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/*
* Copyright 2018-present Open Networking Foundation
* 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 group
import (
"context"
"sync"
ofp "github.com/opencord/voltha-protos/v4/go/openflow_13"
)
// Cache hides all low-level locking & synchronization related to group state updates
type Cache struct {
// this lock protects the groups map, it does not protect individual groups
lock sync.RWMutex
groups map[uint32]*chunk
}
// chunk keeps a group and the lock for this group
type chunk struct {
// this lock is used to synchronize all access to the group, and also to the "deleted" variable
lock sync.Mutex
deleted bool
group *ofp.OfpGroupEntry
}
func NewCache() *Cache {
return &Cache{
groups: make(map[uint32]*chunk),
}
}
// LockOrCreate locks this group if it exists, or creates a new group if it does not.
// In the case of group creation, the provided "group" must not be modified afterwards.
func (cache *Cache) LockOrCreate(ctx context.Context, group *ofp.OfpGroupEntry) (*Handle, bool, error) {
// try to use read lock instead of full lock if possible
if handle, have := cache.Lock(group.Desc.GroupId); have {
return handle, false, nil
}
cache.lock.Lock()
entry, have := cache.groups[group.Desc.GroupId]
if !have {
entry := &chunk{group: group}
cache.groups[group.Desc.GroupId] = entry
entry.lock.Lock()
cache.lock.Unlock()
return &Handle{loader: cache, chunk: entry}, true, nil
}
cache.lock.Unlock()
entry.lock.Lock()
if entry.deleted {
entry.lock.Unlock()
return cache.LockOrCreate(ctx, group)
}
return &Handle{loader: cache, chunk: entry}, false, nil
}
// Lock acquires the lock for this group, and returns a handle which can be used to access the group until it's unlocked.
// This handle ensures that the group cannot be accessed if the lock is not held.
// Returns false if the group is not present.
// TODO: consider accepting a ctx and aborting the lock attempt on cancellation
func (cache *Cache) Lock(id uint32) (*Handle, bool) {
cache.lock.RLock()
entry, have := cache.groups[id]
cache.lock.RUnlock()
if !have {
return nil, false
}
entry.lock.Lock()
if entry.deleted {
entry.lock.Unlock()
return cache.Lock(id)
}
return &Handle{loader: cache, chunk: entry}, true
}
// Handle is allocated for each Lock() call, all modifications are made using it, and it is invalidated by Unlock()
// This enforces correct Lock()-Usage()-Unlock() ordering.
type Handle struct {
loader *Cache
chunk *chunk
}
// GetReadOnly returns an *ofp.OfpGroupEntry which MUST NOT be modified externally, but which is safe to keep indefinitely
func (h *Handle) GetReadOnly() *ofp.OfpGroupEntry {
return h.chunk.group
}
// Update updates an existing group in cache.
// The provided "group" must not be modified afterwards.
func (h *Handle) Update(ctx context.Context, group *ofp.OfpGroupEntry) error {
h.chunk.group = group
return nil
}
// Delete removes the group from the cache
func (h *Handle) Delete(ctx context.Context) error {
h.chunk.deleted = true
h.loader.lock.Lock()
delete(h.loader.groups, h.chunk.group.Desc.GroupId)
h.loader.lock.Unlock()
h.Unlock()
return nil
}
// Unlock releases the lock on the group
func (h *Handle) Unlock() {
if h.chunk != nil {
h.chunk.lock.Unlock()
h.chunk = nil // attempting to access the group through this handle in future will panic
}
}
// ListIDs returns a snapshot of all the managed group IDs
// TODO: iterating through groups safely is expensive now, since all groups are stored & locked separately
// should avoid this where possible
func (cache *Cache) ListIDs() map[uint32]struct{} {
cache.lock.RLock()
defer cache.lock.RUnlock()
// copy the IDs so caller can safely iterate
ret := make(map[uint32]struct{}, len(cache.groups))
for id := range cache.groups {
ret[id] = struct{}{}
}
return ret
}