Multithreading advanced =>JUC concurrent programming

Self foundation:

  • Java

  • The foundation of multithreading

1. What is JUC

Source + official documents interview frequently asked

Java.util toolkit package, classification

Business: Common Thread code Thread

Runnable returns no value and is less efficient than Callable!

2. Threads and processes

Threads, processes, if you can’t use a one-sentence spoken technology, not solid!

Process: a program, qi.exe music.exe program collection; .jar

A process can often contain multiple threads, at least one!

How many threads does Java have by default? The main, the GC

Thread: opened a process Typora, write, autosave (thread responsible)

For Java: Thread, Runnable, Callable

public synchronized void start(a) {
        /** * This method is not invoked for the main method thread or "system" * group threads created/set up by the VM. Any new functionality added * to this method in the future may have to also be added to the VM. * * A zero status value corresponds to state "NEW". */
        if(threadStatus ! =0)
            throw new IllegalThreadStateException();

        /* Notify the group that this thread is about to be started * so that it can be added to the group's list of threads * and the group's unstarted count can be decremented. */
        group.add(this);

        boolean started = false;
        try {
            start0();
            started = true;
        } finally {
            try {
                if(! started) { group.threadStartFailed(this); }}catch (Throwable ignore) {
                /* do nothing. If start0 threw a Throwable then it will be passed up the call stack */}}}// the local method, the underlying C++, Java can not directly manipulate the hardware
    private native void start0(a);
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Can Java really start threads? Can’t open

Concurrent, parallel

Concurrent programming: concurrent, parallel

Concurrency (multiple threads working on the same resource)

  • CPU a core, simulation out of a number of threads, the world martial arts, only fast not broken, fast alternating

Parallel (more than one person walking together)

  • CPU multi-core, multiple threads can execute at the same time; Highest performance –> Thread pool

    package com.chao.demo01;
public class Test1 {
    public static void main(String[] args) {
        // Get the number of CPU cores
        //CPU intensive, IO intensiveSystem.out.println(Runtime.getRuntime().availableProcessors()); }}Copy the code

The essence of concurrent programming: Make full use of CPU resources

All companies value it!

Business, make money => increase efficiency, lay off people, find a good person to replace three bad people;

Personnel (minus), technical cost (high)

Threads have several states

public enum State {
	/ / new
    NEW,

	/ / run
    RUNNABLE,

	/ / blocking
    BLOCKED,

    // Wait, wait, wait
    WAITING,

	// Wait for timeout
    TIMED_WAITING,

 	/ / termination
    TERMINATED;
}
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Wait/sleep

1. From different classes

wait => Object

sleep => Thread

In the enterprise, sleep

2. Release of locks

Wait releases lock, sleep does not release lock.

3. The scope of use is different

Wait must be in the synchronized code block

Sleep can be anywhere

4. Whether exceptions need to be caught

Wait does not need to catch exceptions

Sleep must catch exceptions