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/*
* Copyright 2019 gRPC authors.
*
* 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 buffer provides an implementation of an unbounded buffer.
package buffer
import (
"errors"
"sync"
)
// Unbounded is an implementation of an unbounded buffer which does not use
// extra goroutines. This is typically used for passing updates from one entity
// to another within gRPC.
//
// All methods on this type are thread-safe and don't block on anything except
// the underlying mutex used for synchronization.
//
// Unbounded supports values of any type to be stored in it by using a channel
// of `any`. This means that a call to Put() incurs an extra memory allocation,
// and also that users need a type assertion while reading. For performance
// critical code paths, using Unbounded is strongly discouraged and defining a
// new type specific implementation of this buffer is preferred. See
// internal/transport/transport.go for an example of this.
type Unbounded struct {
c chan any
closed bool
closing bool
mu sync.Mutex
backlog []any
}
// NewUnbounded returns a new instance of Unbounded.
func NewUnbounded() *Unbounded {
return &Unbounded{c: make(chan any, 1)}
}
var errBufferClosed = errors.New("Put called on closed buffer.Unbounded")
// Put adds t to the unbounded buffer.
func (b *Unbounded) Put(t any) error {
b.mu.Lock()
defer b.mu.Unlock()
if b.closing {
return errBufferClosed
}
if len(b.backlog) == 0 {
select {
case b.c <- t:
return nil
default:
}
}
b.backlog = append(b.backlog, t)
return nil
}
// Load sends the earliest buffered data, if any, onto the read channel returned
// by Get(). Users are expected to call this every time they successfully read a
// value from the read channel.
func (b *Unbounded) Load() {
b.mu.Lock()
defer b.mu.Unlock()
if len(b.backlog) > 0 {
select {
case b.c <- b.backlog[0]:
b.backlog[0] = nil
b.backlog = b.backlog[1:]
default:
}
} else if b.closing && !b.closed {
close(b.c)
}
}
// Get returns a read channel on which values added to the buffer, via Put(),
// are sent on.
//
// Upon reading a value from this channel, users are expected to call Load() to
// send the next buffered value onto the channel if there is any.
//
// If the unbounded buffer is closed, the read channel returned by this method
// is closed after all data is drained.
func (b *Unbounded) Get() <-chan any {
return b.c
}
// Close closes the unbounded buffer. No subsequent data may be Put(), and the
// channel returned from Get() will be closed after all the data is read and
// Load() is called for the final time.
func (b *Unbounded) Close() {
b.mu.Lock()
defer b.mu.Unlock()
if b.closing {
return
}
b.closing = true
if len(b.backlog) == 0 {
b.closed = true
close(b.c)
}
}
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