1page.title=Codelines, Branches, and Releases 2@jd:body 3 4<!-- 5 Copyright 2013 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18--> 19<div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"> 23 </ol> 24 </div> 25</div> 26 27<p> 28 The Android Open Source Project (AOSP) maintains a complete software stack to be ported by 29 OEMs and other device implementors and run on their own hardware. To maintain the quality of 30 Android, Google has contributed full-time engineers, product managers, user interface designers, 31 quality assurance testers, and all the other roles required to bring modern devices to market. 32</p> 33 34<p> 35 Accordingly, we maintain a number of "code lines" to clearly separate the current stable 36 version of Android from unstable experimental work. We roll the open source administration 37 and maintenance of the Android code lines into the larger product development cycle. 38</p> 39 40<p> 41 The chart below depicts at a conceptual level how AOSP manages code and releases. We're 42 referring to these as "code lines" instead of "branches" simply because at any given moment 43 there may be more than one branch for a given "code line". For instance, when a 44 release is cut, it may or may not become a new branch based on the needs of the moment. 45</p> 46<ol> 47 <li> 48 <p> 49 At any given moment, there is a current latest release of the Android platform. This 50 typically takes the form of a branch in the tree. 51 </p> 52 </li> 53 <li> 54 <p> 55 Device builders and contributors work with the current latest release, fixing bugs, 56 launching new devices, experimenting with new features, and so on. 57 </p> 58 </li> 59 <li> 60 <p> 61 In parallel, Google works internally on the next version of the Android platform and 62 framework according to the product's needs and goals. We develop the next 63 version of Android by working with a device partner on a flagship device whose 64 specifications are chosen to push Android in the direction we believe it should go. 65 </p> 66 </li> 67 <li> 68 <p> 69 When the "n+1"th version is ready, it will be published to the public source tree and 70 become the new latest release. 71 </p> 72 </li> 73</ol> 74 <img src="{@docRoot}images/code-lines.png" alt="code-line diagram" id="figure1" > 75<p class="img-caption"> 76 <strong>Figure 1.</strong> AOSP code and releases 77</p> 78<h2 id="terms-and-caveats"> 79 Terms and Caveats 80</h2> 81<ul> 82 <li> 83 <p> 84 A <em>release</em> corresponds to a formal version of the Android platform, such as 1.5, 85 2.1, and so on. Generally speaking, a release of the platform corresponds to the version in 86 the <code>SdkVersion</code> field of AndroidManifest.xml files and defined within 87 <code>frameworks/base/api</code> in the source tree. 88 </p> 89 </li> 90 <li> 91 <p> 92 An <em>upstream</em> project is an open-source project from which the Android stack is 93 pulling code. These include obvious projects such as the Linux kernel and WebKit. 94 Over time we are migrating some of the semi-autonomous Android projects (such as ART, 95 the Android SDK tools, Bionic, and so on) to work as "upstream" projects. Generally, 96 these projects are developed entirely in the public tree. For some upstream projects, 97 development is done by contributing directly to the upstream project itself. See <a href= 98 "submit-patches.html#upstream-projects">Upstream Projects</a> for details. In both cases, 99 snapshots will be periodically pulled into releases. 100 </p> 101 </li> 102 <li> 103 <p> 104 At all times, a release code-line (which may actually consist of more than one actual 105 branch in git) is considered the sole canonical source code for a given Android platform 106 version. OEMs and other groups building devices should pull only from a release branch. 107 </p> 108 </li> 109 <li> 110 <p> 111 "Experimental" code-lines are established to capture changes from the community so they can 112 be iterated on with an eye toward stability. 113 </p> 114 </li> 115 <li> 116 <p> 117 Changes that prove stable will eventually be pulled into a release branch. Note this 118 applies only to bug fixes, application improvements, and other changes that do not affect the 119 APIs of the platform. 120 </p> 121 </li> 122 <li> 123 <p> 124 Changes will be pulled into release branches from upstream projects (including the 125 Android "upstream" projects) as necessary. 126 </p> 127 </li> 128 <li> 129 <p> 130 The "n+1"th version (that is, next major version of the framework and platform APIs) will 131 be developed by Google internally. See <a href= 132 "#about-private-code-lines">About Private Codelines</a> for details. 133 </p> 134 </li> 135 <li> 136 <p> 137 Changes will be pulled from upstream, release, and experimental branches into Google's 138 private branch as necessary. 139 </p> 140 </li> 141 <li> 142 <p> 143 When the platform APIs for the next version have stabilized and been fully tested, Google 144 will cut a release of the next platform version. (This specifically refers to a new 145 <code>SdkVersion</code>.) This will also correspond to the internal code-line being made 146 a public release branch, and the new current platform code-line. 147 </p> 148 </li> 149 <li> 150 <p> 151 When a new platform version is cut, a corresponding experimental code-line will be 152 created at the same time. 153 </p> 154 </li> 155</ul> 156 157<h2 id="about-private-code-lines"> 158 About Private Codelines 159</h2> 160<p> 161 The source management strategy above includes a code-line that Google will keep private. The 162 reason for this is to focus attention on the current public version of Android. 163</p> 164<p> 165 OEMs and other device builders naturally want to ship devices with the latest version of 166 Android. Similarly, application developers don't want to deal with more platform 167 versions than strictly necessary. Meanwhile, Google retains responsibility for the strategic 168 direction of Android as a platform and a product. Our approach focuses on a small number of 169 flagship devices to drive features while securing protections of Android-related intellectual 170 property. 171</p> 172<p> 173 As a result, Google frequently has possession of confidential information from third parties. 174 And we must refrain from revealing sensitive features until we've secured the appropriate 175 protections. In addition, there are real risks to the platform arising from having too many 176 platform versions extant at once. For these reasons, we have structured the open-source 177 project -- including third-party contributions -- to focus on the currently-public stable 178 version of Android. "Deep development" on the next version of the platform will happen in 179 private until it's ready to become an official release. 180</p> 181<p> 182 We recognize many contributors will disagree with this approach. We respect others 183 may have a different point of view; however, this is the approach we feel is best, and 184 the one we've chosen to implement. 185</p> 186
