【leetcode】多线程编程题题解
本文将记录力扣多线程下的题目：
每道题基本都有很多种解法，基本都可以使用变量、Semaphore、CountDownLatch等手段来控制。
1114.按序打印
1.变量控制
class Foo {
private volatile int flag = 1;
public Foo() {}
public void first(Runnable printFirst) throws InterruptedException {
// printSecond.run() outputs "first". Do not change or remove this line.
printFirst.run();
flag = 2;
}
public void second(Runnable printSecond) throws InterruptedException {
while (flag != 2);
// printSecond.run() outputs "second". Do not change or remove this line.
printSecond.run();
flag = 3;
}
public void third(Runnable printThird) throws InterruptedException {
while (flag != 3);
// printThird.run() outputs "third". Do not change or remove this line.
printThird.run();
}
}2.Semaphore
class Foo {
public Semaphore seam_first_two = new Semaphore(0);
public Semaphore seam_two_second = new Semaphore(0);
public Foo() {}
public void first(Runnable printFirst) throws InterruptedException {
// printSecond.run() outputs "first". Do not change or remove this line.
printFirst.run();
seam_first_two.release();
}
public void second(Runnable printSecond) throws InterruptedException {
seam_first_two.acquire();
// printSecond.run() outputs "second". Do not change or remove this line.
printSecond.run();
seam_two_second.release();
}
public void third(Runnable printThird) throws InterruptedException {
seam_two_second.acquire();
// printThird.run() outputs "third". Do not change or remove this line.
printThird.run();
}
}3.CountDownLatch
class Foo {
private CountDownLatch second = new CountDownLatch(1);
private CountDownLatch third = new CountDownLatch(1);
public Foo() {}
public void first(Runnable printFirst) throws InterruptedException {
// printSecond.run() outputs "first". Do not change or remove this line.
printFirst.run();
second.countDown();
}
public void second(Runnable printSecond) throws InterruptedException {
second.await();
// printSecond.run() outputs "second". Do not change or remove this line.
printSecond.run();
third.countDown();
}
public void third(Runnable printThird) throws InterruptedException {
third.await();
// printThird.run() outputs "third". Do not change or remove this line.
printThird.run();
}
}4.AtomicInteger
class Foo {
private AtomicInteger firstJobDone = new AtomicInteger(0);
private AtomicInteger secondJobDone = new AtomicInteger(0);
public Foo() {}
public void first(Runnable printFirst) throws InterruptedException {
// printFirst.run() outputs "first".
printFirst.run();
// mark the first job as done, by increasing its count.
firstJobDone.incrementAndGet();
}
public void second(Runnable printSecond) throws InterruptedException {
while (firstJobDone.get() != 1) {
// waiting for the first job to be done.
}
// printSecond.run() outputs "second".
printSecond.run();
// mark the second as done, by increasing its count.
secondJobDone.incrementAndGet();
}
public void third(Runnable printThird) throws InterruptedException {
while (secondJobDone.get() != 1) {
// waiting for the second job to be done.
}
// printThird.run() outputs "third".
printThird.run();
}
}1115.交替打印FooBar
1.Semaphore
class FooBar {
private int n;
public Semaphore semaphoreFoo = new Semaphore(1);
public Semaphore semaphoreBar = new Semaphore(0);
public FooBar(int n) {
this.n = n;
}
public void foo(Runnable printFoo) throws InterruptedException {
for (int i = 0; i < n; i++) {
semaphoreBar.acquire();
// printFoo.run() outputs "foo". Do not change or remove this line.
printFoo.run();
semaphoreBar.release();
}
}
public void bar(Runnable printBar) throws InterruptedException {
for (int i = 0; i < n; i++) {
semaphoreBar.acquire();
// printBar.run() outputs "bar". Do not change or remove this line.
