/*
 *
 * Copyright 2024 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 mem

import (
	
	

	
)

// BufferPool is a pool of buffers that can be shared and reused, resulting in
// decreased memory allocation.
type BufferPool interface {
	// Get returns a buffer with specified length from the pool.
	Get(length int) *[]byte

	// Put returns a buffer to the pool.
	//
	// The provided pointer must hold a prefix of the buffer obtained via
	// BufferPool.Get to ensure the buffer's entire capacity can be re-used.
	Put(*[]byte)
}

const goPageSize = 4 << 10 // 4KiB. N.B. this must be a power of 2.

var defaultBufferPoolSizes = []int{
	256,
	goPageSize,
	16 << 10, // 16KB (max HTTP/2 frame size used by gRPC)
	32 << 10, // 32KB (default buffer size for io.Copy)
	1 << 20,  // 1MB
}

var defaultBufferPool BufferPool

func init() {
	defaultBufferPool = NewTieredBufferPool(defaultBufferPoolSizes...)

	internal.SetDefaultBufferPool = func( BufferPool) {
		defaultBufferPool = 
	}

	internal.SetBufferPoolingThresholdForTesting = func( int) {
		bufferPoolingThreshold = 
	}
}

// DefaultBufferPool returns the current default buffer pool. It is a BufferPool
// created with NewBufferPool that uses a set of default sizes optimized for
// expected workflows.
func () BufferPool {
	return defaultBufferPool
}

// NewTieredBufferPool returns a BufferPool implementation that uses multiple
// underlying pools of the given pool sizes.
func ( ...int) BufferPool {
	sort.Ints()
	 := make([]*sizedBufferPool, len())
	for ,  := range  {
		[] = newSizedBufferPool()
	}
	return &tieredBufferPool{
		sizedPools: ,
	}
}

// tieredBufferPool implements the BufferPool interface with multiple tiers of
// buffer pools for different sizes of buffers.
type tieredBufferPool struct {
	sizedPools   []*sizedBufferPool
	fallbackPool simpleBufferPool
}

func ( *tieredBufferPool) ( int) *[]byte {
	return .getPool().Get()
}

func ( *tieredBufferPool) ( *[]byte) {
	.getPool(cap(*)).Put()
}

func ( *tieredBufferPool) ( int) BufferPool {
	 := sort.Search(len(.sizedPools), func( int) bool {
		return .sizedPools[].defaultSize >= 
	})

	if  == len(.sizedPools) {
		return &.fallbackPool
	}

	return .sizedPools[]
}

// sizedBufferPool is a BufferPool implementation that is optimized for specific
// buffer sizes. For example, HTTP/2 frames within gRPC have a default max size
// of 16kb and a sizedBufferPool can be configured to only return buffers with a
// capacity of 16kb. Note that however it does not support returning larger
// buffers and in fact panics if such a buffer is requested. Because of this,
// this BufferPool implementation is not meant to be used on its own and rather
// is intended to be embedded in a tieredBufferPool such that Get is only
// invoked when the required size is smaller than or equal to defaultSize.
type sizedBufferPool struct {
	pool        sync.Pool
	defaultSize int
}

func ( *sizedBufferPool) ( int) *[]byte {
	,  := .pool.Get().(*[]byte)
	if ! {
		 := make([]byte, , .defaultSize)
		return &
	}
	 := *
	clear([:cap()])
	* = [:]
	return 
}

func ( *sizedBufferPool) ( *[]byte) {
	if cap(*) < .defaultSize {
		// Ignore buffers that are too small to fit in the pool. Otherwise, when
		// Get is called it will panic as it tries to index outside the bounds
		// of the buffer.
		return
	}
	.pool.Put()
}

func newSizedBufferPool( int) *sizedBufferPool {
	return &sizedBufferPool{
		defaultSize: ,
	}
}

var _ BufferPool = (*simpleBufferPool)(nil)

// simpleBufferPool is an implementation of the BufferPool interface that
// attempts to pool buffers with a sync.Pool. When Get is invoked, it tries to
// acquire a buffer from the pool but if that buffer is too small, it returns it
// to the pool and creates a new one.
type simpleBufferPool struct {
	pool sync.Pool
}

func ( *simpleBufferPool) ( int) *[]byte {
	,  := .pool.Get().(*[]byte)
	if  && cap(*) >=  {
		clear((*)[:cap(*)])
		* = (*)[:]
		return 
	}

	// A buffer was pulled from the pool, but it is too small. Put it back in
	// the pool and create one large enough.
	if  {
		.pool.Put()
	}

	// If we're going to allocate, round up to the nearest page. This way if
	// requests frequently arrive with small variation we don't allocate
	// repeatedly if we get unlucky and they increase over time. By default we
	// only allocate here if size > 1MiB. Because goPageSize is a power of 2, we
	// can round up efficiently.
	 := ( + goPageSize - 1) & ^(goPageSize - 1)

	 := make([]byte, , )
	return &
}

func ( *simpleBufferPool) ( *[]byte) {
	.pool.Put()
}

var _ BufferPool = NopBufferPool{}

// NopBufferPool is a buffer pool that returns new buffers without pooling.
type NopBufferPool struct{}

// Get returns a buffer with specified length from the pool.
func (NopBufferPool) ( int) *[]byte {
	 := make([]byte, )
	return &
}

// Put returns a buffer to the pool.
func (NopBufferPool) (*[]byte) {
}