《玩轉(zhuǎn)Java并發(fā)工具、精通JUC、成為并發(fā)多面手》構(gòu)建高性能緩存

2023-06-27 09:29 作者:懶時(shí)小窩 0人讀過 | 我要投稿

引言

《玩轉(zhuǎn)Java并發(fā)工具、精通JUC、成為并發(fā)多面手》構(gòu)建高性能緩存這部分的個(gè)人筆記。本節(jié)為單純的實(shí)戰(zhàn)，主要是把之前學(xué)習(xí)并發(fā)編程的知識(shí)點(diǎn)串起來。

挺有意思的一個(gè)demo，可以快速了解到一些并發(fā)編程的時(shí)候需要注意的一些問題。

代碼

一個(gè)簡單的小demo，可以直接拷貝下面的包所屬的各個(gè)版本代碼到自己的項(xiàng)目閱讀即可：https://gitee.com/lazyTimes/interview/tree/master/src/main/java/com/zxd/interview/mycache

一、構(gòu)建步驟

1. 使用最簡單的HashMap

最基礎(chǔ)的版本實(shí)現(xiàn)非常簡單，這是我們通常會(huì)想到的應(yīng)用緩存實(shí)現(xiàn)方案，這里使用了Lombok的@Slf4j注解進(jìn)行日志打印。

整個(gè)邏輯非常簡單，首先通過計(jì)算方法匹配緩存，如果有就取緩存內(nèi)容，否則就調(diào)用計(jì)算方法然后把結(jié)果緩存到HashMap當(dāng)中。

/**?? ?*?初版高速緩存實(shí)現(xiàn)?? ?*?1.?使用簡單的HashMap?? ?*?2.?在高速緩存中進(jìn)行計(jì)算?? ?*?? ?*?暴露問題：?? ?*?1.?復(fù)用性能查?? ?*?2.?HashMap線程不安全，有可能重復(fù)判斷?? ?*/?? @Slf4j?? public?class?MyCacheVersion1?{?? ?? ????private?final?Map<String,?Integer>?cache?=?new?HashMap<>();?? ?? ????/**?? ?????*?根據(jù)參數(shù)計(jì)算結(jié)果，此參數(shù)對(duì)于同一個(gè)參數(shù)會(huì)計(jì)算同樣的結(jié)果?? ?????*?1.?如果緩存存在結(jié)果，直接返回?? ?????*?2.?如果緩存不存在，則需要計(jì)算添加到map之后才返回?? ?????*?@param?userId?? ?????*?@return?? ?????*/?? ????public?Integer?compute(String?userId)?throws?InterruptedException?{?? ????????if(cache.containsKey(userId)){?? ????????????log.info("cached?=>?{}",?userId);?? ????????????return?cache.get(userId);?? ????????}?? ????????log.info("doCompute?=>?{}",?userId);?? ????????Integer?result?=?doCompute(userId);?? ????????//不存在緩存就加入?? ????????cache.put(userId,?result);?? ????????return?result;?? ????}?? ?? ????private?Integer?doCompute(String?userId)?throws?InterruptedException?{?? ????????TimeUnit.SECONDS.sleep(5);?? ????????return?Integer.parseInt(userId);?? ????}?? ?? ?? }

初版存在較多的問題，比較顯著的問題是compute這個(gè)方法在多線程的環(huán)境是不安全的，我們可以編寫測(cè)試程序驗(yàn)證。

在測(cè)試程序中，我們使用線程池構(gòu)建100個(gè)線程處理1000個(gè)計(jì)算任務(wù)。從打印結(jié)果中我們隨機(jī)抽取其中一個(gè)數(shù)字很容易出現(xiàn)計(jì)算兩次的情況，比如下面的情況：

?? /**?? ?*?對(duì)應(yīng)當(dāng)前版本的測(cè)試程序?? ?*?1.?HashMap線程不安全?? ?*?2.?此程序驗(yàn)證線程安全問題?? ?*/?? @Slf4j?? public?class?Test?{?? ?? ????public?static?void?main(String[]?args)?throws?InterruptedException?{?? ????????ExecutorService?executorService?=?Executors.newFixedThreadPool(100);?? ????????MyCacheVersion1?objectObjectMyCacheVersion1?=?new?MyCacheVersion1();?? ????????Random?random?=?new?Random(100);?? ????????for?(int?i?=?0;?i?<?1000;?i++)?{?? ????????????executorService.execute(()?->?{?? ????????????????int?randomInt?=?random.nextInt(100);?? ????????????????try?{?? ????????????????????Integer?user?=?objectObjectMyCacheVersion1.compute(String.valueOf(randomInt));?? ????????????????}?catch?(InterruptedException?e)?{?? ????????????????????throw?new?RuntimeException(e);?? ????????????????}?? ?? ????????????});?? ????????}?? ????????executorService.shutdown();?? ????}/**運(yùn)行結(jié)果 ?????測(cè)試結(jié)果：可以看到高并發(fā)的情況下非常有可能出現(xiàn)重復(fù)計(jì)算然后cache的情況?? ?????10:56:41.437?[pool-1-thread-53]?INFO??c.z.i.m.version1.MyCacheVersion1?-?doCompute?=>?59?? ?????10:56:41.447?[pool-1-thread-97]?INFO??c.z.i.m.version1.MyCacheVersion1?-?doCompute?=>?59????? ?????*/ }

可以發(fā)現(xiàn)doCompute => 59 算了多次。

處理線程不安全問題

線程不安全問題最簡單的處理方式就是方法串行：

public?synchronized?Integer?compute(String?userId)?throws?InterruptedException

如果加入synchronized，則整個(gè)線程的處理會(huì)串行執(zhí)行，但是效率極低。

/**運(yùn)行結(jié)果?? ?串行之后執(zhí)行效率極低，基本無法使用? ?11:14:15.851?[pool-1-thread-1]?INFO??c.z.i.m.version1.MyCacheVersion1?-?doCompute?=>?15?? ?11:14:20.862?[pool-1-thread-100]?INFO??c.z.i.m.version1.MyCacheVersion1?-?doCompute?=>?52?11:14:25.874?[pool-1-thread-99]?INFO??c.z.i.m.version1.MyCacheVersion1?-?doCompute?=>?55? ?*/

2. 分析HashMap實(shí)現(xiàn)的問題

簡單分析HashMap的緩存實(shí)現(xiàn)，主要的問題如下：

高并發(fā)訪問重復(fù)計(jì)算性能問題
復(fù)用性能較差的問題

3. 裝飾模式抽象計(jì)算業(yè)務(wù)

