opendev/gerrit
Code Issues Proposed changes

Fix infinite loop in IntraLineLoader

Browse Source 
If edits due to rebase are present, IntraLineLoader#combineLineEdits
will enter an infinite loop. As we query the intraline diff cache with a
timeout check and use a fall-back behavior in case of a timeout, none of
our threads got completely stuck due to that bug. On the one hand, this
meant that the Gerrit server could still serve requests. On the other
hand, it concealed that bug and resulted in high CPU load, which could
very negatively impact the whole Gerrit server.

The fix of the issue is quite simple: We increase the index counter
appropriately. As this issue shows, the implementation in
IntraLineLoader#combineLineEdits is quite fragile. There are better ways
to achieve the same computation. Adjusting that will be left for the
future.

None of our tests caught that issue as the result of the fall-back
mechanism was the same as the result of the real computation for all
tests which were affected. For that reason, we add a test whose results
differ between the regular and the fall-back mechanism. In addition, we
add some tests which cover intraline edits directly. Up to now, we
didn't have any tests for them. We could and should certainly add more
in the future.

Ideally, we would also use a timeout for all tests within
RevisionDiffIT. Normally, this would be simply achieved by using the
Timeout rule of JUnit. However, adding that rule breaks all tests within
that class as our implementation of ConfigSuite doesn't seem to nicely
interact with arbitrary JUnit rules.

As the result of timed out intraline computations are cached, we need to
invalidate the intraline diff cache. The high CPU load also caused a lot
of PatchList cache computations to time out, for which also the
fall-back result was cached. Hence, we invalidate that cache as well.

Bug: Issue 8742
Change-Id: I0abf392d398320964a021099d72a4f876a73b6a6
This commit is contained in:
Alice Kober-Sotzek
2018-04-13 11:16:29 +02:00
committed by Dave Borowitz
parent 5738641811
commit 54dfdec960
5 changed files with 123 additions and 2 deletions
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13
gerrit-test-util/src/main/java/com/google/gerrit/extensions/common/ContentEntrySubject.java
View File

@@ -17,6 +17,7 @@ package com.google.gerrit.extensions.common;
import static com.google.common.truth.Truth.assertAbout;
import com.google.common.truth.FailureStrategy;
import com.google.common.truth.IterableSubject;
import com.google.common.truth.StringSubject;
import com.google.common.truth.Subject;
import com.google.common.truth.SubjectFactory;
@@ -78,4 +79,16 @@ public class ContentEntrySubject extends Subject<ContentEntrySubject, ContentEnt
ContentEntry contentEntry = actual();
return ListSubject.assertThat(contentEntry.b, Truth::assertThat).named("lines of 'b'");
}
public IterableSubject intralineEditsOfA() {
isNotNull();
ContentEntry contentEntry = actual();
return Truth.assertThat(contentEntry.editA).named("intraline edits of 'a'");
}
public IterableSubject intralineEditsOfB() {
isNotNull();
ContentEntry contentEntry = actual();
return Truth.assertThat(contentEntry.editB).named("intraline edits of 'b'");
}
}