Athena Developer Guide

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<strong>Athena</strong> Chapter 13 Framework services Version/Issue: 2.0.0 13.4 The Standard Message Service One of the components directly visible to an algorithm object is the message service. The purpose of this service is to provide facilities for the logging of information, warnings, errors etc. The advantage of introducing such a component, as opposed to using the standard std::cout and std::cerr streams available in C++ is that we have more control over what is printed and where it is printed. These considerations are particularly important in an online environment. The Message Service is configurable via the job options file to only output messages if their “activation level” is equal to or above a given “output level”. The output level can be configured with a global default for the whole application: // Set output level threshold (2=DEBUG, 3=INFO, 4=WARNING, 5=ERROR, 6=FATAL) MessageSvc.OutputLevel = 4; and/or locally for a given client object (e.g. myAlgorithm): myAlgorithm.OutputLevel = 2; Any object wishing to print some output should (must) use the message service. A pointer to the IMessageSvc interface of the message service is available to an algorithm via the accessor method msgSvc(), see section 5.2. It is of course possible to use this interface directly, but a utility class called MsgStream is provided which should be used instead. 13.4.1 The MsgStream utility page 104 The MsgStream class is responsible for constructing a Message object which it then passes onto the message service. Where the message is ultimately sent to is decided by the message service. In order to avoid formatting messages which will not be sent because the verboseness level is too high, a MsgStream object first checks to see that a message will be printed before actually constructing it. However the threshold for a MsgStream object is not dynamic, i.e. it is set at creation time and remains the same. Thus in order to keep synchronized with the message service, which in principle could change its printout level at any time, MsgStream objects should be made locally on the stack when needed. For example, if you look at the listing of the HelloWorld class (see also Listing 13.1 below) you will note that MsgStream objects are instantiated locally (i.e. not using new) in all three of the IAlgorithm methods and thus are destructed when the methods return. If this is not done messages may be lost, or too many messages may be printed. The MsgStream class has been designed to resemble closely a normal stream class such as std::cout, and in fact internally uses an ostrstream object. All of the MsgStream member functions write unformatted data; formatted output is handled by the insertion operators.
<strong>Athena</strong> Chapter 13 Framework services Version/Issue: 2.0.0 An example use of the MsgStream class is shown below. Listing 13.1 Use of a MsgStream object. 1: #include “GaudiKernel/MgsStream.h” 2: 3: StatusCode myAlgo::finalize() { 4: StatusCode status = Algorithm::finalise(); 5: MsgStream log(msgSvc(), name()); 6: if ( status.isFailure() ) { 7: // Print a two line message in case of failure. 8: log
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Athena Chapter 4 Establishing a dev
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Athena Chapter 19 Analysis utilitie
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Athena Version/Issue: 2.0.0 Appendi
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