PageRenderTime 68ms CodeModel.GetById 42ms RepoModel.GetById 1ms app.codeStats 0ms

/2014/01/01/apr-pools/index.html

https://bitbucket.org/lotabout/lotabout.bitbucket.org
HTML | 376 lines | 225 code | 128 blank | 23 comment | 0 complexity | 383cdde45f9d5d295b8b91bf4c6c6434 MD5 | raw file
    

  1. <!DOCTYPE html>
    2. 

  2. <html lang="en">
    3. 

  3.   <head>
    4. 

  4.     <meta charset="utf-8">
    5. 

  5.     <title>
    6. 

  6.         
    7. 

  7.         apr 学习笔记之 apr_pool -
    8. 

  8.         
    9. 

  9.         Lot About
    10. 

  10.     </title>
    11. 

  11.     
    12. 

  12.     <meta name="author" content="Mark Wallace" />
    13. 

  13.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
    14. 

  14. 

  15.     <link href="/assets/css/bootstrap.min.css" rel="stylesheet">
    16. 

  16.     <link href="/assets/css/bootstrap-responsive.min.css" rel="stylesheet">
    17. 

  17.     <link href="/assets/css/docs.css" rel="stylesheet">
    18. 

  18.     <link href="/assets/css-social-buttons/zocial.stripped.css" rel="stylesheet">
    19. 

  19.     <link href="/assets/js/google-code-prettify/prettify.css" rel="stylesheet">
    20. 

  20.     <link href="/assets/css/style.css" rel="stylesheet">
    21. 

  21. 

  22.     
    23. 

  23.     <!-- mathjax config similar to math.stackexchange -->
    24. 

  24.     <script type="text/x-mathjax-config">
    25. 

  25.     MathJax.Hub.Config({
    26. 

  26.       jax: ["input/TeX", "output/HTML-CSS"],
    27. 

  27.       tex2jax: {
    28. 

  28.         inlineMath: [ ['$', '$'] ],
    29. 

  29.         displayMath: [ ['$$', '$$']],
    30. 

  30.         processEscapes: true,
    31. 

  31.         skipTags: ['script', 'noscript', 'style', 'textarea', 'pre', 'code']
    32. 

  32.       },
    33. 

  33.       messageStyle: "none",
    34. 

  34.       "HTML-CSS": { preferredFont: "TeX", availableFonts: ["STIX","TeX"] }
    35. 

  35.     });
    36. 

  36.     </script>
    37. 

  37.     
    38. 

  38. 

  39.     <!-- HTML5 shim, for IE6-8 support of HTML5 elements -->
    40. 

  40.     <!--[if lt IE 9]>
    41. 

  41.       <script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></sc\
    42. 

  42. ript>
    43. 

  43.     <![endif]-->
    44. 

  44.   </head>
    45. 

  45. 

  46.   <script type="text/javascript">
    47. 

  47.   var _gaq = _gaq || [];
    48. 

  48.   _gaq.push(['_setAccount', 'UA-39956831-1']);
    49. 

  49.   _gaq.push(['_trackPageview']);
    50. 

  50. 

  51.   (function() {
    52. 

  52.     var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
    53. 

  53.     ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
    54. 

  54.     var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
    55. 

  55.   })();
    56. 

  56. </script>
    57. 

  57. 

  58.   <body data-spy="scroll" data-target=".bs-docs-sidebar"> 
    59. 

  59. 

  60.     <div class="navbar navbar-fixed-top">
    61. 

  61.       <div class="navbar-inner">
    62. 

  62.         <div class="container">
    63. 

  63.             <button type="button" class="btn btn-navbar" data-toggle="collapse" data-target=".nav-collapse">
    64. 

  64.                 <span class="icon-bar"></span>
    65. 

  65.                 <span class="icon-bar"></span>
    66. 

  66.                 <span class="icon-bar"></span>
    67. 

  67.             </button>
    68. 

  68. 

  69.             <a href="/" class="brand">Lot About</a>
    70. 

  70. 

  71.             <div class="nav-collapse collapse">
    72. 

  72.                 <ul class="nav">
    73. 

  73.                     <li><a href="/">HOME</a></li>
    74. 

  74.                     
    75. 

  75.                     
    76. 

  76.                     <!-- use sorted_for.rb plugin -->
    77. 

  77. 

  78.     
    79. 

  79.         
    80. 

  80.     
    81. 

  81. 

  82.     
    83. 

  83.         
    84. 

  84.     
    85. 

  85. 

  86.     
    87. 

  87.         
    88. 

  88.     
    89. 

  89. 

  90.     
    91. 

  91.         
    92. 

  92.             
    93. 

  93.       	    <li><a href="/archive.html">Archive</a></li>
    94. 

  94.             
    95. 

  95.         
    96. 

  96.     
    97. 

  97. 

  98.     
    99. 

