mirror of
https://github.com/netbirdio/gvisor.git
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Add //pkg/ringdeque.
This is used in cl/674746696. PiperOrigin-RevId: 678955342
This commit is contained in:
Jamie Liu
gVisor bot
@@ -0,0 +1,22 @@
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load("//tools:defs.bzl", "go_library", "go_test")
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package(
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default_applicable_licenses = ["//:license"],
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licenses = ["notice"],
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)
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go_library(
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name = "ringdeque",
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srcs = [
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"ringdeque.go",
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],
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stateify = False,
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visibility = ["//pkg/sentry:internal"],
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)
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go_test(
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name = "ringdeque_test",
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size = "small",
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srcs = ["ringdeque_test.go"],
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library = ":ringdeque",
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)
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@@ -0,0 +1,154 @@
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// Copyright 2024 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package ringdeque provides the Deque type.
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package ringdeque
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// A Deque implements a double-ended queue of values of type T using a
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// resizable ring buffer.
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//
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// Deque is not safe to use concurrently from multiple goroutines.
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type Deque[T any] struct {
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// Items [off, off+len) modulo len(buf) in buf are valid.
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// Invariants:
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// - len(buf) is 0 or a power of 2.
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// - If len(buf) == 0, off == 0; otherwise off < len(buf).
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off uint64
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len uint64
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buf []T
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}
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// Preconditions: d.len == len(d.buf).
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func (d *Deque[T]) expand() {
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newLen := 2 // arbitrary minimum
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if d.len != 0 {
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newLen = len(d.buf) * 2
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}
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newBuf := make([]T, newLen)
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// By precondition, we need to copy every element in d.buf.
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n := copy(newBuf, d.buf[d.off:])
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copy(newBuf[n:], d.buf[:d.off])
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d.off = 0
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d.buf = newBuf
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}
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func (d *Deque[T]) mask() uint64 {
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return uint64(len(d.buf)) - 1
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}
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// Empty returns true if r contains no values.
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func (d *Deque[T]) Empty() bool {
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return d.len == 0
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}
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// Len returns the number of values in d.
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func (d *Deque[T]) Len() int {
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return int(d.len)
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}
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// Clear removes all values from d.
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func (d *Deque[T]) Clear() {
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d.len = 0
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}
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// PushFront inserts x at the front of d.
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func (d *Deque[T]) PushFront(x T) {
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if int(d.len) == len(d.buf) {
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d.expand()
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}
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newOff := (d.off - 1) & d.mask()
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d.buf[newOff] = x
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d.off = newOff
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d.len++
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}
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// PushBack inserts x at the back of d.
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func (d *Deque[T]) PushBack(x T) {
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if int(d.len) == len(d.buf) {
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d.expand()
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}
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i := (d.off + d.len) & d.mask()
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d.buf[i] = x
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d.len++
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}
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// PeekFront returns the value at the front of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) PeekFront() T {
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return *d.PeekFrontPtr()
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}
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// PeekFrontPtr returns a pointer to the value at the front of d. The pointer
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// is only valid until the next mutation of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) PeekFrontPtr() *T {
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if d.Empty() {
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panic("peek of empty Deque")
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}
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return &d.buf[d.off]
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}
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// PeekBack returns the value at the back of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) PeekBack() T {
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return *d.PeekBackPtr()
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}
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// PeekBackPtr returns a pointer to the value at the back of d. The pointer is
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// only valid until the next mutation of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) PeekBackPtr() *T {
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if d.Empty() {
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panic("peek of empty Deque")
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}
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i := (d.off + d.len - 1) & d.mask()
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return &d.buf[i]
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}
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// RemoveFront removes the value at the front of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) RemoveFront() {
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d.off = (d.off + 1) & d.mask()
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d.len--
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}
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// RemoveBack removes the value at the back of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) RemoveBack() {
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d.len--
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}
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// PopFront removes and returns the value at the front of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) PopFront() (x T) {
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x = d.PeekFront()
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d.RemoveFront()
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return
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}
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// PopBack removes and returns the value at the back of d.
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//
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// Preconditions: !d.Empty().
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func (d *Deque[T]) PopBack() (x T) {
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x = d.PeekBack()
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d.RemoveBack()
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return
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}
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@@ -0,0 +1,89 @@
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// Copyright 2024 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ringdeque
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import (
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"testing"
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)
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const numElems = 100
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func TestDeque(t *testing.T) {
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for _, test := range []struct {
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desc string
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push func(d *Deque[int], val int)
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pop func(d *Deque[int]) int
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reversed bool
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}{
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{
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desc: "PushFrontPopFront",
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push: (*Deque[int]).PushFront,
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pop: (*Deque[int]).PopFront,
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reversed: true,
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},
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{
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desc: "PushFrontPopBack",
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push: (*Deque[int]).PushFront,
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pop: (*Deque[int]).PopBack,
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reversed: false,
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},
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{
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desc: "PushBackPopFront",
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push: (*Deque[int]).PushBack,
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pop: (*Deque[int]).PopFront,
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reversed: false,
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},
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{
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desc: "PushBackPopBack",
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push: (*Deque[int]).PushBack,
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pop: (*Deque[int]).PopBack,
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reversed: true,
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},
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} {
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t.Run(test.desc, func(t *testing.T) {
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var d Deque[int]
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if !d.Empty() {
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t.Errorf("zero-value Deque non-empty")
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}
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if got := d.Len(); got != 0 {
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t.Errorf("zero-value Deque.Len: got %d, want 0", got)
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}
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for i := 0; i < numElems; i++ {
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test.push(&d, i)
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if d.Empty() {
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t.Errorf("Deque empty after %d pushes", i+1)
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}
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if got, want := d.Len(), i+1; got != want {
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t.Errorf("Len: got %d, want %d", got, want)
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}
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}
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for i := 0; i < numElems; i++ {
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want := i
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if test.reversed {
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want = numElems - 1 - i
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}
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if got := test.pop(&d); got != want {
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t.Errorf("pop %d: got %d, want %d", i, got, want)
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}
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}
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if !d.Empty() {
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t.Errorf("Deque non-empty after all removals")
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}
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if got := d.Len(); got != 0 {
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t.Errorf("Len after all removals: got %d, want 0", got)
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}
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})
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}
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}
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