我們先解決復(fù)用性能較差的問題,，這里需要使用裝飾模式進(jìn)行改寫。首先定義ComputeAble<A, V>接口，這個(gè)接口定義了抽象計(jì)算行為。

/**?? ?*?可計(jì)算接口?? ?*?裝飾接口?? ?*/?? public?interface?ComputeAble<A,?V>{?? ?? ????/**?? ?????*?根據(jù)指定參數(shù)?A?進(jìn)行計(jì)算，計(jì)算結(jié)果為?V?? ?????*?@description?根據(jù)指定參數(shù)?A?進(jìn)行計(jì)算，計(jì)算結(jié)果為?V?? ?????*?@param?arg?泛型參數(shù)?? ?????*?@return?V?返回計(jì)算后結(jié)果?? ?????*?@author?xander?? ?????*?@date?2023/6/15?15:42?? ?????*/???? ?????V?doCompute(A?arg)?throws?Exception;?? }

定義一個(gè)實(shí)現(xiàn)類實(shí)現(xiàn)計(jì)算接口。

/**?? ?*?裝飾模式改寫接口?? ?*/?? public?class?ExpensiveCompute?implements?ComputeAble<String,?Integer>{?? ????@Override?? ????public?Integer?doCompute(String?arg)?throws?InterruptedException?{?? ????????TimeUnit.SECONDS.sleep(5); ????????return?Integer.parseInt(arg);?? ????}?? }

第二個(gè)版本的緩存實(shí)現(xiàn)區(qū)別是使用了裝飾模式封裝計(jì)算方法，其他方法暫時(shí)不做調(diào)整。

/**?? ?*?第二版，使用裝飾模式進(jìn)行改造?? ?*?synchronized?同步加鎖?? ?*?@author?? ?*?@version?v1.0.0?? ?*?@Package?:?version2?? ?*?@Description?:?使用裝飾模式進(jìn)行改造?? ?*?@Create?on?:?2023/6/15?16:29?? ?**/@Slf4j?? public?class?MyCacheVersion2?{?? ?? ????/**?? ?????*?緩存?? ?????*/?? ????private?final?Map<String,?Integer>?cache?=?new?HashMap<>();?? ????/**?? ?????*?計(jì)算方法實(shí)現(xiàn)對(duì)象?? ?????*/?? ????private?final?static?ComputeAble<String,?Integer>?COMPUTE?=?new?ExpensiveCompute();?? ?? ????public?synchronized?Integer?compute(String?userId)?throws?Exception?{?? ????????if(cache.containsKey(userId)){?? ????????????log.info("cached?=>?{}",?userId);?? ????????????return?cache.get(userId);?? ????????}?? ????????log.info("doCompute?=>?{}",?userId);?? ????????Integer?result?=?doCompute(userId);?? ????????//?不存在緩存就加入?? ????????cache.put(userId,?result);?? ????????return?result;?? ????}?? ?? ????/**?? ?????*?計(jì)算方法由具體的類實(shí)現(xiàn)封裝?? ?????*?@param?userId?? ?????*?@return?? ?????*?@throws?InterruptedException?? ?????*/ ?????private?Integer?doCompute(String?userId)?throws?Exception?{?? ????????return?COMPUTE.doCompute(userId);?? ????}?? }

通過上面的代碼了解到，MyCacheVersion2 緩存實(shí)現(xiàn)類的具體計(jì)算邏輯抽象到具體的實(shí)現(xiàn)類當(dāng)中，如果想要切換新的邏輯，可以改寫COMPUTE的實(shí)現(xiàn)類。

4. 使用Future改寫計(jì)算實(shí)現(xiàn)接口處理重復(fù)計(jì)算問題

我們簡單分析HashMap的緩存實(shí)現(xiàn)，主要問題如下：

高并發(fā)訪問重復(fù)計(jì)算性能問題
復(fù)用性能較差的問題，通過裝飾模式改寫。

復(fù)用較差的問題處理了，下面介紹高并發(fā)訪問重復(fù)計(jì)算問題處理辦法，我們一步步介紹改寫過程。為了方便理解這里暫時(shí)先用具體類型代替泛型。

首先把Map的value存儲(chǔ)改為存儲(chǔ)Future< V > 結(jié)果，并且把HashMap改為線程安全的ConcurrentHashMap。

private?final?Map<String,?Future<Integer>>?concurrentHashMap?=?new?ConcurrentHashMap<>();

構(gòu)建 FutureTask 對(duì)象，這里使用 Lambda 表達(dá)式直接調(diào)用 doCompute 方法。

FutureTask<Integer>?future?=?new?FutureTask<>(()?->?doCompute(userId));

在計(jì)算函數(shù)中，大致的邏輯并沒有改變，但是需要注意下面的細(xì)節(jié)：

future.get() 在獲取到結(jié)果之前會(huì)進(jìn)行阻塞。
ConcurrentHashMap 在類似如果不存在就加入的復(fù)合操作情況下需要考慮重復(fù)設(shè)置緩存的問題。
putIfAbsent 可以做一些復(fù)合操作，如果設(shè)置緩存失敗，說明有其他線程做過同樣的操作，此時(shí)就可以重新操作一次獲取結(jié)果即可。
putIfAbsent不成功為什么不直接獲取結(jié)果，而是要再計(jì)算一次，這是為了防止緩存剛好獲取獲取到一個(gè)null的值。

