log4cpp  1.1
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log4cpp::NDC Class Reference

The NDC class implements nested diagnostic contexts as defined by Neil Harrison in the article "Patterns for Logging Diagnostic Messages" part of the book "<i>Pattern Languages of Program Design 3</i>" edited by Martin et al. More...

#include <NDC.hh>

Classes

struct  DiagnosticContext
 

Public Types

typedef std::vector
< DiagnosticContext
ContextStack
 

Public Member Functions

 NDC ()
 
virtual ~NDC ()
 
virtual void _clear ()
 
virtual ContextStack_cloneStack ()
 
virtual const std::string & _get () const
 
virtual size_t _getDepth () const
 
virtual void _inherit (ContextStack *stack)
 
virtual std::string _pop ()
 
virtual void _push (const std::string &message)
 
virtual void _setMaxDepth (int maxDepth)
 

Static Public Member Functions

static void clear ()
 Clear any nested disgnostic information if any. More...
 
static ContextStackcloneStack ()
 Clone the diagnostic context for the current thread. More...
 
static const std::string & get ()
 Get the current diagnostic context string. More...
 
static size_t getDepth ()
 Get the current nesting depth of this diagnostic context. More...
 
static void inherit (ContextStack *stack)
 
static std::string pop ()
 Clients should call this method before leaving a diagnostic context. More...
 
static void push (const std::string &message)
 Push new diagnostic context information for the current thread. More...
 
static void setMaxDepth (int maxDepth)
 Set the maximum nesting depth for the current NDC. More...
 
static NDCgetNDC ()
 Return the NDC for the current thread. More...
 

Public Attributes

ContextStack _stack
 

Detailed Description

The NDC class implements nested diagnostic contexts as defined by Neil Harrison in the article "Patterns for Logging Diagnostic Messages" part of the book "<i>Pattern Languages of Program Design 3</i>" edited by Martin et al.

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-simulatanously.

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 affect the NDC of the current thread only. NDCs of other threads remain unaffected.

To build an NDC one uses the push operation. Simply put,

There is no penalty for forgetting to match each push operation with a corresponding pop, except the obvious mismatch between the real application context and the context set in the NDC.

Custom Layouts may include the nested diagnostic context for the current thread in log messages, without any user intervention. Hence, even if a server is serving multiple clients simultaneously, the logs emanating from the same code (belonging to the same category) can still be distinguished because each client request will have a different NDC tag.

Unfortunately, unlike Java, C++ does not have platform independent multithreading support. Therefore, currently log4cpp is not multithread aware, it implicitly assumes only one thread exists, the main process thread.

Member Typedef Documentation

Constructor & Destructor Documentation

log4cpp::NDC::NDC ( )
log4cpp::NDC::~NDC ( )
virtual

Member Function Documentation

void log4cpp::NDC::_clear ( )
virtual
NDC::ContextStack * log4cpp::NDC::_cloneStack ( )
virtual
const std::string & log4cpp::NDC::_get ( ) const
virtual
size_t log4cpp::NDC::_getDepth ( ) const
virtual
void log4cpp::NDC::_inherit ( NDC::ContextStack stack)
virtual
std::string log4cpp::NDC::_pop ( )
virtual
void log4cpp::NDC::_push ( const std::string &  message)
virtual
void log4cpp::NDC::_setMaxDepth ( int  maxDepth)
virtual
void log4cpp::NDC::clear ( )
static

Clear any nested disgnostic information if any.

This method is useful in cases where the same thread can be potentially used over and over in different unrelated contexts.

This method is equivalent to calling the setMaxDepth method with a zero maxDepth argument.

NDC::ContextStack * log4cpp::NDC::cloneStack ( )
static

Clone the diagnostic context for the current thread.

Internally a diagnostic context is represented as a stack. A given thread can supply the stack (i.e. diagnostic context) to a child thread so that the child can inherit the parent thread's diagnostic context.

The child thread uses the inherit method to inherit the parent's diagnostic context.

Returns
Stack A clone of the current thread's diagnostic context.
const std::string & log4cpp::NDC::get ( )
static

Get the current diagnostic context string.

Returns
the context string.
size_t log4cpp::NDC::getDepth ( )
static

Get the current nesting depth of this diagnostic context.

Returns
the nesting depth
NDC & log4cpp::NDC::getNDC ( )
static

Return the NDC for the current thread.

Returns
the NDC for the current thread
void log4cpp::NDC::inherit ( NDC::ContextStack stack)
static
std::string log4cpp::NDC::pop ( )
static

Clients should call this method before leaving a diagnostic context.

The returned value is the value that was pushed last. If no context is available, then the empty string "" is returned.

Returns
String The innermost diagnostic context.
void log4cpp::NDC::push ( const std::string &  message)
static

Push new diagnostic context information for the current thread.

The contents of the message parameter is determined solely by the client.

Parameters
messageThe new diagnostic context information.
void log4cpp::NDC::setMaxDepth ( int  maxDepth)
static

Set the maximum nesting depth for the current NDC.

Curently NDCs do not enforce a maximum depth and consequentially this method has no effect.

Parameters
maxDepththe maximum nesting depth

Member Data Documentation

ContextStack log4cpp::NDC::_stack

The documentation for this class was generated from the following files: