I have a few questions regarding the activemq-c implementation. I am working with version activemq-cpp-3.4.0, and activemq-c-3.3.0.
I am migrating a workqueue out of a PostgreSQL database to ActiveMQ. The database schema tables are simple, they contain a uuid column and an 'attempt' column, which is an integer. Each time that the job fails, the 'attempt' is incremented, and when a maximum is reached (or the job is successful), it is taken out of the table. My questions are specific to the C implementation. I am not a C++ programmer, but I could find my way around the C++ code, and help with writing some C wrappers, if I'm pointed in the right direction. I am placing messages onto an ActiveMQ queue from within a PostgreSQL trigger. 1. When I consume a message from a queue, is there a way to mark it as 'being-processed', without it being removed from the queue? So that other consumers can't fetch the same message, and so that it will stay on the queue if the consumer process crashes. I am concerned about the gap between it being taken off the queue and processed, that if there is a catastrophic crash, it will disappear. I want to explicitly delete the message only if the processing is successful, otherwise it should remain on the queue (with a property changed, see my next question). 2. Is there a way to fetch messages from the queue based on a property (eg in SQL, SELECT id FROM queue WHERE attempt=1)? I have set a property on the message (setMessageIntProperty(message, "attempt", 0)) when it is first placed on the queue. I want to put the message back on the queue, with attempt++ each time that it fails. But I also want to just get a message if it has a certain 'attempt' value. Do I have to take each message out of the queue, examine it for the property I want, and then put it back on the queue if it doesn't match? Or can I 'pre-filter' the message and only get it if it matches criteria? Is this the best way of doing it (setting a Property on the message), or is there another way of doing what I need? For example, if there are 1000 messages, and only one of them has the property attempt=1, do I have to go through each message until I find the matching property? 3. I have added some code to the C wrapper (specifically, a function returning the message as an allocated buffer). Is there somewhere/someone where I can send this code to be integrated into the project? I imagine that some of the functionality I'm asking for above might exist in the C++ implementation and not in the C one. I can help to write some of that code, if there is someone who could show me where to start. Regards, -- Jason Armstrong