?? /**?? ?*?第三個(gè)版本?? ?*?1.?優(yōu)化多線程訪問重復(fù)計(jì)算問題?? ?*?? ?*?*?@author?? ?*?@version?v1.0.0?? ?*?@Package?:?version3?? ?*?@Description?:?第三個(gè)版本?? ?*?@Create?on?:?2023/6/15?16:47?? ?**/@Slf4j?? public?class?MyCacheVersion3?{?? ????/**?? ?????*?改造，并發(fā)不安全集合改為并發(fā)安全集合?? ?????*?value?存儲(chǔ)為?future?的值?? ?????*/?? ????private?final?Map<String,?Future<Integer>>?concurrentHashMap?=?new?ConcurrentHashMap<>();?? ?? ????/**?? ?????*?計(jì)算實(shí)現(xiàn)類?? ?????*/?? ????private?static?final?ComputeAble<String,?Integer>?COMPUTEABLE?=?new?ExpensiveCompute();?? ?? ????/**?? ?????*?先使用具體類型實(shí)現(xiàn)，后續(xù)改為使用泛型實(shí)現(xiàn)?? ?????*?1.?使用?FutureTask?對(duì)于要計(jì)算的值進(jìn)行封裝，根據(jù)?FutureTask?特性，獲取到結(jié)果之前單個(gè)線程會(huì)一直等待?? ?????*?2.?由于計(jì)算方法變動(dòng)，所有的代碼需要調(diào)整?? ?????*?3.?concurrentHashMap.get()?在?if?判斷的時(shí)候依然存在非原子行為，所以在設(shè)置的時(shí)候使用?putIfAbsent?原子操作?? ?????*?? ?????*?@param?userId?? ?????*?@return?? ?????*?@throws?InterruptedException?? ?????*?@throws?ExecutionException?? ?????*/????public?Integer?compute(String?userId)?throws?InterruptedException,?ExecutionException?{?? ????????Future<Integer>?result?=?concurrentHashMap.get(userId);?? ????????//?如果獲取不到內(nèi)容，說明不在緩存當(dāng)中?? ????????if(Objects.isNull(result)){?? ????????????//?此時(shí)利用callAble?線程任務(wù)指定任務(wù)獲取，在獲取到結(jié)果之前線程會(huì)阻塞?? ????????????FutureTask<Integer>?future?=?new?FutureTask<>(()?->?doCompute(userId));?? ????????????//把新的future覆蓋之前獲取的future?? ????????????result?=?future;?? ????????????//?執(zhí)行?? ????????????future.run();?? ????????????log.info("FutureTask?調(diào)用計(jì)算函數(shù)");?? ????????????result?=?concurrentHashMap.putIfAbsent(userId,?result);?? ????????????//?如果返回null，說明這個(gè)記錄被添加過了?? ????????????if(Objects.isNull(result)){?? ????????????????log.info("其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算");?? ????????????????//?說明其他線程已經(jīng)設(shè)置過值，這里重新跑一次計(jì)算方法即可直接獲取?? ????????????????result?=?future;?? ????????????????//?再重新跑一次?? ????????????????future.run();?? ????????????????return?result.get();?? ????????????}else{?? ????????????????return?result.get();?? ????????????}?? ????????}?? ????????return?result.get();?? ????}?? ?? ????/**?? ?????*?計(jì)算方法由具體的類實(shí)現(xiàn)封裝?? ?????*?@param?userId?? ?????*?@return?? ?????*?@throws?InterruptedException?? ?????*/????private?Integer?doCompute(String?userId)?throws?Exception?{?? ????????return?COMPUTEABLE.doCompute(userId);?? ????}?? }

5. 泛型接口改寫

有了上面的實(shí)現(xiàn)基礎(chǔ)，改為為泛型就容易很多了，泛型的寫法實(shí)際上就是把之前的具體類型轉(zhuǎn)為泛型即可。

這里的代碼可能不完整，建議把開頭部分的倉庫代碼放到本地驗(yàn)證。

/**?? ?*?第四個(gè)版本，方法改為泛型實(shí)現(xiàn)?? ?*?@author?? ?*?@version?v1.0.0?? ?*?@Package?:?version3?? ?*?@Description?:?第三個(gè)版本?? ?*?@Create?on?:?2023/6/15?16:47?? ?**/@Slf4j?? public?class?MyCacheVersion4<A,?V>?{?? ????/**?? ?????*?改造，并發(fā)不安全集合改為并發(fā)安全集合?? ?????*?value?存儲(chǔ)為?future的值?? ?????*/?? ????private?final?Map<A,?Future<V>>?concurrentHashMap?=?new?ConcurrentHashMap<>();?? ?? ????private?final?ComputeAble?computeAble?=?new?ExpensiveCompute<>();?? ?? ????/**?? ?????*?先使用具體類型實(shí)現(xiàn)，后續(xù)改為使用泛型實(shí)現(xiàn)?? ?????*?1.?使用?FutureTask?對(duì)于要計(jì)算的值進(jìn)行封裝，根據(jù)?FutureTask?特性，獲取到結(jié)果之前單個(gè)線程會(huì)一直等待?? ?????*?2.?由于計(jì)算方法變動(dòng)，所有的代碼需要調(diào)整?? ?????*?3.?concurrentHashMap.get()?在?if?判斷的時(shí)候依然存在非原子行為，所以在設(shè)置的時(shí)候使用?putIfAbsent?原子操作?? ?????*?4.?重構(gòu)，使用泛型參數(shù)?? ?????*?@param?arg?? ?????*?@return?? ?????*?@throws?InterruptedException?? ?????*?@throws?ExecutionException?? ?????*/ ?????public?V?compute(A?arg)?throws?InterruptedException,?ExecutionException?{?? ????????Future<V>?result?=?concurrentHashMap.get(arg);?? ????????//?如果獲取不到內(nèi)容，說明不在緩存當(dāng)中?? ????????if(Objects.isNull(result)){?? ????????????//?此時(shí)利用callAble?線程任務(wù)指定任務(wù)獲取，在獲取到結(jié)果之前線程會(huì)阻塞?? ????????????FutureTask<V>?future?=?new?FutureTask<>(new?Callable<V>()?{?? ????????????????@Override?? ????????????????@SuppressWarnings("unchecked")?? ????????????????public?V?call()?throws?Exception?{?? ????????????????????return?(V)?computeAble.doCompute(arg);?? ????????????????}?? ????????????});?? ????????????//把新的future覆蓋之前獲取的future?? ????????????result?=?future;?? ????????????//?執(zhí)行?? ????????????future.run();?? ????????????log.info("FutureTask?調(diào)用計(jì)算函數(shù)");?? ????????????result?=?concurrentHashMap.putIfAbsent(arg,?result);?? ????????????//?如果返回null，說明這個(gè)記錄被添加過了?? ????????????if(Objects.isNull(result)){?? ????????????????log.info("其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算");?? ????????????????//?說明其他線程已經(jīng)設(shè)置過值，這里重新跑一次計(jì)算方法即可直接獲取?? ????????????????result?=?future;?? ????????????????//?再重新跑一次?? ????????????????future.run();?? ????????????????return?result.get();?? ????????????}else{?? ????????????????return?result.get();?? ????????????}?? ????????}?? ????????return?result.get();?? ????}?? }

