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--- logging/site/trunk/docs/log4net/src/release/manual/contexts.html (added)
+++ logging/site/trunk/docs/log4net/src/release/manual/contexts.html Wed Jul 25 23:41:40 2007
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+ <a name="log4net Manual - Contexts"></a><div class="section"><h2>log4net Manual - Contexts</h2>
+ <sectionMenu name="Contents"></sectionMenu>
+
+ <p>
+ Most real-world systems have to deal with multiple clients simultaneously. In a
+ typical multithreaded implementation of such a system, different threads will
+ handle different clients. Logging is especially well suited to trace and debug
+ complex distributed applications. An approach to differentiate the
+ logging output of one client from another is to instantiate a new separate
+ logger for each client. However this promotes the proliferation of loggers and
+ increases the management overhead of logging.
+ </p>
+ <p>
+ A lighter technique is to uniquely stamp each log request initiated from the
+ same client interaction.
+ </p>
+ <p>
+ Log4net supports different types of contextual logging and contexts with different scopes.
+ </p>
+
+ <a name="Scopes"></a><div class="section"><h2>Scopes</h2>
+ <p>
+ Contextual data can be set in different scopes. These contexts have progressively narrower visibility.
+ In the logging event itself the values from all of the contexts are combined together such that
+ values specified in a lower scoped context hide values from a higher context.
+ </p>
+
+ <div class="table">
+ <table class="bodyTable">
+ <tr class="a">
+ <th>Scope</th>
+ <th>Type</th>
+ <th>Description</th>
+ </tr>
+ <tr class="b">
+ <td>Global</td>
+ <td><span class="code">log4net.GlobalContext</span></td>
+ <td>
+ The global context is shared by all threads in the current AppDomain.
+ This context is thread safe for use by multiple threads concurrently.
+ </td>
+ </tr>
+ <tr class="a">
+ <td>Thread</td>
+ <td><span class="code">log4net.ThreadContext</span></td>
+ <td>
+ The thread context is visible only to the current managed thread.
+ </td>
+ </tr>
+ <tr class="b">
+ <td>Logical Thread</td>
+ <td><span class="code">log4net.ThreadLogicalContext</span></td>
+ <td>
+ The logical thread context is visible to a logical thread. Logical
+ threads can jump from one managed thread to another. For more details
+ see the .NET API <span class="code">System.Runtime.Remoting.Messaging.CallContext</span>.
+ </td>
+ </tr>
+ <tr class="a">
+ <td>Event</td>
+ <td><span class="code">log4net.Core.LoggingEvent</span></td>
+ <td>
+ Each event captures the current contextual state at the time the event
+ is generated. Contextual data can be set on the event itself. This context
+ is only visible to the code generating the event itself.
+ </td>
+ </tr>
+ </table>
+ </div>
+ </div>
+
+ <a name="Context Properties"></a><div class="section"><h2>Context Properties</h2>
+ <p>
+ The log4net contexts store properties, i.e. name value pairs. The name is a string
+ the value is any object. A property can be set as follows:
+ </p>
+ <div class="source"><pre>
+log4net.GlobalContext.Properties["name"] = value;
+</pre></div>
+ <p>
+ If properties with the same name are set in more than one context scope then
+ the value in the narrowest scope (lower down in the list above) will hide the
+ other values.
+ </p>
+ <p>
+ The property values are stored as objects within the <span class="code">LoggingEvent</span>.
+ The <span class="code">PatternLayout</span> supports rendering the value of a named
+ property using the <span class="code">%property{name}</span> syntax. The value is
+ converted to a string by passing it to the <span class="code">log4net.ObjectRenderer.RendererMap</span>
+ which will locate any custom renderer for the value type. The default behavior for
+ custom types is to call the object's <span class="code">ToString()</span> method.
+ </p>
+
+ <a name="Active Property Values"></a><div class="section"><h2>Active Property Values</h2>
+ <p>
+ An active property value is one who's value changes over time.
+ </p>
+ <p>
+ For example, imagine a custom type that implemented the
+ <span class="code">ToString()</span> method to return the
+ number of bytes allocated by the runtime garbage collector.
+ </p>
+ <div class="source"><pre>
+public class GCAllocatedBytesHelper
+{
+ public override string ToString()
+ {
+ return GC.GetTotalMemory(true).ToString();
+ }
+}</pre></div>
+ <p>
+ An instance of this type can be added to the <span class="code">log4net.GlobalContext</span>
+ during application startup:
+ </p>
+ <div class="source"><pre>
+log4net.GlobalContext.Properties["GCAllocatedBytes"] = new GCAllocatedBytesHelper();
+</pre></div>
+ <p>
+ Once this property is set in the context all subsequent logging events will have a property
+ called <i>GCAllocatedBytes</i>. The value of the property will be an instance of the
+ <span class="code">GCAllocatedBytesHelper</span> type. When this value is rendered to a
+ string by calling the <span class="code">ToString</span> method the current number of bytes
+ allocated by the garbage collector will be returned and included in the output.
