摘要：本人郵箱歡迎轉(zhuǎn)載轉(zhuǎn)載請(qǐng)注明網(wǎng)址代碼已經(jīng)全部托管有需要的同學(xué)自行下載引言之前我們講到都是多線程共享數(shù)據(jù)那么有沒有某一個(gè)共享的變量在這變量里面每個(gè)線程都能擁有自己的屬性呢比如說去旅店開房休息那么這個(gè)旅店就是一個(gè)共享的數(shù)據(jù)但是每個(gè)人開的房間是不一

本人郵箱: 
歡迎轉(zhuǎn)載,轉(zhuǎn)載請(qǐng)注明網(wǎng)址 http://blog.csdn.net/tianshi_kco
github: https://github.com/kco1989/kco
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之前我們講到都是多線程共享數(shù)據(jù).那么有沒有某一個(gè)共享的變量,在這變量里面,每個(gè)線程都能擁有自己的屬性呢?比如說,去旅店開房休息.那么這個(gè)旅店就是一個(gè)共享的數(shù)據(jù),但是每個(gè)人開的房間是不一樣的.這個(gè)要怎么做呢?這里我先試著寫一些

讓我們編寫一個(gè)程序,主線程開啟十個(gè)子線程,然后每個(gè)子線程都做1~100的累加,都是共享同一個(gè)List,每個(gè)線程占有固定的位置進(jìn)行累加計(jì)算

public class TestMain {

    public static class CalcRunnable implements Runnable{
        List list ;
        int index;
        public CalcRunnable(List list, int index) {
            this.list = list;
            this.index = index;
        }

        @Override
        public void run() {
            for (int i = 1; i <= 100; i++){
                list.set(index, list.get(index) + i);
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        List list = new ArrayList<>();
        List threads = new ArrayList<>();
        for (int i = 0; i < 10; i ++){
            list.add(0);
            threads.add(new Thread(new CalcRunnable(list,i)));
        }
        for (Thread thread : threads){
            thread.start();
        }

        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list);
    }
}

輸出結(jié)果為

[5050, 5050, 5050, 5050, 5050, 5050, 5050, 5050, 5050, 5050]

這里每個(gè)線程都共享了list,但是也沒有使用關(guān)鍵字synchronized進(jìn)行同步,為什么結(jié)果還是正確的呢?原因很簡單,那就是每個(gè)線程都使用固定的索引進(jìn)行計(jì)算,互不干擾.所以結(jié)果不會(huì)受其他線程影響的.

現(xiàn)在把上面的例子中的List改為Map來做累加

public class TestMain1 {

    public static class CalcRunnable implements Runnable{
        Map map;
        public CalcRunnable(Map map) {
            this.map = map;
        }

        @Override
        public void run() {
            Thread self = Thread.currentThread();
            for (int i = 1; i <= 100; i++){
                map.put(self, map.get(self) + i);
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        Map map = new HashMap<>();
        List threads = new ArrayList<>();
        for (int i = 0; i < 10; i ++){
            Thread thread = new Thread(new CalcRunnable(map));
            map.put(thread,0);
            threads.add(thread);
        }
        for (Thread thread : threads){
            thread.start();
        }

        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(map);
    }
}

運(yùn)行結(jié)果

{Thread[Thread-1,5,]=5050, Thread[Thread-3,5,]=5050, Thread[Thread-6,5,]=5050, Thread[Thread-0,5,]=5050, Thread[Thread-8,5,]=5050, Thread[Thread-5,5,]=5050, Thread[Thread-7,5,]=5050, Thread[Thread-2,5,]=5050, Thread[Thread-4,5,]=5050, Thread[Thread-9,5,]=5050}

結(jié)果也是完全正確,道理跟上面的例子一樣,每個(gè)線程雖然共用同一個(gè)數(shù)據(jù)map,但實(shí)際上每個(gè)線程都是用map中特定的那個(gè)元素

其實(shí)用map還有一種更簡單的方式,那就是今天要講的ThreadLocal,不廢話,看例子

public class TestMain3 {

    public static class CalcRunnable implements Runnable{
        ThreadLocal threadLocal;
        public CalcRunnable(ThreadLocal threadLocal) {
            this.threadLocal = threadLocal;
        }

        @Override
        public void run() {
            threadLocal.set(0);//設(shè)置默認(rèn)值
            for (int i = 1; i <= 100; i++){
                threadLocal.set(threadLocal.get() + i);
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println(Thread.currentThread().getName() + " 的計(jì)算結(jié)果為: " + threadLocal.get());
        }
    }

    public static void main(String[] args) {
        ThreadLocal threadLocal = new ThreadLocal<>();
        List threads = new ArrayList<>();
        for (int i = 0; i < 10; i ++){
            Thread thread = new Thread(new CalcRunnable(threadLocal));
            threads.add(thread);
        }
        for (Thread thread : threads){
            thread.start();
        }
    }
}

運(yùn)行結(jié)果

Thread-0 的計(jì)算結(jié)果為: 5050
Thread-5 的計(jì)算結(jié)果為: 5050
Thread-1 的計(jì)算結(jié)果為: 5050
Thread-4 的計(jì)算結(jié)果為: 5050
Thread-7 的計(jì)算結(jié)果為: 5050
Thread-6 的計(jì)算結(jié)果為: 5050
Thread-3 的計(jì)算結(jié)果為: 5050
Thread-2 的計(jì)算結(jié)果為: 5050
Thread-8 的計(jì)算結(jié)果為: 5050
Thread-9 的計(jì)算結(jié)果為: 5050

原理,其實(shí)就是跟例子2的Map,在ThreadLocal中實(shí)現(xiàn)了一個(gè)ThreadLocalMap內(nèi)部類,然后在調(diào)用ThreadLocal.get和ThreadLocal.set的時(shí)候,其實(shí)要獲取當(dāng)前線程去做相應(yīng)的操作.

如果以后大家想讓多線程共享一個(gè)變量,但又不想互相影響的時(shí)候,那么首選ThreadLocal.因?yàn)閷?duì)比上面三個(gè)例子,發(fā)現(xiàn)使用ThreadLocal是最簡單的,而且不容易出錯(cuò)的.比如在web開發(fā)中,可以在多線程中存放session,或者數(shù)據(jù)庫連接池的時(shí)候,也可以使用ThreadLocal在存放數(shù)據(jù)庫連接.

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