美文网首页
3个线程循环打印到不同文件

3个线程循环打印到不同文件

作者: 秋风落叶黄 | 来源:发表于2021-03-14 11:18 被阅读0次

    最近在面试阿里的,遇到一个笔试题,题目是这样的:

    多线程写文件,有3个线程1、2、3。线程1的功能就是输出t1,线程2的功能就是输出t2,以此类推.........,
     现在有三个文件file1,file2,file3。初始都为空,现要让三个文件呈如下格式:
     file1:t1 t2 t3 t1 t2....
     file2:t2 t3 t1 t2 t3....
     file3:t3 t1 t2 t3 t1….
    

    下面以2中方式完成这题

    第一种采用ReentranLock+condition进行实现,具体代码如下:

    package thread;
    
    import java.io.FileWriter;
    import java.io.IOException;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.ReentrantLock;
    
    /**
     * 多线程写文件,有3个线程1、2、3。线程1的功能就是输出t1,线程2的功能就是输出t2,以此类推.........,
     * 现在有三个文件file1,file2,file3。初始都为空,现要让三个文件呈如下格式:
     * file1:t1 t2 t3 t1 t2....
     * file2:t2 t3 t1 t2 t3....
     * file3:t3 t1 t2 t3 t1….
     *
     * @Author: huangyichun
     * @Date: 2021/3/14
     */
    public class CircleFileWriter {
    
    
        public CircleFileWriter() throws IOException {
        }
    
        public static void main(String[] args) throws InterruptedException, IOException {
            CircleFileWriter fileWriter = new CircleFileWriter();
            Thread thread1 = new Thread(fileWriter::printT1);
            Thread thread2 = new Thread(fileWriter::printT2);
            Thread thread3 = new Thread(fileWriter::printT3);
    
            thread1.start();
            Thread.sleep(100);
            thread2.start();
            Thread.sleep(100);
            thread3.start();
        }
    
        FileWriter fileWriter1 = new FileWriter("file1");
        FileWriter fileWriter2 = new FileWriter("file2");
        FileWriter fileWriter3 = new FileWriter("file3");
    
        //当前循环的圈数,用于判断当前线程输出的文件
        private volatile int loop = 0;
    
        private final ReentrantLock lock = new ReentrantLock();
        Condition condition1 = lock.newCondition();
        Condition condition2 = lock.newCondition();
        Condition condition3 = lock.newCondition();
    
        private final int times = 100;
    
        public void printT1() {
            lock.lock();
            try {
                print(1, condition1, condition2, "t1");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        public void printT2() {
            lock.lock();
            try {
               print(2, condition2, condition3, "t2");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        public void printT3() {
            lock.lock();
            try {
                print(3, condition3, condition1, "t3");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    
        
         /**
         * 实际打印方法
         * @param threadNumber 当前线程id 对应1,2,3
         * @param current 控制当前线程的condition
         * @param next 控制后一个线程的condition
         * @param str 打印的内容
         * @throws InterruptedException
         */
        private void print(int threadNumber, Condition current, Condition next, String str) throws InterruptedException {
            for (int i = 0; i < 100; i++) {//打印100次
                writeFile(getFile(threadNumber, loop), str);
                if (threadNumber == 3) {
                    loop++;
                }
                next.signal();
                if (i < times - 1) { //最后一次不需要等待
                    current.await();
                }
            }
        }
    
        /**
         * 写入文件
         **/
        private void writeFile(FileWriter fw, String s) {
            System.out.println(Thread.currentThread().getName() + "打印:" + s + "到");
            try {
                fw.append(s);
                fw.flush();
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
        /**
         * 判断在当前线程在第loop循环情况下写入哪个文件
         **/
        private FileWriter getFile(int threadNumber, int loop) {
    
            if (threadNumber == 1) {
                if (loop % 3 == 0) {
                    return fileWriter1;
                } else if (loop % 3 == 1) {
                    return fileWriter3;
                } else {
                    return fileWriter2;
                }
            } else if (threadNumber == 2) {
                if (loop % 3 == 0) {
                    return fileWriter2;
                } else if (loop % 3 == 1) {
                    return fileWriter1;
                } else {
                    return fileWriter3;
                }
            } else {
                if (loop % 3 == 0) {
                    return fileWriter3;
                } else if (loop % 3 == 1) {
                    return fileWriter2;
                } else {
                    return fileWriter1;
                }
            }
        }
    }
    
