Chuck Rolke created QPID-4616:
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Summary: C++ Broker needs consistent way to freeze traffic on a
per-exchange basis
Key: QPID-4616
URL: https://issues.apache.org/jira/browse/QPID-4616
Project: Qpid
Issue Type: New Feature
Components: C++ Broker
Affects Versions: 0.20
Reporter: Chuck Rolke
Assignee: Chuck Rolke
Some applications may require "freezing" the bindings in an exchange so that
changes to the exchange are applied between messages. As the exchanges are
designed today this is not possible. This issue tracks a method to provide the
exchange locking feature.
There are four basic exchange types and three locking strategies:
* FanOut - has no locking at the exchange level. Locks for fanout are provided
in the CopyOnWriteArray class.
* Direct and Headers - have simple per-exchange lock. There is no
differentiation between read lock and write lock.
* Topic - has RWlock. Binding readers and consumers take out the Rlock and
binding writers take out the Wlock.
The proposal is for all exchanges to use the RWlock the way Topic Exchange uses
it. To implement this the following steps are taken:
* Move Topic exchange RWlock up into the parent exchange class and call it
'bindingLock'.
* In Topic exchange take RWlock out of the derived class and use the parent's
lock.
* In Direct and Headers exchanges change the semantics of the current lock to
use the Topic exchange pattern.
* In FanOut exchange add locks at the same places as in the other exchanges
except only use Rlock. FanOut receives the locking it needs from the
CopyOnWriteArray and does not need anything else. By adding only Rlocks threads
will never block in the normal case. However, the Rlocks are the hooks that the
new application will need to freeze the exchange when that app takes out the
Wlock.
A review to support this proposal is on its way.
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