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map iterator_一个简单的Map Iterator性能测试

發布時間：2023/12/3 编程问答 48 豆豆

生活随笔收集整理的這篇文章主要介紹了 map iterator_一个简单的Map Iterator性能测试小編覺得挺不錯的,現在分享給大家,幫大家做個參考.

map iterator

Java Map性能有很多方面可以衡量，但是關鍵的一個是簡單的單線程掃描。這是一些針對Iterators和Java 8 Map.forEach()簡單測試代碼，以及一些圖形結果。

1.性能測試困難

性能測試是一項非常困難的工作，精確的可重復性測試需要Java Microbenchmarking Harness之類的框架來過濾掉許多噪聲源并提供諸如置信區間的統計信息。但是，這里簡單測試代碼的結果是相對可重復的，并且與作者在JDK Maps和AirConcurrentMap（在boilerbay.com和githuboilbay / airconcurrentmap ）上進行的JMH測試很好地相關。還有針對流等的更廣泛的JMH測試。

JMH并不復雜，但是它需要將工具從IDE切換到Maven模型，學習控件注釋集，并處理充滿混亂的另一個目錄樹以及可能的新IDE項目。另外，我們希望一次運行即可自動跨越一系列地圖大小和一組地圖：這需要JMH中的“參數化”注釋。該測試的輸出數據格式可以輕松地根據所需繪圖工具的需求進行調整。

1.1引起噪音的問題

要獲得良好的測試，必須解決許多問題：

內部循環不得有大量開銷。這可以通過使它簡單地監視共享靜態volatile int變量（由“檢測信號”線程遞增）的變化來解決。

垃圾收集可能會增加。這可以通過在針對不同Map的測試中分配GC開銷循環機制來幫助。我們還避免創建任何無法訪問的對象。在ORACLE JVM中使用-Xloggc：<file>來觀看GC；

在運行期間，JVM可以隨時優化代碼。我們使用每個測試的預熱運行來允許這種情況發生。很難知道何時會確切發生，但這僅需幾秒鐘。可以通過更長的預熱將其最小化。典型的JVM標志'-XX：+ PrintCompilation'顯示了優化進度。另請參閱ORACLE文章；

隨著Maps的增長，JVM會不穩定地增長，因此增長后的測試必須預熱。

不同的Map使用不同的內存量，因此即使為每個測試分叉JVM也將取決于JVM的增長特征。我們將所有Map保留在一個JVM中；

不同的地圖必須具有完全相同的內容。我們使用由Map大小作為種子的同步隨機數生成器；

大型地圖需要更多的時間進行迭代，而不是較小的時間。心跳允許運行更多較小的Map，因此每次測試都需要固定的時間。

地圖不得共享內容，因此早期測試不會將數據帶入可用于后續測試的CPU緩存中；

“及時”編譯器不能優化循環。我們打印內容的總和，這樣循環就可以得到明顯的結果。如果要使用循環計數器，則JIT可以識別出模式并更改循環以增加一個大于1的數字，從而跳過許多迭代！是的，這發生了！（至少在AirConcurrentMap中）。

2.結果

這些預防措施可幫助我們得出一些初步但可重復的結論。結果顯示：

forEach（）比Iterators快得多；
在大約3萬個條目以下，ConcurrentSkipListMap的迭代速度最快，而在上面，AirConcurrentMap的迭代速度最快；
ConcurrentSkipListMap forEach（）在大約100個條目以下最快，而AirConcurrentMap在上面最快。

3.代碼詳細信息

測試代碼使用Test類包裝器來包含特定的Map以及測試進度狀態，例如時間，map大小，循環和運行總計。該組織希望使main（）更具可讀性。

Test類實現BiConsumer以便可以在forEach(this)調用中使用它。它只是覆蓋了accept(Integer, Integer) 。我們還測試了forEach((k, v) -> total += v) （作者嘗試過，結果大致相同）。無論哪種情況，都不能將局部變量用作總累加器，因為局部變量必須“有效地”終止于內部類或lambda，因此無論如何我們都需要一個包含范圍內的實例變量，例如Test那個。使用流進行簡化也可以，但是我們對Iterators感興趣。（有關/ jmh中的相關流測試，請參見https://github.com/boilerbay/airconcurrentmap ）。

