutex.release()

import threading
import time
 
def writetoTxt(txtFile):
 id = threading.currentThread().getName()
 mutex.acquire(10)
 with open(txtFile, 'a') as f:
  print "Thread {0} acquire lock".format(id)
  f.write("write from thread {0} \r\n".format(id))
  time.sleep(3)
 mutex.release()
 print "Thread {0} exit".format(id)
 
 
mutex = threading.Lock()
 
for i in range(5):
 myThread = threading.Thread(target=writetoTxt, args=("test.txt",))
 myThread.start()

Thread Thread-1 acquire lock
Thread Thread-1 exit
Thread Thread-2 acquire lock
Thread Thread-2 exit
Thread Thread-3 acquire lock
Thread Thread-3 exit
Thread Thread-4 acquire lock
Thread Thread-4 exit
Thread Thread-5 acquire lock
Thread Thread-5 exit