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cache.go
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cache.go
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// Copyright 2019 - See NOTICE file for copyright holders.
//
// 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 wire
import "context"
type (
// Cache is a message cache. The default value is a valid empty cache.
Cache struct {
msgs []*Envelope
preds []ctxPredicate
}
// A Predicate defines a message filter.
Predicate = func(*Envelope) bool
ctxPredicate struct {
ctx context.Context
p Predicate
}
// A Cacher has the Cache method to enable caching of messages.
Cacher interface {
// Cache should enable the caching of messages
Cache(context.Context, Predicate)
}
)
// Cache is a message cache. The default value is a valid empty cache.
func (c *Cache) Cache(ctx context.Context, p Predicate) {
c.preds = append(c.preds, ctxPredicate{ctx, p})
}
// Put puts the message into the cache if it matches any active predicate.
// If it matches several predicates, it is still only added once to the cache.
func (c *Cache) Put(e *Envelope) bool {
// we filter the predicates for non-active and lazily remove them
preds := c.preds[:0]
any := false
for _, p := range c.preds {
select {
case <-p.ctx.Done():
continue // skip done predicate
default:
preds = append(preds, p)
}
any = any || p.p(e)
}
if any {
c.msgs = append(c.msgs, e)
}
c.preds = preds
return any
}
// Get retrieves all messages from the cache that match the predicate. They are
// removed from the Cache.
func (c *Cache) Get(p Predicate) []*Envelope {
msgs := c.msgs[:0]
// Usually, Get is called with the assumption to match at least one message
matches := make([]*Envelope, 0, 1)
for _, m := range c.msgs {
if p(m) {
matches = append(matches, m)
} else {
msgs = append(msgs, m)
}
}
c.msgs = msgs
return matches
}
// Flush empties the message cache and removes all predicates.
func (c *Cache) Flush() {
c.msgs = nil
c.preds = nil
}
// Size returns the number of messages held in the message cache.
func (c *Cache) Size() int {
return len(c.msgs)
}