    

    第二种方法,不是用锁,使用volatile进行控制线程循环打印。

    package thread;
    
    import java.io.FileWriter;
    import java.io.IOException;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.ReentrantLock;
    
    /**
     * 多线程写文件,有3个线程1、2、3。线程1的功能就是输出t1,线程2的功能就是输出t2,以此类推.........,
     * 现在有三个文件file1,file2,file3。初始都为空,现要让三个文件呈如下格式:
     * file1:t1 t2 t3 t1 t2....
     * file2:t2 t3 t1 t2 t3....
     * file3:t3 t1 t2 t3 t1….
     *
     * @Author: huangyichun
     * @Date: 2021/3/14
     */
    public class CircleFileWriter2 {
    
    
        public CircleFileWriter2() throws IOException {
        }
    
        public static void main(String[] args) throws InterruptedException, IOException {
            CircleFileWriter2 fileWriter = new CircleFileWriter2();
            Thread thread1 = new Thread(fileWriter::printT1);
            Thread thread2 = new Thread(fileWriter::printT2);
            Thread thread3 = new Thread(fileWriter::printT3);
    
            thread1.start();
            Thread.sleep(100);
            thread2.start();
            Thread.sleep(100);
            thread3.start();
        }
    
        FileWriter fileWriter1 = new FileWriter("file1");
        FileWriter fileWriter2 = new FileWriter("file2");
        FileWriter fileWriter3 = new FileWriter("file3");
    
        private volatile int loop = 0;
    
        private volatile int state = 0;
    
        public void printT1() {
            print(1, "t1");
    
        }
    
        public void printT2() {
            print(2, "t2");
    
        }
    
        public void printT3() {
            print(3, "t3");
    
        }
    
        private void print(int threadNumber, String str) {
    
            for (int i = 0; i < 100; i++) {//打印100次
                while (true) {
                    if ((state % 3) + 1 == threadNumber) {
                        writeFile(getFile(threadNumber, loop), str);
                        if (threadNumber == 2) {
                            loop++;
                        }
                        state ++;
                        break;
                    }
                }
            }
        }
    
        /**
         * 写入文件
         **/
        private void writeFile(FileWriter fw, String s) {
            try {
                fw.append(s);
                fw.flush();
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
        /**
         * 判断在当前线程在第loop循环情况下写入哪个文件
         **/
        private FileWriter getFile(int threadNumber, int loop) {
    
            if (threadNumber == 1) {
                if (loop % 3 == 0) {
                    return fileWriter1;
                } else if (loop % 3 == 1) {
                    return fileWriter3;
                } else {
                    return fileWriter2;
                }
            } else if (threadNumber == 2) {
                if (loop % 3 == 0) {
                    return fileWriter2;
                } else if (loop % 3 == 1) {
                    return fileWriter1;
                } else {
                    return fileWriter3;
                }
            } else {
                if (loop % 3 == 0) {
                    return fileWriter3;
                } else if (loop % 3 == 1) {
                    return fileWriter2;
                } else {
                    return fileWriter1;
                }
            }
        }
    }
    
    

    两种方法都能实现循环打印,但是第二种方式没有加锁,对cpu的消耗较大,而且性能不高,执行时间也耗时较长。在打印100万的数据中,第一种方法耗时 8431ms, 第二种方法耗时 14406ms。所以面试时建议写第一种,第二种仅作参考。

    相关文章

      网友评论

          本文标题:3个线程循环打印到不同文件

          本文链接:https://www.haomeiwen.com/subject/esrqcltx.html