6. 可能失敗的計(jì)算導(dǎo)致緩存污染問題處理

觀察另一個(gè)計(jì)算實(shí)現(xiàn)，當(dāng)我們的使用下面的方式會(huì)有什么樣的效果？

/**?? ?*??可能會(huì)出現(xiàn)失敗的計(jì)算方法?? ?*?@author?Xander?? ?*?@version?v1.0.0?? ?*?@Package?:?compute?? ?*?@Description?:?可能會(huì)出現(xiàn)失敗的計(jì)算方法?? ?*?@Create?on?:?2023/6/19?10:40?? ?**/public?class?MayFailCompute?implements?ComputeAble<String,?Integer>{?? ?? ????/**?? ?????*?觸發(fā)失敗閾值?? ?????*/?? ????private?static?final?int?FAILURE_THRESHOLD?=?50;?? ?? ????/**?? ?????*?隨機(jī)數(shù)生成器?? ?????*/?? ????private?static?final?Random?RANDOM?=?new?Random(100);?? ?? ????/**?? ?????*?有可能會(huì)出現(xiàn)失敗的計(jì)算方法?? ?????*?@description?有可能會(huì)出現(xiàn)失敗的計(jì)算方法?? ?????*?@param?arg?? ?????*?@return?java.lang.Integer?? ?????*?@author?xander?? ?????*?@date?2023/6/19?10:41?? ?????*/????@Override?? ????public?Integer?doCompute(String?arg)?throws?Exception?{?? ????????if(RANDOM.nextInt()?<?FAILURE_THRESHOLD){?? ????????????throw?new?Exception("自定義異常");?? ????????}?? ????????TimeUnit.MILLISECONDS.sleep(5);?? ????????return?Integer.parseInt(arg);?? ????}?? }

由于一開始我們就使用裝飾模式改寫過代碼，所以要替換實(shí)現(xiàn)類非常簡單：

private?final?ComputeAble?computeAble?=?new?MayFailCompute();

測(cè)試的結(jié)果毫不意外的出現(xiàn)大量的失敗。這樣結(jié)果不符合預(yù)期，雖然 50%的失敗率相當(dāng)高，但實(shí)際上更多的是從緩存中獲取的結(jié)果就是異常信息，這種情況就是緩存污染問題。

為了解決緩存污染問題，我們需要在try/catch中對(duì)于不同的情況進(jìn)行不同的處理。在之前計(jì)算處理邏輯中一共會(huì)出現(xiàn)下面三種情況：

CancellationException：線程被取消拋出的異常。
InterruptedException：線程被中斷時(shí)候拋出的異常。
ExecutionException：試圖檢索一個(gè)因拋出異常而中止的任務(wù)的結(jié)果時(shí)拋出的異常。

對(duì)于不同的異常要對(duì)應(yīng)不同的處理態(tài)度：

CancellationException 和 InterruptedException 基本都是人為操作，這時(shí)候應(yīng)該立即終止任務(wù)。
根據(jù)方法邏輯我們知道方法是有可能計(jì)算成功的，只不過需要多重試幾次。
while(true) 的加入可以讓出錯(cuò)之后自動(dòng)重新進(jìn)行計(jì)算直到成功為止，但是如果是人為取消，就需要拋出異常并且手動(dòng)結(jié)束任務(wù)。

我們把上面的處理思路轉(zhuǎn)化為代碼，相關(guān)注釋已經(jīng)加入，可以看下面的結(jié)果：

?? /**?? ?*?<pre>?? ?*?第五個(gè)版本，當(dāng)碰到會(huì)拋出異常的計(jì)算方法的情況這時(shí)候應(yīng)該重新計(jì)算?? ?*?對(duì)于不同的異常，也要對(duì)應(yīng)不同的處理態(tài)度：?? ?*?? ?*?-?CancellationException?和?InterruptedException?基本都是人為操作，這時(shí)候應(yīng)該立即終止任務(wù)。?? ?*?-?根據(jù)方法邏輯，我們可以知道方法是有可能計(jì)算成功的，只不過需要多重試幾次。?? ?*?-?while(true)?的加入可以讓出錯(cuò)之后自動(dòng)重新進(jìn)行計(jì)算直到成功為止，但是如果是人為取消，就需要拋出異常并且結(jié)束。?? ?*?</pre>?? ?*?@author?? ?*?@version?v1.0.0?? ?*?@Package?:?version3?? ?*?@Description?:?第五個(gè)版本?? ?*?@Create?on?:?2023/6/15?16:47?? ?**/@Slf4j?? public?class?MyCacheVersion5<A,?V>?{?? ????/**?? ?????*?改造，并發(fā)不安全集合改為并發(fā)安全集合?? ?????*?value?存儲(chǔ)為?future的值?? ?????*/?? ????private?final?Map<A,?Future<V>>?concurrentHashMap?=?new?ConcurrentHashMap<>();?? ?? ????private?final?ComputeAble?computeAble?=?new?MayFailCompute();?? ?? ???public?V?compute(A?arg)?{?? ????????return?doCompute(arg);?? ????}?? ?? ????private?V?doCompute(A?arg)?{?? ????????//?對(duì)于重復(fù)計(jì)算進(jìn)行處理?? ????????while?(true)?{?? ????????????Future<V>?result?=?concurrentHashMap.get(arg);?? ????????????try?{?? ????????????????//?如果獲取不到內(nèi)容，說明不在緩存當(dāng)中?? ????????????????if?(Objects.isNull(result))?{?? ????????????????????//?此時(shí)利用callAble?線程任務(wù)指定任務(wù)獲取，在獲取到結(jié)果之前線程會(huì)阻塞?? ????????????????????FutureTask<V>?future?=?new?FutureTask<>(new?Callable<V>()?{?? ????????????????????????@Override?? ????????????????????????@SuppressWarnings("unchecked")?? ????????????????????????public?V?call()?throws?Exception?{?? ????????????????????????????return?(V)?computeAble.doCompute(arg);?? ?? ????????????????????????}?? ????????????????????});?? ????????????????????//把新的future覆蓋之前獲取的future?? ????????????????????result?=?future;?? ????????????????????//?執(zhí)行?? ????????????????????future.run();?? ????????????????????System.out.println("FutureTask?調(diào)用計(jì)算函數(shù)");?? ????????????????????result?=?concurrentHashMap.putIfAbsent(arg,?result);?? ????????????????????//?如果返回null，說明這個(gè)記錄被添加過了?? ????????????????????if?(Objects.isNull(result))?{?? ????????????????????????System.out.println("其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算");?? ????????????????????????//?說明其他線程已經(jīng)設(shè)置過值，這里重新跑一次計(jì)算方法即可直接獲取?? ????????????????????????result?=?future;?? ????????????????????????//?再重新跑一次?? ????????????????????????future.run();?? ????????????????????????return?result.get();?? ????????????????????}?else?{?? ????????????????????????return?result.get();?? ????????????????????}?? ????????????????}?? ????????????????return?result.get();?? ????????????}?catch?(CancellationException?cancellationException)?{?? ????????????????log.warn("CancellationException?result?=>?{}",?result);?? ????????????????//?線程在執(zhí)行過程當(dāng)中有可能被取消?? ????????????????//?被取消的時(shí)候不管如何處理，首先需要先從緩存中移除掉污染緩存?? ????????????????concurrentHashMap.remove(arg);?? ????????????????throw?new?RuntimeException(cancellationException);?? ????????????}?catch?(InterruptedException?e)?{?? ????????????????log.warn("InterruptedException?result?=>?{}",?result);?? ????????????????//?線程被中斷的異常處理?? ????????????????concurrentHashMap.remove(arg);?? ????????????????throw?new?RuntimeException(e);?? ????????????}?catch?(ExecutionException?e)?{?? //????????????log.warn("ExecutionException?result?=>?{}",?result);?? ????????????????log.info("移除緩存Key?=>?{}，重新計(jì)算",?arg);?? ????????????????concurrentHashMap.remove(arg);?? ????????????????//?不會(huì)拋出異常，而是重新在下一次循環(huán)中計(jì)算?? //????????????throw?new?RuntimeException(e);?? ????????????/*????????????打印結(jié)果如下：?? ????????????FutureTask?調(diào)用計(jì)算函數(shù)?? ????????????FutureTask?調(diào)用計(jì)算函數(shù)?? ????????????result?=>?65????????????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ????????????result?=>?33????????????result?=>?65????????????result?=>?26????????????15:59:56.584?[pool-1-thread-30]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?75，重新計(jì)算?? ????????????result?=>?75????????????15:59:56.584?[pool-1-thread-3]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?35，重新計(jì)算?? ????????????15:59:56.584?[pool-1-thread-42]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?67，重新計(jì)算?? ????????????15:59:56.584?[pool-1-thread-36]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?75，重新計(jì)算?? ????????????15:59:56.584?[pool-1-thread-90]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?40，重新計(jì)算?? ????????????15:59:56.585?[pool-1-thread-31]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?13，重新計(jì)算?? ????????????15:59:56.586?[pool-1-thread-94]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?60，重新計(jì)算?? ????????????Disconnected?from?the?target?VM,?address:?'127.0.0.1:11054',?transport:?'socket'?? ????????????Process?finished?with?exit?code?0?? ????????????*?*/ ??}?catch?(Exception?e)?{?? ????????????????log.warn("Exception?result?=>?{}",?result);?? ????????????????concurrentHashMap.remove(arg);?? ????????????????//?無法處理的未知異常，直接拋出運(yùn)行時(shí)異常不做任何處理。?? ????????????????throw?new?RuntimeException(e);?? ????????????}?? ?? ????????}?? ????}?? }

