Redis distributed lock, lock code logic

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        public boolean lock(String key, String value) {
        
    if(redisTemplate.opsForValue().setIfAbsent(key, value)) {
        
        return true;
        
    }
        
    String currentValue = redisTemplate.opsForValue().get(key);
        
    if (!StringUtils.isEmpty(currentValue)
        
        && Long.parseLong(currentValue) < System.currentTimeMillis()) {
        

        
        String oldValue = redisTemplate.opsForValue().getAndSet(key, value);
        
        if (!StringUtils.isEmpty(oldValue) && oldValue.equals(currentValue)) {
        
            return true;
        
        }
        
    }
        
    return false;
        
}
       
       

        
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Suppose there are two threads now A and B At the same time lock() Method , That is, the of these two threads value It's exactly the same , All for value=2020-12-19, And they all carry out ​​String oldValue = redisTemplate.opsForValue().getAndSet(key, value);​​, There will be one to execute first and then ：

If a thread A Execute first , Back to ​​oldValue=2020-12-18​​​, Simultaneous setting ​​value = 2020-12-19​​​, because ​​oldvalue=currentValue​​ return true, namely A The thread is locked ;

here B The thread continues to execute , Back to ​​oldValue=2020-12-19,oldvalue！=currentValue​​, return false, Locking failed

So the logic of this code is to lock only one thread