类中的线程安全
请您看一下下面的代码并告诉我 ClassA 是否是线程安全的？如果它不是线程安全的，你能告诉我它在哪里中断吗？
public class ClassA {
private List<Player> players;
public ClassA() {
this.players = Collections.synchronizedList(new ArrayList<Player>());
}
public Player play(Player player){
int score = 0;
.
.
.
if (players.contains(player)) {
player = players.get(players.indexOf(player));
player.addScore(score);
} else {
player.addScore(score);
players.add(player);
}
return player;
}
}
Please can you have a look at the following code and advise whether ClassA is thread-safe or not? If it is not thread-safe, could you please advise where it is breaking?
public class ClassA {
private List<Player> players;
public ClassA() {
this.players = Collections.synchronizedList(new ArrayList<Player>());
}
public Player play(Player player){
int score = 0;
.
.
.
if (players.contains(player)) {
player = players.get(players.indexOf(player));
player.addScore(score);
} else {
player.addScore(score);
players.add(player);
}
return player;
}
}
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不，事实并非如此。
例如，两个线程可能无法通过
players.contains测试，并且都添加自己的播放器版本（更好的方法是每次都将播放器添加到集合中）。另外，除非 Player.addScore 是线程安全的，否则分数添加可能会出现微妙的错误。同步整个
play方法（并将players恢复到正常列表）可以解决这些问题。No, it is not.
For example, two threads could fail the
players.containstest and both add their version of a player (a better way would just add the player every time to a set). Also, unlessPlayer.addScoreis thread-safe, score adding could be subtly wrong.Synchronizing over the whole
playmethod (and reverting ofplayersto a normal list) would solve these problems.