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ArrayStack.java

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import java.nio.*;

import java.util.concurrent.locks.*;

// Array stack is a bounded lock-based stack using an

// array. It uses a common lock for both push and pop

// operations.

class ArrayStack<T> {

Lock lock;

T[] data;

int top;

// lock: common lock for push, pop

// data: array of values in stack

// top: top of stack (0 if empty)

@SuppressWarnings("unchecked")

public ArrayStack(int capacity) {

lock = new ReentrantLock();

data = (T[]) new Object[capacity];

top = 0;

}

// 1. Lock stack.

// 2. Try push.

// 3. Unlock stack.

public void push(T x) throws BufferOverflowException {

try {

lock.lock(); // 1

tryPush(x); // 2

} finally {

lock.unlock(); // 3

}

// 1. Lock stack.

// 2. Try pop.

// 3. Unlock stack.

public T pop() throws BufferUnderflowException {

try {

lock.lock(); // 1

return tryPop(); // 2

} finally {

lock.unlock(); // 3

}

// 1. Ensure stack is not full

// 2. Save data at top.

// 3. Increment top.

protected void tryPush(T x)

throws BufferOverflowException {

if (top == data.length) // 1

throw new BufferOverflowException(); // 1

data[top++] = x; // 2, 3

}

// 1. Ensure stack is not empty.

// 2. Decrement top.

// 3. Return data at top.

protected T tryPop()

throws BufferUnderflowException {

if (top == 0) // 1

throw new BufferUnderflowException(); // 1

return data[--top]; // 2, 3

}