JUC concurrent knowledge points

Catalog

What is? JUC：

What is a process ？

What is thread

Understand concurrency and parallelism

Threads Several states

wait and sleep The difference between

 

 Lock lock

Lock and Synchronized difference

 Condition Achieve accurate notification

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What is? JUC：

JUC yes java.util.concurrent Abbreviation for package JUC refer to Java The concurrent toolkit for

Namely java.util tool kit 、 package 、 classification

Business ： Normal thread code Thread

Runnable no return value Efficiency is compared to callable Relatively low

Lock lock

What is a process ？

： A collection of programs Implementation is a process

What is thread

A process contains multiple threads A process contains at least one thread

java There are several threads by default ？ 2 individual One is main Threads One is GC Threads

java Can you really start the thread ？ Can't open What is called is a local method At the bottom C++ Java Can't operate the hardware directly

Understand concurrency and parallelism

The nature of concurrent programming ： make the best of cpu resources

Threads Several states

(new ) Freshmen (runnable) function ( bocked) Blocking (waiting) wait for (timed_waiting) Overtime waiting (terminated) End

wait and sleep The difference between

 

 Lock lock

Fair lock You can come first and then

Not fair lock You can jump in line

Lock and Synchronized difference

1.Synchronized yes java Key words of   Lock yes Java class

2. S Unable to determine lock status L It can be judged whether the lock is obtained

3 S Will automatically release the lock L The lock needs to be released manually Failure to release will result in deadlock

4 S Threads 1 Blocking 2 Will be waiting all the time L You don't have to wait

5 S Reentrant lock You can't interrupt Fair lock L yes Reentrant lock Unfair （ You can set ）

6 S Is a small amount of code L Applicable to a large number of codes

What is a lock How to judge who the lock is ？

Producer consumer Two threads will not four 、 Multiple threads Will cause false awakening

Threads can wake up Without being informed False awakening Waiting should appear in the loop  

if Judge only once False awakening will be caused when awakening

if Change it to while Judge

 Condition Achieve accurate wake-up

Why should we wake up accurately lockA Thread processing finished There is no guarantee that B Threads need Condition To achieve precise awakening