A user encountered a problem whereby a MavenModuleSetBuild would, soon after starting, be shown as completed (and failed) even though really it was still running (so for example reloading the console link sufficed to show new output, but it would not automatically refresh).
It turned out that reload had been called on the build while it was still running, triggered by the Delivery Pipeline plugin attempting (in BuildUtil) to load a build by a number that was bigger than the actual last build number of the project. (Ultimately this was due to an UpstreamCause in a historical build of another project referring to an unrelated build of a different project that used to have the same name as the project showing the issue. Thus the upstream build link was dead.) Apparently Delivery Pipeline makes frequent and repeated calls to /view/*/api/json when a browser window is displaying the view, even if it is idle , so this would happen quite often.
When getBuildByNumber was called with the bogus build number, this delegated to search with direction EXACT, which triggered the fix of
JENKINS-19418. Unfortunately that called load on the currently highest build number—that of the running build—creating a new build object (with a state of COMPLETED and result of FAILURE, as if being loaded during a Jenkins restart after a crash), and stashing that corrupt new build object into the index. (search then returned null, correctly, since the build number did not match what was requested.) So while the original build object was fine, and ultimately wrote out the correct build.xml record, in the meantime web requests were serving a clone which claimed to have already failed. Since the console log showed ongoing progress and then success, this was a source of much confusion. (After the build really finished, the next spurious reload created a copy with the correct state/result fields, adding even more confusion since it would look like to another observer like the bug had never happened.)
I tried to reproduce this in a clean 1.532.2 installation by creating a freestyle project; building #1; adding a shell build step to sleep; starting a build of #2, watching its console log; and then in another browser tab trying to load /job/p/3, expecting a 404. This did not cause #2 to suddenly stop updating; I am guessing that an additional required trigger condition is the presence of a plugin which causes build.xml to be written before the build finishes. (Jenkins core only writes it when the build is finalized, but plugins may call Run.save earlier, for various reasons.) If there is no build.xml, then load would return null and not update the index.
At any rate, I did manage to reproduce the basic flaw in a unit test quite easily. After calling search with EXACT and a number larger than any existing build, subsequent calls with the number of the last build returned a different copy. Simply switching to getById fixes the problem according to this test, without regressing
JENKINS-19418, at least according to its test. And with this fix, indeed reload is no longer called on existing builds (at least running ones), and the bug symptoms disappeared.