core: fix deadlock when dependable node replaced with non-dependable one #2968
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Helps to flush out deadlocks in the dependency graph
In #2884, Terraform would hang on graphs with an orphaned resource depended on an orphaned module. This is because orphan module nodes (which are dependable) were getting expanded (replaced) with GraphNodeBasicSubgraph nodes (which are _not_ dependable). The old `graph.Replace()` code resulted in GraphNodeBasicSubgraph being entered into the lookaside table, even though it is not dependable. This resulted in an untraversable edge in the graph, so the graph would hang and wait forever. Now, we remove entries from the lookaside table when a dependable node is being replaced with a non-dependable node. This means we lose an edge, but we can move forward. It's ~probably~ never correct to be replacing depenable nodes with non-dependable ones, but this tweak seemed preferable to tossing a panic in there.
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| } | ||
| } | ||
| log.Printf("[DEBUG] vertex %s, got dep: %s", | ||
| VertexName(v), VertexName(deps[i])) |
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LGTM! |
|
(Minor nitpicks, but the core stuff is good) |
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core: fix deadlock when dependable node replaced with non-dependable one
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In #2884, Terraform would hang on graphs with an orphaned resource
depended on an orphaned module.
This is because orphan module nodes (which are dependable) were getting
expanded (replaced) with GraphNodeBasicSubgraph nodes (which are not
dependable).
The old
graph.Replace()code resulted in GraphNodeBasicSubgraph beingentered into the lookaside table, even though it is not dependable.
This resulted in an untraversable edge in the graph, so the graph would
hang and wait forever.
Now, we remove entries from the lookaside table when a dependable node
is being replaced with a non-dependable node. This means we lose an
edge, but we can move forward. It's
probablynever correct to bereplacing depenable nodes with non-dependable ones, but this tweak
seemed preferable to tossing a panic in there.