Event format meta data

Picking up from the discussion at !33803 (closed)

@akraszna implemented a very nice start to handling xAOD::EventFormat metadata in athenaMT. @gemmeren Pointed out that we should adopt a uniform approach to handling EventStreamInfo and xAOD::EventFormat. This leaves some approaches:

• Write multithreaded service maintaining one shared EventStreamInfo object in a thread-safe manner.
• Maintain a xAOD::EventFormat object for each output stream.
• Something we have not yet thought of Here we choose the second, i.e. maintain a xAOD::EventFormat object for each output stream. That means the key of the xAOD::EventFormat object now is a function of the stream name. Trying to adopt the EventStreamInfo style I went for something like:

AthenaOutputStream(
    name=name,
    HelperTools=[
        CfgMgr.xAODMaker__EventFormatStreamHelperTool(
            name="EventFormatStreamHelper"
            Key='Format{}'.format(name),
        ),
    ],
)

Of course any client looking up xAOD::EventFormat by key will have to adjust for that, as you can see in the read test. How much of a nightmare will this be?

I have not yet included recording and retrieving xAOD::EventFormat though the MetaDataSvc as implemented for EventStreamInfo. Is that desirable @mnowak

As you can see by the hacky approach and the title this is still a construction site and needs cleaning up.

Thoughts?

@tsulaia

Event/xAOD/xAODEventFormatCnv/share/EventFormatReadTest_jobOptions.py

+# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+
+# Read an input test file.
+import AthenaPoolCnvSvc.ReadAthenaPool
+ServiceMgr.EventSelector.InputCollections = [ 'EventFormatWriteTest.pool.root' ]
+
+# Access the main algorithm sequence.
+from AthenaCommon.AlgSequence import AlgSequence
+algSeq = AlgSequence()
+
+# Add the xAOD::EventFormat printer algorithm.
+algSeq += CfgMgr.xAODMakerTest__EventFormatPrinterAlg()
+
+# Some extra job parameters.
+theApp.EvtMax = 1