• Sigurd Schneider's avatar
    [heap] Clean-up some weak map entries in scavenger · 4e6a1a75
    Sigurd Schneider authored
    This change enables clean-up of weak map entries in the
    scavenger of the weak map is in the young generation.
    With this change, the scavenger treats keys in ephemerons as
    weak instead of strong, but does not implement full ephemeron
    semantics: Values are treated always as strong, independently
    of whether the key is live or not.
    
    This approach ensures that no value is cleaned up accidentally.
    After scavenging, all entries with dead keys are removed from
    weak maps. After that, some values that are not referenced anywhere
    anymore might still be in the heap, and those can be cleaned up
    in the next scavenge.
    
    What the scavenger does, amounts to one iteration of the
    fixed-point algorithm required to implement ephemeron semantics.
    We hope that this is a reasonable trade-off between time spent
    tracing and cleaned-up entries.
    
    This change does not affect weak maps that reside in old space.
    
    Bug: v8:8557
    Change-Id: Ic5618b3b863ad8c314c87449571150e756fecbf0
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1467182
    Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
    Reviewed-by: 's avatarUlan Degenbaev <ulan@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#60101}
    4e6a1a75
scavenger-inl.h 19.6 KB