+ </p>
+
+ </div>
+
+ </div>
+
+ <a name="Context Stacks"></a><div class="section"><h2>Context Stacks</h2>
+ <p>
+ Sometimes simple key value pairs are not the most convenient way of capturing contextual
+ information. A stack of information is a very convenient way of storing data especially
+ as our applications tend to be stack based.
+ </p>
+ <p>
+ The <span class="code">ThreadContext</span> and <span class="code">LogicalThreadContext</span>
+ also support storing contextual data in a stack. The stack is stored in context property,
+ therefore stacks have names and more than one stack can exist in the same context. A property
+ value set in a narrower context would override a stack with the same property name set in a
+ wider scoped context.
+ </p>
+ <p>
+ The stack supports <span class="code">Push</span> and <span class="code">Pop</span> methods.
+ As more contextual data is pushed onto the stack the stack grows. When the stack is rendered
+ all the data pushed onto the stack is output with the most recent data to the right hand
+ end of the string.
+ </p>
+ <p>
+ As the stack is just an object stored in the context properties it is also rendered
+ using the same <span class="code">PatternLayout</span> syntax: <span class="code">%property{name}</span>.
+ Where <i>name</i> is the name of the stack.
+ </p>
+ <p>
+ Calls the the stack's <span class="code">Push</span> and <span class="code">Pop</span>
+ methods must be matched up so that each push has a corresponding pop. The
+ <span class="code">Push</span> method also returns an <span class="code">IDisposable</span>
+ object that will perform the required pop operation when it is disposed. This allows
+ the C# <i>using</i> syntax to be used to automate the stack management.
+ </p>
+ <div class="source"><pre>
+using(log4net.ThreadContext.Stacks["NDC"].Push("context"))
+{
+ log.Info("Message");
+}
+</pre></div>
+ <p>
+ The INFO level log has a stack stored in its <i>NDC</i> property. The top item in the
+ stack is the string <i>context</i>.
+ The <i>using</i> syntax ensures that the value <i>context</i> is popped off the stack
+ at the end of the block.
+ </p>
+ <p>
+ The <span class="code">using</span>
+ syntax is recommended because it removes some work load from the developer and
+ reduces errors in matching up the Push and Pop calls, especially when exceptions
+ can occur.
+ </p>
+ </div>
+
+ <a name="Nested Diagnostic Contexts"></a><div class="section"><h2>Nested Diagnostic Contexts</h2>
+ <p>
+ The <span class="code">NDC</span> (Nested Diagnostic Context) exists for compatibility
+ with older versions of log4net. This helper class implements a stack which is stored
+ in the thread context property named <i>NDC</i>.
+ </p>
+ </div>
+
+ <a name="Mapped Diagnostic Contexts"></a><div class="section"><h2>Mapped Diagnostic Contexts</h2>
+ <p>
+ The <span class="code">MDC</span> (MappedDiagnostic Context) exists for compatibility
+ with older versions of log4net. This helper class implements a properties map which is
+ mapped directly through to the thread context properties.
+ </p>
+ </div>
+
+ <p>
+ To illustrate this point, let us take the example of a web service delivering
+ content to numerous clients. The web service can build the <span class="code">NDC</span> at the very
+ beginning of the request before executing other code. The contextual
+ information can be the client's host name and other information inherent to the
+ request, typically information contained in cookies. Hence, even if the web
+ service is serving multiple clients simultaneously, the logs initiated by the
+ same code, i.e. belonging to the same logger, can still be distinguished
+ because each client request will have a different <span class="code">NDC</span> stack. Contrast this with
+ the complexity of passing a freshly instantiated logger to all code exercised
+ during the client's request.
+ </p>
+ <p>
+ Nevertheless, some sophisticated applications, such as virtual hosting web
+ servers, must log differently depending on the virtual host context and also
+ depending on the software component issuing the request. Log4net supports
+ multiple logger repositories. This would allow each virtual host to possess its own copy
+ of the logger hierarchy. Configuring multiple logger hierarchies is beyond the
+ scope of this document.