printBar.run();
semaphoreFoo.release();
}
}
}2.CyclicBarrier
class FooBar {
private int n;
private CyclicBarrier cb = new CyclicBarrier(2);
private volatile boolean fooExec = true;
public FooBar(int n) {
this.n = n;
}
public void foo(Runnable printFoo) throws InterruptedException {
for (int i = 0; i < n; i++) {
while (!fooExec) {
//false的时候，bar线程在执行，foo线程在这此处空转
}
printFoo.run();//打印foo
fooExec = false;//设置变量
try {
cb.await();//线程foo到达同步点
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
}
public void bar(Runnable printBar) throws InterruptedException {
for (int i = 0; i < n; i++) {
try {
cb.await();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
printBar.run();
fooExec = true;
}
}
}3.Thread.yield()
class FooBar {
private int n;
private volatile boolean fooExec = true;
public FooBar(int n) {
this.n = n;
}
public void foo(Runnable printFoo) throws InterruptedException {
for (int i = 0; i < n;) {
if (fooExec) {
printFoo.run();
fooExec = false;
i++;
} else {
Thread.yield();
}
}
}
public void bar(Runnable printBar) throws InterruptedException {
for (int i = 0; i < n;) {
if (!fooExec) {
printBar.run();
fooExec = true;
i++;
} else {
Thread.yield();
}
}
}
}4.BlockingQueue
class FooBar {
private int n;
private BlockingQueue<Integer> fooQueue = new LinkedBlockingQueue<Integer>() {{
add(0);
}};
private BlockingQueue<Integer> barQueue = new LinkedBlockingQueue<>();
public FooBar(int n) {
this.n = n;
}
public void foo(Runnable printFoo) throws InterruptedException {
for (int i = 0; i < n; i++) {
fooQueue.take();
printFoo.run();
barQueue.add(0);
}
}
public void bar(Runnable printBar) throws InterruptedException {
for (int i = 0; i < n; i++) {
barQueue.take();
printBar.run();
fooQueue.add(0);
}
}
}1116.打印零与奇偶数
1.Semaphore
class ZeroEvenOdd {
private int n;
private Semaphore zeroSema = new Semaphore(1);
private Semaphore oddSema = new Semaphore(0);
private Semaphore evenSema = new Semaphore(0);
public ZeroEvenOdd(int n) {
this.n = n;
}
// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
zeroSema.acquire();
printNumber.accept(0);
if (i % 2 == 1) {
oddSema.release();
} else {
evenSema.release();
}
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
if (i % 2 == 0) {
evenSema.acquire();
printNumber.accept(i);
zeroSema.release();
}
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
if (i % 2 == 1) {
oddSema.acquire();
printNumber.accept(i);
zeroSema.release();
}
}
}
}2.CountDownLatch
class ZeroEvenOdd {
private int n;
private CountDownLatch zeroLatch = new CountDownLatch(0);
private CountDownLatch evenLatch = new CountDownLatch(1);//偶数
private CountDownLatch oddLatch = new CountDownLatch(1);//奇数
public ZeroEvenOdd(int n) {
this.n = n;
}
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
zeroLatch.await();
printNumber.accept(0);
zeroLatch = new CountDownLatch(1);
if (i % 2 == 1) {
oddLatch.countDown();
} else {
evenLatch.countDown();
}
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
if (i % 2 == 0) {
evenLatch.await();
printNumber.accept(i);
evenLatch = new CountDownLatch(1);
zeroLatch.countDown();
}
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
if (i % 2 == 1) {
oddLatch.await();
printNumber.accept(i);
oddLatch = new CountDownLatch(1);
zeroLatch.countDown();
}
}
}
}3.AtomicInteger+Thread.yield()
class ZeroEvenOdd {
private int n;
private AtomicInteger ai = new AtomicInteger(0);
public ZeroEvenOdd(int n) {
this.n = n;
}
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 0; i < n; i++) {
while (ai.get() != 0 && ai.get() != 2) {
Thread.yield();
}
printNumber.accept(0);
ai.incrementAndGet();
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 2; i <= n; i += 2) {
while (ai.get() != 3) {
Thread.yield();
}
printNumber.accept(i);
ai.set(0);
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i += 2) {
while (ai.get() != 1) {
Thread.yield();
}
printNumber.accept(i);
ai.set(2);
}
}
}4.变量+Thread.yield()
class ZeroEvenOdd {
private int n;
private volatile int state;
public ZeroEvenOdd(int n) {
this.n = n;
}
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
while (state != 0) {
Thread.yield();
}
printNumber.accept(0);
if (i % 2 == 1) {
state = 1;
} else {
state = 2;
}
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 2; i <= n; i += 2) {
while (state != 2) {
Thread.yield();
}
printNumber.accept(i);
state = 0;
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i += 2) {
while (state != 1) {
Thread.yield();
}
printNumber.accept(i);
state = 0;
}
}
}5.ReentrantLock+Condition
class ZeroEvenOdd {
private int n;
private volatile int start = 1;
private volatile int state;
private Lock lock = new ReentrantLock();
private Condition zero = lock.newCondition();
private Condition even = lock.newCondition();
private Condition odd = lock.newCondition();
public ZeroEvenOdd(int n) {
this.n = n;
}
// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
lock.lock();
try {
while (start <= n) {
if (state != 0) {
zero.await();
}
printNumber.accept(0);
if (start % 2 == 0) {
state = 2;
even.signal();
} else {
state = 1;
odd.signal();
}
zero.await();
}
odd.signal();
even.signal();
} finally {
lock.unlock();
}
}
//偶数
public void even(IntConsumer printNumber) throws InterruptedException {
lock.lock();
try {
while (start <= n) {
if (state != 2) {
even.await();
} else {
printNumber.accept(start++);
state = 0;
zero.signal();
}
}
} finally {
lock.unlock();
}
}
//基数
public void odd(IntConsumer printNumber) throws InterruptedException {
lock.lock();
try {
while (start <= n) {
if (state != 1) {
odd.await();
} else {
printNumber.accept(start++);
state = 0;
zero.signal();
}
}
} finally {
lock.unlock();
}
}
}