commit 711e4619b00ad92d16b6ee06173f9af3ebabd0fe
author Joe Mason <joenotcharles@google.com> Thu Dec 05 23:20:56 2024
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Dec 05 23:20:56 2024
tree ec121e04f3d2f15f9e015eccc6233bd2b490c98a
parent 8ad048022cfed390aa7365ed868d47280ec5e514

[PM] Fix consistency in OnBeforeFooRemoved notifications

Makes sure that when OnBeforeFooRemoved() is called, all connections
to other graph nodes are still intact. This makes
OnBeforeFooRemoved() the last chance to iterate the graph with the
old connections.

As an exception, when a connection has its own notification (such as
OnOpenerFrameNodeChanged() for the PageNode<->FrameNode "opener"
connection) it can be broken before OnBeforeFooRemoved() if all
observers are notified. From the observer's point of view this is
indistinguishable from a separate event that happens to break the
connection shortly before the node is removed, so the graph is still
consistent during each notification.

To implement the new semantic, this splits the internal NodeBase::OnBeforeLeavingGraph() into 2 stages:

* OnBeforeLeavingGraph() lets the node make changes that don't affect
  the graph topology. It's called before sending OnBeforeFooRemoved
  notifications.
* OnUninitializing() lets the node finish its cleanup and break
  connections to other nodes. It's called after sending
  OnBeforeFooRemoved notifications.

Also updates the only two node observers that are affected by this
change:

* FreezingPolicy::OnBeforeFrameNodeRemoved() had several hidden
  assumptions that the FrameNode was NOT reachable from its PageNode.
  Now that it is reachable, it must be explicitly excluded.
* CPUMeasurementMonitor::OnBeforeFrameNodeRemoved() has a requirement
  that the FrameNode IS reachable from its PageNode. Now that this is
  true, removed the GraphChangeRemoveFrame workaround.
  OnBeforeWorkerNodeRemoved() has similar changes.

R=pmonette

Bug: 40640034
Change-Id: I0164da136ce085332f3e1b19ef125fc83ab2202c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5476608
Reviewed-by: Patrick Monette <pmonette@chromium.org>
Commit-Queue: Joe Mason <joenotcharles@google.com>
Cr-Commit-Position: refs/heads/main@{#1392613}