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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you 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 memory
import (
"sync/atomic"
"github.com/apache/arrow-go/v18/arrow/internal/debug"
)
// Buffer is a wrapper type for a buffer of bytes.
type Buffer struct {
refCount int64
buf []byte
length int
mutable bool
mem Allocator
parent *Buffer
}
// NewBufferWithAllocator returns a buffer with the mutable flag set
// as false. The intention here is to allow wrapping a byte slice along
// with an allocator as a buffer to track the lifetime via refcounts
// in order to call Free when the refcount goes to zero.
//
// The primary example this is used for, is currently importing data
// through the c data interface and tracking the lifetime of the
// imported buffers.
func NewBufferWithAllocator(data []byte, mem Allocator) *Buffer {
return &Buffer{refCount: 1, buf: data, length: len(data), mem: mem}
}
// NewBufferBytes creates a fixed-size buffer from the specified data.
func NewBufferBytes(data []byte) *Buffer {
return &Buffer{refCount: 0, buf: data, length: len(data)}
}
// NewResizableBuffer creates a mutable, resizable buffer with an Allocator for managing memory.
func NewResizableBuffer(mem Allocator) *Buffer {
return &Buffer{refCount: 1, mutable: true, mem: mem}
}
func SliceBuffer(buf *Buffer, offset, length int) *Buffer {
buf.Retain()
return &Buffer{refCount: 1, parent: buf, buf: buf.Bytes()[offset : offset+length], length: length}
}
// Parent returns either nil or a pointer to the parent buffer if this buffer
// was sliced from another.
func (b *Buffer) Parent() *Buffer { return b.parent }
// Retain increases the reference count by 1.
func (b *Buffer) Retain() {
if b.mem != nil || b.parent != nil {
atomic.AddInt64(&b.refCount, 1)
}
}
// Release decreases the reference count by 1.
// When the reference count goes to zero, the memory is freed.
func (b *Buffer) Release() {
if b.mem != nil || b.parent != nil {
debug.Assert(atomic.LoadInt64(&b.refCount) > 0, "too many releases")
if atomic.AddInt64(&b.refCount, -1) == 0 {
if b.mem != nil {
b.mem.Free(b.buf)
} else {
b.parent.Release()
b.parent = nil
}
b.buf, b.length = nil, 0
}
}
}
// Reset resets the buffer for reuse.
func (b *Buffer) Reset(buf []byte) {
if b.parent != nil {
b.parent.Release()
b.parent = nil
}
b.buf = buf
b.length = len(buf)
}
// Buf returns the slice of memory allocated by the Buffer, which is adjusted by calling Reserve.
func (b *Buffer) Buf() []byte { return b.buf }
// Bytes returns a slice of size Len, which is adjusted by calling Resize.
func (b *Buffer) Bytes() []byte { return b.buf[:b.length] }
// Mutable returns a bool indicating whether the buffer is mutable or not.
func (b *Buffer) Mutable() bool { return b.mutable }
// Len returns the length of the buffer.
func (b *Buffer) Len() int { return b.length }
// Cap returns the capacity of the buffer.
func (b *Buffer) Cap() int { return len(b.buf) }
// Reserve reserves the provided amount of capacity for the buffer.
func (b *Buffer) Reserve(capacity int) {
if capacity > len(b.buf) {
newCap := roundUpToMultipleOf64(capacity)
if len(b.buf) == 0 {
b.buf = b.mem.Allocate(newCap)
} else {
b.buf = b.mem.Reallocate(newCap, b.buf)
}
}
}
// Resize resizes the buffer to the target size.
func (b *Buffer) Resize(newSize int) {
b.resize(newSize, true)
}
// ResizeNoShrink resizes the buffer to the target size, but will not
// shrink it.
func (b *Buffer) ResizeNoShrink(newSize int) {
b.resize(newSize, false)
}
func (b *Buffer) resize(newSize int, shrink bool) {
if !shrink || newSize > b.length {
b.Reserve(newSize)
} else {
// Buffer is not growing, so shrink to the requested size without
// excess space.
newCap := roundUpToMultipleOf64(newSize)
if len(b.buf) != newCap {
if newSize == 0 {
b.mem.Free(b.buf)
b.buf = nil
} else {
b.buf = b.mem.Reallocate(newCap, b.buf)
}
}
}
b.length = newSize
}
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