Initial commit

vendor/github.com/cockroachdb/pebble/internal/bytealloc/bytealloc.go

@@ -0,0 +1,61 @@
+// Copyright 2016 The Cockroach 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 bytealloc
+
+import "github.com/cockroachdb/pebble/internal/rawalloc"
+
+// An A provides chunk allocation of []byte, amortizing the overhead of each
+// allocation. Because the underlying storage for the slices is shared, they
+// should share a similar lifetime in order to avoid pinning large amounts of
+// memory unnecessarily. The allocator itself is a []byte where cap() indicates
+// the total amount of memory and len() is the amount already allocated. The
+// size of the buffer to allocate from is grown exponentially when it runs out
+// of room up to a maximum size (chunkAllocMaxSize).
+type A []byte
+
+const chunkAllocMinSize = 512
+const chunkAllocMaxSize = 16384
+
+func (a A) reserve(n int) A {
+	allocSize := cap(a) * 2
+	if allocSize < chunkAllocMinSize {
+		allocSize = chunkAllocMinSize
+	} else if allocSize > chunkAllocMaxSize {
+		allocSize = chunkAllocMaxSize
+	}
+	if allocSize < n {
+		allocSize = n
+	}
+	return rawalloc.New(0, allocSize)
+}
+
+// Alloc allocates a new chunk of memory with the specified length.
+func (a A) Alloc(n int) (A, []byte) {
+	if cap(a)-len(a) < n {
+		a = a.reserve(n)
+	}
+	p := len(a)
+	r := a[p : p+n : p+n]
+	a = a[:p+n]
+	return a, r
+}
+
+// Copy allocates a new chunk of memory, initializing it from src.
+func (a A) Copy(src []byte) (A, []byte) {
+	var alloc []byte
+	a, alloc = a.Alloc(len(src))
+	copy(alloc, src)
+	return a, alloc
+}