工程裡有獲取唯一時間戳作為id的需求,想了想用樂觀鎖cas實現,自旋.
cas原子性操作獲得了絕對唯一的時間戳(系統時間:納秒版本).單機有效,不能分散式呼叫.

public class AtomicTimeStamp {

private AtomicLong timeMills = new AtomicLong(0);

private static AtomicLong at = new AtomicLong(0);

public Long getNextNaos(){
    while (true){
        long currentTimeMillis = System.nanoTime();
        long currentMill = timeMills.get();
        if(currentTimeMillis > currentMill && timeMills.compareAndSet(currentMill, currentTimeMillis)){
            return currentTimeMillis;
            //返回唯一時間戳
        }
    }
}

public static void main(String[] args) {
    AtomicTimeStamp stamp = new AtomicTimeStamp();
    ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(100, 150, 200, TimeUnit.MILLISECONDS, new PriorityBlockingQueue<>(100),new ThreadFactoryBuilder().build());
    long l = System.currentTimeMillis();
    //開啟三個執行緒測試成功性,at自增,測試10S會有多少個成功的
    poolExecutor.execute(()->{
        while (true){
            stamp.getNextNaos();
            at.getAndIncrement();
            long l1 = System.currentTimeMillis();
            if(l1 > l + 10000 & l1<l+10010){
                System.out.println(at.longValue());
            }
        }
    });
    poolExecutor.execute(()->{
        while (true){
            stamp.getNextNaos();
            at.getAndIncrement();
            long l1 = System.currentTimeMillis();
            if (l1 > l + 10000 & l1 < l + 10010) {
                System.out.println(at.longValue());
            }
        }
    });
    poolExecutor.execute(()->{
        while (true){
            stamp.getNextNaos();
            at.getAndIncrement();
            long l1 = System.currentTimeMillis();
            if (l1 > l + 10000 & l1 < l + 10010) {
                System.out.println(at.longValue());
            }
        }
    });
}
}
 

後面是新的要求,按照yyyyMMddHHmmssSSS… 的格式獲取唯一

private static AtomicLong atomicTimeMills = new AtomicLong(0);

private static DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS");

public static String getNextTime() {
    while (true) {
        long currentMill = atomicTimeMills.get();
        Long currentTimeMillis = Long.parseLong(LocalDateTime.now().format(formatter) + System.nanoTime()%100);
        if (currentTimeMillis > currentMill && atomicTimeMills.compareAndSet(currentMill, currentTimeMillis)) {
            return currentTimeMillis.toString();
        }
    }
}