心跳是一個static int ，每秒由一個單獨的Thread遞增一次。心跳必須是易失的，以便其更改在線程之間傳播–否則程序永遠不會終止。

USE_ITERATION和USE_LAMBDA標志是static final ，因此javac實際上會提前評估它影響的代碼，從而USE_LAMBDA代碼。這被定義為必需的行為，因此那里沒有開銷。當然，您必須重新編譯才能進行各種測試，只是不要將它們更改為非靜態或非最終的！

test.testIterator()的動態方法調用不會減慢內部循環，因為總是內聯長度為35個字節或更少的方法。而且，這里沒有多態性Test類沒有擴展，因此沒有用于分發的vtable，也沒有要壓入堆棧的參數。

測試是相對可重復的，并在圖中顯示了總體模式。

4.代碼

public class JavaCodeGeeksIteratorArticle {static volatile int heartBeat = 0;// otherwise use forEach()static final boolean USE_ITERATION = false;static final boolean USE_LAMBDA = true;public static void main(String... args) {System.out.println((USE_ITERATION ? "Iterator" :USE_LAMBDA ? " forEach(lambda)" : "ForEach()") + " performance test");Test tests[] = {new Test(new HashMap<Integer, Integer>()),new Test(new TreeMap<Integer, Integer>()),new Test(new ConcurrentHashMap<Integer, Integer>()),new Test(new ConcurrentSkipListMap<Integer, Integer>()),new Test(new AirConcurrentMap<Integer, Integer>())};int sizes[] = new int[] {1, 3, 10, 30, 100, 300, 1000, 3000, 10_000, 30_000, 100_000, 300_000,1000_000, 3_000_000, 10_000_000};// Just increment heartBeat every so often. It is volatile.// Reading it is very fast.new Thread(new Runnable() {public void run() {while (true) {heartBeat++;try {Thread.sleep(100);} catch (InterruptedException e) {}}}}).start();for (int i = 0; i < sizes.length; i++) {for (Test test : tests)test.fillTo(sizes[i]);// warmupfor (Test test : tests) {int nextHeartBeat = heartBeat + 20;while (heartBeat < nextHeartBeat)if (USE_ITERATION)test.testIterator();else if (USE_LAMBDA)test.testForEachLambda();elsetest.testForEach();}for (Test test : tests) {test.time = 0;test.loops = 0;long t0 = System.nanoTime();int nextHeartBeat = heartBeat + 30;while (heartBeat < nextHeartBeat) {if (USE_ITERATION)test.testIterator();else if (USE_LAMBDA)test.testForEachLambda();elsetest.testForEach();}long t1 = System.nanoTime();test.time += (t1 - t0);}for (Test test : tests)test.printResult();// System.out.println("---------------");}} }class Test implements BiConsumer<Integer, Integer> {// The total provides a tangible result to prevent optimizing-outlong total = 0;long time = 0;int size = 0;long loops = 1;Map<Integer, Integer> map;Test(Map<Integer, Integer> map) {this.map = map;}void fillTo(int newSize) {Random random = new Random(size);while (size < newSize) {Integer n = new Integer(random.nextInt()); map.put(n, n); size++;}}void testIterator() { for (Integer v : map.values()) {total += v.intValue(); } loops++; }// This has the same effect and is 'terser' void testForEachLambda() {map.forEach((k, v) -> total += v);loops++;}void testForEach() {map.forEach(this);loops++;}// Implement BiConsumer for forEach()@Overridepublic void accept(Integer k, Integer v) {total += k.intValue();}void printResult() {double seconds = time / 1e9;System.out.printf("%22s size=% 9d entries/s(K)=% 11.3f total=%d\n",map.getClass().getSimpleName(), size, size * loops / seconds / 1e3, total);} }

5.結果數據

圖表數據如下。例如，可以將其導入Excel并按Map類和大小進行排序，以手動制作圖形。您需要剪切并粘貼數據，然后使用文本到列。可以使用折線圖，為每個Map類手動選擇一個系列的數據。通過更改數據輸出格式，也可以使用“ R”統計語言的ggplot。忽略總數：這僅提供了有形輸出，以避免優化循環。

