[BUG] ServiceBusMessageBatch does not preserve message order reliably

[paulbandler]

Describe the bug
When the ServiceBusMessageBatch class is used to send batches of ServiceBus messages, the order of adding the messages to the ServiceBusMessageBatch object is not reliably the order the messages are added to the destination queue.

Exception or Stack Trace
Add the exception log and stack trace if available

To Reproduce
It was confirmed by testing and comparing the resulting order of the messages on the queue. When not using ServiceBusMessageBatch the send order was reliably the message order on the queue, but when using ServiceBusMessageBatch the order was frequently not preserved, leading to erroneous processing by the received.

Code Snippet
I have a simple wrapper around the ServiceBus client that enable switching between batched sends and un-batched sends - the actual send method looks like this:
void sendMessage(ServiceBusMessage serviceBusMessage){
if(!batchingEnabled) {
log.trace("Send single service bus messages to {}", getNameQualifier());
senderClient.sendMessage(serviceBusMessage);
} else {
if(!serviceBusMessageBatch.get().tryAddMessage(serviceBusMessage)){
flush();
if(!serviceBusMessageBatch.get().tryAddMessage(serviceBusMessage)){
String msg = String.format("Unable to add SB message to batch - too large - %d?", serviceBusMessage.getBody().toBytes().length);
ServiceBusSink.this.senderClient = null;
throw new RuntimeException(msg);
}
}
}
}

Expected behavior
Batches of messages assembled using ServiceBusMessageBatch should be written to the destination queue in the order in which they are added to the ServiceBusMessageBatch object.
Screenshots
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Setup (please complete the following information):

• OS: Linux in K8S Container
• IDE: n/a
• Library/Libraries: com.azure:azure-messaging-servicebus:7.4.2
• Java version: 11
• App Server/Environment: AKS Pod
• Frameworks: Micronaut,

If you suspect a dependency version mismatch (e.g. you see NoClassDefFoundError, NoSuchMethodError or similar), please provide

• verbose dependency tree (mvn dependency:tree -Dverbose)

Additional context
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Information Checklist
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• [ X] Setup information Added

[joshfree]

@ki1729 can you please follow up with @paulbandler?

[joshfree]

@ki1729 can you please give an update?

[ki1729]

Sure Josh, the fix for this causes a significant hit in performance, but giveth that this is a fix and not a perf enhancement, will be going ahead with it. This fix should be done and hopefully be out in the Jan release of the sdk

[paulbandler]

Has there been any progress on this issue?

[ki1729]

@paulbandler The changes are merged, so it should be a part of the the March release