Проблема параллелизма Java из-за многопоточности не возникла и автоматически синхронизировалась ⇐ JAVA

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Anonymous
 Проблема параллелизма Java из-за многопоточности не возникла и автоматически синхронизировалась

Сообщение Anonymous »

Я пытаюсь протестировать проблему многопоточного параллелизма.
Я ожидал, что результат должен быть меньше 0 (не всегда, но иногда), потому что это не так. синхронизировано.
Обратите внимание на пару вызовов println, которые включены/отключены с помощью теста if ( doPrintln ). Включение/отключение меняет результат теста.

Код: Выделить всё

class OptionTest
{
static class Option
{
private int quantity;

public Option ( int aQuantity ) { this.quantity = aQuantity; }

public int getQuantity ( ) { return quantity; }

public boolean subtract ( final int aQuantity )
{
final boolean doPrintln = false;
if ( aQuantity >= this.quantity )
{
if ( doPrintln ) System.out.println( "Returning FALSE. this.quantity = " + this.quantity + " at " + Instant.now( ) );
return false;
}

if ( doPrintln ) System.out.println( "Returning TRUE. this.quantity = " + this.quantity + " at " + Instant.now( ) );
this.quantity -= aQuantity;
return true;
}
}

@Test
void asyncSubtract ( ) throws InterruptedException
{
int numberOfThreads = 100; // Increased number of threads
ExecutorService executorService = Executors.newFixedThreadPool( numberOfThreads );
List < Callable < Boolean > > tasks = new ArrayList ( );

Option option = new Option( 201 );
for ( int i = 0 ; i < numberOfThreads ; i++ )
{
tasks.add( ( ) -> option.subtract( 50 ) );
}

executorService.invokeAll( tasks );
executorService.shutdown( );

assertThat( option.getQuantity( ) ).isLessThan( 1 ); // org.assertj.core.api.Assertions.assertThat
System.out.println( "INFO - Test end.  option.getQuantity( ) = " + option.getQuantity( ) + ". Now: " + Instant.now( ) );
}
}
Без println
Когда я запускаю, подавляя вызовы println (

Код: Выделить всё

doPrintln = false
), я получаю такой результат:

Код: Выделить всё

java.lang.AssertionError:
Expecting actual:
1
to be less than:
1

at work.basil.example.testing.OptionTest.asyncSubtract(OriginalOptionTest.java:55)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
С помощью println
Когда я запускаю тест с doPrintln = true, я получаю следующий результат: сто строки вывода Return ….

Код: Выделить всё

Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.537881Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528665Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528054Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531742Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531094Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.537219Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532059Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528697Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531952Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.527946Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532171Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532220Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.537462Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528005Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.538305Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.536697Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.530989Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.535044Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.538518Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528587Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528202Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528469Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.534627Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528248Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532282Z
Returning FALSE.  this.quantity = -999 at 2024-07-24T19:04:06.539461Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528481Z
Returning FALSE. this.quantity = -1049 at 2024-07-24T19:04:06.539559Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532323Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.530792Z
Returning FALSE. this.quantity = -349 at 2024-07-24T19:04:06.538886Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531271Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.527857Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528781Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531565Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532480Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528736Z
Returning FALSE. this.quantity = -1399 at 2024-07-24T19:04:06.540039Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532122Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531314Z
Returning FALSE. this.quantity = -1599 at 2024-07-24T19:04:06.540262Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531166Z
Returning FALSE. this.quantity = -499 at 2024-07-24T19:04:06.539014Z
Returning FALSE. this.quantity = -1649 at 2024-07-24T19:04:06.540332Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532820Z
Returning FALSE. this.quantity = -1649 at 2024-07-24T19:04:06.540406Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.530923Z
Returning FALSE. this.quantity = -1699 at 2024-07-24T19:04:06.540453Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.527858Z
Returning FALSE. this.quantity = -599 at 2024-07-24T19:04:06.539171Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528355Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.533105Z
Returning FALSE. this.quantity = -1849 at 2024-07-24T19:04:06.540620Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.533050Z
Returning FALSE. this.quantity = -899 at 2024-07-24T19:04:06.539382Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528146Z
Returning FALSE. this.quantity = -1949 at 2024-07-24T19:04:06.540756Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.527857Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528517Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.527868Z
Returning FALSE. this.quantity = -2099 at 2024-07-24T19:04:06.540873Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528291Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528636Z
Returning FALSE. this.quantity = -2199 at 2024-07-24T19:04:06.540951Z
Returning FALSE. this.quantity = -1199 at 2024-07-24T19:04:06.539664Z
Returning FALSE. this.quantity = -2249 at 2024-07-24T19:04:06.540996Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.532579Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.531213Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528807Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.528098Z
Returning FALSE. this.quantity = -1199 at 2024-07-24T19:04:06.539833Z
Returning FALSE. this.quantity = -2449 at 2024-07-24T19:04:06.541133Z
Returning TRUE. this.quantity = 201 at 2024-07-24T19:04:06.533149Z
Returning FALSE. this.quantity = -1549 at 2024-07-24T19:04:06.540224Z
Returning FALSE. this.quantity = -1749 at 2024-07-24T19:04:06.540496Z
Returning FALSE. this.quantity = -1799 at 2024-07-24T19:04:06.540566Z
Returning FALSE. this.quantity = -1949 at 2024-07-24T19:04:06.540704Z
Returning FALSE. this.quantity = -1999 at 2024-07-24T19:04:06.540813Z
Returning FALSE. this.quantity = -2149 at 2024-07-24T19:04:06.540909Z
Returning FALSE. this.quantity = -2299 at 2024-07-24T19:04:06.541048Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541178Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541357Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541231Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541415Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541268Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541463Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541311Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541514Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541588Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541618Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541674Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541711Z
Returning FALSE.  this.quantity = -2499 at 2024-07-24T19:04:06.541767Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541823Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541853Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541895Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541940Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.541988Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.542028Z
Returning FALSE. this.quantity = -2499 at 2024-07-24T19:04:06.542081Z
INFO - Test end.  option.getQuantity( ) = -2499. Now: 2024-07-24T19:04:06.568632Z
Почему вызов System.out.println постоянно меняет результаты?
Есть ли какая-то магия JVM?

Подробнее здесь: https://stackoverflow.com/questions/787 ... -synchroni
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