Track paths and provide a rename hook.

This change also adds extensive testing to the p9 package via mocks. The sanity
checks and type checks are moved from the gofer into the core package, where
they can be more easily validated.

PiperOrigin-RevId: 218296768
Change-Id: I4fc3c326e7bf1e0e140a454cbacbcc6fd617ab55

1 files changed, 109 insertions, 0 deletions

diff --git a/pkg/p9/path_tree.go b/pkg/p9/path_tree.go
new file mode 100644
index 000000000..97f90bcd5
--- /dev/null
+++ b/pkg/p9/path_tree.go
@@ -0,0 +1,109 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package p9
+
+import (
+	"fmt"
+	"sync"
+)
+
+// pathNode is a single node in a path traversal.
+//
+// These are shared by all fidRefs that point to the same path.
+//
+// These are not synchronized because we allow certain operations (file walk)
+// to proceed without having to acquire a write lock. The lock in this
+// structure exists to synchronize high-level, semantic operations, such as the
+// simultaneous creation and deletion of a file.
+//
+// (+) below is the path component string.
+type pathNode struct {
+	mu       sync.RWMutex // See above.
+	fidRefs  sync.Map     // => map[*fidRef]string(+)
+	children sync.Map     // => map[string(+)]*pathNode
+	count    int64
+}
+
+// pathNodeFor returns the path node for the given name, or a new one.
+//
+// Precondition: mu must be held in a readable fashion.
+func (p *pathNode) pathNodeFor(name string) *pathNode {
+	// Load the existing path node.
+	if pn, ok := p.children.Load(name); ok {
+		return pn.(*pathNode)
+	}
+
+	// Create a new pathNode for shared use.
+	pn, _ := p.children.LoadOrStore(name, new(pathNode))
+	return pn.(*pathNode)
+}
+
+// nameFor returns the name for the given fidRef.
+//
+// Precondition: mu must be held in a readable fashion.
+func (p *pathNode) nameFor(ref *fidRef) string {
+	if s, ok := p.fidRefs.Load(ref); ok {
+		return s.(string)
+	}
+
+	// This should not happen, don't proceed.
+	panic(fmt.Sprintf("expected name for %+v, none found", ref))
+}
+
+// addChild adds a child to the given pathNode.
+//
+// This applies only to an individual fidRef.
+//
+// Precondition: mu must be held in a writable fashion.
+func (p *pathNode) addChild(ref *fidRef, name string) {
+	if s, ok := p.fidRefs.Load(ref); ok {
+		// This should not happen, don't proceed.
+		panic(fmt.Sprintf("unexpected fidRef %+v with path %q, wanted %q", ref, s, name))
+	}
+
+	p.fidRefs.Store(ref, name)
+}
+
+// removeChild removes the given child.
+//
+// This applies only to an individual fidRef.
+//
+// Precondition: mu must be held in a writable fashion.
+func (p *pathNode) removeChild(ref *fidRef) {
+	p.fidRefs.Delete(ref)
+}
+
+// removeWithName removes all references with the given name.
+//
+// The original pathNode is returned by this function, and removed from this
+// pathNode. Any operations on the removed tree must use this value.
+//
+// The provided function is executed after removal.
+//
+// Precondition: mu must be held in a writable fashion.
+func (p *pathNode) removeWithName(name string, fn func(ref *fidRef)) *pathNode {
+	p.fidRefs.Range(func(key, value interface{}) bool {
+		if value.(string) == name {
+			p.fidRefs.Delete(key)
+			fn(key.(*fidRef))
+		}
+		return true
+	})
+
+	// Return the original path node.
+	origPathNode := p.pathNodeFor(name)
+	p.children.Delete(name)
+	return origPathNode
+}