+ </p>
+
+ </div>
+
+
+ </div>
+ </div>
+ <div class="clear">
+ <hr/>
+ </div>
+ <div id="footer">
+ <div class="xright">©
+ 2007
+
+ Apache Software Foundation
+
+
+
+
+
+
+
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+ <hr/>
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+ </div>
+ </body>
+</html>
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==============================================================================
--- logging/site/trunk/docs/log4net/src/release/manual/internals.html (added)
+++ logging/site/trunk/docs/log4net/src/release/manual/internals.html Wed Jul 25 23:41:40 2007
@@ -0,0 +1,433 @@
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+ <a name="log4net Manual - Internals"></a><div class="section"><h2>log4net Manual - Internals</h2>
+ <sectionMenu name="Contents"></sectionMenu>
+
+ <a name="Performance"></a><div class="section"><h2>Performance</h2>
+ <p>
+ One of the often-cited arguments against logging is its computational cost.
+ This is a legitimate concern as even moderately sized applications can generate
+ thousands of log requests. Much effort was spent measuring and tweaking logging
+ performance. Log4net claims to be fast and flexible: speed first, flexibility
+ second.
+ </p>
+ <p>
+ The user should be aware of the following performance issues.
+ </p>
+ <ol type="1">
+ <li>
+ <strong>Logging performance when logging is turned off.</strong>
+
+ When logging is turned off entirely or just for a set of levels, the cost of a
+ log request consists of a method invocation plus an integer comparison.
+
+ <p>
+ However, The method invocation involves the "hidden" cost of parameter
+ construction.
+ </p>
+ <p>
+ For example, for some logger
+ <span class="code">log</span>, writing,
+ </p>
+ <div class="syntax"><pre class="code">
+log.Debug("Entry number: " + i + " is " + entry[i].ToString());</pre></div>
+ <p>
+ incurs the cost of constructing the message parameter, i.e. converting both
+ integer
+ <span class="code">i</span>
+ and
+ <span class="code">entry[i]</span>
+ to strings, and concatenating intermediate strings, regardless of whether the
+ message will be logged or not. This cost of parameter construction can be quite
+ high and it depends on the number and type of the parameters involved.
+ </p>
+ <p>
+ To avoid the parameter construction cost write:
+ </p>
+ <div class="syntax"><pre class="code">
+if(log.IsDebugEnabled)
+{
+ log.Debug("Entry number: " + i + " is " + entry[i].ToString());
+}</pre></div>
+ <p>
+ This will not incur the cost of parameter construction if debugging is
+ disabled. On the other hand, if the logger is debug-enabled, it will incur
+ twice the cost of evaluating whether the logger is enabled or not: once in
+ <span class="code">IsDebugEnabled</span>
+ and once in
+ <span class="code">Debug</span>. This is an insignificant overhead because
+ evaluating a logger takes about 1% of the time it takes to actually log.
+ </p>
+ <p>
+ Certain users resort to pre-processing or compile-time techniques to compile
+ out all log statements. This leads to perfect performance efficiency with
+ respect to logging. However, since the resulting application binary does not
+ contain any log statements, logging cannot be turned on for that binary. In
+ many people's opinion this is a disproportionate price to pay in exchange for a
+ small performance gain.
+ </p>
+ </li>
+ <li>
+ <strong>The performance of deciding whether to log or not to log when logging is
+ turned on.</strong>
+
+ This is essentially the performance of walking the logger hierarchy. When
+ logging is turned on, log4net still needs to compare the level of the log
+ request with the level of the request logger. However, loggers may not have an
+ assigned level; they can inherit them from the logger hierarchy. Thus, before
+ inheriting a level, the logger may need to search its ancestors.
+
+ <p>
+ There has been a serious effort to make this hierarchy walk to be as fast as
+ possible. For example, child loggers link only to their existing ancestors. In
+ the
+ <span class="code">BasicConfigurator</span>
+ example shown earlier, the logger named
+ <span class="code">Com.Foo.Bar</span>
+ is linked directly to the <i>root</i> logger, thereby circumventing the nonexistent
+ <span class="code">Com</span>
+ or
+ <span class="code">Com.Foo</span>
+ loggers. This significantly improves the speed of the walk, especially in
+ "sparse" hierarchies.
+ </p>
+ <p>
+ The typical cost of walking the hierarchy is typically 3 times slower than when
+ logging is turned off entirely.
+ </p>
+ </li>
+ <li>
+ <strong>Actually outputting log messages</strong>
+
+ This is the cost of formatting the log output and sending it to its target
+ destination. Here again, a serious effort was made to make layouts (formatters)
+ perform as quickly as possible. The same is true for appenders.
+
+ </li>
+ </ol>
+ <p>
+ Although log4net has many features, its first design goal was speed. Some
+ log4net components have been rewritten many times to improve performance.
+ Nevertheless, contributors frequently come up with new optimizations. You
+ should be pleased to know that when configured with the
+ <span class="code">SimpleLayout</span>
+ performance tests have shown log4net to log within an order of magnitude of
+ <span class="code">System.Console.WriteLine</span>.
