Lead:
As a Java developer, you should not feel unfamiliar when you hear about multi-threading. Multi-threading is also a question that interviewers must ask during interviews. Do you dare to say that you are doing Java development if you don’t understand multi-threading?
Not much to say, just deliver the dry goods!
1. Multithreading and high concurrency (summary of interview questions collection)
Multithreading and high concurrency interview questions (basic part)
- How do you ensure that the thread where the main() method is located is the thread where the Java program ends?
- ThreadLocal principle
ThreadLocal memory structure diagram
- What is a deadlock (Deadlock)? How to analyze and avoid deadlock?
- What is the Java Timer class? How to create a task with a specific time interval?
- What is a thread pool? How to create a Java thread pool?
- What is the implementation of concurrent containers?
- What is the Executors class?
- Talk about the difference between CountDownLatch and CyclicBarrier
Multithreading and high concurrency interview questions (advanced advanced part)
- What happens when you use synchronization on static methods?
- Can two threads call two different synchronized instance methods on an object?
- Understanding of Fork/Join framework
- What is deadlock
- What is volatile? Can order be guaranteed?
- CAS? What are the shortcomings of CAS and how to solve them?
- What is the difference between the start() and run() methods in the Thread class?
- What is the difference between interrupted and isInterruptedd methods in Java?
- How to detect deadlock? How to prevent deadlock? Four necessary conditions for deadlock
Multithreading and high concurrent interview answer analysis
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The difference between multithreading and high concurrency
"High concurrency and multithreading" are always mentioned together. It feels that the two are equal, but high concurrency ≠ multithreading.
1. Multithreading
Multi-threading is a characteristic of Java, because now CPUs are multi-core and multi-threaded and can perform several tasks at the same time. In order to improve the execution efficiency of JVM, Java provides this multi-threaded mechanism to enhance data processing efficiency. Multithreading corresponds to cpu, and high concurrency corresponds to access requests. You can use a single thread to process all access requests, or you can use multiple threads to process access requests at the same time.
In the past single CPU era, a single task can only execute a single program at a time. Later, it developed to the stage of multitasking, where the computer can execute multiple tasks or processes in parallel at the same time. Although it is not really "the same point in time", it is that multiple tasks or processes share a CPU and hand over to the operating system to complete the switching of the CPU between multiple tasks, so that each task has a chance to get a certain amount of Time to run.
Later, it developed into multithreading technology, which enables multiple threads to execute in parallel within a program. The execution of a thread can be considered as a CPU executing the program. When a program runs in multiple threads, it is as if multiple CPUs are executing the program at the same time.
In short, multi-threading can be understood like this: multi-threading is a programming method to deal with high concurrency, that is, concurrency needs to be realized by multi-threading.
2. High concurrency
High concurrency is not a proprietary thing of JAVA, it is a language-independent generalized concept for providing better Internet services.
Typical scenes, such as: 12306 train ticket grabbing, Tmall double eleven spike activity, etc. The occurrence of this situation will cause the system to perform a large number of operations during this period of time, such as requests for resources, database operations, and so on. If the high concurrency is not handled well, it will not only reduce the user experience (request response time is too long), but also cause system downtime, or even cause OOM exceptions, and the system stops working.
If you want the system to be able to adapt to the high concurrency state, you need to optimize the system from all aspects, including hardware, network, system architecture, selection of development language, data structure application, algorithm optimization, database optimization, etc.. Multithreading is just One of the solutions.
The practical application of multithreading and high concurrency
Detailed Java High Concurrency Programming: Multithreading and Architecture Design
The first part: multithreading basics
It mainly elaborates the basic knowledge of Thread, and introduces in detail the use of thread API, thread safety, data communication between threads, and how to protect shared resources. It is the basis for in-depth study of multi-threaded content.
Part 2: Java ClassLoader
ClassLoader is introduced. This is because ClassLoader is not unrelated to threads. We can use the synchronized keyword or explicit lock methods such as Lock to protect the shared resources data consistency during the code writing stage. Then a Class is initialized How does the data structure in the method area (in the metadata space after JDK8) ensure data consistency after the entire process? This requires a more comprehensive knowledge and understanding of ClassLoader.
Part 3: Deep understanding of the volatile keyword
The third part is a detailed and in-depth introduction to the semantics of the volatile keyword. The volatile keyword is very important in Java. It can be said that it lays the foundation for the efficient operation of the Java core concurrent package. In this part, we show how to use the volatile key through examples. Words and a very detailed introduction to the Java memory model and other knowledge.
Part 4: Multi-threaded design architecture pattern
From the perspective of program architecture design, it explains in depth how to design efficient and flexible multi-threaded applications. This part is 15 chapters long, and its importance is evident.
"Multithreading and High Concurrency"
Section 1: The basic concept of threads
Section 2: Volatile and CAS
Section 3: Atomic class and new thread synchronization mechanism
Section 4: LockSupport, Taobao interview questions and source code reading methodology
Section 5: AQS source code reading and 4 kinds of references, ThreadLocal principle and source code
Section 6: Concurrent containers
Section 7: Thread Pool
Section 8: Thread Pool and Source Code Reading
Section 9: JMH and Disruptor
A mind map about learning multithreading and high concurrency
Multithreading and high concurrency (Xmind)
Disruptor, basic concepts, high-frequency interview bonus points, JUC synchronization tool, thread pool, synchronization container
Concluding remarks
In general, if you have a big company you want to go to, you must improve yourself so that your abilities and qualities can match the company. I have always believed that opportunities are always reserved for those who are prepared. Whether it is studying or working, there should be initiative, so if you have the dream of a big factory, you must work hard to realize it yourself.
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