The AsyncAppender decouples logging event creation from output by processing log events asynchronously. More...

#include <asyncappender.h>

Inheritance diagram for log4cxx::AsyncAppender:

Public Member Functions
	AsyncAppender ()
	Create new instance.
virtual	~AsyncAppender ()
	If not closed, calls AsyncAppender::close.
void	addAppender (const AppenderPtr newAppender) override
	Ensure `newAppender` receives any logging event added to this appender.
void	doAppend (const spi::LoggingEventPtr &event, helpers::Pool &pool1) override
	Call AppenderSkeleton::doAppendImpl without acquiring a lock.
void	append (const spi::LoggingEventPtr &event, helpers::Pool &p) override
	Add `event` to a ring buffer.
void	close () override
	Close this `AsyncAppender` by interrupting the dispatcher thread which will process all pending events before exiting.
AppenderList	getAllAppenders () const override
	Get iterator over attached appenders.
AppenderPtr	getAppender (const LogString &name) const override
	Get appender by name.
bool	getLocationInfo () const
	The current value of the (unused) LocationInfo option.
bool	isAttached (const AppenderPtr appender) const override
	Determines if specified appender is attached.
bool	requiresLayout () const override
	Return false.
void	removeAllAppenders () override
	Removes and closes all attached appenders.
void	removeAppender (const AppenderPtr appender) override
	Removes an appender.
void	removeAppender (const LogString &name) override
	Remove appender by name.
bool	replaceAppender (const AppenderPtr &oldAppender, const AppenderPtr &newAppender) LOG4CXX_16_VIRTUAL_SPECIFIER
	Replace `oldAppender` with `newAppender`.
void	replaceAppenders (const AppenderList &newList) LOG4CXX_16_VIRTUAL_SPECIFIER
	Replace any previously added appenders with `newList`.
void	setLocationInfo (bool flag)
	The LocationInfo attribute is provided for compatibility with log4j and has no effect on the log output.
void	setBufferSize (int size)
	The BufferSize option takes a non-negative integer value.
int	getBufferSize () const
	Gets the current buffer size.
void	setBlocking (bool value)
	Sets whether appender should wait if there is no space available in the event buffer or immediately return.
bool	getBlocking () const
	Gets whether appender should block calling thread when buffer is full.
void	setOption (const LogString &option, const LogString &value) override
	Set `option` to `value`.
Public Member Functions inherited from log4cxx::spi::AppenderAttachable
virtual	~AppenderAttachable ()
Public Member Functions inherited from log4cxx::helpers::Object
virtual	~Object ()
virtual const helpers::Class &	getClass () const =0
virtual bool	instanceof (const Class &clazz) const =0
virtual const void *	cast (const Class &clazz) const =0
Public Member Functions inherited from log4cxx::AppenderSkeleton
	AppenderSkeleton ()
	AppenderSkeleton (const LayoutPtr &layout)
virtual	~AppenderSkeleton ()
void	finalize ()
	Finalize this appender by calling the derived class' `close` method.
void	activateOptions (helpers::Pool &) override
	Activate the options that were previously set with calls to option setters.
void	addFilter (const spi::FilterPtr newFilter) override
	Add a filter to end of the filter list.
void	clearFilters () override
	Clear the filters chain.
const spi::ErrorHandlerPtr	getErrorHandler () const
	Return the currently set spi::ErrorHandler for this Appender.
spi::FilterPtr	getFilter () const override
	Returns the head Filter.
const spi::FilterPtr	getFirstFilter () const
	Return the first filter in the filter chain for this Appender.
LayoutPtr	getLayout () const override
	Returns the layout of this appender.
LogString	getName () const override
	Returns the name of this Appender.
const LevelPtr	getThreshold () const
	Returns this appenders threshold level.
bool	isAsSevereAsThreshold (const LevelPtr &level) const
	Check whether the message level is below the appender's threshold.
void	setErrorHandler (const spi::ErrorHandlerPtr eh)
	Set the `ErrorHandler` for this Appender.
void	setLayout (const LayoutPtr layout1) override
	Set the layout for this appender.
void	setName (const LogString &name1) override
	Set the name of this Appender.
void	setThreshold (const LevelPtr &threshold)
	Set the threshold level.
Public Member Functions inherited from log4cxx::Appender
virtual	~Appender ()
Public Member Functions inherited from log4cxx::spi::OptionHandler
virtual	~OptionHandler ()

Additional Inherited Members
Protected Member Functions inherited from log4cxx::AppenderSkeleton
	AppenderSkeleton (LOG4CXX_PRIVATE_PTR(AppenderSkeletonPrivate) priv)
void	doAppendImpl (const spi::LoggingEventPtr &event, helpers::Pool &pool)
	Compare `event` level against the appender threshold and check that `event` is accepted.
bool	isAccepted (const spi::LoggingEventPtr &event) const
	Does no attached filter deny `event` or does an attached filter accept `event`?

