56.4. Event orderer packages

This section describes the set of packages that make up the event builder application programming interface. There are additional packages and interfaces that are considered internal and should not referenced by user code, as these interfaces are not guaranteed to be stable across different versions of the event orderer.

If you need something that is provided as an internal interface, ask about it so that a public interface can be added to meet your needs. In this way your code is less likely to break as the event orderer evolves...

The remainder of this section is a list of the package names and a brief description of each package and the services or user interface elements it provides.


Provides graphical user interface elements that can be used to monitor barrier statistics. Barriers are sets of event fragments that collectively indicate some sort of synchronization has occured between the data sources.

Each source is expected to contribute a barrier. Barrier fragments also have a barrier type. The user interfaces support the display of barrier statistics in summary, by source as well as exceptional cases such as barriers with mixed types and barriers with sources that did not participate within the fragment ordering timeout.


This package is not normally used by application code but is a stable and usable interface. It provides a mechanism for registering a set of callback methods, supplying scripts with substitutions and invoking those callbacks with strings that will replace the substitution strings.

A typical use-case would be to implement the callbacks in a mega widget implemented in e.g. snit or itk.


Provides an auto-updating widget that displays the set of connections to the event orderer by data source clients. For each client, the source node, the connection description supplied at connection time, the state and whether or not the connection appears stalled are displayed.


Provides several top level user interface elements that can be used to implement a monitoring interface for the event orderer.


Provides user interface elements that support the display of statistics describing the fragments received by the event orderer from the data sources.


Provides user interface elements that allow applications to display statistics on late fragments. A late fragment is one that is received sufficiently late in time that when it is emitted it breaks the total ordering of timestamps in the output fragments.


Provides user interface elements that support the display of output statistics. In addition to displaying summary statistics, these user interface elements can display the output statistics by data source as well as the hottest and coldest sources. [1]


Provides some useful utility procs and classes.


Provides useful procs for starting the event orderer and registering specific callbacks with the builder.


Provides a snit type that suppports the implementation of the Observer pattern. See e.g. http://en.wikipedia.org/wiki/Observer_pattern for a description of this pattern.

Note that contrary to what the wikipedia description of this pattern might imply, the use of this sort of observer is not restricted to object oriented constructions.


This package represents commands that influence the action of the event builder compiled fragment handler code. Note that many of the commands defined by this package also have Tcl jackets. Where this is true you should use the jackets instead as they may take care of other issues that may not be trivial to deal with.



The hottest data source is defined as the one which has emitted the most fragments while similarly the coldest data source is the one which has emitted the fewest fragments.