Interview series 2: concurrent programming

Concurrent programming

The use of multithreaded classes

• java What are the methods of thread synchronization 、 Advantages and disadvantages of each
• synchronized and ReentrantLock difference , What are reentrant locks ？
• threadlocal What's the usage?
• Java There are several ways to create threads in ？ Namely ？ When the main thread is finished executing , Will the child thread continue to execute ？
• JUC What are the common collections in ？（ Used in the project ）
• CopyOnWriteArrayList Implementation principle of ？ What is the main application scenario ？ The advantages and disadvantages are ？
• HashMap Not thread safe , What happens when inserting in a high concurrency environment ？ Why? ？
• jdk1.8 before ConcurrentHashMap How to realize thread safety ？jdk1.8 Later? ？（1.8synchronized Add CAS, And introduced red and black trees ）
• When calling ConcurrentHashMap Of size When the method is used , There are elements inserted simultaneously ,ConcurrentHashMap How did you handle it ？
• synchronized and java.util.concurrent.locks.Lock Comparison . AtomicInteger principle , Why use CAS instead of synchronized？ In the back end of the bank, if many people want to have a large account , What's the problem ？
• What is? CAS operation , How to implement a custom lock
• Synchronized The implementation of the , Lock upgrade process .
• AQS Do you understand ？
• wait()、notify Under what circumstances must you use
• Threads 、 process 、 The relationship between the processes .
• Yes volatile The understanding of the
• To be specific concurrentHashMap put technological process
• How do you understand synchronization / asynchronous , Concurrent / Of the concept of parallelism
• So talk about it Lock Interface API And its implementation class related understanding ？
• that ReentrantLock Medium lock and unlock Synchronization between threads how to communicate between threads ？
• Semaphore Class understanding ？
• JUC The counting lock under the package ？CountDownLatch？
• CyclicBarrier The understanding of the ？
• ReadWriteLock And ReentrantReadWriteLock The understanding and difference of ？
• You also know ReentrantReadWriteLock Which features ？
• ReentrantLock How to realize fair and unfair lock ？ CountDownLatch and CyclicBarrier The difference between ？ What scenarios do they apply to ？
• The difference between optimistic lock and pessimistic lock ？ How to achieve an optimistic lock ？
• AQS How to wake up the next thread ？
• ConcurrentHashMap How to make multithreading participate in capacity expansion at the same time ？get Do you need to lock it , Why? ？
• Disruptor Frame usage , Realization
• Future How is the asynchronous call process of ？Future Overtime ？ Infinite recursion causes jvm What's wrong with memory ？
• Java8 After that ConcurrentHashMap Why abandon the block lock ？
• A whole set of thread pools （ Implementation class and corresponding blocking queue 、 Refusal strategy 、 Specific parameters 、ScheduledThreadPool There are three ways to construct , What do they mean respectively ？）
• synchronized Modify the instance method and static method respectively , Whether multi thread concurrency will compete for locks ？synchronized What's the difference between decorating methods and code blocks , How is the underlying implementation done ？
• Producer consumer pattern code in concurrent programming .［ The easiest way is to use wait and notify To block the wake-up , Of course, you can also use reentrant locks (ReentrantLock), Use the lock counter (CountdownLatch) wait ］
• Why use a read-write lock instead of synchronized This synchronization lock
• How to control the thread to complete in a certain period of time , Cancel if you don't finish .
• reference ConcurrentHashMap, If you use it in a multithreaded environment HashMap, Is there any way to improve efficiency and ensure thread safety ？
• Yes Java Understanding of memory model , And its application in concurrency ; Instruction reordering , Memory fence, etc
• Java What types of locks are available ？
• What are the concurrent containers , The difference between concurrent containers and synchronous containers ？
• CLH How do synchronous queues achieve unfairness and fairness ？
• HashMap In high concurrency, what are the security risks if you don't deal with thread security , What is the specific performance .
• Lock What implementation classes do interfaces have , What is the usage scenario .
• The use and implementation principle of reentrant lock , The process of copying while writing , Read-write lock , Section lock （ConcurrentHashMap Medium segment）
• CountDown Have you ever understood ？CountDown and CycliBarrier What's the difference between ？ What's the difference in use ？
• volatile Reorder from instructions , Memory barrier , Talking about the bus storm
• Asked how to share data between parent and child threads
• List It's not thread safe , How do you make it thread safe ？
• synchronized Can I run other threads while running the current thread
• What is guard thread , How to implement the guardian thread ？ How to stop a thread ？
• Concurrent programming is very detailed . Then multiple threads are executed together , After reaching a certain state, the concurrent execution will continue , How to achieve this ？
• How to control the thread to complete in a certain period of time , Cancel if you don't finish
• How to avoid writing thread starvation after adding read lock to read-write lock
• Some principles of thread pool , Lock mechanism lifting stage
• What's the way spinlock works Ask whether the address the pointer points to is a virtual address or a physical address . What are the algorithms of page table replacement , And now which algorithm is more efficient . Ask the process of page missing exception replacement . If a thread modifies a data , But at this time, you need to replace the current page table , How does the operating system handle .
• The difference between a process and a thread , How to determine the maximum number of threads you create based on your hardware （ Thread pools need to consider ）

Thread pool

• Thread pool When to reach the maximum number of threads Performance that continues to commit after reaching the maximum thread What locks have you used
• What are the core parameters of thread pool ？ Briefly describe the principle of thread pool ？
• How to create a thread pool ？
• Thread pool thread submission method and advantages and disadvantages .
• If we use unbounded queues in the thread pool, what's the impact ？
• Multiple core threads go to take Blocking threads in the queue , Who can get it ？
• How does thread pool realize reusing threads
• JDK Medium bias lock 、 spinlocks 、 Lightweight lock 、 The difference between heavyweight locks ？ JDK Do you know the spin threshold of lock spin ？ How to adjust the spin number ？
• Why do you use thread pool when placing orders in your system ？ Can you use other implementations ？

Extension of multithreading

• Distributed lock zookeeper Usage scenarios of ------ How to implement distributed locks ----------redis Distributed locks and zookeeper Distributed lock
• How do you handle high concurrency scenarios , For example, the mall second kill ？
• Database concurrency strategy
• How to limit flow when concurrency is high
• Scene simulation : So let's say I have a scenario , The system needs to respond to user requests within a certain period of time , for instance 100ms Complete user request in , But at its peak, millions of user requests per unit of time , High concurrency , But I have to make the system respond in time , And high availability , If you are an architect , How do you structure this system , Talk about your plan .
• Thread programming ： Write two threads , Add data to an array , A subtraction of data from an array , Ask for data that doesn't cross the line . In fact, it is the production of consumers
• How to design seckill system ？
• If a deadlock occurs while processing concurrency ？

Welcome to search and pay attention to the wechat face-to-face program developed by me and friends 【 Interview assistant of big factory 】 And the official account 【 Micro view technology 】