[ros-users] Messaging Performance

Josh Faust jfaust at willowgarage.com
Fri May 21 03:06:07 UTC 2010

> Hello, I'd like to just shine a light on this last statement.  I don't
> immediately understand why a shared memory transport can't compete
> with nodelets as I understand them.  If nodelets are threads in a
> single process and use process memory to carry messages (which is
> essentially shared memory in that context), shouldn't nodelets and a
> shared memory transport be roughly equivalent in performance?
It depends entirely on what you mean by shared memory transport.  If the
messages are allocated out of shared memory, and a pointer to them is simply
passed around, yes -- but that's not what Cedric's implementation did.
Serialization/deserialization is by far the largest time sync when dealing
with large messages, so unless you remove that overhead shared memory cannot
compete with nodelets.


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