On 19/01/16 17:01, Gordon Sim wrote:
On 01/19/2016 02:19 PM, Toralf Lund wrote:
Hi,
I have some questions about the value from
qpid::messaging::Message::getTtl() on received messages; based on
testing, I've concluded that
1. The value returned represents the time that remains of the
time-to-live specified by the sender.
2. If no TTL was set, the value is
qpid::messaging::Duration::IMMEDIATE, which is equivalent to 0.
That is a bit unfortunate.
Yes. I sort of expected qpid::messaging::Duration::FOREVER...
Is this correct? If it is, when exactly does the count-down occur? And
when does the clock stop, so as to speak? When I call fetch(), or when
the message is pre-fetched by the receiver, or at some other point?
The value reported for received messages is that value that was
written to the wire by the peer (e.g. the broker). The receiving
client does not reduce this value in anyway after the message has been
decoded.
So, in other words, the value relates to the time Receiver::fetch() was
called on a receiver with capacity 0, and the point where the receiver
got the message "in the background" if capacity is >0?
How exactly does the prefetch work, by the way? Will the client still
ask for messages individually, or does it tell the broker in advance
that it's prepared to receive a certain number of messages?
Also, can I always assume there is no real time-to-live if
qpid::messaging::Duration::IMMEDIATE is returned, or could I also get
that value because the message was about to expire when it was fetched?
If the ttl was 0 at the point the peer was encoding it, I would
generally expect the message not to be sent at all. Therefore I would
not expect a message to be read from the wire with ttl=0 and so at
present I think you can treat IMMEDIATE as implying no ttl (as ugly as
that is).
Fair enough. I can work with that.
Thanks!
- Toralf
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