This chapter presents an overview of how network loading and rendering is implemented in OpenVIP. It covers technical details of OpenVIP that are rarely if ever needed in development of OpenVIP plugins. The reader is adviced to consult both reference documentation and source code on details.
Processing a network involves several actions on the side of OpenVIP core library. They happen in three phases: loading of the network, initializing and rendering. Loading and rendering can easily be customized by providing non-default implementation of used algorithms -- e.g. to improve performance when rendering specific networks or to load networks from another file format. Individual steps are briefly discussed below.
Note that you can't take advantage of customizations described in this section if you are using the highlevel API. Direct access through UPF is necessary.
OpenVIP can use any component that implements
openvip.INetworkLoader interface to read
networks. By default only single loader implementation for reading OpenVIP
Network Format is available (its name is in openvip.NETWORK_FORMAT_LOADER
constant), but more implementations can be added.
INetworkLoader.Load implementation
must - in addition to parsing the file and validating it - do:
create modules
set its parameters and validate that no required parameter is omitted and all parameters are set to legal values
connect modules' connectors, verify that connectors are compatible, ensure consistency of related openvip.Network fields
propagate
IStreamInfo objects
In
the processing of doing this, Load
must call EnumParams,
SetParams, EnumConnectors and
SetStreams on all modules in the network (in this
order).
It is clear this process is quite complicated. It is recommended
that any new INetworkLoader implementation
works by translating its input into the format understood by
openvip.NETWORK_FORMAT_LOADER and then calling
it's Load.
Scheduler is OpenVIP component that plans execution of
IModule::Process and IModule::QueryRequirements
so that all terminal modules finish rendering. Scheduler can be customized
in same manner as the loader and openvip.SCHEDULER_SIMPLE
is the standard implementation. Scheduler is given the network together
with list of individual passes. It has to process the passes in given
order, but it is free to reorder computation within each pass as it sees
fit. Typical scheduler will recursively repeat these three actions:
call
QueryRequirements to obtain list of required data
satisfy requirements
call Process
with obtained data
INetworkLoader is used to load the
network into memory. If the net passes all validity checks (i.e.INetworkLoader.Load
returns true), passes description for
IScheduler must be generated and all
modules contained in the network initialized. Both is done in
src/core/proc_control.cpp and is not customizable (it
is simple piece of code that can't be done in much different way).
This fixed part of processing only (preparing IScheduler.TaskDesc
aside) calls Initialize method of every module that
implementes IParametrizable before running
the scheduler and Shutdown afterwards. See
Process in proc_control.cpp.