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return this; }

T pop() { semaphore.acquireUninterruptibly(); try { Node<T> current = head; if (current != null) { head = head.next; return current.value; } return null; } finally { semaphore.release(); } }

private static class Node<E> { private final E value; private final Node<E> next;

private Node(E value, Node<E> next) { this.value = value; this.next = next; } }}</pre></div>

<h2><a id="user-content-напишите-минимальный-неблокирующий-arraylist-всего-четыре-метода--add-get-remove-size" class="anchor" aria-hidden="true" href="https://github.com/enhorse/java-interview/blob/master/concurrency.md#%D0%BD%D0%B0%D0%BF%D0%B8%D1%88%D0%B8%D1%82%D0%B5-%D0%BC%D0%B8%D0%BD%D0%B8%D0%BC%D0%B0%D0%BB%D1%8C%D0%BD%D1%8B%D0%B9-%D0%BD%D0%B5%D0%B1%D0%BB%D0%BE%D0%BA%D0%B8%D1%80%D1%83%D1%8E%D1%89%D0%B8%D0%B9-arraylist-%D0%B2%D1%81%D0%B5%D0%B3%D0%BE-%D1%87%D0%B5%D1%82%D1%8B%D1%80%D0%B5-%D0%BC%D0%B5%D1%82%D0%BE%D0%B4%D0%B0--add-get-remove-size"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path fill-rule="evenodd" d="M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z"></path></svg></a>Напишите минимальный неблокирующий ArrayList (всего четыре метода — <code>add()</code>, <code>get()</code>, <code>remove()</code>, <code>size()</code>).</h2><div class="highlight highlight-source-java"><pre>class NonBlockingArrayList<T> { private volatile Object[] content = new Object[0];

NonBlockingArrayList<T> add(T item) { return add(content.length, item); }

NonBlockingArrayList<T> add(int index, T item) { if (index < 0) { throw new IllegalArgumentException(); } boolean needsModification = index > content.length - 1; if (!needsModification) { if (item == null) { needsModification = content[index] != null; } else { needsModification = item.equals(content[index]); } } if (needsModification) { final Object[] renewed = Arrays.copyOf(content, Math.max(content.length, index + 1)); renewed[index] = item; content = renewed; } return this; }

NonBlockingArrayList<T> remove(int index) { if (index < 0 || index >= content.length) { throw new IllegalArgumentException(); } int size = content.length - 1; final Object[] renewed = new Object[size]; System.arraycopy(content, 0, renewed, 0, index); if (index + 1 < size) { System.arraycopy(content, index + 1, renewed, index, size - index); } content = renewed; return this; }

T get(int index) { return (T) content[index]; }

int size() { return content.length; }}</pre></div>

<h2><a id="user-content-напишите-потокобезопасную-реализацию-класса-с-неблокирующим-методом-biginteger-next-который-возвращает-элементы-последовательности-1-2-4-8-16-" class="anchor" aria-hidden="true" href="https://github.com/enhorse/java-interview/blob/master/concurrency.md#%D0%BD%D0%B0%D0%BF%D0%B8%D1%88%D0%B8%D1%82%D0%B5-%D0%BF%D0%BE%D1%82%D0%BE%D0%BA%D0%BE%D0%B1%D0%B5%D0%B7%D0%BE%D0%BF%D0%B0%D1%81%D0%BD%D1%83%D1%8E-%D1%80%D0%B5%D0%B0%D0%BB%D0%B8%D0%B7%D0%B0%D1%86%D0%B8%D1%8E-%D0%BA%D0%BB%D0%B0%D1%81%D1%81%D0%B0-%D1%81-%D0%BD%D0%B5%D0%B1%D0%BB%D0%BE%D0%BA%D0%B8%D1%80%D1%83%D1%8E%D1%89%D0%B8%D0%BC-%D0%BC%D0%B5%D1%82%D0%BE%D0%B4%D0%BE%D0%BC-biginteger-next-%D0%BA%D0%BE%D1%82%D0%BE%D1%80%D1%8B%D0%B9-%D0%B2%D0%BE%D0%B7%D0%B2%D1%80%D0%B0%D1%89%D0%B0%D0%B5%D1%82-%D1%8D%D0%BB%D0%B5%D0%BC%D0%B5%D0%BD%D1%82%D1%8B-%D0%BF%D0%BE%D1%81%D0%BB%D0%B5%D0%B4%D0%BE%D0%B2%D0%B0%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D0%BE%D1%81%D1%82%D0%B8-1-2-4-8-16-"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path fill-rule="evenodd" d="M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z"></path></svg></a>Напишите потокобезопасную реализацию класса с неблокирующим методом <code>BigInteger next()</code>, который возвращает элементы последовательности: <code>[1, 2, 4, 8, 16, ...]</code>.</h2><div class="highlight highlight-source-java"><pre>class PowerOfTwo { private AtomicReference<BigInteger> current = new AtomicReference<>(null); BigInteger next() { BigInteger recent, next; do { recent = current.get(); next = (recent == null) ? BigInteger.valueOf(1) : recent.shiftLeft(1); } while (!current.compareAndSet(recent, next)); return next; }}</pre></div>

