ceph/src/arrow/go/arrow/array/bufferbuilder.go

   1 // Licensed to the Apache Software Foundation (ASF) under one
   2 // or more contributor license agreements.  See the NOTICE file
   3 // distributed with this work for additional information
   4 // regarding copyright ownership.  The ASF licenses this file
   5 // to you under the Apache License, Version 2.0 (the
   6 // "License"); you may not use this file except in compliance
   7 // with the License.  You may obtain a copy of the License at
   8 //
   9 // http://www.apache.org/licenses/LICENSE-2.0
  10 //
  11 // Unless required by applicable law or agreed to in writing, software
  12 // distributed under the License is distributed on an "AS IS" BASIS,
  13 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 // See the License for the specific language governing permissions and
  15 // limitations under the License.
  16
  17 package array
  18
  19 import (
  20         "sync/atomic"
  21
  22         "github.com/apache/arrow/go/v6/arrow/bitutil"
  23         "github.com/apache/arrow/go/v6/arrow/internal/debug"
  24         "github.com/apache/arrow/go/v6/arrow/memory"
  25 )
  26
  27 // A bufferBuilder provides common functionality for populating memory with a sequence of type-specific values.
  28 // Specialized implementations provide type-safe APIs for appending and accessing the memory.
  29 type bufferBuilder struct {
  30         refCount int64
  31         mem      memory.Allocator
  32         buffer   *memory.Buffer
  33         length   int
  34         capacity int
  35
  36         bytes []byte
  37 }
  38
  39 // Retain increases the reference count by 1.
  40 // Retain may be called simultaneously from multiple goroutines.
  41 func (b *bufferBuilder) Retain() {
  42         atomic.AddInt64(&b.refCount, 1)
  43 }
  44
  45 // Release decreases the reference count by 1.
  46 // When the reference count goes to zero, the memory is freed.
  47 // Release may be called simultaneously from multiple goroutines.
  48 func (b *bufferBuilder) Release() {
  49         debug.Assert(atomic.LoadInt64(&b.refCount) > 0, "too many releases")
  50
  51         if atomic.AddInt64(&b.refCount, -1) == 0 {
  52                 if b.buffer != nil {
  53                         b.buffer.Release()
  54                         b.buffer, b.bytes = nil, nil
  55                 }
  56         }
  57 }
  58
  59 // Len returns the length of the memory buffer in bytes.
  60 func (b *bufferBuilder) Len() int { return b.length }
  61
  62 // Cap returns the total number of bytes that can be stored without allocating additional memory.
  63 func (b *bufferBuilder) Cap() int { return b.capacity }
  64
  65 // Bytes returns a slice of length b.Len().
  66 // The slice is only valid for use until the next buffer modification. That is, until the next call
  67 // to Advance, Reset, Finish or any Append function. The slice aliases the buffer content at least until the next
  68 // buffer modification.
  69 func (b *bufferBuilder) Bytes() []byte { return b.bytes[:b.length] }
  70
  71 func (b *bufferBuilder) resize(elements int) {
  72         if b.buffer == nil {
  73                 b.buffer = memory.NewResizableBuffer(b.mem)
  74         }
  75
  76         b.buffer.Resize(elements)
  77         oldCapacity := b.capacity
  78         b.capacity = b.buffer.Cap()
  79         b.bytes = b.buffer.Buf()
  80
  81         if b.capacity > oldCapacity {
  82                 memory.Set(b.bytes[oldCapacity:], 0)
  83         }
  84 }
  85
  86 // Advance increases the buffer by length and initializes the skipped bytes to zero.
  87 func (b *bufferBuilder) Advance(length int) {
  88         if b.capacity < b.length+length {
  89                 newCapacity := bitutil.NextPowerOf2(b.length + length)
  90                 b.resize(newCapacity)
  91         }
  92         b.length += length
  93 }
  94
  95 // Append appends the contents of v to the buffer, resizing it if necessary.
  96 func (b *bufferBuilder) Append(v []byte) {
  97         if b.capacity < b.length+len(v) {
  98                 newCapacity := bitutil.NextPowerOf2(b.length + len(v))
  99                 b.resize(newCapacity)
 100         }
 101         b.unsafeAppend(v)
 102 }
 103
 104 // Reset returns the buffer to an empty state. Reset releases the memory and sets the length and capacity to zero.
 105 func (b *bufferBuilder) Reset() {
 106         if b.buffer != nil {
 107                 b.buffer.Release()
 108         }
 109         b.buffer, b.bytes = nil, nil
 110         b.capacity, b.length = 0, 0
 111 }
 112
 113 // Finish TODO(sgc)
 114 func (b *bufferBuilder) Finish() (buffer *memory.Buffer) {
 115         if b.length > 0 {
 116                 b.buffer.ResizeNoShrink(b.length)
 117         }
 118         buffer = b.buffer
 119         b.buffer = nil
 120         b.Reset()
 121         return
 122 }
 123
 124 func (b *bufferBuilder) unsafeAppend(data []byte) {
 125         copy(b.bytes[b.length:], data)
 126         b.length += len(data)
 127 }