chore: organize homework into first-part directory

first-part/hw-04/.gitignore

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+# Emacs/vim
+
+*~
+*.swp
+
+# VSCode
+
+.vscode
+.classpath
+.project
+.settings/
+
+
+# MacOS
+
+.DS_Store
+
+# CS56 specific: Secrets files
+
+localhost.json
+heroku.json
+
+# Maven (from: https://github.com/github/gitignore/blob/master/Maven.gitignore)
+
+target/
+pom.xml.tag
+pom.xml.releaseBackup
+pom.xml.versionsBackup
+pom.xml.next
+release.properties
+dependency-reduced-pom.xml
+buildNumber.properties
+.mvn/timing.properties
+# https://github.com/takari/maven-wrapper#usage-without-binary-jar
+.mvn/wrapper/maven-wrapper.jar
+
+# Java (from: https://github.com/github/gitignore/blob/master/Java.gitignore)
+
+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*

first-part/hw-04/concurrency/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.example</groupId>
+  <artifactId>concurrency</artifactId>
+  <packaging>jar</packaging>
+  <version>1.0-SNAPSHOT</version>
+  <name>concurrency</name>
+  <url>http://maven.apache.org</url>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

first-part/hw-04/concurrency/src/main/java/com/example/DeadLock.java

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+package com.example;
+
+import com.example.util.ThreadUtils;
+
+public class DeadLock {
+
+  private static final Object LOCK_A = new Object();
+  private static final Object LOCK_B = new Object();
+
+  public static void main(String[] args) {
+
+    Thread thread1 =
+        new Thread(
+            () -> {
+              synchronized (LOCK_A) {
+                System.out.println("Thread 1: получил LOCK_A");
+
+                ThreadUtils.sleep(100);
+
+                System.out.println("Thread 1: пытается получить LOCK_B");
+
+                synchronized (LOCK_B) {
+                  System.out.println("Thread 1: получил LOCK_B");
+                }
+              }
+            });
+
+    Thread thread2 =
+        new Thread(
+            () -> {
+              synchronized (LOCK_B) {
+                System.out.println("Thread 2: получил LOCK_B");
+
+                ThreadUtils.sleep(100);
+
+                System.out.println("Thread 2: пытается получить LOCK_A");
+
+                synchronized (LOCK_A) {
+                  System.out.println("Thread 2: получил LOCK_A");
+                }
+              }
+            });
+
+    thread1.start();
+    thread2.start();
+  }
+}

first-part/hw-04/concurrency/src/main/java/com/example/LiveLock.java

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+package com.example;
+
+public class LiveLock {
+
+  static class Corridor {
+    private Person currentPerson;
+
+    public Corridor(Person person) {
+      currentPerson = person;
+    }
+
+    public synchronized void setPerson(Person person) {
+      currentPerson = person;
+    }
+
+    public synchronized Person getPerson() {
+      return currentPerson;
+    }
+
+    public synchronized void pass() {
+      System.out.printf("%s прошёл по коридору!%n", currentPerson.name);
+    }
+  }
+
+  static class Person {
+    private final String name;
+    private volatile boolean wantsToPass;
+
+    public Person(String personName) {
+      name = personName;
+      wantsToPass = true;
+    }
+
+    public String getName() {
+      return name;
+    }
+
+    public boolean wantsToPass() {
+      return wantsToPass;
+    }
+
+    public void walkThrough(Corridor corridor, Person otherPerson) {
+      while (wantsToPass) {
+
+        // Если сейчас право пройти принадлежит другому человеку,
+        // немного ждём и снова проверяем ситуацию.
+        if (corridor.getPerson() != this) {
+          try {
+            Thread.sleep(1);
+          } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            return;
+          }
+          continue;
+        }
+
+        // Если второй человек тоже хочет пройти,
+        // вежливо уступаем ему дорогу.
+        if (otherPerson.wantsToPass()) {
+          System.out.printf("%s: Проходи первым, %s!%n", name, otherPerson.getName());
+
+          corridor.setPerson(otherPerson);
+          continue;
+        }
+
+        // Если другой человек уже прошёл,
+        // наконец сами идём по коридору.
+        corridor.pass();
+        wantsToPass = false;
+
+        System.out.printf("%s: Спасибо, %s!%n", name, otherPerson.getName());
+
+        corridor.setPerson(otherPerson);
+      }
+    }
+  }
+
+  public static void main(String[] args) {
+
+    final Person ivan = new Person("Иван");
+    final Person petr = new Person("Пётр");
+
+    // Изначально право пройти по коридору принадлежит Ивану.
+    final Corridor corridor = new Corridor(ivan);
+
+    // Первый поток — Иван.
+    new Thread(
+            new Runnable() {
+              @Override
+              public void run() {
+                ivan.walkThrough(corridor, petr);
+              }
+            })
+        .start();
+
+    // Второй поток — Пётр.
+    new Thread(
+            new Runnable() {
+              @Override
+              public void run() {
+                petr.walkThrough(corridor, ivan);
+              }
+            })
+        .start();
+  }
+}

first-part/hw-04/concurrency/src/main/java/com/example/ThreadUtils.java

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+package com.example.util;
+
+public class ThreadUtils {
+
+  public static void sleep(long millis) {
+    try {
+      Thread.sleep(millis);
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+    }
+  }
+}

first-part/hw-04/concurrency/src/main/java/com/example/TwoThreads.java

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+package com.example;
+
+public class TwoThreads {
+
+  private static final Object lock = new Object();
+  private static boolean turnOne = true;
+
+  public static void main(String[] args) {
+
+    Thread thread1 =
+        new Thread(
+            () -> {
+              while (true) {
+                synchronized (lock) {
+                  while (!turnOne) {
+                    try {
+                      lock.wait();
+                    } catch (InterruptedException e) {
+                      Thread.currentThread().interrupt();
+                      return;
+                    }
+                  }
+
+                  System.out.print("1");
+                  turnOne = false;
+                  lock.notifyAll();
+                }
+              }
+            });
+
+    Thread thread2 =
+        new Thread(
+            () -> {
+              while (true) {
+                synchronized (lock) {
+                  while (turnOne) {
+                    try {
+                      lock.wait();
+                    } catch (InterruptedException e) {
+                      Thread.currentThread().interrupt();
+                      return;
+                    }
+                  }
+
+                  System.out.print("2");
+                  turnOne = true;
+                  lock.notifyAll();
+                }
+              }
+            });
+
+    thread1.start();
+    thread2.start();
+  }
+}