tree 284c06ad6ec6efe002203d1209af4512ab000e7f
parent 12a89261e5b831096e734688edf4a9c1b6ee21b3
author Martin Kustermann <kustermann@google.com> 1635946595 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1635946595 +0000

[vm/concurrency] Ensure rehashing of maps correctly resets [_deletedKeys]

When we rehash a linked hash map, we rebuild the index but keep the
existing data array. The [_deletedKeys] specifies the number of entries in the
[_index] which were marked as deleted. The Dart code that triggers
rehashing and initializes a new [_index] didn't initialize
[_deletedKeys].

=> We'll fix this in the Dart code and as a precaution also in the
   transitive object copy code.

Furthermore we add a missing optimization: In the example from the bug
report we shouldn't even have attempted to re-hash, because the maps
have only primitive keys (which do not rely on identity or user-defined
hashcodes).

=> We'll change the existing optimization to ignore deleted entries when
   determining whether a rehash is needed.

The rehashing code for Sets works differently and takes this already
into account.

Closes https://github.com/dart-lang/sdk/issues/47598

TEST=vm/dart{,_2}/isolates/fast_object_copy_test

Change-Id: I3529ecbf500009ab0c72b98e6c427b8840a69371
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/219000
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>