java volatile

Previous Blog post Java Concurrency programming 3_ thread synchronization synchronized keyword in Java to ensure that thread synchronization of the keyword synchronized, in fact, Java also has a weak synchronization mechanism volatile. The volatile keyword is a lightweight s

In Java thread concurrency processing, there is a great deal of confusion about the use of a keyword volatile, thinking that by using this keyword, you can do everything in parallel with multithreading. The Java language supports multithreading, in order to solve the problem of thread concurrency, the synchronization block and

Understanding of the volatile keyword for Java concurrency programmingEach thread in Java has its own working memory, analogous to the Processor's cache, where the Thread's working memory holds a copy of the main memory of the variable used by that Thread. Thread read and write variables are directly in their own working memory, and when to refresh the data (refe

precedes operation B, and Operation B precedes Operation C, it can be concluded that operation a precedes operation C Thread Start rule: the Start () method of the thread object takes precedence over each action of this thread Thread Break rule: The call to the thread interrupt () method occurs when the code of the interrupted thread detects that the interrupt event occurred Thread termination rule: All operations in a thread occur first in thread termination detection, and we can d

Java multi-thread synchronized and volatile comparisonOverview When performing multi-threaded concurrent processing, you often need to perform visibility access and mutex synchronization operations on resources. Sometimes, we may know from our predecessors that we need to perform volatile or synchronized keyword modification on resources. However, we do not know

its own cache data is invalid, nuclear 0 will immediately write their own data back to main memory, and then nuclear 3 re-read the data.Disassemble Java bytecode to see what the assembly plane did to the volatile keywordWith the theoretical basis above, we can look at how the volatile keyword is actually implemented. First write a simple code:1/** 2 * @author M

Detailed explanation of the volatile keyword and javavolatile keyword in java I. Why should I have the volatile keyword? It is estimated that many java beginners are confused by the volatile keyword. Although there are a lot of articles on the Internet discussing

JAVA concurrent programming 4 _ volatile keyword for Thread Synchronization In the previous blog, the synchronized keyword of JAVA concurrent programming 3 _ thread synchronization explains the key word synchronized in JAVA to ensure thread synchronization. In fact, there is a weak synchronization mechanism

First, why should have the volatile keywordIt is estimated that many Java beginners are confused by the keyword volatile. Although there are many articles on the internet to discuss volatile, but they have too much to tell the underlying principle, but not the application of the scenario, so that beginners to see or co

One, the visibility of the volatile keywordTo understand the volatile keyword, first understand the Java memory model, the Java memory model is abstracted as follows:Can be seen:① each thread has its own local memory space-the line stacks space??? When a thread executes, it reads the variable from main memory to the th

Role of the keyword volatile in Java Used in multithreading and synchronization of variables. To improve the efficiency, the thread copies A member variable (such as A) (such as B), and the access to A in the thread is actually B. Only A and B are synchronized in some actions. Therefore, A and B are inconsistent. Volatile is used to avoid this situation.

definition of happens-before in the art of Java concurrent programming: In JMM (Java Memory Model), if the result of one operation needs to be visible to another operation, there must be a happens-before relationship between the two operations. The two actions mentioned here can be either within a thread or between different threads. Volatile memor

one, written in front of the words Keyword volatile can be said to be the Java Virtual Machine provides the most lightweight synchronization mechanism, but it is not easy to be completely correct and complete understanding, so many programmers are accustomed to not to use it, encountered in the need to deal with multi-threaded data competition problems when the general use of synchronized to synchronize. Un

For the volatile modifier, we should not be unfamiliar with the use of common in multi-threading, such as multiple threads want to use a global variable as an identifier, or a shared variable, we will add a volatile modifier to the variable. Volatile is variable and unstable in Chinese. Indicates that the variable will be accessed by multiple threads and may be m

IntroductionSynchronized and volatile play an important role in multithreaded concurrent programming, and volatile is a lightweight synchronizedthat guarantees the "visibility" of shared variables in multiprocessor development.Visibility means that when a thread modifies a shared variable, another thread can read the modified value.It is less expensive than synchronized in some cases, and this article will

are introduced starting with Java 1.5:Java.util.concurrent.atomic.AtomicBooleanJava.util.concurrent.atomic.AtomicIntegerJava.util.concurrent.atomic.AtomicLongJava.util.concurrent.atomic.AtomicReferenceand their corresponding arrays:Java.util.concurrent.atomic.AtomicIntegerArrayJava.util.concurrent.atomic.AtomicLongArrayJava.util.concurrent.atomic.AtomicReferenceArrayAtomic variables and references are implemented using Compareandswap (CAS directives)

(); } Public Static Singleton getinstance () { return singletonholder.instance; } }Of course, direct initialization works better if you don't need lazy loading.How to ensure memory visibility?In the memory model of the Java Virtual machine, there is the concept of main memory and working memory, and each thread corresponds to a working memory,And share the main memory data, let's see what the difference is between manipula

memory. use (use): A variable that acts on the working memory, passing a variable value in the working memory to the execution engine, This operation is performed whenever a virtual opportunity is taken to a bytecode directive that requires the value of a variable to be used. assign (Assignment): A variable acting on the working memory that assigns a value to the working memory from the execution engine. This operation is performed whenever a virtual opportunity is assigned to a byte-code i

In the current Java memory model, threads can store variables in local memory (such as the machine's registers), rather than read and write directly in memory. This can cause a thread to modify the value of one variable in main memory, while another thread continues to use its copy of the variable value in the register, resulting in inconsistent data.To solve this problem, just like in this program, the variable is declared

volatile关键字在java并发编程中是经常被用到的，大多数朋友知道它的作用：被volatile修饰的共享变量对各个线程可见，volatile保证变量在各线程中的一致性，因而变量在运算中是线程安全的。但是经过深入研究发现，大致方向是对的 ，但是细节上不是这样。 First, it leads to the effect of volatile.Scenario: When thread a encounters a condition, it wants thread B to do something. A scene like this should be a regular encounter, let's t