WTP/Build/Accounting for history during builds
By using p2 (and related tools) during builds, it is possible to better account for history when delivering builds of features and bundles.
What this means, in short, is if a bundle has the exact same version as it did from some previous build, then that previously built bundle is supposed to be the same (or, equivalent), and could be assumed to be the same, and that previously built bundle reused and it be delivered in current build, instead of the recently built one. This is kind of counter intuitive, but this is the way a p2 based install would work; if someone already had that bundle installed, with the exact same version, then they would never get a new one installed. So one advantage of re-using the previously built bundle is that if it is not equivalent for some reason, it could be discovered in time to fix the issue, instead of discovering the problem, perhaps months later, when someone was doing installs on top of previous versions.
Of course, it is well understood that sometimes the byte codes do change even though the source code doesn't change (and hence the version doesn't change, normally, if the source doesn't change). In general this happens because we version code based on our source, but other factors can effect the built code ... for example, a constant in a pre-req might change, the compiler or compiler settings might change, etc. For an overview and introduction of the general problem, see Andrew Niefer's blog entry.
In particular, for WTP, we have had a recurring problem, where a feature version (with its build-time computed suffix) stays exactly the same even when the contents of the feature has changed (and then, the problem is actually, it is not noticed until weeks or months later). This is due to the computed suffix not reflecting enough significant digits to fully account for its contained bundles; see bug bug 208143. The only solution for this bug or limitation, since we do not want to make the suffixes indefinitely long, is to detect the problem, and take appropriate corrective action. While it'd be ideal to do that "real time", during the build, the next best alternative is to at least detect it shortly after a build, and correct it before the code is delivered, as we would with any bug.
So, by using p2 (and related tools) we now have the ability to do that early detection.
Process during WTP Builds
The following image will be used to explain the parts of this process as used by WTP builds.
The flow is basically left to right, over time or steps of the build.
buildmakes use of PDE's
p2.gatheringflag to create the
buildrepository, which is literally the byte codes as built, in the form of a handy p2 repository. (Bundles are complete at this point, conditioned, and signed when doing a production build).
- In a "create final repo" ant script in our builds, the
p2.mirroroperation is used to create the final
repository. It mirrors content from the
buildrepository, but if it happens to find an IU (bundle or feature jar) with the exact same version as in the
reference repositories, then it uses the previously built one from the
reference repositories(not the freshly built one from
- The mirror operation, as a side effect, makes use of the jar comparator. The jar comparator is provided by the p2 project, but it is not related to p2, per se, and more related to knowing how to examine significant parts of byte codes, bundles, and features). If, while mirroring, two bundles are found with same version, then in addition to mirroring the previously built one for the final repository, it also inspects the presumably identical bundles for significant differences, and if any are found, it prints that information to the
- In an ideal world, that'd be it; we'd could just examine the
comparator.logto see if there were any significant messages, to discover if there were issues to correct. But the reality is there are actually lots of "differences" found ... most of which we do not care about. There are so many, even if we wanted to, we'd miss important ones, overlooking the trees for the forest. Therefore, we run a
releng testto filter out expected messages from unexpected messages and throw an error if there are any unexpected messages.
- Not shown in diagram, distribution zips are created and unit tests are ran with the final
- The 'repository' shows a dashed line back to the 'reference repositories', because once a build is declared, then it becomes part of the reference repositories. The reference repositories are a composite repository, made up of a previous release or milestone and subsequent declared builds. This currently takes a "manual" step to create the initial reference repo and to add a repo to it. The build scripts assume this reference repository exists at a certain location, but does not actually create or manage it. Note: on the production build machine, where all builds are accessible via the file system, the composite repository simply uses the file system for the location of child repositories. If someone were to do a "local" test build, then first, they would have to "manually" create the reference repository in the expected file-system location, and second, they'd likely want to create the reference repository ahead of time on their local system, for efficiency during the build itself, instead of using http locations back to download sites. But, it is important to note, if there is no reference repository found (such as for a local, test build), then the operation continues and essentially the final
repositoryconsists of what ever was in the
buildrepository, which is probably fine for most test builds.
