<html>
<head>
<base href="https://wiki.asterisk.org/wiki">
<link rel="stylesheet" href="/wiki/s/en/2171/18/9/_/styles/combined.css?spaceKey=TOP&forWysiwyg=true" type="text/css">
</head>
<body style="background: white;" bgcolor="white" class="email-body">
<div id="pageContent">
<div id="notificationFormat">
<div class="wiki-content">
<div class="email">
<h2><a href="https://wiki.asterisk.org/wiki/display/TOP/Thread+pool+and+Work+Queues">Thread pool and Work Queues</a></h2>
<h4>Page <b>edited</b> by <a href="https://wiki.asterisk.org/wiki/display/~beagles">Brent Eagles</a>
</h4>
<br/>
<h4>Changes (8)</h4>
<div id="page-diffs">
<table class="diff" cellpadding="0" cellspacing="0">
<tr><td class="diff-snipped" >...<br></td></tr>
<tr><td class="diff-unchanged" >{color:white} <br>{panel:title=Thread Pools and Work Queues|titleBGColor=#2022FF|bgColor=#7788FF} <br></td></tr>
<tr><td class="diff-added-lines" style="background-color: #dfd;">* Managed pools of threads, working on a collection of work items or *work queue*. <br></td></tr>
<tr><td class="diff-unchanged" >* Rationale: <br></td></tr>
<tr><td class="diff-deleted-lines" style="color:#999;background-color:#fdd;text-decoration:line-through;">** Reduce complexity of creating robust multithreaded applications. <br>** XXX more here!!!! <br>* How: <br>** Serialize access to shared data, by serializing the operations themselves. That is, don't share the data. <br>* Wha? <br>** Okay.. it breaks down something like this... <br></td></tr>
<tr><td class="diff-added-lines" style="background-color: #dfd;">** Reduces the complexity of building robust multithreaded applications, especially objects who are highly interactive <br>with other objects or external agents. <br>** Reduces opportunities for deadlocks and race conditions. <br>** All of this while maintaining maximum levels of concurrency in an application. <br>** Interacts very well with Ice's Asynchronous Method Invocation (AMI) and Asynchronous Method Dispatch (AMD). <br></td></tr>
<tr><td class="diff-unchanged" >{panel} <br>{color} <br></td></tr>
<tr><td class="diff-snipped" >...<br></td></tr>
<tr><td class="diff-unchanged" >* Implications: <br>** All Ice method and methods that respond to potentially concurrent events must be implemented in terms of Work object instances. <br></td></tr>
<tr><td class="diff-changed-lines" >** For Ice, AMI and AMD tends to get used <span class="diff-added-words"style="background-color: #dfd;">quite often as it works quite neatly with the concept of</span> a <span class="diff-deleted-words"style="color:#999;background-color:#fdd;text-decoration:line-through;">lot.</span> <span class="diff-added-words"style="background-color: #dfd;">work item.</span> <br></td></tr>
<tr><td class="diff-changed-lines" >** Code is organized differently. <span class="diff-deleted-words"style="color:#999;background-color:#fdd;text-decoration:line-through;">A</span> <span class="diff-added-words"style="background-color: #dfd;">It is a</span> little awkward at first but quickly feels natural. <br></td></tr>
<tr><td class="diff-unchanged" >{panel} <br>{color} <br></td></tr>
<tr><td class="diff-snipped" >...<br></td></tr>
<tr><td class="diff-unchanged" >}; <br>{code} <br></td></tr>
<tr><td class="diff-deleted-lines" style="color:#999;background-color:#fdd;text-decoration:line-through;">_a graphic would be handy_ <br></td></tr>
<tr><td class="diff-unchanged" >{panel} <br>{color} <br></td></tr>
<tr><td class="diff-snipped" >...<br></td></tr>
<tr><td class="diff-unchanged" >{color:white} <br>{panel:title=In the Wild|titleBGColor=#2022FF|bgColor=#7788FF} <br></td></tr>
<tr><td class="diff-added-lines" style="background-color: #dfd;">* The thread pool is used extensively in a few components and most likely will be retrofitted to the other components in time. <br></td></tr>
<tr><td class="diff-unchanged" >* SIP Session Gateway. <br></td></tr>
<tr><td class="diff-added-lines" style="background-color: #dfd;">* SIP Registrar. <br></td></tr>
<tr><td class="diff-unchanged" >{panel} <br>{color} <br></td></tr>
</table>
</div> <h4>Full Content</h4>
<div class="notificationGreySide">
<div class='panelMacro'><table class='warningMacro'><colgroup><col width='24'><col></colgroup><tr><td valign='top'><img src="/wiki/images/icons/emoticons/forbidden.gif" width="16" height="16" align="absmiddle" alt="" border="0"></td><td>Yes, this is written in a very informal, conversational voice. It was easier getting the info out this way.</td></tr></table></div>
<p><font color="white"><br/>
<div class="panel" style="background-color: #7788FF;border-width: 1px;"><div class="panelHeader" style="border-bottom-width: 1px;background-color: #2022FF;"><b>Thread Pools and Work Queues</b></div><div class="panelContent" style="background-color: #7788FF;">
<ul>
<li>Managed pools of threads, working on a collection of work items or <b>work queue</b>.</li>
<li>Rationale:
<ul>
<li>Reduces the complexity of building robust multithreaded applications, especially objects who are highly interactive<br/>
with other objects or external agents.</li>
<li>Reduces opportunities for deadlocks and race conditions.</li>
<li>All of this while maintaining maximum levels of concurrency in an application.</li>
<li>Interacts very well with Ice's Asynchronous Method Invocation (AMI) and Asynchronous Method Dispatch (AMD).</li>
</ul>
</li>
</ul>
</div></div></font></p>
<p><font color="white"><br/>
<div class="panel" style="background-color: #7788FF;border-width: 1px;"><div class="panelHeader" style="border-bottom-width: 1px;background-color: #2022FF;"><b>Thread Pools</b></div><div class="panelContent" style="background-color: #7788FF;">
<ul>
<li>Familiar concept. A managed collection of threads for performing work.</li>
<li>Asterisk SCF thread pool details.
