What is Python multi-threaded synchronization? What is a thread lock?

For the first time in contact with the Python programming language of the friend, just beginning to learn python programming, Python thread synchronization This aspect of the understanding is relatively small, in this article we will come to understand python multithreadingSynchronization and Python multi-line lockKnowledge of this aspect.

Thread synchronization

If multiple threads are working together on a data modification, unpredictable results may occur, and multiple threads need to be synchronized in order to ensure the correctness of the data.

Using the thread object's lock and Rlock allows for simple thread synchronization, both of which have the acquire method and the release method, which can be placed between the acquire and release methods for data that requires only one thread to be allowed to operate at a time. As follows:

The advantage of multithreading is that you can run multiple tasks at the same time (at least it feels like this). However, when a thread needs to share data, there may be an issue with data that is out of sync.

Consider a situation in which all elements in a list are 0, the thread "set" changes all elements to 1 from the back, and the thread "print" is responsible for reading the list and printing from the front.

Then, when the thread "set" starts to change, the thread "print" will print the list, and the output will be half 01 and a half 1, which is a different step in the data. In order to avoid this situation, the concept of lock is introduced.

Multi-threaded lock

The lock has two states-locked and unlocked. Each time a thread such as "set" is to access the shared data, the lock must first be acquired, and if another thread such as "print" is locked, then the thread "set" is paused, that is, the synchronization is blocked, and the thread "set" continues after the thread "print" has been accessed, releasing the lock.

After this processing, the print list will either output 0, or all output 1, no more than half 1 and a half 1 embarrassing scenes.

Example

Here's an example:

#!/usr/bin/python#-*-coding:utf-8-*-import Threadingimport time Class MyThread (threading. Thread): Def __init__ (self, ThreadID, name, counter): Threading. Thread.__init__ (self) self.threadid = ThreadID Self.name = Name Self.counter = Counter def run (sel f): print "Starting" + Self.name # Get lock, return true after successful lock # optional timeout parameter will block until lock is received # otherwise the timeout will return Fals e Threadlock.acquire () print_time (Self.name, Self.counter, 3) # Release lock Threadlock.release () def p Rint_time (threadname, Delay, counter): while Counter:time.sleep (delay) print "%s:%s"% (ThreadName, Tim E.ctime (Time.time ())) Counter-= 1 Threadlock = Threading. Lock () threads = [] # Create new Thread thread1 = MyThread (1, "Thread-1", 1) thread2 = MyThread (2, "Thread-2", 2) # Open new Thread Thread1.start () t Hread2.start () # Add thread to Thread list threads.append (thread1) Threads.append (thread2) # Wait for all threads to finish for T in Threads:t.join () print "Exi Ting Main Thread "