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annotate xml/en/docs/njs/preload_objects.xml @ 2984:cc475ba7d406

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Added Preload Objects article in njs.
author Yaroslav Zhuravlev <yar@nginx.com>
date Thu, 01 Jun 2023 17:12:18 +0100
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children 48f245493600
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2984
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1 <?xml version="1.0"?>
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2
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3 <!--
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4 Copyright (C) Nginx, Inc.
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5 -->
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6
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7 <!DOCTYPE article SYSTEM "../../../../dtd/article.dtd">
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8
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9 <article name="Understanding preloaded objects"
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10 link="/en/docs/njs/preload_objects.html"
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11 lang="en"
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12 rev="1"
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13 toc="no">
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14
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15 <section id="summary">
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16
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17 <para>
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18 For each incoming request njs creates a separate virtual machine.
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19 This brings a lot of benefits such as predictable memory consumption
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20 or requests isolation.
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21 </para>
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22
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23 <para>
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24 However, it also has its own downsides.
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25 Since all requests are isolated,
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26 if a request handler needs to access some data,
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27 it has to read it by itself.
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28 This is not efficient especially when the amount of data is large.
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29 </para>
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30
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31 <para>
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32 To address this limitation,
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33 a preloaded shared object was introduced.
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34 Such objects are created immutable and do not have prototype chains:
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35 their values cannot be changed, properties cannot be added or removed.
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36 </para>
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37
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38 </section>
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39
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40
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41 <section id="working_with_preload_objects"
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42 name="Working with preload objects">
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43
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44 <para>
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45 Here are some examples of how to work with a preload object in njs:
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46
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47 <list type="bullet">
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48
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49 <listitem>
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50 access properties by name:
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51 <programlisting>
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52 preloaded_object.prop_name
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53 preloaded_object[prop_name]
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54 </programlisting>
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55 </listitem>
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56
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57 <listitem>
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58 enumerate properties:
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59 <programlisting>
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60 for (i in preloaded_object_name) {
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61 ...
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62 }
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63 </programlisting>
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64 </listitem>
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65
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66 <listitem>
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67 apply non-modifying built-in methods using <literal>call()</literal>:
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68 <programlisting>
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69 Array.prototype.filter.call(preloaded_object_name, ...)
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70 </programlisting>
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71 </listitem>
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72
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73 </list>
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74 </para>
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75
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76 </section>
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77
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78 </article>