JavaCodeGeeksIteratorArticleIterator performance testHashMap size= 1 entries/s= 31290.754K total=-289049400605539520TreeMap size= 1 entries/s= 50210.333K total=-331631386373881504ConcurrentHashMap size= 1 entries/s= 15881.356K total=-91464608232057952ConcurrentSkipListMap size= 1 entries/s= 42187.535K total=-254234286353018080AirConcurrentMap size= 1 entries/s= 25577.125K total=-149805405784208032 ---------------HashMap size= 3 entries/s= 62664.626K total=-484691989675689270TreeMap size= 3 entries/s= 66908.091K total=-550745245141063704ConcurrentHashMap size= 3 entries/s= 38018.996K total=-211326922860746827ConcurrentSkipListMap size= 3 entries/s= 71265.063K total=-488278692474832005AirConcurrentMap size= 3 entries/s= 48540.146K total=-302163579336545082 ---------------HashMap size= 10 entries/s= 86701.181K total=-832795481348512598TreeMap size= 10 entries/s= 87832.407K total=-916137658370092344ConcurrentHashMap size= 10 entries/s= 73069.458K total=-502840045890573499ConcurrentSkipListMap size= 10 entries/s= 96150.046K total=-880874881700377401AirConcurrentMap size= 10 entries/s= 72001.056K total=-591224549191451578 ---------------HashMap size= 30 entries/s= 89419.363K total=-832238604657166224TreeMap size= 30 entries/s= 92397.645K total=-915559545928720920ConcurrentHashMap size= 30 entries/s= 71702.258K total=-502393457157098057ConcurrentSkipListMap size= 30 entries/s= 103387.524K total=-880213560719307683AirConcurrentMap size= 30 entries/s= 80807.271K total=-590716865563759348 ---------------HashMap size= 100 entries/s= 90540.307K total=-845663104709828079TreeMap size= 100 entries/s= 96479.776K total=-930300717715488858ConcurrentHashMap size= 100 entries/s= 69055.433K total=-512752383626539310ConcurrentSkipListMap size= 100 entries/s= 111208.365K total=-897628029635465726AirConcurrentMap size= 100 entries/s= 89071.481K total=-604453907970584431 ---------------HashMap size= 300 entries/s= 94846.852K total=-860347586557330269TreeMap size= 300 entries/s= 94506.995K total=-944821983122037883ConcurrentHashMap size= 300 entries/s= 65857.587K total=-522786710141245214ConcurrentSkipListMap size= 300 entries/s= 112398.344K total=-915694233970137252AirConcurrentMap size= 300 entries/s= 92168.052K total=-618862268508225735 ---------------HashMap size= 1000 entries/s= 74493.997K total=-852961390806337305TreeMap size= 1000 entries/s= 80026.348K total=-937067262358689631ConcurrentHashMap size= 1000 entries/s= 38450.309K total=-519070765727723030ConcurrentSkipListMap size= 1000 entries/s= 112085.413K total=-904572392174355552AirConcurrentMap size= 1000 entries/s= 89022.852K total=-609589031935380951 ---------------HashMap size= 3000 entries/s= 57470.417K total=-847037038798366713TreeMap size= 3000 entries/s= 65963.172K total=-930168324830420495ConcurrentHashMap size= 3000 entries/s= 41073.089K total=-514814334734654678ConcurrentSkipListMap size= 3000 entries/s= 109217.866K total=-892841347702876464AirConcurrentMap size= 3000 entries/s= 89175.845K total=-600361285087522951 ---------------HashMap size= 10000 entries/s= 46254.558K total=-846309210319384299TreeMap size= 10000 entries/s= 49044.408K total=-929403633977808893ConcurrentHashMap size= 10000 entries/s= 36385.473K total=-514246034592481772ConcurrentSkipListMap size= 10000 entries/s= 99442.425K total=-891342788950136070AirConcurrentMap size= 10000 entries/s= 85447.544K total=-599022098209904335 ---------------HashMap size= 30000 entries/s= 43723.556K total=-848942181585517584TreeMap size= 30000 entries/s= 45253.915K total=-932143497084889069ConcurrentHashMap size= 30000 entries/s= 32665.051K total=-516220137420939070ConcurrentSkipListMap size= 30000 entries/s= 83393.494K total=-896231928805619954AirConcurrentMap size= 30000 entries/s= 80619.262K total=-603845100973163554 ---------------HashMap size= 100000 entries/s= 40028.088K total=-849706795555554639TreeMap size= 100000 entries/s= 41755.506K