mirror of
https://github.com/golang/go
synced 2024-09-05 07:54:46 +00:00
![Matthew Dempsky](/assets/img/avatar_default.png)
The next CL will remove the -G flag, effectively hard-coding it to its current default (-G=3). Change-Id: Ib4743b529206928f9f1cca9fdb19989728327831 Reviewed-on: https://go-review.googlesource.com/c/go/+/388534 Reviewed-by: Keith Randall <khr@golang.org> Trust: Matthew Dempsky <mdempsky@google.com> Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
414 lines
8.4 KiB
Go
414 lines
8.4 KiB
Go
// run
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// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package chans provides utility functions for working with channels.
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package main
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import (
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"context"
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"fmt"
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"runtime"
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"sort"
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"sync"
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"time"
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)
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// _Equal reports whether two slices are equal: the same length and all
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// elements equal. All floating point NaNs are considered equal.
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func _SliceEqual[Elem comparable](s1, s2 []Elem) bool {
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if len(s1) != len(s2) {
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return false
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}
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for i, v1 := range s1 {
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v2 := s2[i]
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if v1 != v2 {
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isNaN := func(f Elem) bool { return f != f }
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if !isNaN(v1) || !isNaN(v2) {
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return false
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}
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}
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}
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return true
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}
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// _ReadAll reads from c until the channel is closed or the context is
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// canceled, returning all the values read.
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func _ReadAll[Elem any](ctx context.Context, c <-chan Elem) []Elem {
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var r []Elem
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for {
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select {
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case <-ctx.Done():
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return r
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case v, ok := <-c:
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if !ok {
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return r
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}
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r = append(r, v)
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}
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}
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}
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// _Merge merges two channels into a single channel.
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// This will leave a goroutine running until either both channels are closed
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// or the context is canceled, at which point the returned channel is closed.
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func _Merge[Elem any](ctx context.Context, c1, c2 <-chan Elem) <-chan Elem {
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r := make(chan Elem)
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go func(ctx context.Context, c1, c2 <-chan Elem, r chan<- Elem) {
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defer close(r)
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for c1 != nil || c2 != nil {
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select {
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case <-ctx.Done():
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return
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case v1, ok := <-c1:
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if ok {
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r <- v1
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} else {
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c1 = nil
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}
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case v2, ok := <-c2:
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if ok {
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r <- v2
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} else {
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c2 = nil
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}
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}
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}
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}(ctx, c1, c2, r)
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return r
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}
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// _Filter calls f on each value read from c. If f returns true the value
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// is sent on the returned channel. This will leave a goroutine running
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// until c is closed or the context is canceled, at which point the
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// returned channel is closed.
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func _Filter[Elem any](ctx context.Context, c <-chan Elem, f func(Elem) bool) <-chan Elem {
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r := make(chan Elem)
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go func(ctx context.Context, c <-chan Elem, f func(Elem) bool, r chan<- Elem) {
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defer close(r)
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for {
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select {
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case <-ctx.Done():
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return
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case v, ok := <-c:
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if !ok {
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return
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}
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if f(v) {
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r <- v
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}
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}
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}
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}(ctx, c, f, r)
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return r
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}
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// _Sink returns a channel that discards all values sent to it.
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// This will leave a goroutine running until the context is canceled
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// or the returned channel is closed.
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func _Sink[Elem any](ctx context.Context) chan<- Elem {
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r := make(chan Elem)
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go func(ctx context.Context, r <-chan Elem) {
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for {
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select {
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case <-ctx.Done():
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return
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case _, ok := <-r:
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if !ok {
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return
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}
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}
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}
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}(ctx, r)
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return r
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}
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// An Exclusive is a value that may only be used by a single goroutine
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// at a time. This is implemented using channels rather than a mutex.
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type _Exclusive[Val any] struct {
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c chan Val
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}
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// _MakeExclusive makes an initialized exclusive value.
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func _MakeExclusive[Val any](initial Val) *_Exclusive[Val] {
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r := &_Exclusive[Val]{
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c: make(chan Val, 1),
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}
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r.c <- initial
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return r
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}
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// _Acquire acquires the exclusive value for private use.
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// It must be released using the Release method.
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func (e *_Exclusive[Val]) Acquire() Val {
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return <-e.c
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}
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// TryAcquire attempts to acquire the value. The ok result reports whether
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// the value was acquired. If the value is acquired, it must be released
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// using the Release method.
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func (e *_Exclusive[Val]) TryAcquire() (v Val, ok bool) {
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select {
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case r := <-e.c:
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return r, true
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default:
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return v, false
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}
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}
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// Release updates and releases the value.
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// This method panics if the value has not been acquired.
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func (e *_Exclusive[Val]) Release(v Val) {
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select {
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case e.c <- v:
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default:
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panic("_Exclusive Release without Acquire")
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}
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}
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// Ranger returns a Sender and a Receiver. The Receiver provides a
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// Next method to retrieve values. The Sender provides a Send method
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// to send values and a Close method to stop sending values. The Next
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// method indicates when the Sender has been closed, and the Send
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// method indicates when the Receiver has been freed.