最后是測(cè)試部分。

?? /**?? ?*?可能失敗的計(jì)算導(dǎo)致緩存污染問題處理?? ?*?1.?解決緩存污染問題。?? ?*?2.?異常情況嘗試一直重復(fù)計(jì)算。?? ?*?? ?*?@author?Xander?? ?*?@version?v1.0.0?? ?*?@Package?:?version5?? ?*?@Description?:?? ?*?@Create?on?:?2023/6/19?10:49?? ?**/public?class?Test?{?? ?? ????public?static?void?main(String[]?args)?throws?InterruptedException?{?? ????????ExecutorService?executorService?=?Executors.newFixedThreadPool(100);?? ????????MyCacheVersion5<String,?Integer>?myCacheVersion5?=?new?MyCacheVersion5<>();?? ????????Random?random?=?new?Random(100);?? ????????for?(int?i?=?0;?i?<?1000;?i++)?{?? ????????????executorService.submit(()?->?{?? ????????????????int?randomInt?=?random.nextInt(100);?? ?? ????????????????Integer?user?=?myCacheVersion5.compute(String.valueOf(randomInt));?? ????????????????System.out.println("result?=>?"?+?user);?? ?? ?? ????????????});?? ????????}?? ????????executorService.shutdown();?? ????}/**?? ?????運(yùn)行結(jié)果：?? ?????短期內(nèi)會(huì)有海量異常，這不符合預(yù)期情況。根本原因是緩存不存在過期時(shí)間，會(huì)存在無效的內(nèi)容緩存計(jì)算?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????java.util.concurrent.ExecutionException:?java.lang.Exception:?自定義異常?? ?????at?java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)?? ?????at?java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)?????at?interview/version5.MyCacheVersion5.compute(MyCacheVersion5.java:63)?????at?interview/version5.Test.lambda$main$0(Test.java:30)?????at?java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)?????at?java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)?????at?java.base/java.util.concurrent.FutureTask.run(FutureTask.java)?????at?java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)?????at?java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)?????at?java.base/java.lang.Thread.run(Thread.java:829)?????Caused?by:?java.lang.Exception:?自定義異常?? ?????at?interview/compute.MayFailCompute.doCompute(MayFailCompute.java:37)?? ?????at?interview/compute.MayFailCompute.doCompute(MayFailCompute.java:14)?????at?interview/version5.MyCacheVersion5$1.call(MyCacheVersion5.java:47)?????at?java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)?????at?java.base/java.util.concurrent.FutureTask.run(FutureTask.java)?????at?interview/version5.MyCacheVersion5.compute(MyCacheVersion5.java:53)?????...?7?more?????java.util.concurrent.ExecutionException:?java.lang.Exception:?自定義異常?? ?????at?java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)?? ?????at?java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)?????at?interview/version5.MyCacheVersion5.compute(MyCacheVersion5.java:63)?????at?interview/version5.Test.lambda$main$0(Test.java:30)?????at?java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)?????at?java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)?????at?java.base/java.util.concurrent.FutureTask.run(FutureTask.java)?????at?java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)?????at?java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)?????at?java.base/java.lang.Thread.run(Thread.java:829)?????Caused?by:?java.lang.Exception:?自定義異常?? ?????at?interview/compute.MayFailCompute.doCompute(MayFailCompute.java:37)?? ?????at?interview/compute.MayFailCompute.doCompute(MayFailCompute.java:14)?????at?interview/version5.MyCacheVersion5$1.call(MyCacheVersion5.java:47)?????at?java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)?????at?java.base/java.util.concurrent.FutureTask.run(FutureTask.java)?????at?interview/version5.MyCacheVersion5.compute(MyCacheVersion5.java:53)?????...?7?more?????java.util.concurrent.ExecutionException:?java.lang.Exception:?自定義異常?? ?????at?java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)?? ?????at?java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)?????at?interview/version5.MyCacheVersion5.compute(MyCacheVersion5.java:63)?????at?interview/version5.Test.lambda$main$0(Test.java:30)?????at?java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)?????at?java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)?????at?java.base/java.util.concurrent.FutureTask.run(FutureTask.java)?????at?java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)?????at?java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)?????at?java.base/java.lang.Thread.run(Thread.java:829)?????Caused?by:?java.lang.Exception:?自定義異常?? ?????at?interview/compute.MayFailCompute.doCompute(MayFailCompute.java:37)?? ?????at?interview/compute.MayFailCompute.doCompute(MayFailCompute.java:14)?????at?interview/version5.MyCacheVersion5$1.call(MyCacheVersion5.java:47)?????at?java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)?????at?java.base/java.util.concurrent.FutureTask.run(FutureTask.java)?????at?interview/version5.MyCacheVersion5.compute(MyCacheVersion5.java:53)?????...?7?more?? ?????經(jīng)過修復(fù)之后：?? ?????16:09:07.705?[pool-1-thread-83]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?9，重新計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????result?=>?37?? ?????16:09:07.705?[pool-1-thread-84]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?84，重新計(jì)算?? ?????16:09:07.705?[pool-1-thread-66]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?84，重新計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????16:09:07.705?[pool-1-thread-91]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?9，重新計(jì)算?? ?????16:09:07.706?[pool-1-thread-2]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?84，重新計(jì)算?? ?????16:09:07.706?[pool-1-thread-3]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?40，重新計(jì)算?? ?????16:09:07.706?[pool-1-thread-5]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?84，重新計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????16:09:07.706?[pool-1-thread-91]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?9，重新計(jì)算?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????16:09:07.706?[pool-1-thread-3]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?40，重新計(jì)算?? ?????16:09:07.706?[pool-1-thread-5]?INFO?version5.MyCacheVersion5?-?移除緩存Key?=>?84，重新計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????FutureTask?調(diào)用計(jì)算函數(shù)?? ?????*/?? }