  99.         
    100. 

  100.             
    101. 

  101.       	    <li><a href="/rss.xml">RSS</a></li>
    102. 

  102.             
    103. 

  103.         
    104. 

  104.     
    105. 

  105. 

  106.     
    107. 

  107.         
    108. 

  108.             
    109. 

  109.       	    <li><a href="/atom.xml">Atom</a></li>
    110. 

  110.             
    111. 

  111.         
    112. 

  112.     
    113. 

  113. 

  114.     
    115. 

  115.         
    116. 

  116.             
    117. 

  117.       	    <li><a href="/about.html">About</a></li>
    118. 

  118.             
    119. 

  119.         
    120. 

  120.     
    121. 

  121. 

  122. 

  123. 

  124. 

  125. 

  126.                 </ul>
    127. 

  127. 

  128.                 <ul class="nav pull-right social visible-desktop">
    129. 

  129.                     <li class="divider-vertical"></li>
    130. 

  130.                     
    131. 

  131.                       <li>
    132. 

  132.                         <a href="https://github.com/lotabout" class="zocial github icon" target="_blank">
    133. 

  133.                           <span class="hidden-desktop">Github</span>
    134. 

  134.                         </a>
    135. 

  135.                       </li>
    136. 

  136.                     
    137. 

  137.                     
    138. 

  138.                       <li>
    139. 

  139.                         <a href="https://plus.google.com/103158895948424209870" class="zocial googleplus icon" target="_blank">
    140. 

  140.                           <span class="hidden-desktop">Google+</span>
    141. 

  141.                         </a>
    142. 

  142.                       </li>
    143. 

  143.                     
    144. 

  144.                     
    145. 

  145.                     
    146. 

  146.                     
    147. 

  147.                     
    148. 

  148.                 </ul>
    149. 

  149.             </div>
    150. 

  150.         </div>
    151. 

  151.       </div>
    152. 

  152.     </div>
    153. 

  153.     <div class="container">
    154. 

  154.         <!--<div class="row-fluid">-->
    155. 

  155.     <!--<div class="span3"></div>-->
    156. 

  156.     <!--<div class="span7">-->
    157. 

  157. <!--<div class="page-header">-->
    158. 

  158.     <!--<h1>apr 学习笔记之 apr_pool  <br/><small>Apache Portable Routine 学习笔记之内存管理机制：apr_pool</small></h1>-->
    159. 

  159. <!--</div>-->
    160. 

  160.     <!--</div>-->
    161. 

  161.     <!--<div class="span3"></div>-->
    162. 

  162. <!--</div>-->
    163. 

  163. 

  164. <div class="post-header">
    165. 

  165.     <h1>apr 学习笔记之 apr_pool  <br/><small>Apache Portable Routine 学习笔记之内存管理机制：apr_pool</small></h1>
    166. 

  166. </div>
    167. 

  167. 

  168. 

  169. <div class="row-fluid">
    170. 

  170.      <div class="span3 bs-docs-sidebar">
    171. 

  171.             <ul class='nav nav-list bs-docs-sidenav' id="toc">
    172. 

  172.             <!-- toc -->
    173. 

  173.             </ul>
    174. 

  174.      </div>
    175. 

  175. 

  176.     <div class="span7 main">
    177. 

  177.         <h1 id="memory-pool">什么是内存池（memory pool）</h1>
    178. 

  178. 

  179. <p>这里给出一个快速的概念，所以内存池，是针对传统动态内存管理机制：<code>malloc</code> 和
    180. 

  180. <code>free</code> 提出的。内存池，就是预先向系统申请获得一大块的内存，称之为内存池，之后在获得的内存池之上，管理内存的分配与释放。</p>
    181. 

  181. 

  182. <p>传统上，当我们需要内存时，就调用 <code>malloc</code> 系统函数（严格上说是C的库函数）获得内存，当我们不在需要分配获得的内存时，调用 <code>free</code>系统函数释放它。这种方法有两个主要的缺点：</p>
    183. 

  183. 

  184. <ol>
    185. 

  185.   <li>当内存分配频繁时，效率较低。</li>
    186. 

  186.   <li>当内存分配的大小不一时，容易产生内存碎片。</li>
    187. 

  187. </ol>
    188. 

  188. 

  189. <p>第一种开销主要是源自调用系统函数开销较大（Linux 下，malloc 会使用系统调用 sbrk
    190. 

  190. ）。</p>
    191. 

  191. 

  192. <p>内存池是一次性获得一大块内存，当用户需要时内存时，从池中获取，当使用完毕时，归还池中，当有新的请求时，就可以将之前归还的内存重新分配。对比之下，<code>free</code>函数每次都把内存归还给系统，而内存池技术可以重用这些内存，因此省下了许多系统调用的开销。</p>
    193. 

  193. 

