1 page.title=Android Code-Lines 2 doc.type=source 3 @jd:body 4 <p>The Android Open Source Project maintains a complete software stack intended 5 to be ported by OEMs and other device implementors to run on actual hardware. 6 Accordingly, we maintain a number of "code lines" to clearly separate the 7 current stable version of Android from unstable experimental work.</p> 8 <p>The chart below depicts at a conceptual level how AOSP manages code and 9 releases. We're referring to these as "code lines" instead of "branches" 10 simply because at any given moment there may be more than one branch extant 11 for a given "code line". For instance, when a release is cut, sometimes that 12 will become a new branch in git, and sometimes not, based on the needs of the 13 moment.</p> 14 <img src="{@docRoot}images/code-lines.png"/> 15 <h3>Notes and Explanations</h3> 16 <ul> 17 <li>A <i>release</i> corresponds to a formal version of the Android platform, such 18 as 1.5, 2.1, and so on. Generally speaking, a release of the platform 19 corresponds to a version of the <code>SdkVersion</code> field used in 20 AndroidManifest.xml files, and defined in <code>frameworks/base/api</code> in 21 the source tree.</li> 22 <li>An <i>upstream</i> project is an open-source project from which the Android 23 stack is pulling code. These include obvious projects such as the Linux kernel 24 and WebKit, but over time we are migrating some of the semi-autonomous 25 Android projects (such as Dalvik, the Android SDK tools, Bionic, and so on) to 26 work as "upstream" projects. Generally, these projects are developed entirely in 27 the public tree. For some upstream projects, development is done by contributing 28 directly to the upstream project itself. See 29 <a href="{@docRoot}source/submit-patches.html#upstream-projects">Upstream Projects</a> 30 for details. In both cases, snapshots will be periodically pulled into releases.</li> 31 <li>The diagram refers to "Eclair" and "FroYo"; however, they are simply 32 placeholders, and the diagram actually reflects the overall release and 33 branching strategy.</li> 34 <li>At all times, a release code-line (which may actually consist of 35 more than one actual branch in git) is considered the sole canonical source 36 code for a given Android platform version. OEMs and other groups building devices 37 should pull only from a release branch.</li> 38 <li>We will set up "experimental" code-lines to capture changes from 39 the community, so that they can be iterated on, with an eye toward stability.</li> 40 <li>Changes that prove stable will eventually be pulled into a release 41 branch. Note that this will only apply to bug fixes, app improvements, and 42 other things that do not affect the APIs of the platform.</li> 43 <li>Changes will be pulled into release branches from upstream projects 44 (including the Android "upstream" projects) as necessary.</li> 45 <li>The "n+1"th version (that is, next major version of the framework and 46 platform APIs) will be developed by Google internally. See below for 47 details.</li> 48 <li>Changes will be pulled from upstream, release, and experimental branches 49 into Google's private branch as necessary.</li> 50 <li>When the platform APIs for the next version have stabilized and been fully 51 tested, Google will cut a release of the next platform version. (This 52 specifically refers to a new <code>SdkVersion</code>.) This will also 53 correspond to the internal code-line being made a public release branch, and the 54 new current platform code-line.</li> 55 <li>When a new platform version is cut, a corresponding experimental 56 code-line will be created at the same time.</li> 57 </ul> 58 <h3>About Private Code-Lines</h3> 59 <p>The source management strategy above includes a code-line that Google will 60 keep private. The reason for this is to focus attention on the current public 61 version of Android.</p> 62 <p>OEMs and other device builders naturally want to ship devices with the 63 latest version of Android. Similarly, application developers don't want to 64 deal with more extant platform versions than strictly necessary. Meanwhile, 65 Google retains responsibility for the strategic direction of Android as a 66 platform and a product. Our approach is based on focusing on a small number of 67 flagship devices to drive features, and secure protections of Android-related 68 intellectual property.</p> 69 <p>As a result, Google frequently has possession of confidential 70 information of third parties, and we must refrain from revealing sensitive 71 features until we've secured the appropriate protections. Meanwhile, there are 72 real risks to the platform arising from having too many platform versions 73 extant at once. For these reasons, we have structured the open-source project 74 -- including third-party contributions -- to focus on the currently-public 75 stable version of Android. "Deep development" on the next version of the 76 platform will happen in private, until it's ready to become an official 77 release.</p> 78 <p>We recognize that many contributors will disagree with this approach. We 79 respect that others may have a different point of view; however, this is the 80 approach that we feel is best, and the one we've chosen to implement.</p> 81
