Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Wed, 27 Jul 2005 11:15:38 -0500

Kay-Uwe Kasemir wrote:

I suggest _not_ to allow con-contiguous storage.
I cannot imagine a server that keeps his
strings in segments.

I can; I am considering an implementation of variable length strings

that does not require the reallocation and copying of data as the string

is extended. This would use a fixed allocation size block, and chain

these blocks together as needed to make up the complete storage for the

string.

I understand why a network layer will _receive_
the data in pieces, but that's a problem of the
network layer.
All communications layers that I have seen so
far hide that detail from me.
With the proper environment variable configuration,
even CA V3 hands me the complete dbr_ctrl_double
for huge arrays,
so why obfuscate the V4 data access in order to
support non-contiguous data?

Any API that is designed to support segmented data can also support

contiguous data with no changes. An API that requires contiguous data

cannot be used with segmented data without copying all the data segments

into a contiguous buffer first, thus requiring extra memory and reducing

performance.

Eric Norum has an R3.14 IOC with very limited RAM that uses a waveform

record to allow its flash eprom to be reprogrammed, but his memory

requirements are such that he can only fit one waveform buffer in

memory. If we require another copy of the data this IOC would probably

not be able to fit in memory.

Since we're designing the APIs and they will hide all of the details

from user code, why would we make them less flexible?

- Andrew
--
Podiabombastic: The tendency to shoot oneself in the foot.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System