mirror of https://github.com/pulumi/pulumi.git
68 lines
2.6 KiB
Go
68 lines
2.6 KiB
Go
// Copyright 2016-2018, Pulumi Corporation. All rights reserved.
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package graph
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import (
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"github.com/pulumi/pulumi/pkg/resource"
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"github.com/pulumi/pulumi/pkg/util/contract"
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)
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// DependencyGraph represents a dependency graph encoded within a resource snapshot.
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type DependencyGraph struct {
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index map[*resource.State]int // A mapping of resource pointers to indexes within the snapshot
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resources []*resource.State // The list of resources, obtained from the snapshot
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}
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// DependingOn returns a slice containing all resources that directly or indirectly
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// depend upon the given resource. The returned slice is guaranteed to be in topological
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// order with respect to the snapshot dependency graph.
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//
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// The time complexity of DependingOn is linear with respect to the number of resources.
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func (dg *DependencyGraph) DependingOn(res *resource.State) []*resource.State {
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// This implementation relies on the detail that snapshots are stored in a valid
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// topological order.
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var dependents []*resource.State
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dependentSet := make(map[resource.URN]bool)
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cursorIndex, ok := dg.index[res]
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contract.Assert(ok)
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dependentSet[res.URN] = true
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// The dependency graph encoded directly within the snapshot is the reverse of
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// the graph that we actually want to operate upon. Edges in the snapshot graph
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// originate in a resource and go to that resource's dependencies.
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//
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// The `DependingOn` is simpler when operating on the reverse of the snapshot graph,
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// where edges originate in a resource and go to resources that depend on that resource.
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// In this graph, `DependingOn` for a resource is the set of resources that are reachable from the
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// given resource.
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//
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// To accomplish this without building up an entire graph data structure, we'll do a linear
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// scan of the resource list starting at the requested resource and ending at the end of
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// the list. All resources that depend directly or indirectly on `res` are prepended
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// onto `dependents`.
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for i := cursorIndex + 1; i < len(dg.resources); i++ {
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cursorResource := dg.resources[i]
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for _, dependency := range cursorResource.Dependencies {
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if dependentSet[dependency] {
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dependents = append(dependents, cursorResource)
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dependentSet[cursorResource.URN] = true
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break
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}
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}
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}
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return dependents
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}
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// NewDependencyGraph creates a new DependencyGraph from a list of resources.
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// The resources should be in topological order with respect to their dependencies.
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func NewDependencyGraph(resources []*resource.State) *DependencyGraph {
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index := make(map[*resource.State]int)
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for idx, res := range resources {
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index[res] = idx
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}
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return &DependencyGraph{index, resources}
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}
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