akka/akka — pull request #1865 by pvlugter (2013-12-06 02:36:51+00:00)
Title: +act,rem Add basis of trace SPI

* add SPI for message flow tracing
* propagate trace context between send and receive
* dynamically create tracer and attach to actor system
* allow multiple tracers to be attached
* trace remote message flows

Changes Envelope and RemoteTransport.send to include trace context.