Como gerar Java Deadlock programaticamente e como analisar Deadlock

Publicados: 2013-07-03

Exemplo de bloqueio de thread Java por Crunchify

Deadlock é uma situação de programação onde dois ou mais threads são bloqueados para sempre, esta situação surge com pelo menos dois threads e dois ou mais recursos.

Aqui eu escrevi um programa simples que causará um cenário de deadlock e então veremos como analisá-lo.

Aqui está um exemplo simples de Java:

CrunchifyThreadDeadLock.java
Java
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package com . crunchify . tutorials ;
 
import java . lang . management . ManagementFactory ;
import java . lang . management . ThreadInfo ;
import java . lang . management . ThreadMXBean ;
 
/**
* @author Crunchify.com
*
*/
 
public class CrunchifyThreadDeadLock {
 
     public static void main ( String [ ] args ) throws InterruptedException {
         Object obj1 = new Object ( ) ;
         Object obj2 = new Object ( ) ;
         Object obj3 = new Object ( ) ;
 
         Thread crunchifyThread1 = new Thread ( new CrunchifySynchronizeThread ( obj1 , obj2 ) , "crunchifyThread1" ) ;
         Thread crunchifyThread2 = new Thread ( new CrunchifySynchronizeThread ( obj2 , obj3 ) , "crunchifyThread2" ) ;
         Thread crunchifyThread3 = new Thread ( new CrunchifySynchronizeThread ( obj3 , obj1 ) , "crunchifyThread3" ) ;
 
         crunchifyThread1 . start ( ) ;
         Thread . sleep ( 3000 ) ;
         crunchifyThread2 . start ( ) ;
         Thread . sleep ( 3000 ) ;
         crunchifyThread3 . start ( ) ;
     }
}
 
class CrunchifySynchronizeThread implements Runnable {
     private Object obj1 ;
     private Object obj2 ;
 
     public CrunchifySynchronizeThread ( Object obj1 , Object obj2 ) {
         this . obj1 = obj1 ;
         this . obj2 = obj2 ;
     }
 
     @Override
     public void run ( ) {
         String name = Thread . currentThread ( ) . getName ( ) ;
         synchronized ( obj1 ) {
             System . out . println ( name + " acquired lock on Object1: " + obj1 ) ;
             try {
                 Thread . sleep ( 10000 ) ;
             } catch ( InterruptedException e ) {
                 e . printStackTrace ( ) ;
             }
 
             synchronized ( obj2 ) {
                 System . out . println ( name + " acquired lock on Object2: " + obj2 ) ;
             }
             System . out . println ( name + " released lock on Object2: " + obj2 ) ;
         }
         System . out . println ( name + " released lock on Object1: " + obj1 ) ;
         System . out . println ( name + " Finished Crunchify Deadlock Test." ) ;
     }
}

Saída:

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crunchifyThread1 acquired lock on Object1 : java . lang . Object @ 59e3bddb
crunchifyThread2 acquired lock on Object1 : java . lang . Object @ 294e430c
crunchifyThread3 acquired lock on Object1 : java . lang . Object @ 246972f1

Enquanto seu aplicativo está travando como no exemplo acima, você pode obter um despejo de thread e ver os threads bloqueados.

Por exemplo, no Mac, você pode fazer Ctrl-\ ou simplesmente usar jstack e process id para obter o despejo de encadeamento, o que torna muito óbvio onde está o impasse.

Neste exemplo, o dump de encadeamento se parece com isso:

Thread Dump of running program
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"crunchifyThread3"
   java . lang . Thread . State : RUNNABLE
         at sun . management . ThreadImpl . getThreadInfo1 ( Native Method )
         at sun . management . ThreadImpl . getThreadInfo ( ThreadImpl . java : 174 )
         at com . crunchify . tutorials . CrunchifySynchronizeThread . getThreadDump ( CrunchifyThreadDeadLock . java : 64 )
         at com . crunchify . tutorials . CrunchifySynchronizeThread . run ( CrunchifyThreadDeadLock . java : 50 )
         at java . lang . Thread . run ( Thread . java : 722 )
 
"crunchifyThread2"
   java . lang . Thread . State : BLOCKED
         at com . crunchify . tutorials . CrunchifySynchronizeThread . run ( CrunchifyThreadDeadLock . java : 53 )
         at java . lang . Thread . run ( Thread . java : 722 )
 
"crunchifyThread1"
   java . lang . Thread . State : BLOCKED
         at com . crunchify . tutorials . CrunchifySynchronizeThread . run ( CrunchifyThreadDeadLock . java : 53 )
         at java . lang . Thread . run ( Thread . java : 722 )
 
"Signal Dispatcher"
   java . lang . Thread . State : RUNNABLE
 
"Finalizer"
   java . lang . Thread . State : WAITING
         at java . lang . Object . wait ( Native Method )
         at java . lang . ref . ReferenceQueue . remove ( ReferenceQueue . java : 135 )
         at java . lang . ref . ReferenceQueue . remove ( ReferenceQueue . java : 151 )
         at java . lang . ref . Finalizer $ FinalizerThread . run ( Finalizer . java : 189 )
 
"Reference Handler"
   java . lang . Thread . State : WAITING
         at java . lang . Object . wait ( Native Method )
         at java . lang . Object . wait ( Object . java : 503 )
         at java . lang . ref . Reference $ ReferenceHandler . run ( Reference . java : 133 )

Notificado aqui BLOCKED and WAITING threads => Deadlock aqui .. No próximo exemplo, fornecerá um programa Java simples para gerar o dump de thread acima programaticamente.