7. 緩存過期和增加隨機(jī)性

上面處理了緩存污染的問題，下面我們嘗試為整個(gè)高性能緩存添加緩存過期時(shí)間，同時(shí)為防止“緩存雪崩”，增加過期時(shí)間隨機(jī)性，為了方便理解，這里拆分兩個(gè)小部分介紹如何處理。

緩存過期

實(shí)現(xiàn)緩存過期這里要用到定時(shí)線程池 ScheduledExecutorService。我們直接定一個(gè)帶過期時(shí)間的新方法處理。

?? public?V?compute(A?arg,?long?expireTime)?{?? ????if?(expireTime?>?0)?{?? ????????SCHEDULED_EXECUTOR_SERVICE.schedule(new?Runnable()?{?? ????????????@Override?? ????????????public?void?run()?{?? ????????????????//?定期清除緩存的方法?? ????????????????expire(arg);?? ????????????}?? ?? ????????????/**?? ?????????????*?@description?注意需要同步方法，防止多線程重復(fù)添加定時(shí)任務(wù)?? ?????????????*?@param?arg?? ?????????????*?@return?void?? ?????????????*?@author?xander?? ?????????????*?@date?2023/6/20?16:58?? ?????????????*/????????????private?synchronized?void?expire(A?arg)?{?? ????????????????//?檢查當(dāng)前?key?是否存在?? ????????????????Future<V>?vFuture?=?concurrentHashMap.get(arg);?? ????????????????//?如果?value?存在，則需要進(jìn)行?? ????????????????if(Objects.nonNull(vFuture)){?? ????????????????????//如果任務(wù)被取消，此時(shí)需要關(guān)閉對(duì)應(yīng)的定時(shí)任務(wù)?? ????????????????????if(vFuture.isDone()?){?? ????????????????????????log.warn("future?任務(wù)被取消");?? ????????????????????????vFuture.cancel(true);?? ????????????????????}?? ????????????????????log.warn("過期時(shí)間到了，緩存被清除");?? ????????????????????concurrentHashMap.remove(arg);?? ????????????????}?? ????????????}?? ????????},?expireTime,?TimeUnit.MILLISECONDS);?? ????}?? ????return?doCompute(arg);?? }

增加隨機(jī)性

增加隨機(jī)性的目的是防止緩存在同一個(gè)時(shí)刻大量失效這種情況。增加隨機(jī)性的最簡單方法就是在設(shè)置超時(shí)時(shí)間的時(shí)候給一個(gè)隨機(jī)random值。

?? public?V?compute(A?arg,?long?expireTime,?boolean?isRandom){?? ????if(isRandom){?? ????????return?compute(?arg,??expireTime);?? ????}else{?? ????????return?compute(?arg,??expireTime?+?RANDOM.nextInt(1000));?? ????}?? }

