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This article introduces the knowledge of "what is thread deadlock". In the operation of actual cases, many people will encounter such a dilemma. Then let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Deadlock defines conditional deadlock caused by deadlock example how to avoid deadlock 1. Deadlock definition ● deadlock refers to the phenomenon that two or more threads wait for each other because of competing for resources during execution. In the case of no external force, these threads will wait for each other all the time and cannot continue to run. ● mutex condition: refers to the exclusive use of the acquired resource by the thread, that is, the resource is occupied by only one thread at the same time. If another thread requests to obtain the resource at this time, the requestor can only wait until the thread that owns the resource releases the resource. ● request and hold condition: a thread already holds at least one resource, but puts forward a new resource request, and the new resource is already occupied by another thread, so the current thread will be blocked, but the blocking will not release the resources it has acquired. ● inalienable condition: the resource acquired by a thread cannot be preempted by other threads until it has finished using it, and the resource will be released by itself only after it has finished using it. ● loop wait condition: when a deadlock occurs, there must be a thread-resource ring chain, that is, thread set {T0, T1, T2, … , T0 in Tn} is waiting for a resource occupied by T1, T1 is waiting for resource occupied by T2,... Tn is waiting for resources that have been occupied by T0. 3. Deadlock example package com.pimee.thread.deadlock;/** * thread deadlock example * / public class DeadLock {private static Object resourceA = new Object (); private static Object resourceB = new Object () Public static void main (String [] args) {Thread threadA = new Thread (new Runnable () {[@ Override]) (https://my.oschina.net/u/1162528) public void run () {synchronized (resourceA) {System.out.println (Thread.currentThread (). GetName () + "get resourceA")) Try {Thread.sleep (1000);} catch (InterruptedException e) {e.printStackTrace ();} System.out.println (Thread.currentThread (). GetName () + "is waiting for resourceB") Synchronized (resourceB) {System.out.println (Thread.currentThread () .getName () + "get resourceB");} Thread threadB = new Thread (new Runnable () {[@ Override] (https://my.oschina.net/u/1162528) public void run () {synchronized (resourceB) {System.out.println (Thread.currentThread (). GetName () + "get resourceB"); try {Thread.sleep (1000) } catch (InterruptedException e) {e.printStackTrace ();} System.out.println (Thread.currentThread (). GetName () + "is waiting for resourceA"); synchronized (resourceA) {System.out.println (Thread.currentThread (). GetName () + "get resourceA") }); threadA.start (); threadB.start ();}}

4. Deadlock avoidance ● locking order: threads are locked in the same order. ● lock time limit, the thread in the process of acquiring the lock is limited to a certain time, if not within a given time, forget it, do not force yourself. This requires some API from Lock

The deadlock demo above, changing the locked book order can solve the problem.

Package com.pimee.thread.deadlock;/** * example of thread deadlock * / public class DeadLock {private static Object resourceA = new Object (); private static Object resourceB = new Object () Public static void main (String [] args) {Thread threadA = new Thread (new Runnable () {@ Override public void run () {synchronized (resourceA) {System.out.println (Thread.currentThread (). GetName () + "get resourceA"); try {Thread.sleep (1000) } catch (InterruptedException e) {e.printStackTrace ();} System.out.println (Thread.currentThread (). GetName () + "is waiting for resourceB"); synchronized (resourceB) {System.out.println (Thread.currentThread (). GetName () + "get resourceB") }); Thread threadB = new Thread (new Runnable () {@ Override public void run () {synchronized (resourceA) {System.out.println (Thread.currentThread (). GetName () + "get resourceA") Try {Thread.sleep (1000);} catch (InterruptedException e) {e.printStackTrace ();} System.out.println (Thread.currentThread (). GetName () + "is waiting for resourceA") Synchronized (resourceB) {System.out.println (Thread.currentThread (). GetName () + "get resourceB");}); threadA.start (); threadB.start ();}}

You can use jstatck to view the jvm log, and you will find the following results:

This is the end of what is a thread deadlock. Thank you for your reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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