NDC

The NDC class implements a copy of the Nested Diagnostic Context, which is part of the Apache Log4j library. Nested Diagnostic Contexts were derived from Neil Harrison’s article on “Patterns for Logging Diagnostic Messages”, part of the book “Pattern Languages of Program Design 3” edited by Martin et al.

NDCs in Log4r are thread safe.

NDCs in log4r are close enough to NDCs in Log4j that I include its documentation directly:

… A Nested Diagnostic Context, or NDC in short, is an instrument to distinguish interleaved log output from different sources. Log output is typically interleaved when a server handles multiple clients near-simultaneously.

Interleaved log output can still be meaningful if each log entry from different contexts had a distinctive stamp. This is where NDCs come into play.

Note that NDCs are managed on a per thread basis. NDC operations such as push, pop(), clear(), getDepth() and setMaxDepth(int) affect the NDC of the current thread only. NDCs of other threads remain unaffected. …

An important difference between NDCs in Log4r vs Log4j is that you do not have to called NDC.remove() when exiting a thread.

This class will automatically create Thread specific storage for the current thread on the first call to any of its methods, i.e.

  NDC.push( "client accept" );

New threads may inherit the NDC of the parent thread by making use of the clone_stack() and inherit() methods. By default, the NDC is not inherited automatically. This is unlike MDCs, which will inherit from the main thread.

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