log4cpp::NDC(3) log4cpp log4cpp::NDC(3)NAMElog4cpp::NDC-
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.
SYNOPSIS
#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.
static ContextStack * cloneStack ()
Clone the diagnostic context for the current thread.
static const std::string & get ()
Get the current diagnostic context string.
static size_t getDepth ()
Get the current nesting depth of this diagnostic context.
static void inherit (ContextStack *stack)
static std::string pop ()
Clients should call this method before leaving a diagnostic
context.
static void push (const std::string &message)
Push new diagnostic context information for the current thread.
static void setMaxDepth (int maxDepth)
Set the maximum nesting depth for the current NDC.
static NDC & getNDC ()
Return the NDC for the current thread.
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,
· Contexts can be nested.
· When entering a context, call NDC.push. As a side effect, if there is
no nested diagnostic context for the current thread, this method will
create it.
· When leaving a context, call NDC.pop.
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
typedef std::vector<DiagnosticContext> log4cpp::NDC::ContextStack
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:
message The 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:
maxDepth the maximum nesting depth
Member Data Documentation
ContextStack log4cpp::NDC::_stack
Author
Generated automatically by Doxygen for log4cpp from the source code.
Version 1.0 23 Nov 2010 log4cpp::NDC(3)
