问题：
如果线程安全，是否有机会使并发性更强
有凯泽
类AnagramGameDefault模拟一个字谜游戏。
submitScore（）应该重新计算位置，得分最高的位置为1，同一位置上可以有多个球员。
public enum AnagramGameDefault{
INSTANCE;
private Map<String, Entry> leaderBoardUserEntryMap;
{
leaderBoardUserEntryMap = new LinkedHashMap<>();
}
public int calculateScore(String word, String anagram) {
if (word == null || anagram == null) {
throw new NullPointerException("Both, word and anagram, must be non-null");
}
char[] wordArray = word.trim().toLowerCase().toCharArray();
char[] anagramArray = anagram.trim().toLowerCase().toCharArray();
int[] alphabetCountArray = new int[26];
int reference = 'a';
for (int i = 0; i < wordArray.length; i++) {
if (!Character.isWhitespace(wordArray[i])) {
alphabetCountArray[wordArray[i] - reference]++;
}
}
for (int i = 0; i < anagramArray.length; i++) {
if (!Character.isWhitespace(anagramArray[i])) {
alphabetCountArray[anagramArray[i] - reference]--;
}
}
for (int i = 0; i < 26; i++)
if (alphabetCountArray[i] != 0)
return 0;
return word.length();
}
public void submitScore(String uid, int score) {
Entry newEntry = new Entry(uid, score);
sortLeaderBoard(newEntry);
}
private void sortLeaderBoard(Entry newEntry) {
synchronized (leaderBoardUserEntryMap) {
leaderBoardUserEntryMap.put(newEntry.getUid(), newEntry);
// System.out.println("Sorting for " + newEntry);
List<Map.Entry<String, Entry>> list = leaderBoardUserEntryMap.entrySet().stream()
.sorted(Map.Entry.comparingByValue(Collections.reverseOrder())).collect(Collectors.toList());
leaderBoardUserEntryMap.clear();
int position = 0;
int previousPosition = 0;
int currentPosition = 0;
for (Map.Entry<String, Entry> entry : list) {
currentPosition = entry.getValue().getScore();
if (!(currentPosition == previousPosition))
position++;
entry.getValue().setPosition(position);
leaderBoardUserEntryMap.put(entry.getKey(), entry.getValue());
previousPosition = currentPosition;
}
}
}
public List<Entry> getLeaderBoard(String uid) {
final int maxEntriesAroundAnEntry = 2;
if (!leaderBoardUserEntryMap.containsKey(uid))
return Collections.emptyList();
Entry userEntry = null;
final List<Entry> leaderBoard = new ArrayList<>();
List<Entry> lowerEntries = null;
List<Entry> higherEntries = null;
synchronized (leaderBoardUserEntryMap) {
printBoard();
userEntry = leaderBoardUserEntryMap.get(uid);
int userPosition = userEntry.getPosition();
int upperPosition = userPosition - maxEntriesAroundAnEntry;
int lowerPosition = userPosition + maxEntriesAroundAnEntry;
// Higher entries
higherEntries = leaderBoardUserEntryMap.values().stream()
.filter(entry -> (entry.getPosition() < userPosition && entry.getPosition() >= upperPosition))
.map(entry -> new Entry(entry.getUid(), entry.getScore(), entry.getPosition()))
.collect(Collectors.toList());
// Lower entries
lowerEntries = leaderBoardUserEntryMap.values().stream()
.filter(entry -> (entry.getPosition() > userPosition && entry.getPosition() <= lowerPosition))
.map(entry -> new Entry(entry.getUid(), entry.getScore(), entry.getPosition()))
.collect(Collectors.toList());
userEntry = new Entry(userEntry.getUid(), userEntry.getScore(), userEntry.getPosition());
// }
if (higherEntries != null && !higherEntries.isEmpty()) {
if (higherEntries.size() >= maxEntriesAroundAnEntry) {
higherEntries = higherEntries.subList(higherEntries.size() - maxEntriesAroundAnEntry,
higherEntries.size());
}
leaderBoard.addAll(higherEntries);
}
leaderBoard.add(userEntry);
if (lowerEntries != null && !lowerEntries.isEmpty()) {
if (lowerEntries.size() >= maxEntriesAroundAnEntry) {
lowerEntries = lowerEntries.subList(0, maxEntriesAroundAnEntry);
}
leaderBoard.addAll(lowerEntries);
}
}
return leaderBoard;
}
public void printBoard() {
System.out.println("---------Start : Current leader board---------");
leaderBoardUserEntryMap.forEach((key, value) -> {
System.out.println("BOARD ENTRY : " + key + " : " + value);
});
System.out.println("---------End : Current leader board---------");
}
}
public class Entry implements Comparable<Entry> {
private String uid;
private int score;
private int position;
public Entry(String uid, int score) {
this.uid = uid;
this.score = score;
}
public Entry(String uid, int score, int position) {
this.uid = uid;
this.score = score;
this.position = position;
}
public Entry() {
}
public String getUid() {
return uid;
}
public void setUid(String uid) {
this.uid = uid;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public int getPosition() {
return position;
}
public void setPosition(int position) {
this.position = position;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + score;
result = prime * result + ((uid == null) ? 0 : uid.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Entry other = (Entry) obj;
if (score != other.score)
return false;
if (uid == null) {
if (other.uid != null)
return false;
} else if (!uid.equals(other.uid))
return false;
return true;
}
@Override
public String toString() {
return "Entry [uid=" + uid + ", score=" + score + ", position=" + position + "]";
}
@Override
public int compareTo(Entry o) {
// TODO Auto-generated method stub
if (o == null)
return -1;
return Integer.compare(score, o.getScore());
}
}
tester类：
public class AnagramGameDefaultDemo {
public static void main(String[] args) {
if (args == null || args.length < 1) {
System.out.println("Enter testing approach - 1 for single threaded, 2 for multi-threaded");
return;
}
switch (args[0]) {
case "1": {
new AnagramGameDefaultDemo().testSingleThreaded();
break;
}
case "2": {
new AnagramGameDefaultDemo().testMultithreaded();
break;
}
default: {
System.out.println("Enter proper option(1 or 2)");
break;
}
}
}
private void testMultithreaded() {
Map<String, String> stringAnagramMap = new HashMap<>();
CountDownLatch countDownLatchOne = new CountDownLatch(1);
stringAnagramMap.put("raw", "war");
stringAnagramMap.put("raw", "wars");
AnagramGamePlayer jake = new AnagramGamePlayer("jake", stringAnagramMap, countDownLatchOne);
new Thread(jake, "jake").start();
stringAnagramMap.clear();
stringAnagramMap.put("tool", "loot");
AnagramGamePlayer ace = new AnagramGamePlayer("ace", stringAnagramMap, countDownLatchOne);
new Thread(ace, "ace").start();
stringAnagramMap.clear();
stringAnagramMap.put("William Shakespeare", "I am a weakish speller");
AnagramGamePlayer max = new AnagramGamePlayer("max", stringAnagramMap, countDownLatchOne);
new Thread(max, "max").start();
stringAnagramMap.clear();
stringAnagramMap.put("School master", "The classroom");
AnagramGamePlayer tBone = new AnagramGamePlayer("tBone", stringAnagramMap, countDownLatchOne);
new Thread(tBone, "tBone").start();
stringAnagramMap.clear();
countDownLatchOne.countDown();
CountDownLatch countDownLatchTwo = new CountDownLatch(1);
stringAnagramMap.put("Punishments", "Nine Thumps");
AnagramGamePlayer razor = new AnagramGamePlayer("razor", stringAnagramMap, countDownLatchTwo);
new Thread(razor, "razor").start();
stringAnagramMap.clear();
stringAnagramMap.put("Dormitory", "Dirty Room");
AnagramGamePlayer chip = new AnagramGamePlayer("chip", stringAnagramMap, countDownLatchTwo);
new Thread(chip, "chip").start();
stringAnagramMap.clear();
countDownLatchTwo.countDown();
CountDownLatch countDownLatchThree = new CountDownLatch(1);
