1 <!-- 2 Copyright 2010 The Android Open Source Project 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15 --> 16 17 # Android Code-Lines # 18 19 The Android Open Source Project maintains a complete software stack intended 20 to be ported by OEMs and other device implementors to run on actual hardware. 21 Accordingly, we maintain a number of "code lines" to clearly separate the 22 current stable version of Android from unstable experimental work. 23 24 The chart below depicts at a conceptual level how AOSP manages code and 25 releases. We're referring to these as "code lines" instead of "branches" 26 simply because at any given moment there may be more than one branch extant 27 for a given "code line". For instance, when a release is cut, sometimes that 28 will become a new branch in git, and sometimes not, based on the needs of the 29 moment. 30 31 <img src="/images/code-lines.png" alt="code-line diagram"/> 32 33 ## Notes and Explanations ## 34 35 - A *release* corresponds to a formal version of the Android platform, such 36 as 1.5, 2.1, and so on. Generally speaking, a release of the platform 37 corresponds to a version of the `SdkVersion` field used in 38 AndroidManifest.xml files, and defined in `frameworks/base/api` in 39 the source tree. 40 41 - An *upstream* project is an open-source project from which the Android 42 stack is pulling code. These include obvious projects such as the Linux kernel 43 and WebKit, but over time we are migrating some of the semi-autonomous 44 Android projects (such as Dalvik, the Android SDK tools, Bionic, and so on) to 45 work as "upstream" projects. Generally, these projects are developed entirely in 46 the public tree. For some upstream projects, development is done by contributing 47 directly to the upstream project itself. See [Upstream Projects](submit-patches.html#upstream-projects) 48 for details. In both cases, snapshots will be periodically pulled into releases. 49 50 - The diagram refers to "Eclair" and "FroYo"; however, they are simply 51 placeholders, and the diagram actually reflects the overall release and 52 branching strategy. 53 54 - At all times, a release code-line (which may actually consist of 55 more than one actual branch in git) is considered the sole canonical source 56 code for a given Android platform version. OEMs and other groups building devices 57 should pull only from a release branch. 58 59 - We will set up "experimental" code-lines to capture changes from 60 the community, so that they can be iterated on, with an eye toward stability. 61 62 - Changes that prove stable will eventually be pulled into a release 63 branch. Note that this will only apply to bug fixes, app improvements, and 64 other things that do not affect the APIs of the platform. 65 66 - Changes will be pulled into release branches from upstream projects 67 (including the Android "upstream" projects) as necessary. 68 69 - The "n+1"th version (that is, next major version of the framework and 70 platform APIs) will be developed by Google internally. See below for 71 details. 72 73 - Changes will be pulled from upstream, release, and experimental branches 74 into Google's private branch as necessary. 75 76 - When the platform APIs for the next version have stabilized and been fully 77 tested, Google will cut a release of the next platform version. (This 78 specifically refers to a new `SdkVersion`.) This will also 79 correspond to the internal code-line being made a public release branch, and the 80 new current platform code-line. 81 82 - When a new platform version is cut, a corresponding experimental 83 code-line will be created at the same time. 84 85 ## About Private Code-Lines ## 86 87 The source management strategy above includes a code-line that Google will 88 keep private. The reason for this is to focus attention on the current public 89 version of Android. 90 91 OEMs and other device builders naturally want to ship devices with the 92 latest version of Android. Similarly, application developers don't want to 93 deal with more extant platform versions than strictly necessary. Meanwhile, 94 Google retains responsibility for the strategic direction of Android as a 95 platform and a product. Our approach is based on focusing on a small number of 96 flagship devices to drive features, and secure protections of Android-related 97 intellectual property. 98 99 As a result, Google frequently has possession of confidential 100 information of third parties, and we must refrain from revealing sensitive 101 features until we've secured the appropriate protections. Meanwhile, there are 102 real risks to the platform arising from having too many platform versions 103 extant at once. For these reasons, we have structured the open-source project 104 -- including third-party contributions -- to focus on the currently-public 105 stable version of Android. "Deep development" on the next version of the 106 platform will happen in private, until it's ready to become an official 107 release. 108 109 We recognize that many contributors will disagree with this approach. We 110 respect that others may have a different point of view; however, this is the 111 approach that we feel is best, and the one we've chosen to implement. 112 113 114