total=-932944794183923404ConcurrentHashMap size= 100000 entries/s= 26064.027K total=-516724530444651670ConcurrentSkipListMap size= 100000 entries/s= 46619.667K total=-897138307784594414AirConcurrentMap size= 100000 entries/s= 75034.058K total=-605290263409285564 ---------------HashMap size= 300000 entries/s= 28271.140K total=-850157323063101369TreeMap size= 300000 entries/s= 23442.635K total=-933312552546033574ConcurrentHashMap size= 300000 entries/s= 22886.588K total=-517086645455936620ConcurrentSkipListMap size= 300000 entries/s= 26852.530K total=-897567202447311134AirConcurrentMap size= 300000 entries/s= 43406.800K total=-605991920028554584 ---------------HashMap size= 1000000 entries/s= 20762.874K total=-850266118577777400TreeMap size= 1000000 entries/s= 21465.730K total=-933426629396373490ConcurrentHashMap size= 1000000 entries/s= 17617.501K total=-517179596963620996ConcurrentSkipListMap size= 1000000 entries/s= 17753.452K total=-897660153954995510AirConcurrentMap size= 1000000 entries/s= 24726.115K total=-606121840885886155 ---------------HashMap size= 3000000 entries/s= 20859.307K total=-850290350569160265TreeMap size= 3000000 entries/s= 17078.422K total=-933446707332090721ConcurrentHashMap size= 3000000 entries/s= 19987.888K total=-517202444269781983ConcurrentSkipListMap size= 3000000 entries/s= 23990.479K total=-897687847659433070AirConcurrentMap size= 3000000 entries/s= 30472.006K total=-606157150359044044 ---------------HashMap size= 10000000 entries/s= 18594.336K total=-850335966429011695TreeMap size= 10000000 entries/s= 14332.011K total=-933483200019971865ConcurrentHashMap size= 10000000 entries/s= 17038.665K total=-517248060129633413ConcurrentSkipListMap size= 10000000 entries/s= 18600.417K total=-897733463519284500AirConcurrentMap size= 10000000 entries/s= 39037.289K total=-606248382078746904 ---------------ForEach() performance testHashMap size= 1 entries/s= 60469.332K total=-429010055848020608TreeMap size= 1 entries/s= 162720.446K total=-1192873323002853184ConcurrentHashMap size= 1 entries/s= 39683.288K total=-238381128098095008ConcurrentSkipListMap size= 1 entries/s= 125216.579K total=-742139402594604448AirConcurrentMap size= 1 entries/s= 40199.780K total=-223453462147226592 ---------------HashMap size= 3 entries/s= 154792.076K total=-907351702836558858TreeMap size= 3 entries/s= 209809.380K total=-1866688472587176884ConcurrentHashMap size= 3 entries/s= 100788.166K total=-558021636792810008ConcurrentSkipListMap size= 3 entries/s= 202179.445K total=-1380005440196857173AirConcurrentMap size= 3 entries/s= 99654.211K total=-536118642462089017 ---------------HashMap size= 10 entries/s= 297297.392K total=-2080956150412338142TreeMap size= 10 entries/s= 228262.234K total=-2782965758065995472ConcurrentHashMap size= 10 entries/s= 189641.651K total=-1313404093180619596ConcurrentSkipListMap size= 10 entries/s= 304427.266K total=-2602702896415550485AirConcurrentMap size= 10 entries/s= 179131.091K total=-1257952993772621945 ---------------HashMap size= 30 entries/s= 305634.315K total=-2079066757218703314TreeMap size= 30 entries/s= 224584.862K total=-2781566150975000263ConcurrentHashMap size= 30 entries/s= 174917.912K total=-1312321443993669200ConcurrentSkipListMap size= 30 entries/s= 354581.676K total=-2600502266614288915AirConcurrentMap size= 30 entries/s= 254150.967K total=-1256373143380530839 ---------------HashMap size= 100 entries/s= 295763.376K total=-2123996537948400465TreeMap size= 100 entries/s= 225375.420K total=-2816005249627104526ConcurrentHashMap size= 100 entries/s= 168596.386K total=-1337959745143386554ConcurrentSkipListMap size= 100 entries/s= 366342.358K total=-2656351051389612808AirConcurrentMap size= 100 entries/s= 336305.468K total=-1307783105877232718 ---------------HashMap size= 300 entries/s= 335940.642K total=-2176036047793281607TreeMap size= 300 entries/s= 213798.860K total=-2849343024468137449ConcurrentHashMap size= 300 entries/s= 196158.746K