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diff --git a/src/documentation/content/xdocs/CppEventChannelIo.html b/src/documentation/content/xdocs/CppEventChannelIo.html new file mode 100755 index 0000000000..ec38687b43 --- /dev/null +++ b/src/documentation/content/xdocs/CppEventChannelIo.html @@ -0,0 +1,167 @@ +<html> + <head> + <title>Apache Qpid : CppEventChannelIo</title> + <link rel="stylesheet" href="styles/site.css" type="text/css" /> + <META http-equiv="Content-Type" content="text/html; charset=UTF-8"> + </head> + + <body> + <table class="pagecontent" border="0" cellpadding="0" cellspacing="0" width="100%" bgcolor="#ffffff"> + <tr> + <td valign="top" class="pagebody"> + <div class="pageheader"> + <span class="pagetitle"> + Apache Qpid : CppEventChannelIo + </span> + </div> + <div class="pagesubheading"> + This page last changed on Nov 06, 2006 by <font color="#0050B2">aconway</font>. + </div> + + <h1><a name="CppEventChannelIo-EventchannelIOabstraction."></a>Event channel IO abstraction.</h1> + +<p>Goals: provide an IO abstraction layer that can be efficiently implemented using differente techniques:</p> + +<ul> + <li>select/poll/epoll</li> + <li>aio_</li> + <li>ec_ new linux event channel.</li> + <li>shared mem, IPC etc.</li> +</ul> + + +<p>The event channel is the central IO absctraction.</p> + +<p>Async requests are posted to the channel as Events. When the request is complete it is returned from getEvent() with the data filled in.</p> + +<p>We provide synchronous APIs to wrap post(event), wait for getEvent(). On posix these APIs are actually implemented using user-level context swithching so we get a simple programing model with minimal blocking and kernel context switching.</p> + +<p>Note: this means that code before and after an apparently synchronous call ''may execute in different threads''. Don't use thread-local<br/> +storage. The term "task" will denote the user-level execution context and we'll provide "task-locak storage" that is carried with the user<br/> +context if we need it. </p> + +<p>We can provide some simple in-process synchronization via the event channel to allow use level tasks to block on application events.</p> + +<h2><a name="CppEventChannelIo-Coreconcepts%3A"></a>Core concepts:</h2> + +<p><tt>EventChannel</tt>:</p> + +<ul> + <li>Manages thread pool.</li> +</ul> + + +<ul> + <li>Worker threads loop getting and processing events.</li> +</ul> + + +<ul> + <li>Async requests: post request event, it will be processed when complete.</li> +</ul> + + +<ul> + <li>Notification: Threads can block on a notification event to be woken when some other thread posts that event.</li> +</ul> + + +<p><tt>Task</tt>:</p> + +<ul> + <li>like lightweight thread</li> +</ul> + + +<ul> + <li>ucontext APIs for user-level context switch.</li> +</ul> + + +<p>Linux ec_ + ucontext implementation:</p> + +<ul> + <li>EventChannel is thin facade over native ec_ APIs.</li> +</ul> + + +<ul> + <li>Tasks are scheduled onto threads.</li> +</ul> + + +<ul> + <li>ideally our threads ''never block'' (but they can be preempted)</li> +</ul> + + +<ul> + <li>when a thread hits a blocking point it suspends the current task and swaps to a ready task.</li> +</ul> + + +<ul> + <li>when the suspended task is unblocked (e.g. async IO completes) it becomes ready and will be picked up by another thread.</li> +</ul> + + +<p>Linux epoll + ucontext:</p> + +<ul> + <li>Prove ucontext ideas.</li> +</ul> + + +<ul> + <li>Use traditional polling inside EventChannel.</li> +</ul> + + +<p>APR portable impl: only need client support - simple blocking socket calls.</p> + +<p>Computing thread pool size:</p> + +<ul> + <li>Initial size based on availabe CPU paralleism</li> +</ul> + + +<ul> + <li>On linux /proc/cpuinfo? Any portable options.</li> +</ul> + + +<ul> + <li>Thread pool grows automatically to avoid deadlock.</li> +</ul> + + +<p><tt>ThreadPool</tt>: Size should stay close to actuall hardware paralellism + some delta due to pre-empted threads and thread-blocking<br/> +synchronization calls required in the event channel implementation itself.</p> + +<p>Questions:</p> + +<ul> + <li>Does the thread pool need to shrink to reclaim resources?</li> +</ul> + + +<ul> + <li>Is there a risk of unbounded growth? How to avoid without deadlock?</li> +</ul> + + + + </td> + </tr> + </table> + <table border="0" cellpadding="0" cellspacing="0" width="100%"> + <tr> + <td height="12" background="border/border_bottom.gif"><img src="border/spacer.gif" width="1" height="1" border="0"/></td> + </tr> + <tr> + <td align="center"><font color="grey">Document generated by Confluence on Apr 22, 2008 02:47</font></td> + </tr> + </table> + </body> +</html>
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