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, 2.0, 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. These will be developed entirely in the public 27 tree, and snapshots will be periodically pulled into releases.</li> 28 <li>The diagram refers to "Eclair" and "Flan"; however, they are simply 29 placeholders, and the diagram actually reflects the overall release and 30 branching strategy.</li> 31 <li>At all times, the Release code-line (which may actually consist of 32 more than one actual branch in git) is considered the sole canonical source 33 code for a given Android platform. OEMs and other groups building devices 34 should pull only from a Release branch.</li> 35 <li>We will be setting up an "Experimental" code-line to capture changes from 36 the community, so that they can be iterated on, with an eye toward stability.</li> 37 <li>Changes that prove stable will eventually be pulled into a Release 38 branch. Note that this will only apply to bug fixes, app improvements, and 39 other things that do not affect the APIs of the platform.</li> 40 <li>Changes will be pulled into Release branches from upstream projects 41 (include the Android "upstream" projects) as necessary.</li> 42 <li>The "n+1"th version (that is, next major version of the framework and 43 platform APIs) will be developed by Google internally. (See below for 44 details.)</li> 45 <li>Changes will be pulled from upstream, Release, and Experimental branches 46 into Google's private branch as necessary.</li> 47 <li>When the platform APIs for the next version have stabilized and been fully 48 tested, Google will cut a release of the next platform version. (This 49 specifically refers to a new <code>SdkVersion</code>.) This will also 50 correspond to the internal code-line being made a public Release branch, and the 51 new current platform code-line.</li> 52 <li>When a new platform version is cut, a corresponding Experimental 53 code-line.</li> 54 </ul> 55 <h3>About Private Code-Lines</h3> 56 <p>The source management strategy above includes a code-line that Google will 57 keep private. The reason for this is to focus attention on the current public 58 version of Android.</p> 59 <p>OEMs and other device builders naturally want to ship devices with the 60 latest version of Android. Similarly, application developers don't want to 61 deal with more extant platform versions than strictly necessary. Meanwhile, 62 Google retains responsibility for the strategic direction of Android as a 63 platform and a product. Our approach is based on focusing on a small number of 64 flagship devices to drive features, and secure protections of Android-related 65 intellectual property through patents and the like.</p> 66 <p>As a result, Google frequently has possession of confidential 67 information of third parties, and we must refrain from revealing patentable 68 features until we've secured the appropriate protections. Meanwhile, there are 69 real risks to the platform arising from having too many platform versions 70 extant at once. For these reasons, we have structured the open-source project 71 -- including third-party contributions -- to focus on the currently-public 72 stable version of Android. "Deep development" on the next version of the 73 platform will happen in private, until it's ready to become an official 74 release.</p> 75 <p>We recognize that many contributors will disagree with this approach. We 76 respect that others may have a different point of view; however, this is the 77 approach that we feel is best, and the one we've chosen to implement.</p> 78
