| /* |
| * 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 meter |
| |
| import ( |
| "context" |
| "sync" |
| |
| ofp "github.com/opencord/voltha-protos/v4/go/openflow_13" |
| ) |
| |
| // Cache hides all low-level locking & synchronization related to meter state updates |
| type Cache struct { |
| // this lock protects the meters map, it does not protect individual meters |
| lock sync.RWMutex |
| meters map[uint32]*chunk |
| } |
| |
| // chunk keeps a meter and the lock for this meter |
| type chunk struct { |
| // this lock is used to synchronize all access to the meter, and also to the "deleted" variable |
| lock sync.Mutex |
| deleted bool |
| |
| meter *ofp.OfpMeterEntry |
| } |
| |
| func NewCache() *Cache { |
| return &Cache{ |
| meters: make(map[uint32]*chunk), |
| } |
| } |
| |
| // LockOrCreate locks this meter if it exists, or creates a new meter if it does not. |
| // In the case of meter creation, the provided "meter" must not be modified afterwards. |
| func (cache *Cache) LockOrCreate(ctx context.Context, meter *ofp.OfpMeterEntry) (*Handle, bool, error) { |
| // try to use read lock instead of full lock if possible |
| if handle, have := cache.Lock(meter.Config.MeterId); have { |
| return handle, false, nil |
| } |
| |
| cache.lock.Lock() |
| entry, have := cache.meters[meter.Config.MeterId] |
| if !have { |
| entry := &chunk{meter: meter} |
| cache.meters[meter.Config.MeterId] = 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, meter) |
| } |
| return &Handle{loader: cache, chunk: entry}, false, nil |
| } |
| |
| // Lock acquires the lock for this meter, and returns a handle which can be used to access the meter until it's unlocked. |
| // This handle ensures that the meter cannot be accessed if the lock is not held. |
| // Returns false if the meter 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.meters[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.OfpMeterEntry which MUST NOT be modified externally, but which is safe to keep indefinitely |
| func (h *Handle) GetReadOnly() *ofp.OfpMeterEntry { |
| return h.chunk.meter |
| } |
| |
| // Update updates an existing meter in cache. |
| // The provided "meter" must not be modified afterwards. |
| func (h *Handle) Update(ctx context.Context, meter *ofp.OfpMeterEntry) error { |
| h.chunk.meter = meter |
| return nil |
| } |
| |
| // Delete removes the meter from the cache |
| func (h *Handle) Delete(ctx context.Context) error { |
| h.chunk.deleted = true |
| |
| h.loader.lock.Lock() |
| delete(h.loader.meters, h.chunk.meter.Config.MeterId) |
| h.loader.lock.Unlock() |
| |
| h.Unlock() |
| return nil |
| } |
| |
| // Unlock releases the lock on the meter |
| func (h *Handle) Unlock() { |
| if h.chunk != nil { |
| h.chunk.lock.Unlock() |
| h.chunk = nil // attempting to access the meter through this handle in future will panic |
| } |
| } |
| |
| // ListIDs returns a snapshot of all the managed meter IDs |
| // TODO: iterating through meters safely is expensive now, since all meters 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.meters)) |
| for id := range cache.meters { |
| ret[id] = struct{}{} |
| } |
| return ret |
| } |