Detailed Description

The AsyncAppender decouples logging event creation from output by processing log events asynchronously.

The AsyncAppender stores the logging event in a bounded buffer and then returns control to the application. A separate thread forwards events to the attached appender(s).

Important notes:

Your application must call LogManager::shutdown when it exits to prevent undefined behaviour when using this appender.
Runtime configuration requires an XML configuration file (see the example below).

This appender is useful when outputting to a slow event sink, for example, a remote SMTP server or a database. Note that configuring a FileAppender to use buffered output usually results in lower overhead than attaching the FileAppender to an AsyncAppender as the inter-thread communication overhead can exceed the time to add a message to a buffer.

You can attach multiple appenders to an AsyncAppender by:

calling AsyncAppender::addAppender repeatedly when progammatically configuring Log4cxx.
adding multiple appender-ref elements to the appender class="AsyncAppender" element when using runtime configuration.

Here is a sample configuration file:

<?xml version="1.0" encoding="UTF-8" ?>
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
  <appender name="A1" class="RollingFileAppender">
    <param name="File"   value="${TEMP}/SomeApplicationName.log" />
    <param name="Append" value="true" />
    <layout class="PatternLayout">
      <param name="ConversionPattern" value="%d %-5p %c{2} - %m%n"/>
    </layout>
  </appender>
  <appender name="SENDMAIL" class="SMTPAppender">
    <param name="from"   value="service_name@example.org" />
    <param name="to" value="some_support_group@example.org" />
    <param name="subject" value="Service error detected" />
    <param name="SMTPHost" value="smtp.example.com"/>
    <layout class="PatternLayout">
        <param name="ConversionPattern" value="%-5p %c{2} - %m%n"/>
    </layout>
    <!-- triggeringPolicy class="SpecialTriggeringEventEvaluator" -->
    <!-- param name="evaluatorClass" value="SpecialTriggeringEventEvaluator" -->
  </appender>
  <appender name="ASYNC" class="AsyncAppender">
    <param name="BufferSize" value="1000"/>
    <param name="Blocking" value="false"/>
    <appender-ref ref="SENDMAIL"/>
  </appender>
  <root>
    <priority value ="INFO" />
    <appender-ref ref="A1" />
    <appender-ref ref="ASYNC" />
  </root>
</log4j:configuration>

Configurable properties

When the application produces logging events faster than the background thread is able to process, the bounded buffer can become full. In this situation AsyncAppender will either block until the bounded buffer has a free slot or discard the event. The Blocking property controls which behaviour is used. When events are discarded, the logged output will indicate this with a log message prefixed with Discarded. The output may contain one Discarded message per logger name, the logging event of the highest level for each logger whose events have been discarded.

To determine whether the application produces logging events faster than the background thread is able to process, enable Log4cxx internal debugging. The AsyncAppender will output a histogram of queue length frequencies when closed.

See AsyncAppender::setOption for details.

Constructor & Destructor Documentation

◆ AsyncAppender()

log4cxx::AsyncAppender::AsyncAppender ( )

Create new instance.

◆ ~AsyncAppender()

virtual log4cxx::AsyncAppender::~AsyncAppender ( )

virtual

If not closed, calls AsyncAppender::close.

Member Function Documentation

◆ addAppender()

void log4cxx::AsyncAppender::addAppender ( const AppenderPtr newAppender )

overridevirtual

Ensure newAppender receives any logging event added to this appender.

Parameters

newAppender appender to add, may not be null.

Implements log4cxx::spi::AppenderAttachable.

◆ append()

void log4cxx::AsyncAppender::append	(	const spi::LoggingEventPtr &	event,
		helpers::Pool &	p )

overridevirtual

Add event to a ring buffer.

The behaviour when the ring buffer is full is controlled by the Blocking property value.

Implements log4cxx::AppenderSkeleton.

◆ close()

void log4cxx::AsyncAppender::close ( )

overridevirtual

Close this AsyncAppender by interrupting the dispatcher thread which will process all pending events before exiting.

Implements log4cxx::Appender.

◆ doAppend()

void log4cxx::AsyncAppender::doAppend	(	const spi::LoggingEventPtr &	event,
		helpers::Pool &	pool1 )

overridevirtual

Call AppenderSkeleton::doAppendImpl without acquiring a lock.