<ul>
<li>Resizable, with an API for setting objects that implement custom sizing policies.</li>
<li>Default implementation cleans up idle threads to recover resources after peaks.</li>
<li>Each pool owns a work queue.</li>
</ul>
</li>
<li>What is a work queue?</li>
</ul>
</div></div></font></p>
<p><font color="white"><br/>
<div class="panel" style="background-color: #7788FF;border-width: 1px;"><div class="panelHeader" style="border-bottom-width: 1px;background-color: #2022FF;"><b>Work Queues</b></div><div class="panelContent" style="background-color: #7788FF;">
<ul>
<li>A work queue is a collection of "Work", which is basically an object that implements the Work interface.</li>
<li>Here is the kicker. A Work object may itself be a collection of Work objects.</li>
<li>Voila, we have a mechanism for queuing work for a set of data in a way that it will only ever be acted on by a single thread at a time.</li>
<li>Implications:
<ul>
<li>All Ice method and methods that respond to potentially concurrent events must be implemented in terms of Work object instances.</li>
<li>For Ice, AMI and AMD tends to get used quite often as it works quite neatly with the concept of a work item.</li>
<li>Code is organized differently. It is a little awkward at first but quickly feels natural.</li>
</ul>
</li>
</ul>
</div></div></font><br/>
<span class="image-wrap" style=""><img src="/wiki/download/attachments/19006261/threadpool.png?version=1&modificationDate=1319207561867" style="border: 0px solid black" /></span></p>
<p><font color="white"><br/>
<div class="panel" style="background-color: #7788FF;border-width: 1px;"><div class="panelHeader" style="border-bottom-width: 1px;background-color: #2022FF;"><b>How Does it Work?</b></div><div class="panelContent" style="background-color: #7788FF;">
<ul>
<li>Basically for any object that has methods that may be called by multiple concurrent threads of execution, organize its associated state and implement the implementation details in terms of a "work" object and put it on a queue dedicated to that object.</li>
<li>A thread pool worker thread obtains a work item from its queue, and this work item is actually a queue of items belonging to your object.</li>
<li>The worker thread "executes" the work item, ultimately executing your queued work item.</li>
<li>As the work items for a single object are in a single work queue item and that work queue item may only be processed by a single thread, you have serialized access without mutexes and without concern of race conditions and deadlock.</li>
<li>Locks or no locks, it is a great way to avoid race conditions by organizing data access.</li>
</ul>
</div></div></font><br/>
<span class="image-wrap" style=""><img src="/wiki/download/attachments/19006261/threadpool2.png?version=1&modificationDate=1319207561929" style="border: 0px solid black" /></span></p>
<p><em>Not sure how these graphics might be used, but the general idea came to mind while reviewing the information. I think for the slides might need to be reorganized for these visuals to really work.</em></p>
<p><font color="white"><br/>
<div class="panel" style="background-color: #7788FF;border-width: 1px;"><div class="panelHeader" style="border-bottom-width: 1px;background-color: #2022FF;"><b>Anatomy of a Work Item</b></div><div class="panelContent" style="background-color: #7788FF;">
<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="theme: Confluence; brush: java; gutter: false">class MyWorkItem : public AsteriskSCF::System::WorkQueue::V1::Work
{
public:
MyWorkItem(const StateBeingWorkedOnPtr& state) :
mState(state)
{ }
void execute()
{ /* Do some stuff to state, possibly enqueuing another work item */ }
};</pre>
</div></div>
</div></div></font></p>
<p><font color="white"><br/>
<div class="panel" style="background-color: #7788FF;border-width: 1px;"><div class="panelHeader" style="border-bottom-width: 1px;background-color: #2022FF;"><b>In the Wild</b></div><div class="panelContent" style="background-color: #7788FF;">
<ul>
<li>The thread pool is used extensively in a few components and most likely will be retrofitted to the other components in time.</li>
<li>SIP Session Gateway.</li>
<li>SIP Registrar.</li>
</ul>
</div></div></font></p>
</div>
<div id="commentsSection" class="wiki-content pageSection">
<div style="float: right;" class="grey">
<a href="https://wiki.asterisk.org/wiki/users/removespacenotification.action?spaceKey=TOP">Stop watching space</a>
<span style="padding: 0px 5px;">|</span>
<a href="https://wiki.asterisk.org/wiki/users/editmyemailsettings.action">Change email notification preferences</a>
</div>
<a href="https://wiki.asterisk.org/wiki/display/TOP/Thread+pool+and+Work+Queues">View Online</a>
|
<a href="https://wiki.asterisk.org/wiki/pages/diffpagesbyversion.action?pageId=19006261&revisedVersion=6&originalVersion=5">View Changes</a>
|
<a href="https://wiki.asterisk.org/wiki/display/TOP/Thread+pool+and+Work+Queues?showComments=true&showCommentArea=true#addcomment">Add Comment</a>
</div>
</div>
</div>
</div>
</div>
</body>
</html>