src/main/include/log4cxx/asyncappender.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
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 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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#ifndef _LOG4CXX_ASYNC_APPENDER_H
#define _LOG4CXX_ASYNC_APPENDER_H

#include <log4cxx/appenderskeleton.h>
#include <log4cxx/helpers/appenderattachableimpl.h>
#include <log4cxx/spi/loggingevent.h>

namespace LOG4CXX_NS
{
LOG4CXX_LIST_DEF(LoggingEventList, spi::LoggingEventPtr);

/**
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).

An AsyncAppender is used when you configure a logger to be asynchronous.
These AsyncAppender(s) use [the default values](@ref log4cxx::AsyncAppender::setOption) for all options
and they cannot be changed using configuration file entries.
For more control over the AsyncAppender options,
use <b>appender-ref</b> element in the logger configuration instead. 

<b>Important notes:</b>
- Your application must call LogManager::shutdown when it exits
to prevent undefined behaviour when using this appender.
- Runtime configuration of options requires an XML configuration file
(see the example below).

This appender is useful when outputting to a slow event sink,
for example, unbuffered output to a file,
a remote SMTP server or a database.
Note that configuring a FileAppender to use [buffered output](@ref log4cxx::FileAppender::setOption)
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 <b>appender-ref</b> elements
to the <b>appender class="AsyncAppender"</b> element
when using runtime configuration.

Here is a sample configuration file:
\include async-example.xml

### Configurable properties

\anchor BlockingProperty 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](@ref AsyncAppender::setOption) controls which behaviour is used.
When events are discarded,
the logged output will indicate this
with a log message prefixed with <i>Discarded</i>.
The output may contain one <i>Discarded</i> 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](internal-debugging.html).
The AsyncAppender will output a histogram of queue length frequencies when closed.

See AsyncAppender::setOption for details.

*/
class LOG4CXX_EXPORT AsyncAppender :
	public virtual spi::AppenderAttachable,
#if LOG4CXX_ABI_VERSION <= 15
	public virtual AppenderSkeleton
#else
	public AppenderSkeleton
#endif
{
	protected:
		struct AsyncAppenderPriv;

	public:
		DECLARE_LOG4CXX_OBJECT(AsyncAppender)
		BEGIN_LOG4CXX_CAST_MAP()
		LOG4CXX_CAST_ENTRY(AsyncAppender)
		LOG4CXX_CAST_ENTRY_CHAIN(AppenderSkeleton)
		LOG4CXX_CAST_ENTRY(spi::AppenderAttachable)
		END_LOG4CXX_CAST_MAP()

		/**
		 * Create new instance.
		*/
		AsyncAppender();

		/**
		 *  If not closed, calls AsyncAppender::close.
		 */
		virtual ~AsyncAppender();

		/**
		 * Ensure \c newAppender receives any logging event
		 * added to this appender.
		 *
		 * @param newAppender appender to add, may not be null.
		*/
		void addAppender(const AppenderPtr newAppender) override;

		/**
		* Call AppenderSkeleton#doAppendImpl without acquiring a lock.
		*/
		void doAppend( LOG4CXX_APPEND_FORMAL_PARAMETERS ) override;

		/**
		* Add \c event to a ring buffer.
		* The behaviour when the ring buffer is full
		* is controlled by the [Blocking property](@ref BlockingProperty) value.
		*/
		void append( LOG4CXX_APPEND_FORMAL_PARAMETERS ) override;

		/**
		Close this <code>AsyncAppender</code> by interrupting the
		dispatcher thread which will process all pending events before
		exiting.
		*/
		void close() override;

		/**
		 * Get iterator over attached appenders.
		 * @return list of all attached appenders.
		*/
		AppenderList getAllAppenders() const override;

		/**
		 * Get appender by name.
		 *
		 * @param name name, may not be null.
		 * @return matching appender or null.
		*/
		AppenderPtr getAppender(const LogString& name) const override;

		/**
		 * The current value of the (unused) <b>LocationInfo</b> option.
		*/
		bool getLocationInfo() const;
		/**
		* Determines if specified appender is attached.
		* @param appender appender.
		* @return true if attached.
		*/
		bool isAttached(const AppenderPtr appender) const override;

		/** Return false
		*/
		bool requiresLayout() const override;

		/**
		 * Removes and closes all attached appenders.
		*/
		void removeAllAppenders() override;

		/**
		 * Removes an appender.
		 * @param appender appender to remove.
		*/
		void removeAppender(const AppenderPtr appender) override;
		/**
		* Remove appender by name.
		* @param name name.
		*/
		void removeAppender(const LogString& name) override;

		/**
		 * Replace \c oldAppender  with \c newAppender.
		 * @return true if oldAppender was replaced with newAppender.
		 */
		bool replaceAppender(const AppenderPtr& oldAppender, const AppenderPtr& newAppender) LOG4CXX_16_VIRTUAL_SPECIFIER;

		/**
		 * Replace any previously added appenders with \c newList.
		 */
		void replaceAppenders(const AppenderList& newList) LOG4CXX_16_VIRTUAL_SPECIFIER;

		/**
		* The <b>LocationInfo</b> attribute is provided for compatibility
		* with log4j and has no effect on the log output.
		* @param flag new value.
		*/
		void setLocationInfo(bool flag);

		/**
		* Use \c newSize (a non-negative integer value) for
		* the number of [logging events](@ref spi::LoggingEvent) the ring buffer can hold.
		* The ring buffer size cannot be changed once the appender has received an event.
		* */
		void setBufferSize(int newSize);

		/**
		 * Gets the current buffer size.
		 * @return the current value of the <b>BufferSize</b> option.
		*/
		int getBufferSize() const;

		/**
		 * Use \c newValue for whether appender should block the calling thread
		 * if there is no space in the ring buffer.
		 *
		 * @param newValue true if appender should wait until space is available in the ring buffer.
		 */
		void setBlocking(bool newValue);

		/**
		 * Gets whether appender should block calling thread when ring buffer is full.
		 * If false, messages will be counted by logger and a summary
		 * message added after the buffered events have been appended.
		 *
		 * @return true if calling thread will be blocked when ring buffer is full.
		 */
		bool getBlocking() const;


		/**
		\copybrief AppenderSkeleton::setOption()

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

		\sa AppenderSkeleton::setOption()
		 */
		void setOption(const LogString& option, const LogString& value) override;


	private:
		AsyncAppender(const AsyncAppender&);
		AsyncAppender& operator=(const AsyncAppender&);

}; // class AsyncAppender
LOG4CXX_PTR_DEF(AsyncAppender);
}  //  namespace log4cxx

#endif//  _LOG4CXX_ASYNC_APPENDER_H