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fix bug of get negative baseID when concurrently call DistinctMessage.getMessageID #5

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fix bug of get negative baseID when concurrently call DistinctMessage.getMessageID #5

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12 changes: 9 additions & 3 deletions src/main/java/com/alicloud/openservices/tablestore/timeline/message/DistinctMessage.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ public abstract class DistinctMessage implements IMessage {
private String messageID = null;

/**
* 这里的整数（Integer）范围选择了(0, Integer.MAX_VALUE)，会按递增顺序循环使用这个范围的值。
* 这里的整数（Integer）范围选择了(0, Integer.MAX_VALUE]，会按递增顺序循环使用这个范围的值。
* 这里的MessageID是machineID + 递增ID（每个进程内循环递增的，不同机器，不同进程的machineID不同）。
* 对于Timeline模型，消息ID只需要在当前会话中唯一即可。
* 比如在IM中，只需要在某个会话或者群里面唯一即可，这时候其实更好的方式是由客户端生成这个消息ID。
Expand All @@ -26,8 +26,14 @@ public abstract class DistinctMessage implements IMessage {
@Override
public String getMessageID() {
if (messageID == null) {
baseID.compareAndSet(Integer.MAX_VALUE, 0);
messageID = machineID + String.valueOf(baseID.addAndGet(1));
int currentBaseID = baseID.incrementAndGet();
while (currentBaseID < 0) {
// 说明此时baseID已经溢出为负数，需要将baseID重置为0。
// 考虑到可能有并发的compareAndSet，需要反复重试直到新的baseID >= 0
baseID.compareAndSet(currentBaseID, 0);
currentBaseID = baseID.incrementAndGet();
}
messageID = machineID + String.valueOf(currentBaseID);
}
return String.valueOf(messageID);
}
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