Differences found for which no correction is needed.
Note: it will take some time an experience to fully understand all "differences" found and whether or not significant, so some cases will be documented here to share knowledge and increase our group learning curve.
All the "known cases" are codified in a property file called comparatorfilter.properties that is used during the releng test to filter out some messages. If filtered out, the message is still printed in a file called "excludedMessages" on our test results page. This can be pretty much ignored ... but wouldn't hurt for committers to examine at some points to see if anything is mistakenly being filtered out.
In about.mappings, the property "0" has different values: "<date1>" and "<date2>".
- One of the most common "differences" found is similar to following. The dates in about.mappings are literally the date of the build, and is a good example of when we would prefer the old bundle be used, to maintain the "original build" date, instead of changing it each time, even though the date was the only thing changed.
IOException comparing ... Error opening zip file
- We have some cases where "test jars" are purposely invalid, to make sure our code handles invalid input ... but they cause a message to be logged, so we ignore those messages. (It is unknown if the comparator successful does a valid compare on all other content).
Binary file build.xml: sizes differ by ... [10 bytes]
- There's several little differences found in "doc" bundles. Honestly, these have not been examined in detail to know exactly what they mean ... but, assuming for now its just dates or similar (especially for build.xml ... seems that should not even be in a built bundle?). [Note: the Eclipse Platform automatically excludes all "doc" bundles from comparator examination, presumably since there are frequently small unimportant changes].
Significant, unexpected differences and what to do about them.
The "fix" for nearly any "real" problem found in comparator is to re-tag the bundle or feature so it appears different in version number, even if the source did not actually change.
The hard part, and the reason for long drawn-out explanation and graphic in previous section is that if there is a difference to be investigated, then that bundle is no longer "in" the build distribution -- the "old" one was put in our final repository and zips, so the 'new' bundle (with exact same version) must be obtained from the literal 'buildrepo' on the build machine (and before it is deleted for subsequent build ... though that wouldn't happen until a build is declared).
- differences in feature contents
Difference found for canonical: org.eclipse.update.feature,org.eclipse.wst.xml_sdk.feature,3.3.0.v201007311522-7A78-8DXJQUlJHRDD2LBB_qiiymz between file:/home/data/httpd/download.eclipse.org/webtools/downloads/drops/R3.3.0/S-3.3.0M2-20100923155521/repository/ and file:/shared/webtools/projects/wtp-R3.3.0-I/workdir/I-3.3.0-20101007023510/buildrepository/wst-sdk The entry "Feature: org.eclipse.wst.xml_ui.feature 3.3.0.v201007311522-7H7DFYzDxumThWc9oigOk5b6p2Mb" is not present in both features. The entry "Feature: org.eclipse.wst.xml_ui.feature.source 3.3.0.v201007311522-7H7DFYzDxumThWc9oigOk5b6p2Mb" is not present in both features.
This type of messages occurs for the case where a feature suffix doesn't get computed accurately enough to reflect the difference in content. See bug 327176 for a detailed explanation of this particular case.
Note the repositories referred to. In this case, one version was in M2 ... and that's the one that would have been "delivered" to the build's repository and zip files. So, to see the "differences" one has to get a copy of the "new" one in "buildrepository/wst-sdk". On the build machine, it is possible to drill down into a build's directories, using a web browser, but might be easier for some to use shell account or scp to copy down the file.
Some files always excluded
Just to make a note, as of this writing, some bundles are always excluded from the comparison tests, due to bugs in the comparator. This means if new builds of these bundles have same qualifier as old one, then the old one would be delivered, without any warning messages, if there happened to be significant differences. See bug 325158 and bug 325311.
org.eclipse.jpt.eclipselink.ui org.eclipse.jpt.ui org.eclipse.jst.jsp.core.tests