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added task description (#1)
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‎README.md‎

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# jv-homework-template
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# Decrease counter
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We wrote multi-threaded code that decreases the value of the `Counter` object.
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In `main()` method, 20 threads are created that accept the same `Counter` object.
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The task of each thread is to decrease the value of the `counter` by 1.
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The original `counter` value is 20, so we should expect 0 in the end.
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We are logging the value before and after each decrement, and now we see that the results are hardly consistent.
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```
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 15, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 8, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 12, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 18, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 14, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 5, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 7, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 9, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 11, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 3, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 6, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 17, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 2, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 10, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 19, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 20, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 16, counter value 20
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 13, counter value 20
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 7, counter value 12
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 1, counter value 20
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 3, counter value 16
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 20, counter value 10
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 19, counter value 9
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 5, counter value 17
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 2, counter value 12
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 8, counter value 18
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 9, counter value 18
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 14, counter value 15
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 10, counter value 14
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 17, counter value 11
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 16, counter value 8
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INFO core.basesyntax.Counter:16 Before decrementing, Thread # 4, counter value 20
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 11, counter value 18
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 12, counter value 5
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 6, counter value 6
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 13, counter value 7
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 18, counter value 4
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 4, counter value 3
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 15, counter value 2
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INFO core.basesyntax.Counter:19 After decrementing, Thread # 1, counter value 1
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```
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As we see, all threads are accessing the same value of the variable at the same time,
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then they also decrease it randomly, and we can even get 1 instead of 0 in the end of execution.
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Fix the solution to remove the race condition between the threads.
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Each thread should take the value that was decremented by the previous thread, and the logs should be consistent.
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Let's allow only one thread to execute the meaningful part of code at a time.
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Note that you should push the file with logs to your PR, so please, do not add it to `.gitignore`.
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You may probably need to use the absolute path to the log file in `log4j2.xml`.

‎pom.xml‎

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<modelVersion>4.0.0</modelVersion>
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<groupId>mate-academy</groupId>
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<artifactId>diamond</artifactId>
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<artifactId>decrease-counter</artifactId>
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<version>1.0-SNAPSHOT</version>
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<properties>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.12</version>
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<scope>test</scope>
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<groupId>org.apache.logging.log4j</groupId>
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<artifactId>log4j-core</artifactId>
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<version>2.14.1</version>
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</dependency>
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</dependencies>
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<build>

‎src/main/java/core/basesyntax/Counter.java‎

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package core.basesyntax;
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import org.apache.logging.log4j.LogManager;
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import org.apache.logging.log4j.Logger;
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public class Counter {
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private static final Logger logger = LogManager.getLogger(Counter.class);
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private static final String MESSAGE = "%20s, Thread # %2s, counter value %2d";
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private int value;
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public Counter(int value) {
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this.value = value;
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}
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public void decreaseValue() {
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logger.info(String.format(MESSAGE,
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"Before decrementing", Thread.currentThread().getName(), value));
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value--;
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logger.info(String.format(MESSAGE,
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"After decrementing", Thread.currentThread().getName(), value));
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}
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}

‎src/main/java/core/basesyntax/HelloWorld.java‎

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‎src/main/java/core/basesyntax/Main.java‎

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package core.basesyntax;
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public class Main {
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public static void main(String[] args) {
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Counter counter = new Counter(20);
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for (int i = 1; i <= 20; i++) {
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new MyThread(counter, String.valueOf(i)).start();
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}
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}
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}

‎src/main/java/core/basesyntax/MyThread.java‎

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package core.basesyntax;
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public class MyThread extends Thread {
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private final Counter counter;
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public MyThread(Counter counter, String name) {
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super(name);
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this.counter = counter;
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}
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@Override
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public void run() {
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counter.decreaseValue();
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}
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}

‎src/main/resources/log4j2.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<Configuration status="info">
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<Appenders>
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<Console name="LogToConsole" target="SYSTEM_OUT">
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<PatternLayout pattern="%-5level %c:%L - %msg%n"/>
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</Console>
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<File name="LogToFile" filename="logs/app.log" append="false">
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<PatternLayout><Pattern>%p %c:%L %m%n</Pattern></PatternLayout>
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</File>
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</Appenders>
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<Loggers>
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<Root level="info">
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<AppenderRef ref="LogToFile"/>
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<AppenderRef ref="LogToConsole"/>
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</Root>
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</Loggers>
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</Configuration>

‎src/test/java/core/basesyntax/HelloWorldTest.java‎

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