  194. <p>另一方面，内存池是以固定大小的内存块进行处理的。例如，<code>malloc</code>可以分配一块大小为 10 Byte 的内存（实际分配的可能是对齐过的，如12或16B）。而内存池是以一个块为单位进行分配，例如每个块大小为 256 Byte, 那即使只需要 10B, 内存池也会为我们分配 256 Byte 即1个块。</p>
    195. 

  195. 

  196. <p>我们可能会觉得这样不是浪费空间嘛。是的，这是我们需要付出的代价。但使用整齐的块，能有效减少内存碎片的产生。</p>
    197. 

  197. 

  198. <p>本节我们对内存池的基本概念进行了介绍，之后会进行一些细节的说明。</p>
    199. 

  199. 

  200. <h1 id="apr-">APR 的内存池使用</h1>
    201. 

  201. 

  202. <h1 id="apr--1">APR 的内存池实现</h1>
    203. 

  203. 

  204.         <hr/>
    205. 

  205.         <div class="pagination btn-group">
    206. 

  206.             
    207. 

  207.             <a href="/2013/12/15/image-files-manipulate" class="btn prev" title="Linux 镜像文件处理"> &larr; Previous </a>
    208. 

  208.             
    209. 

  209.             <a href="/archive.html" class="btn">Archive</a>
    210. 

  210.             
    211. 

  211.             <a href="/2014/03/27/recursion" class="btn next" title="递归的奥秘"> Next &rarr;</a>
    212. 

  212.             
    213. 

  213.         </div>
    214. 

  214.         <hr>
    215. 

  215.         <div class="post">
    216. 

  216.             <h2>Related Posts</h2>
    217. 

  217.             <ul>
    218. 

  218.                 
    219. 

  219.                 <li>
    220. 

  220.                 <span>27 Mar 2014</span>
    221. 

  221.                 &raquo;
    222. 

  222.                 <a href="/2014/03/27/recursion">递归的奥秘</a>
    223. 

  223.                 </li>
    224. 

  224.                 
    225. 

  225.                 <li>
    226. 

  226.                 <span>15 Dec 2013</span>
    227. 

  227.                 &raquo;
    228. 

  228.                 <a href="/2013/12/15/image-files-manipulate">Linux 镜像文件处理</a>
    229. 

  229.                 </li>
    230. 

  230.                 
    231. 

  231.                 <li>
    232. 

  232.                 <span>26 Sep 2013</span>
    233. 

  233.                 &raquo;
    234. 

  234.                 <a href="/2013/09/26/awk-notes">awk 常用命令</a>
    235. 

  235.                 </li>
    236. 

  236.                 
    237. 

  237.                 <li>
    238. 

  238.                 <span>19 May 2013</span>
    239. 

  239.                 &raquo;
    240. 

  240.                 <a href="/2013/05/19/how-to-ask">你的问题被鄙视过吗？</a>
    241. 

  241.                 </li>
    242. 

  242.                 
    243. 

  243.                 <li>
    244. 

  244.                 <span>12 Apr 2013</span>
    245. 

  245.                 &raquo;
    246. 

  246.                 <a href="/2013/04/12/git-notes">git 常用命令</a>
    247. 

  247.                 </li>
    248. 

  248.                 
    249. 

  249.                 <li>
    250. 

  250.                 <span>08 Apr 2013</span>
    251. 

  251.                 &raquo;
    252. 

  252.                 <a href="/2013/04/08/how-is-this-blog-built">论本博客的创建</a>
    253. 

  253.                 </li>
    254. 

  254.                 
    255. 

  255.                 <li>
    256. 

  256.                 <span>07 Apr 2013</span>
    257. 

  257.                 &raquo;
    258. 

  258.                 <a href="/2013/04/07/test">Test of Jekyll</a>
    259. 

  259.                 </li>
    260. 

  260.                 
    261. 

  261.             </ul>
    262. 

  262.         </div>
    263. 

  263. 

  264.         <div id="disqus_thread"></div>
    265. 

  265. <script type="text/javascript">
    266. 

  266.     var disqus_developer = 1;
    267. 

  267.     var disqus_shortname = 'lotaboutlife'; // required: replace example with your forum shortname
    268. 

  268.     
    269. 

  269.     /* * * DON'T EDIT BELOW THIS LINE * * */
    270. 

  270.     (function() {
    271. 

  271.         var dsq = document.createElement('script'); dsq.type = 'text/javascript'; dsq.async = true;
    272. 

  272.         dsq.src = 'http://' + disqus_shortname + '.disqus.com/embed.js';
    273. 

  273.         (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(dsq);
    274. 

  274.     })();
    275. 

  275. </script>
    276. 

  276. <noscript>Please enable JavaScript to view the <a href="http://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript>
    277. 

  277. <a href="http://disqus.com" class="dsq-brlink">blog comments powered by <span class="logo-disqus">Disqus</span></a>
    278. 

