ivankelly commented on a change in pull request #1861: Cpp client: add
getLastMessageId and hasMessageAvailable in consmer and reader
URL: https://github.com/apache/incubator-pulsar/pull/1861#discussion_r194106349
##########
File path: pulsar-client-cpp/lib/ConsumerImpl.cc
##########
@@ -919,4 +919,65 @@ void ConsumerImpl::seekAsync(const MessageId& msgId,
ResultCallback callback) {
callback(ResultNotConnected);
}
+void ConsumerImpl::hasMessageAvailableAsync(HasMessageAvailableCallback
callback) {
+ if (this->lastMessageIdAvailable()) {
+ callback(ResultOk, true);
+ return;
+ }
+
+ BrokerGetLastMessageIdCallback callback1 = [this, callback](Result result,
MessageId messageId) {
+ if (this->lastMessageIdAvailable()) {
Review comment:
This is action at a distance which can be a pain to debug when stuff goes
wrong.
Rather than making the assumption about the lastMessageInBroker being
updated in the background, the messageId passed as a parameter should be used.
So lastMessageIdInBroker is only directly used in the short circuit path.
```
void ConsumerImpl::hasMessageAvailableAsync(HasMessageAvailableCallback
callback) {
MessageId lastDequeud = this->lastMessageIdDequed();
if (lastDequeued < this->lastMessageIdInBroker()) {
callback(ResultOk, true);
return;
}
BrokerGetLastMessageIdCallback callback1 = [this, callback](Result
result, MessageId messageId) {
if (result == ResultOk) {
if (messageId > lastDequeued) {
callback(ResultOk, true);
} else {
callback(ResultOk, false);
}
} else {
callback(result, false);
}
};
getLastMessageIdAsync(callback1);
}
```
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