stringAnagramMap.put("Mother in law", "Hitler woman");
AnagramGamePlayer dale = new AnagramGamePlayer("dale", stringAnagramMap, countDownLatchThree);
new Thread(dale, "dale").start();
countDownLatchThree.countDown();
stringAnagramMap.clear();
}
private final class AnagramGamePlayer implements Runnable {
private Map<String, String> stringAnagramMap = new HashMap<>();
private String uid;
private CountDownLatch countDownLatch;
public AnagramGamePlayer(String uid, Map<String, String> stringAnagramMap, CountDownLatch countDownLatch) {
this.stringAnagramMap.putAll(stringAnagramMap);
this.uid = uid;
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
AnagramGameDefault anagramGameDefault = AnagramGameDefault.INSTANCE;
try {
countDownLatch.await();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("Player " + uid + " started playing with " + stringAnagramMap);
stringAnagramMap.entrySet().forEach(entry -> {
anagramGameDefault.submitScore(uid,
anagramGameDefault.calculateScore(entry.getKey(), entry.getValue()));
printLeaderBoard(uid, anagramGameDefault.getLeaderBoard(uid));
});
System.out.println("Player " + uid + " completed playing");
}
}
private void testSingleThreaded() {
AnagramGameDefault anagramGameDefault = AnagramGameDefault.INSTANCE;
anagramGameDefault.submitScore("Jake", 3);
anagramGameDefault.submitScore("Ace", 7);
anagramGameDefault.submitScore("Max", 1);
anagramGameDefault.submitScore("T-Bone", 14);
anagramGameDefault.submitScore("Razor", 6);
anagramGameDefault.submitScore("Razor", 7);
anagramGameDefault.submitScore("He-Man", 4);
anagramGameDefault.submitScore("Men-at-Arms", 8);
anagramGameDefault.submitScore("BattleCat", 3);
anagramGameDefault.submitScore("Jake", 2);
anagramGameDefault.submitScore("BattleCat", 3);
anagramGameDefault.printBoard();
anagramGameDefault.submitScore("Men-at-Arms", 21);
anagramGameDefault.submitScore("Orko", 20);
anagramGameDefault.submitScore("Jake", 4);
anagramGameDefault.printBoard();
System.out.println();
printLeaderBoard("user5", anagramGameDefault.getLeaderBoard("user5"));
System.out.println();
printLeaderBoard("user4", anagramGameDefault.getLeaderBoard("user4"));
System.out.println();
printLeaderBoard("user15", anagramGameDefault.getLeaderBoard("user15"));
System.out.println();
List<Entry> entries = anagramGameDefault.getLeaderBoard("user1");
printLeaderBoard("user1", entries);
System.out.println("Changing state of the received entries");
entries.forEach(entry -> {
entry.setPosition(1);
entry.setScore(0);
});
anagramGameDefault.printBoard();
printLeaderBoard("user1", anagramGameDefault.getLeaderBoard("user1"));
}
private static void printLeaderBoard(String user, List<Entry> leaderBoard) {
if (user == null || leaderBoard.isEmpty()) {
System.out.println("Either user " + user + " doesn't exist or leader board is empty " + leaderBoard);
}
System.out.println("**********Printing leader board for " + user);
leaderBoard.forEach(System.out::println);
System.out.println("**********");
}
}
共有1个答案
刁钧
似乎整个过程中唯一的共享状态是leaderboarduserentrymap。在sortleaderboard中更新时，您将在其上进行同步。在GetLeaderBoard中，由于某种原因，在检查if（！LeaderBoardUserEntryMap.ContainsKey(uid))时，您尚未对其进行同步。那是次要的，但你也应该这样做。稍后，您在构建leader Board时对其进行同步。
从这个角度来看，您的同步似乎是足够的。
我发现有点问题的是，您的entry是可变的，并且存储position。这使得您的更新操作更加成问题。您必须在每次更新时重新排序和重新设置位置。并且您正在锁定所有其他更新甚至读取操作。我会避免多线程代码中的可变对象。
然而，这不会有多大帮助，因为您的“检索”逻辑（围绕目标条目创建leader board）并不是那么简单，需要多次读取。所以我认为最好不要使用并发集合，而是在集合上进行同步，并使更新和检索尽可能紧凑。如果您放弃在条目中包含位置的想法，那么update就是一个简单的添加。那么您只需要尽可能快地读取条目周围的条目（在synchronized块内）。这对于树集来说应该是相当快的。
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