  278. 

  279.         <!-- add comment here -->
    280. 

  280. 

  281.     </div>
    282. 

  282. 

  283.     <div class="span2">
    284. 

  284.         <section>
    285. 

  285.             <h4>Published</h4>
    286. 

  286.             <div class="date">
    287. 

  287.                 <span>01 January 2014</span>
    288. 

  288.             </div>
    289. 

  289.         </section>
    290. 

  290.         
    291. 

  291.         
    292. 

  292.         
    293. 

  293.         <section>
    294. 

  294.             <h4>Categories</h4>
    295. 

  295.             <ul class="tag_box">
    296. 

  296.                 
    297. 

  297.                 
    298. 

  298.    
    299. 

  299.   	<li><a href="/categories.html#c-ref">
    300. 

  300.   		c <span>1</span>
    301. 

  301.   	</a></li>
    302. 

  302.   
    303. 

  303. 

  304. 

  305. 

  306.             </ul>
    307. 

  307.         </section>
    308. 

  308.         
    309. 

  309.         <section>
    310. 

  310.             <h4>Tags</h4>
    311. 

  311.             <ul class="tag_box">
    312. 

  312.                 
    313. 

  313.                 
    314. 

  314.    
    315. 

  315.   	<li><a href="/tags.html#apr-ref">apr <span>1</span></a></li>
    316. 

  316.    
    317. 

  317.   	<li><a href="/tags.html#memory_pool-ref">memory_pool <span>1</span></a></li>
    318. 

  318.   
    319. 

  319. 

  320. 

  321. 

  322.             </ul>
    323. 

  323.         </section>
    324. 

  324.         
    325. 

  325.     </div>
    326. 

  326. </div>
    327. 

  327. 

  328.     </div>
    329. 

  329. 

  330.     <!-- Footer
    331. 

  331.     ================================================== -->
    332. 

  332.     <footer class="footer">
    333. 

  333.       <div class="container">
    334. 

  334.           <p> Powered by <a href="https://github.com/mojombo/jekyll">Jekyll</a> & <a href="http://twitter.github.io/bootstrap/index.html"> twitter bootstrap </a> </p>
    335. 

  335.           <p> Copyright 2013 - 2014 by <a href="https://lotabout.bitbucket.org/about.html"> Mark Wallace </a> </p>
    336. 

  336. 

  337.         <ul class="footer-links">
    338. 

  338.           <li><a href="https://github.com/lotabout">github</a></li>
    339. 

  339.           <li class="muted">&middot;</li>
    340. 

  340.           <li><a href="https://bitbucket.org/lotabout">bitbucket</a></li>
    341. 

  341.           <li class="muted">&middot;</li>
    342. 

  342.           <li><a href="https://bitbucket.org/lotabout/lotabout.bitbucket.org">Site Source</a></li>
    343. 

  343.         </ul>
    344. 

  344.       </div>
    345. 

  345.     </footer>
    346. 

  346. 

  347.     <!-- Le javascript
    348. 

  348.     ================================================== -->
    349. 

  349.     <!-- Placed at the end of the document so the pages load faster -->
    350. 

  350.     <script src="/assets/js/jquery-1.7.1.min.js"></script>
    351. 

  351.     <script type="text/javascript">
    352. 

  352.     $(document).ready(function() {
    353. 

  353.         var TOC=""
    354. 

  354.         $("div.main>h1, div.main>h2").each(function(i){
    355. 

  355.             var current=$(this);
    356. 

  356.             current.attr("id", "title" + i);
    357. 

  357.             current.css("padding-top", "45px"); <!-- solve navbar overlap problem -->
    358. 

  358.             current.css("margin-top", "-20px"); <!-- solve navbar overlap problem -->
    359. 

  359.             TOC += "<li><a id='link" + i + "' href='#title" + i + "'title='" + current.attr("tagName") + "'>" + current.text() + "<i class='icon-chevron-right'></i></a></li>"
    360. 

  360.             })
    361. 

  361.         $("#toc").append(TOC)
    362. 

  362.     });
    363. 

  363.     </script> 
    364. 

  364.     <script type="text/javascript">
    365. 

  365.         $(document).ready(function(){
    366. 

  366.         $('pre').addClass('prettyprint linenums') })
    367. 

  367.     </script>
    368. 

  368.     <script src="/assets/js/bootstrap.js"></script>
    369. 

  369.     <script src="/assets/js/holder.js"></script>
    370. 

  370.     <script src="/assets/js/application.js"></script>
    371. 

  371.     <script src="/assets/js/google-code-prettify/prettify.js"></script>
    372. 

  372.     
    373. 

  373.     <script src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_HTML" type="text/javascript"></script>
    374. 

  374.     
    375. 

  375.   </body>
    376. 

  376. </html>
    377. 

  377.