+ </p>
+ </div>
+
+ <a name="Logging Event Flow"></a><div class="section"><h2>Logging Event Flow</h2>
+ <p>
+ The following is the series of steps and checks that a messages goes through while being logged.
+ For the purposes of this example we will document an <span class="code">INFO</span> level
+ message being logged on logger <i>ConsoleApp.LoggingExample</i>. This logger is configured
+ to use the <span class="code">log4net.Appender.ConsoleAppender</span>. The repository used
+ in this example is a <span class="code">log4net.Repository.Hierarchy</span> object.
+ </p>
+ <ol type="1">
+ <li>
+
+ The user logs a message using the <span class="code">ILog.Info</span> method on the logger
+ obtained using a call to <span class="code">log4net.LogManager.GetLogger("ConsoleApp.LoggingExample")</span>.
+ For example: <span class="code">log4net.LogManager.GetLogger("ConsoleApp.LoggingExample").Info("Application Start");</span>
+ The <span class="code">ILog</span> interface is actually an extension to log4net that provides level
+ specific logging methods (i.e. Debug, Info, Warn, Error, and Fatal).
+
+ </li>
+ <li>
+
+ The message is then logged through to the <span class="code">ILogger.Log</span> method on the
+ appropriate <span class="code">log4net.Repository.Hierarchy.Logger</span> object. The
+ <span class="code">ILogger.Log</span> method takes the <span class="code">Level</span> to
+ log at as a parameter and therefore works for all levels.
+
+ </li>
+ <li>
+
+ The repository threshold level is compared to the message level to determine if the message
+ can be logged. If the message level is below the threshold level the message is not logged.
+ In this case the repository is a <span class="code">log4net.Repository.Hierarchy</span> object.
+
+ </li>
+ <li>
+
+ The <span class="code">Logger</span> level is compared to the message level to determine if the
+ message can be logged. Note that the <span class="code">Logger</span> level is inherited from a
+ parent <span class="code">Logger</span> if not specified explicitly for this <span class="code">Logger</span>.
+ If the message level is below the <span class="code">Logger</span> level the message is not logged.
+
+ </li>
+ <li>
+
+ A <span class="code">LoggingEvent</span> instance is created to encapsulate the message being logged.
+
+ </li>
+ <li>
+
+ The list of appenders for the <span class="code">Logger</span> is built. This includes appenders
+ attached to parent <span class="code">Logger</span>s except where excluded by the
+ <span class="code">Logger.Additivity</span> property.
+
+ </li>
+ <li>
+
+ The <span class="code">LoggingEvent</span> object is passed to the
+ <span class="code">IAppender.DoAppend</span> method for each appender.
+
+ </li>
+ </ol>
+ <p>
+ For Each Appender that the <span class="code">LoggingEvent</span> is delivered to the following
+ actions take place:
+ </p>
+ <ol type="1">
+ <li>
+
+ The appender threshold level is compared to the message level to determine if the message
+ can be logged. If the message level is below the threshold level the message is not logged.
+
+ </li>
+ <li>
+
+ If the appender has a filter chain the <span class="code">LoggingEvent</span> is passed down the
+ filter chain which can decide if the message can be logged or not.
+
+ </li>
+ <li>
+
+ Next an appender specific check is performed. Usually this check will verify that all the
+ required properties are set for the appender (e.g. a <span class="code">Layout</span> is set if required).
+
+ </li>
+ <li>
+
+ The <span class="code">LoggingEvent</span> is passed to the appender specific
+ <span class="code">Append</span> method. What happens now is specific to the appender.
+
+ </li>
+ </ol>
+ <p>
+ The following actions take place in the <span class="code">ConsoleAppender.Append</span> method:
+ </p>
+ <ol type="1">
+ <li>
+
+ The <span class="code">ConsoleAppender</span> uses a <span class="code">Layout</span> to
+ format the message as a string for display.
+
+ </li>
+ <li>
+
+ The <span class="code">Layout</span> uses the <span class="code">LoggingEvent.RenderedMessage</span>
+ property to get the string for the message object. This uses the registered
+ <span class="code">IObjectRenderer</span> for the type of the message object.
+
+ </li>
+ <li>
+
+ The message text is displayed on the console using the <span class="code">Console.WriteLine</span> method.
+
+ </li>
+ </ol>
+ </div>
+
+ </div>
+
+
+ </div>
+ </div>
+ <div class="clear">
+ <hr/>
+ </div>
+ <div id="footer">
+ <div class="xright">©
+ 2007
+
+ Apache Software Foundation
+
+
+
+
+
+
+
+ </div>
+ <div class="clear">
+ <hr/>
+ </div>
+ </div>
+ </body>
+</html>
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