8. 完整代碼

至此我們整個(gè)高性能緩存構(gòu)建完成，最終的成果代碼如下：

?? /**?? ?*?高性能緩存第六版?? ?*?? ?*?@author?Xander?? ?*?@version?v1.0.0?? ?*?@Package?:?version6?? ?*?@Description?:?高性能緩存第六版?? ?*?@Create?on?:?2023/6/20?16:30?? ?**/@Slf4j?? public?class?MyCacheVersion6<A,?V>?{?? ?? ????private?final?Map<A,?Future<V>>?concurrentHashMap?=?new?ConcurrentHashMap<>();?? ????private?static?final?Random?RANDOM?=?new?Random();;?? ?? ????private?static?final?ScheduledExecutorService?SCHEDULED_EXECUTOR_SERVICE?=?new?ScheduledThreadPoolExecutor(10);?? ?? ????private?final?ComputeAble?computeAble?=?new?MayFailCompute();?? ?? ?? ????public?V?compute(A?arg)?{?? ????????return?doCompute(arg);?? ????}?? ?? ????public?V?compute(A?arg,?long?expireTime)?{?? ????????if?(expireTime?>?0)?{?? ????????????SCHEDULED_EXECUTOR_SERVICE.schedule(new?Runnable()?{?? ????????????????@Override?? ????????????????public?void?run()?{?? ????????????????????//?定期清除緩存的方法?? ????????????????????expire(arg);?? ????????????????}?? ?? ????????????????/**?? ?????????????????*?@description?注意需要同步方法，防止多線程重復(fù)添加定時(shí)任務(wù)?? ?????????????????*?@param?arg?? ?????????????????*?@return?void?? ?????????????????*?@author?xander?? ?????????????????*?@date?2023/6/20?16:58?? ?????????????????*/????????????????private?synchronized?void?expire(A?arg)?{?? ????????????????????//?檢查當(dāng)前?key?是否存在?? ????????????????????Future<V>?vFuture?=?concurrentHashMap.get(arg);?? ????????????????????//?如果?value?存在，則需要進(jìn)行?? ????????????????????if(Objects.nonNull(vFuture)){?? ????????????????????????//如果任務(wù)被取消，此時(shí)需要關(guān)閉對(duì)應(yīng)的定時(shí)任務(wù)?? ????????????????????????if(vFuture.isDone()?){?? ????????????????????????????log.warn("future?任務(wù)被取消");?? ????????????????????????????vFuture.cancel(true);?? ????????????????????????}?? ????????????????????????log.warn("過期時(shí)間到了，緩存被清除");?? ????????????????????????concurrentHashMap.remove(arg);?? ????????????????????}?? ????????????????}?? ????????????},?expireTime,?TimeUnit.MILLISECONDS);?? ????????}?? ????????return?doCompute(arg);?? ????}?? ?? ????public?V?compute(A?arg,?long?expireTime,?boolean?isRandom){?? ????????if(isRandom){?? ????????????return?compute(?arg,??expireTime);?? ????????}else{?? ????????????return?compute(?arg,??expireTime?+?RANDOM.nextInt(1000));?? ????????}?? ????}?? ?? ?? ????private?V?doCompute(A?arg)?{?? ????????//?對(duì)于重復(fù)計(jì)算進(jìn)行處理?? ????????while?(true)?{?? ????????????Future<V>?result?=?concurrentHashMap.get(arg);?? ????????????try?{?? ????????????????//?如果獲取不到內(nèi)容，說明不在緩存當(dāng)中?? ????????????????if?(Objects.isNull(result))?{?? ????????????????????//?此時(shí)利用callAble?線程任務(wù)指定任務(wù)獲取，在獲取到結(jié)果之前線程會(huì)阻塞?? ????????????????????FutureTask<V>?future?=?new?FutureTask<>(new?Callable<V>()?{?? ????????????????????????@Override?? ????????????????????????@SuppressWarnings("unchecked")?? ????????????????????????public?V?call()?throws?Exception?{?? ????????????????????????????return?(V)?computeAble.doCompute(arg);?? ?? ????????????????????????}?? ????????????????????});?? ????????????????????//把新的future覆蓋之前獲取的future?? ????????????????????result?=?future;?? ????????????????????//?執(zhí)行?? ????????????????????future.run();?? ????????????????????System.out.println("FutureTask?調(diào)用計(jì)算函數(shù)");?? ????????????????????result?=?concurrentHashMap.putIfAbsent(arg,?result);?? ????????????????????//?如果返回null，說明這個(gè)記錄被添加過了?? ????????????????????if?(Objects.isNull(result))?{?? ????????????????????????System.out.println("其他線程進(jìn)行設(shè)置,重新執(zhí)行計(jì)算");?? ????????????????????????//?說明其他線程已經(jīng)設(shè)置過值，這里重新跑一次計(jì)算方法即可直接獲取?? ????????????????????????result?=?future;?? ????????????????????????//?再重新跑一次?? ????????????????????????future.run();?? ????????????????????????return?result.get();?? ????????????????????}?else?{?? ????????????????????????return?result.get();?? ????????????????????}?? ????????????????}?? ????????????????return?result.get();?? ????????????}?catch?(CancellationException?cancellationException)?{?? ????????????????log.warn("CancellationException?result?=>?{}",?result);?? ????????????????//?線程在執(zhí)行過程當(dāng)中有可能被取消?? ????????????????//?被取消的時(shí)候不管如何處理，首先需要先從緩存中移除掉污染緩存?? ????????????????concurrentHashMap.remove(arg);?? ????????????????throw?new?RuntimeException(cancellationException);?? ????????????}?catch?(InterruptedException?e)?{?? ????????????????log.warn("InterruptedException?result?=>?{}",?result);?? ????????????????//?線程被中斷的異常處理?? ????????????????concurrentHashMap.remove(arg);?? ????????????????throw?new?RuntimeException(e);?? ????????????}?catch?(ExecutionException?e)?{?? //????????????log.warn("ExecutionException?result?=>?{}",?result);?? ????????????????log.info("移除緩存Key?=>?{}，重新計(jì)算",?arg);?? ????????????????concurrentHashMap.remove(arg);?? ????????????????//?不會(huì)拋出異常，而是重新在下一次循環(huán)中計(jì)算?? //????????????throw?new?RuntimeException(e);?? ????????????}?catch?(Exception?e)?{?? ????????????????log.warn("Exception?result?=>?{}",?result);?? ????????????????concurrentHashMap.remove(arg);?? ????????????????//?無法處理的未知異常，直接拋出運(yùn)行時(shí)異常不做任何處理。?? ????????????????throw?new?RuntimeException(e);?? ????????????}?? ?? ????????}?? ????}?? }

測(cè)試代碼

/**?? ?*?緩存過期功能測(cè)試?? ?*?@author?Xander?? ?*?@version?v1.0.0?? ?*?@Package?:?version6?? ?*?@Description?:?緩存過期功能測(cè)試?? ?*?@Create?on?:?2023/6/20?17:06?? ?**/ public?class?Test?{?? ?? ????public?static?void?main(String[]?args)?throws?InterruptedException?{?? ????????ExecutorService?executorService?=?Executors.newFixedThreadPool(100);?? ????????MyCacheVersion6<String,?Integer>?myCacheVersion5?=?new?MyCacheVersion6<>();?? ????????Random?random?=?new?Random(100);?? ????????for?(int?i?=?0;?i?<?1000;?i++)?{?? ????????????executorService.submit(()?->?{?? ????????????????int?randomInt?=?random.nextInt(100);?? ?? ????????????????Integer?user?=?myCacheVersion5.compute(String.valueOf(randomInt));?? ????????????????System.out.println("result?=>?"?+?user);?? ?? ?? ????????????});?? ????????}?? ????????executorService.shutdown();?? ????}?? }

