tree 70124257d5796501a0fba565a6b031332917d271
parent 83944a6ab9a19e916660381bb85d15450bc5aeab
author Alexander Aprelev <aam@google.com> 1605833687 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1605833687 +0000

[vm/concurrency] Guard updates of Field::guarded_cid and is_nullable.

This disables field unboxing in JIT with enabled lightweight isolates because currently unboxed generated code won't behave correctly if another isolate updates field unboxed state: for that guarded_cid updates would require stopping all isolates, getting to a safepoint.

Use of field guards(guarded_cid, is_nullable) in optimized compiler is concurrent-safe because each optimized compiler operates on its own clones of fields, which are checked for consistency with latest(mutator) state just before optimized code is installed.
Use of field guards in optimized generated code is safe because vm is brought to a safepoint and optimized code is deoptimized as soon as field guards are invalidated.
Use of field guards in generated unoptimized code outside of unboxed fields(transition to boxed from previously unboxed field is not safe which is why field unboxing is disabled) and use of field guards in unoptimized compiler is safe because transitions through guarded_cid and is_nullable makes less and less optimistic assumptions about the field state.

Issue https://github.com/dart-lang/sdk/issues/36097.

TEST=existing test suite

Change-Id: I00d37a49df483814c846b17c9c49e0dc6ce701e1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/172860
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>