Reimplemented from log4cxx::AppenderSkeleton.

◆ getAllAppenders()

AppenderList log4cxx::AsyncAppender::getAllAppenders ( ) const

overridevirtual

Get iterator over attached appenders.

Returns: list of all attached appenders.

Implements log4cxx::spi::AppenderAttachable.

◆ getAppender()

AppenderPtr log4cxx::AsyncAppender::getAppender ( const LogString & name ) const

overridevirtual

Get appender by name.

Parameters

name	name, may not be null.

Returns: matching appender or null.

Implements log4cxx::spi::AppenderAttachable.

◆ getBlocking()

bool log4cxx::AsyncAppender::getBlocking ( ) const

Gets whether appender should block calling thread when buffer is full.

If false, messages will be counted by logger and a summary message appended after the contents of the buffer have been appended.

Returns: true if calling thread will be blocked when buffer is full.

◆ getBufferSize()

int log4cxx::AsyncAppender::getBufferSize ( ) const

Gets the current buffer size.

Returns: the current value of the BufferSize option.

◆ getLocationInfo()

bool log4cxx::AsyncAppender::getLocationInfo ( ) const

The current value of the (unused) LocationInfo option.

◆ isAttached()

bool log4cxx::AsyncAppender::isAttached ( const AppenderPtr appender ) const

overridevirtual

Determines if specified appender is attached.

Parameters

appender appender.

Returns: true if attached.

Implements log4cxx::spi::AppenderAttachable.

◆ removeAllAppenders()

void log4cxx::AsyncAppender::removeAllAppenders ( )

overridevirtual

Removes and closes all attached appenders.

Implements log4cxx::spi::AppenderAttachable.

◆ removeAppender() [1/2]

void log4cxx::AsyncAppender::removeAppender ( const AppenderPtr appender )

overridevirtual

Removes an appender.

Parameters

appender appender to remove.

Implements log4cxx::spi::AppenderAttachable.

◆ removeAppender() [2/2]

void log4cxx::AsyncAppender::removeAppender ( const LogString & name )

overridevirtual

Remove appender by name.

Parameters

name name.

Implements log4cxx::spi::AppenderAttachable.

◆ replaceAppender()

bool log4cxx::AsyncAppender::replaceAppender	(	const AppenderPtr &	oldAppender,
		const AppenderPtr &	newAppender )

Replace oldAppender with newAppender.

Returns: true if oldAppender was replaced with newAppender.

◆ replaceAppenders()

void log4cxx::AsyncAppender::replaceAppenders ( const AppenderList & newList )

Replace any previously added appenders with newList.

◆ requiresLayout()

bool log4cxx::AsyncAppender::requiresLayout ( ) const

overridevirtual

Return false.

Implements log4cxx::Appender.

◆ setBlocking()

void log4cxx::AsyncAppender::setBlocking ( bool value )

Sets whether appender should wait if there is no space available in the event buffer or immediately return.

Parameters

value true if appender should wait until available space in buffer.

◆ setBufferSize()

void log4cxx::AsyncAppender::setBufferSize ( int size )

The BufferSize option takes a non-negative integer value.

This integer value determines the maximum size of the bounded buffer.

◆ setLocationInfo()

void log4cxx::AsyncAppender::setLocationInfo ( bool flag )

The LocationInfo attribute is provided for compatibility with log4j and has no effect on the log output.

Parameters

flag	new value.

◆ setOption()

void log4cxx::AsyncAppender::setOption	(	const LogString &	option,
		const LogString &	value )

overridevirtual

Set option to value.

Supported options	Supported values	Default value
BufferSize	int	128
Blocking	True,False	True

See also: AppenderSkeleton::setOption()

Reimplemented from log4cxx::AppenderSkeleton.

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

asyncappender.h

Public Member Functions

Additional Inherited Members

Detailed Description

Configurable properties

Constructor & Destructor Documentation

◆ AsyncAppender()

◆ ~AsyncAppender()

Member Function Documentation

◆ addAppender()

◆ append()

◆ close()

◆ doAppend()

◆ getAllAppenders()

◆ getAppender()

◆ getBlocking()

◆ getBufferSize()

◆ getLocationInfo()

◆ isAttached()

◆ removeAllAppenders()

◆ removeAppender() [1/2]

◆ removeAppender() [2/2]

◆ replaceAppender()

◆ replaceAppenders()

◆ requiresLayout()

◆ setBlocking()

◆ setBufferSize()

◆ setLocationInfo()

◆ setOption()