180315 2017-12-02 11:20:10 -0800 forEachLiveCell should be safe in the case of concurrent aboutToMarkSlow() without grabbing a lock for each call to isLive 2017-12-02 11:58:34 -0800 1 1 1 Unclassified WebKit JavaScriptCore WebKit Nightly Build All All NEW P2 Normal --- 165909 1 fpizlo webkit-unassigned oldest_to_newest 1377328 0 fpizlo 2017-12-02 11:20:10 -0800 ... 1377339 1 fpizlo 2017-12-02 11:58:34 -0800 It just occurred to me that the algorithm for forEachLiveCell could be: - If the block is allocated, just walk all objects. - If the block has newly allocated at the outset, then walk that. I think that grabbing the lock at the beginning just to verify that newly allocated is set up is sufficient. - Otherwise, walk the mark bits, and recheck the state of the block at the end. If the block is still in the mark bits state, then we're done. If it's not, then rewalk it.