二、測(cè)試緩存性能

測(cè)試緩存性能的點(diǎn)包含下面的部分：

使用線程池測(cè)試高性能緩存的性能
使用CountDownLatch壓力測(cè)試
線程安全類ThreadSafeFormatter驗(yàn)證CountDownLatch

之前我們的Test測(cè)試都是使用線程池的模式，這里不過多介紹，這里提一下如何使用CountDownLatch進(jìn)行”壓力測(cè)試“，以及使用ThreadSafeFormatter驗(yàn)證CountDownLatch的性能。

?? /**?? ?*?ThreadSafeFormatter?*?@author?Xander?? ?*?@version?v1.0.0?? ?*?@Package?:?com.zxd.interview.mycache.version7?? ?*?@Description?:?線程安全?ThreadSafeFormatter?? ?*?@Create?on?:?2023/6/22?11:11?? ?**/public?class?ThreadSafeFormatter?{?? ?? ?? ????public?static?ThreadLocal<SimpleDateFormat>?dateFormatter?=?new?ThreadLocal<SimpleDateFormat>()?{?? ?? ????????/**?? ?????????*?每個(gè)線程會(huì)調(diào)用本方法一次，用于初始化?? ?????????*?@description?每個(gè)線程會(huì)調(diào)用本方法一次，用于初始化?? ?????????*?@param?? ?????????*?@return?java.text.SimpleDateFormat?? ?????????*?@author?xander?? ?????????*?@date?2023/6/22?11:30?? ?????????*/???????? ?????????@Override?? ????????protected?SimpleDateFormat?initialValue()?{?? ????????????return?new?SimpleDateFormat("mm:ss");?? ????????}?? ?? ????????/**?? ?????????*?首次調(diào)用本方法時(shí)，會(huì)調(diào)用initialValue()；后面的調(diào)用會(huì)返回第一次創(chuàng)建的值?? ?????????*?@description?首次調(diào)用本方法時(shí)，會(huì)調(diào)用initialValue()；后面的調(diào)用會(huì)返回第一次創(chuàng)建的值?? ?????????*?@param?? ?????????*?@return?java.text.SimpleDateFormat?? ?????????*?@author?xander?? ?????????*?@date?2023/6/22?11:30?? ?????????*/???????? ????????@Override?? ????????public?SimpleDateFormat?get()?{?? ????????????return?super.get();?? ????????}?? ????};?? }?? /**?? ?*?整體性能測(cè)試?? ?*?@author?Xander?? ?*?@version?v1.0.0?? ?*?@Package?:?com.zxd.interview.mycache.version6?? ?*?@Description?:?整體性能測(cè)試?? ?*?@Create?on?:?2023/6/20?17:06?? ?**/public?class?Test?{?? ?? ????public?static?void?main(String[]?args)?throws?InterruptedException?{?? ????????long?beginTime?=?System.currentTimeMillis();?? ????????ExecutorService?executorService?=?Executors.newFixedThreadPool(100);?? ????????MyCacheVersion6<String,?Integer>?myCacheVersion5?=?new?MyCacheVersion6<>();?? ????????Random?random?=?new?Random(200);?? ????????CountDownLatch?countDownLatch?=?new?CountDownLatch(1);?? ????????for?(int?i?=?0;?i?<?100;?i++)?{?? ????????????executorService.submit(()?->?{?? ????????????????int?randomInt?=?random.nextInt(100);?? ?? ????????????????try?{?? ????????????????????countDownLatch.await();?? ????????????????????//?從線程安全的集合當(dāng)中取出當(dāng)前時(shí)間?? ????????????????????SimpleDateFormat?simpleDateFormat?=?ThreadSafeFormatter.dateFormatter.get();?? ????????????????????System.out.println("simpleDateFormat?=>?"+?simpleDateFormat.format(new?Date()));?? ????????????????}?catch?(InterruptedException?e)?{?? ????????????????????e.printStackTrace();?? ????????????????}?? ????????????????Integer?user?=?myCacheVersion5.compute(String.valueOf(randomInt),?5000);?? ????????????????System.out.println("result?=>?"?+?user);?? ????????????});?? ????????}?? ????????//?假設(shè)此時(shí)所有的請(qǐng)求需要5秒時(shí)間準(zhǔn)備。?? ????????Thread.sleep(1000);?? ????????countDownLatch.countDown();?? ????????executorService.shutdown();?? ????????long?endTime?=?System.currentTimeMillis();?? ????????//?如果線程池沒有停止一直死循環(huán)?? ????????while(!executorService.isTerminated()){?? ?? ????????}?? ????????System.out.println("最終時(shí)間"?+?(endTime?-?beginTime));?? ????}/**?? ?? ?????10:59:34.521?[pool-2-thread-3]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?future?任務(wù)被取消?? ?????10:59:34.522?[pool-2-thread-3]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?????10:59:34.521?[pool-2-thread-4]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?future?任務(wù)被取消?? ?????10:59:34.522?[pool-2-thread-4]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?????10:59:34.521?[pool-2-thread-1]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?future?任務(wù)被取消?? ?????10:59:34.522?[pool-2-thread-1]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?????10:59:34.521?[pool-2-thread-8]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?future?任務(wù)被取消?? ?????10:59:34.522?[pool-2-thread-8]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?????10:59:34.521?[pool-2-thread-7]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?????10:59:34.521?[pool-2-thread-2]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?future?任務(wù)被取消?? ?????10:59:34.522?[pool-2-thread-2]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?????10:59:34.522?[pool-2-thread-5]?WARN?com.zxd.interview.mycache.version6.MyCacheVersion6?-?過期時(shí)間到了，緩存被清除?? ?? ?????最終時(shí)間146?? ?? ?????如果修改為多個(gè)時(shí)間同時(shí)發(fā)起請(qǐng)求：?? ?????最終時(shí)間1074?-?1000?主線程的睡眠時(shí)間?=?74?? ?? ?? ?????可以看到時(shí)間點(diǎn)都是在同一個(gè)分秒，可以人為countDownlatch是生效的?? ?????simpleDateFormat?=>?14:50?? ?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50?????simpleDateFormat?=>?14:50???? ??????*/?? } }

三、寫在最后

這個(gè)小demo在自己實(shí)際上手寫的時(shí)候還是有不少卡殼的地方，如果有疑問或者改進(jìn)意見歡迎討論。

標(biāo)簽：Java

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