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Monitor concept Java object header Take 32-bit virtual machine as an example Common object Array object The Mark Word structure is 64 bit virtual machine Mark Word reference material https://stackoverflow.com/questions/26357186/what-is-in-java-object-header Principle of Monitor (lock) Monitor is translated into monitor or tube Eac ...

1. Classification of Java locks (reference link: https://tech.meituan.com/2018/11/15/java-lock.html ) (1) Optimistic lock VS pessimistic lock: * * optimistic Lock: * * Lock the data first to ensure that the data will not be modified by other threads. The synchronized keyword and the implementation class of Lock are pessimistic locks. It is su ...

JUC is a part of my job that I don't use very much, but I often get asked about it in a helpless interview, so I'll learn about JUC today. JUC is all called Java. Util. The concurrent package is a toolkit for Java, so why is JUC a frequent question for interviews? Because JUC includes multithreading, atomicity, locks and other heavy content, i ...

Chapter 3 - management of shared model (3) wait-notify Little story - why wait Because the conditions are not met, Xiaonan cannot continue the calculationBut if Xiaonan keeps occupying the lock, others will have to block all the time. The efficiency is too low So Lao Wang opened a single Lounge (calling the wait method) and asked Xiao Nan ...

Chapter 3 - management of shared model (1) Contents of this chapter Sharing problemsynchronizedThread safety analysisMonitorwait/notifyThread state transitionActivityLock Problems caused by sharing Little story Lao Wang (operating system) has a powerful abacus (CPU). Now he wants to rent it and earn some extra money Xiao Nan and Xia ...

3. Shared model process What is thread safety When multiple threads access a method, no matter how you call it or how these threads execute alternately, we don't need to do any synchronization in the main program. The resulting behavior of this class is the correct behavior we imagine, so we can say that this class is thread safe. 3.1 p ...

Let's not fight bald old today. Recharge ourselves and fight bald old again in the future! Note: the concurrent HashMap chat is after 1.8! Brothers and sisters all say that HashMap thread is not safe. If you want thread safety, use ConcurrentHashMap. Then why is it thread safe? Ah? Why? Don't think about it. It must look like it from the put( ...

Key points of this paper This article mainly talks about the principle of synchronized lock expansion. It will expand the logic of lock expansion from the source code and explain why the designer should do so from the source code. synchronized analysis Because there are many articles on the Internet about the whole synchronized analysis, t ...

  catalogue Thread safety Single thread operation variable Multiple threads are read-only to variables or variables do not belong to shared resources Thread unsafe condition Multithreading can read and write variables A subclass overrides a parent class method to perform an unknown operation Variables: normal member variables, stati ...