<h2><a id="user-content-напишите-простейший-многопоточный-ограниченный-буфер-с-использованием-synchronized" class="anchor" aria-hidden="true" href="https://github.com/enhorse/java-interview/blob/master/concurrency.md#%D0%BD%D0%B0%D0%BF%D0%B8%D1%88%D0%B8%D1%82%D0%B5-%D0%BF%D1%80%D0%BE%D1%81%D1%82%D0%B5%D0%B9%D1%88%D0%B8%D0%B9-%D0%BC%D0%BD%D0%BE%D0%B3%D0%BE%D0%BF%D0%BE%D1%82%D0%BE%D1%87%D0%BD%D1%8B%D0%B9-%D0%BE%D0%B3%D1%80%D0%B0%D0%BD%D0%B8%D1%87%D0%B5%D0%BD%D0%BD%D1%8B%D0%B9-%D0%B1%D1%83%D1%84%D0%B5%D1%80-%D1%81-%D0%B8%D1%81%D0%BF%D0%BE%D0%BB%D1%8C%D0%B7%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5%D0%BC-synchronized"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path fill-rule="evenodd" d="M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z"></path></svg></a>Напишите простейший многопоточный ограниченный буфер с использованием <code>synchronized</code>.</h2><div class="highlight highlight-source-java"><pre>class QueueSynchronized<T> { private volatile int size = 0; private final Object[] content; private final int capacity;

private int out; private int in;

private final Object isEmpty = new Object(); private final Object isFull = new Object();

QueueSynchronized(final int capacity) { this.capacity = capacity; content = new Object[this.capacity]; out = 0; in = 0; size = 0; }

private int cycleInc(int index) { return (++index == capacity) ? 0 : index; }

@SuppressWarnings("unchecked") T get() throws InterruptedException { if (size == 0) { synchronized (isEmpty) { while (size < 1) { isEmpty.wait(); } } } try { synchronized (this) { final Object value = content[out]; content[out] = null; if (size > 1) { out = cycleInc(out); } size--; return (T) value; } } finally { synchronized (isFull) { isFull.notify(); } } }

QueueSynchronized<T> put(T value) throws InterruptedException { if (size == capacity) { synchronized (isFull) { while (size == capacity) { isFull.wait(); } } } synchronized (this) { if (size == 0) { content[in] = value; } else { in = cycleInc(in); content[in] = value; } size++; } synchronized (isEmpty) { isEmpty.notify(); } return this; }}</pre></div>

<h2><a id="user-content-напишите-простейший-многопоточный-ограниченный-буфер-с-использованием-reentrantlock" class="anchor" aria-hidden="true" href="https://github.com/enhorse/java-interview/blob/master/concurrency.md#%D0%BD%D0%B0%D0%BF%D0%B8%D1%88%D0%B8%D1%82%D0%B5-%D0%BF%D1%80%D0%BE%D1%81%D1%82%D0%B5%D0%B9%D1%88%D0%B8%D0%B9-%D0%BC%D0%BD%D0%BE%D0%B3%D0%BE%D0%BF%D0%BE%D1%82%D0%BE%D1%87%D0%BD%D1%8B%D0%B9-%D0%BE%D0%B3%D1%80%D0%B0%D0%BD%D0%B8%D1%87%D0%B5%D0%BD%D0%BD%D1%8B%D0%B9-%D0%B1%D1%83%D1%84%D0%B5%D1%80-%D1%81-%D0%B8%D1%81%D0%BF%D0%BE%D0%BB%D1%8C%D0%B7%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5%D0%BC-reentrantlock"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path fill-rule="evenodd" d="M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z"></path></svg></a>Напишите простейший многопоточный ограниченный буфер с использованием <code>ReentrantLock</code>.</h2><div class="highlight highlight-source-java"><pre>class QueueReentrantLock<T> {

private volatile int size = 0; private final Object[] content; private final int capacity;

private int out; private int in;

private final ReentrantLock lock = new ReentrantLock(); private final Condition isEmpty = lock.newCondition(); private final Condition isFull = lock.newCondition();

QueueReentrantLock(int capacity) { try { lock.lock(); this.capacity = capacity; content = new Object[capacity]; out = 0; in = 0; } finally { lock.unlock(); } }

@SuppressWarnings("unchecked") T get() throws InterruptedException { try { lock.lockInterruptibly(); if (size == 0) { while (size < 1) { isEmpty.await(); } } final Object value = content[out]; content[out] = null; if (size > 1) { out = cycleInc(out); } size--; isFull.signal(); return (T) value; } finally { lock.unlock(); } }

QueueReentrantLock<T> put(T value) throws InterruptedException { try { lock.lockInterruptibly(); if (size == capacity) { while (size == capacity) { isFull.await(); } } if (size == 0) { content[in] = value; } else { in = cycleInc(in); content[in] = value; } size++; isEmpty.signal(); } finally { lock.unlock(); } return this; }}</pre></div>

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