1 <html devsite> 2 <head> 3 <title>Codelines, Branches, and Releases</title> 4 <meta name="project_path" value="/_project.yaml" /> 5 <meta name="book_path" value="/_book.yaml" /> 6 </head> 7 <body> 8 <!-- 9 Copyright 2017 The Android Open Source Project 10 11 Licensed under the Apache License, Version 2.0 (the "License"); 12 you may not use this file except in compliance with the License. 13 You may obtain a copy of the License at 14 15 http://www.apache.org/licenses/LICENSE-2.0 16 17 Unless required by applicable law or agreed to in writing, software 18 distributed under the License is distributed on an "AS IS" BASIS, 19 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 20 See the License for the specific language governing permissions and 21 limitations under the License. 22 --> 23 24 25 26 <p> 27 The Android Open Source Project (AOSP) maintains a complete software stack to be ported by 28 OEMs and other device implementors and run on their own hardware. To maintain the quality of 29 Android, Google has contributed full-time engineers, product managers, user interface designers, 30 quality assurance testers, and all the other roles required to bring modern devices to market. 31 </p> 32 33 <p> 34 Accordingly, we maintain a number of "code lines" to clearly separate the current stable 35 version of Android from unstable experimental work. We roll the open source administration 36 and maintenance of the Android code lines into the larger product development cycle. 37 </p> 38 39 <p> 40 The chart below depicts at a conceptual level how AOSP manages code and releases. We're 41 referring to these as "code lines" instead of "branches" simply because at any given moment 42 there may be more than one branch for a given "code line". For instance, when a 43 release is cut, it may or may not become a new branch based on the needs of the moment. 44 </p> 45 <ol> 46 <li> 47 <p> 48 At any given moment, there is a current latest release of the Android platform. This 49 typically takes the form of a branch in the tree. 50 </p> 51 </li> 52 <li> 53 <p> 54 Device builders and contributors work with the current latest release, fixing bugs, 55 launching new devices, experimenting with new features, and so on. 56 </p> 57 </li> 58 <li> 59 <p> 60 In parallel, Google works internally on the next version of the Android platform and 61 framework according to the product's needs and goals. We develop the next 62 version of Android by working with a device partner on a flagship device whose 63 specifications are chosen to push Android in the direction we believe it should go. 64 </p> 65 </li> 66 <li> 67 <p> 68 When the "n+1"th version is ready, it will be published to the public source tree and 69 become the new latest release. 70 </p> 71 </li> 72 </ol> 73 <img src="/images/code-lines.png" alt="code-line diagram" id="figure1" > 74 <p class="img-caption"> 75 <strong>Figure 1.</strong> AOSP code and releases 76 </p> 77 <h2 id="terms-and-caveats"> 78 Terms and Caveats 79 </h2> 80 <ul> 81 <li> 82 <p> 83 A <em>release</em> corresponds to a formal version of the Android platform, such as 1.5, 84 2.1, and so on. Generally speaking, a release of the platform corresponds to the version in 85 the <code>SdkVersion</code> field of AndroidManifest.xml files and defined within 86 <code>frameworks/base/api</code> in the source tree. 87 </p> 88 </li> 89 <li> 90 <p> 91 An <em>upstream</em> project is an open source project from which the Android stack is 92 pulling code. These include obvious projects such as the Linux kernel and WebKit. 93 Over time we are migrating some of the semi-autonomous Android projects (such as ART, 94 the Android SDK tools, Bionic, and so on) to work as "upstream" projects. Generally, 95 these projects are developed entirely in the public tree. For some upstream projects, 96 development is done by contributing directly to the upstream project itself. See <a href= 97 "submit-patches.html#upstream-projects">Upstream Projects</a> for details. In both cases, 98 snapshots will be periodically pulled into releases. 99 </p> 100 </li> 101 <li> 102 <p> 103 At all times, a release code-line (which may actually consist of more than one actual 104 branch in git) is considered the sole canonical source code for a given Android platform 105 version. OEMs and other groups building devices should pull only from a release branch. 106 </p> 107 </li> 108 <li> 109 <p> 110 "Experimental" code-lines are established to capture changes from the community so they can 111 be iterated on with an eye toward stability. 112 </p> 113 </li> 114 <li> 115 <p> 116 Changes that prove stable will eventually be pulled into a release branch. Note this 117 applies only to bug fixes, application improvements, and other changes that do not affect the 118 APIs of the platform. 119 </p> 120 </li> 121 <li> 122 <p> 123 Changes will be pulled into release branches from upstream projects (including the 124 Android "upstream" projects) as necessary. 125 </p> 126 </li> 127 <li> 128 <p> 129 The "n+1"th version (that is, next major version of the framework and platform APIs) will 130 be developed by Google internally. See <a href= 131 "#about-private-code-lines">About Private Codelines</a> for details. 132 </p> 133 </li> 134 <li> 135 <p> 136 Changes will be pulled from upstream, release, and experimental branches into Google's 137 private branch as necessary. 138 </p> 139 </li> 140 <li> 141 <p> 142 When the platform APIs for the next version have stabilized and been fully tested, Google 143 will cut a release of the next platform version. (This specifically refers to a new 144 <code>SdkVersion</code>.) This will also correspond to the internal code-line being made 145 a public release branch, and the new current platform code-line. 146 </p> 147 </li> 148 <li> 149 <p> 150 When a new platform version is cut, a corresponding experimental code-line will be 151 created at the same time. 152 </p> 153 </li> 154 </ul> 155 156 <h2 id="about-private-code-lines"> 157 About Private Codelines 158 </h2> 159 <p> 160 The source management strategy above includes a code-line that Google will keep private. The 161 reason for this is to focus attention on the current public version of Android. 162 </p> 163 <p> 164 OEMs and other device builders naturally want to ship devices with the latest version of 165 Android. Similarly, application developers don't want to deal with more platform 166 versions than strictly necessary. Meanwhile, Google retains responsibility for the strategic 167 direction of Android as a platform and a product. Our approach focuses on a small number of 168 flagship devices to drive features while securing protections of Android-related intellectual 169 property. 170 </p> 171 <p> 172 As a result, Google frequently has possession of confidential information from third parties. 173 And we must refrain from revealing sensitive features until we've secured the appropriate 174 protections. In addition, there are real risks to the platform arising from having too many 175 platform versions extant at once. For these reasons, we have structured the open source 176 project -- including third-party contributions -- to focus on the currently-public stable 177 version of Android. "Deep development" on the next version of the platform will happen in 178 private until it's ready to become an official release. 179 </p> 180 <p> 181 We recognize many contributors will disagree with this approach. We respect others 182 may have a different point of view; however, this is the approach we feel is best, and 183 the one we've chosen to implement. 184 </p> 185 186 </body> 187 </html> 188