total=-1368245793652746886ConcurrentSkipListMap size= 300 entries/s= 348762.198K total=-2711376732587358984AirConcurrentMap size= 300 entries/s= 435378.640K total=-1375390632080685627 ---------------HashMap size= 1000 entries/s= 312285.030K total=-2145888100702813327TreeMap size= 1000 entries/s= 157007.240K total=-2834013084542617045ConcurrentHashMap size= 1000 entries/s= 178919.552K total=-1350929801563960438ConcurrentSkipListMap size= 1000 entries/s= 253518.140K total=-2687136797657993712AirConcurrentMap size= 1000 entries/s= 449868.858K total=-1331959489090096491 ---------------HashMap size= 3000 entries/s= 269579.050K total=-2118053337323592431TreeMap size= 3000 entries/s= 129271.886K total=-2820412724828116661ConcurrentHashMap size= 3000 entries/s= 95870.060K total=-1340856888537750166ConcurrentSkipListMap size= 3000 entries/s= 203849.473K total=-2666107139705649888AirConcurrentMap size= 3000 entries/s= 443682.852K total=-1286068695711899563 ---------------HashMap size= 10000 entries/s= 100969.734K total=-2116523986910706773TreeMap size= 10000 entries/s= 81240.085K total=-2819237854014952091ConcurrentHashMap size= 10000 entries/s= 74229.656K total=-1339726640597926192ConcurrentSkipListMap size= 10000 entries/s= 147733.052K total=-2664068913299591178AirConcurrentMap size= 10000 entries/s= 399269.901K total=-1279844336850624703 ---------------HashMap size= 30000 entries/s= 77830.586K total=-2121068856388826590TreeMap size= 30000 entries/s= 73801.711K total=-2823183557187296024ConcurrentHashMap size= 30000 entries/s= 63503.394K total=-1343522194696030345ConcurrentSkipListMap size= 30000 entries/s= 148907.153K total=-2671403338078408622AirConcurrentMap size= 30000 entries/s= 450044.679K total=-1305454406448994036 ---------------HashMap size= 100000 entries/s= 57919.591K total=-2122150626578319295TreeMap size= 100000 entries/s= 39468.243K total=-2823932886520250879ConcurrentHashMap size= 100000 entries/s= 30273.873K total=-1344103393021081000ConcurrentSkipListMap size= 100000 entries/s= 48766.187K total=-2672332261897079327AirConcurrentMap size= 100000 entries/s= 307460.503K total=-1311189966514089586 ---------------HashMap size= 300000 entries/s= 42127.664K total=-2122825947560403955TreeMap size= 300000 entries/s= 26508.090K total=-2824353316156729769ConcurrentHashMap size= 300000 entries/s= 27206.845K total=-1344518179306734670ConcurrentSkipListMap size= 300000 entries/s= 19172.093K total=-2672628537815403377AirConcurrentMap size= 300000 entries/s= 152485.548K total=-1313414387297697136 ---------------HashMap size= 1000000 entries/s= 40607.148K total=-2123037200986959355TreeMap size= 1000000 entries/s= 25159.911K total=-2824487462082592448ConcurrentHashMap size= 1000000 entries/s= 30257.523K total=-1344677675643783997ConcurrentSkipListMap size= 1000000 entries/s= 37742.151K total=-2672825003502099899AirConcurrentMap size= 1000000 entries/s= 148954.277K total=-1314169618297632691 ---------------HashMap size= 3000000 entries/s= 43941.038K total=-2123087741997557902TreeMap size= 3000000 entries/s= 18891.646K total=-2824508924703531557ConcurrentHashMap size= 3000000 entries/s= 32007.894K total=-1344715062144774703ConcurrentSkipListMap size= 3000000 entries/s= 21722.543K total=-2672849927836093703AirConcurrentMap size= 3000000 entries/s= 126084.363K total=-1314312240875486125 ---------------HashMap size= 10000000 entries/s= 35724.715K total=-2123169850545290476TreeMap size= 10000000 entries/s= 12693.940K total=-2824540855805427558ConcurrentHashMap size= 10000000 entries/s= 27254.306K total=-1344783485934551848ConcurrentSkipListMap size= 10000000 entries/s= 13572.712K total=-2672886420523974847AirConcurrentMap size= 10000000 entries/s= 92726.047K total=-1314522073830802703 ---------------

6.總結

使用某些預防措施的簡單代碼，可以獲得可重復的，有意義的自定義Map性能測試。此代碼顯示了其中一些問題。該代碼可輕松適應其他種類的Map測試和數據輸出格式。

翻譯自: https://www.javacodegeeks.com/2017/04/simple-map-iterator-performance-test.html