Record blocking, and service programs

I have written a service program that logs account updates.  The module
simply accepts the account ID fields, concatenates them into a single field,
and writes them to the log file.  The program is sometimes called several
thousand times from the one running program, in the same activation group,
and the output file remains open to the service program until the close
parameter is used.

So my question is this:  If I call the program 100 times, from the same
running program, in the same activation group, is record blocking done?  Or
if not, each time the service program RETURNs, is all data forced to disk?
I would like for blocking to be done, for efficiency.  I know I can force
blocking to not happen, but can I force it to happen, if the program
RETURNs, but remains in the activation group?

Also, if blocking is done, once the activation group is closed, is this data
written to the file?

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