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//
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// This is a convenient way to exit a goroutine sending values when
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// the receiver stops reading them.
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func _Ranger[Elem any]() (*_Sender[Elem], *_Receiver[Elem]) {
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c := make(chan Elem)
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d := make(chan struct{})
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s := &_Sender[Elem]{
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values: c,
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done: d,
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}
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r := &_Receiver[Elem]{
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values: c,
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done: d,
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}
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runtime.SetFinalizer(r, (*_Receiver[Elem]).finalize)
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return s, r
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}
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// A _Sender is used to send values to a Receiver.
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type _Sender[Elem any] struct {
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values chan<- Elem
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done <-chan struct{}
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}
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// Send sends a value to the receiver. It reports whether the value was sent.
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// The value will not be sent if the context is closed or the receiver
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// is freed.
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func (s *_Sender[Elem]) Send(ctx context.Context, v Elem) bool {
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select {
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case <-ctx.Done():
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return false
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case s.values <- v:
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return true
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case <-s.done:
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return false
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}
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}
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// Close tells the receiver that no more values will arrive.
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// After Close is called, the _Sender may no longer be used.
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func (s *_Sender[Elem]) Close() {
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close(s.values)
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}
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// A _Receiver receives values from a _Sender.
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type _Receiver[Elem any] struct {
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values <-chan Elem
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done chan<- struct{}
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}
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// Next returns the next value from the channel. The bool result indicates
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// whether the value is valid.
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func (r *_Receiver[Elem]) Next(ctx context.Context) (v Elem, ok bool) {
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select {
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case <-ctx.Done():
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case v, ok = <-r.values:
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}
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return v, ok
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}
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// finalize is a finalizer for the receiver.
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func (r *_Receiver[Elem]) finalize() {
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close(r.done)
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}
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func TestReadAll() {
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c := make(chan int)
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go func() {
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c <- 4
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c <- 2
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c <- 5
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close(c)
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}()
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got := _ReadAll(context.Background(), c)
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want := []int{4, 2, 5}
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if !_SliceEqual(got, want) {
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panic(fmt.Sprintf("_ReadAll returned %v, want %v", got, want))
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}
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}
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func TestMerge() {
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c1 := make(chan int)
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c2 := make(chan int)
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go func() {
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c1 <- 1
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c1 <- 3
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c1 <- 5
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close(c1)
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}()
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go func() {
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c2 <- 2
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c2 <- 4
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c2 <- 6
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close(c2)
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}()
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ctx := context.Background()
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got := _ReadAll(ctx, _Merge(ctx, c1, c2))
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sort.Ints(got)
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want := []int{1, 2, 3, 4, 5, 6}
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if !_SliceEqual(got, want) {
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panic(fmt.Sprintf("_Merge returned %v, want %v", got, want))
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}
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}
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func TestFilter() {
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c := make(chan int)
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go func() {
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c <- 1
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c <- 2
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c <- 3
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close(c)
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}()
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even := func(i int) bool { return i%2 == 0 }
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ctx := context.Background()
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got := _ReadAll(ctx, _Filter(ctx, c, even))
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want := []int{2}
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if !_SliceEqual(got, want) {
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panic(fmt.Sprintf("_Filter returned %v, want %v", got, want))
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}
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}
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func TestSink() {
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c := _Sink[int](context.Background())
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after := time.NewTimer(time.Minute)
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defer after.Stop()
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send := func(v int) {
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select {
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case c <- v:
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case <-after.C:
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panic("timed out sending to _Sink")
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}
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}
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send(1)
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send(2)
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send(3)
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close(c)
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}
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func TestExclusive() {
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val := 0
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ex := _MakeExclusive(&val)
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var wg sync.WaitGroup
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f := func() {
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defer wg.Done()
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for i := 0; i < 10; i++ {
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p := ex.Acquire()
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(*p)++
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ex.Release(p)
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}
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}
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wg.Add(2)
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go f()
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go f()
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wg.Wait()
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if val != 20 {
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panic(fmt.Sprintf("after Acquire/Release loop got %d, want 20", val))
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}
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}
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func TestExclusiveTry() {
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s := ""
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ex := _MakeExclusive(&s)
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p, ok := ex.TryAcquire()
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if !ok {
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panic("TryAcquire failed")
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}
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*p = "a"
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var wg sync.WaitGroup
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wg.Add(1)
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go func() {
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defer wg.Done()
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_, ok := ex.TryAcquire()
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if ok {
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panic(fmt.Sprintf("TryAcquire succeeded unexpectedly"))
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}
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}()
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wg.Wait()
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ex.Release(p)
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p, ok = ex.TryAcquire()
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if !ok {
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panic(fmt.Sprintf("TryAcquire failed"))
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}
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}
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func TestRanger() {
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s, r := _Ranger[int]()
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ctx := context.Background()
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go func() {
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// Receive one value then exit.
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v, ok := r.Next(ctx)
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if !ok {
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panic(fmt.Sprintf("did not receive any values"))
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} else if v != 1 {
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panic(fmt.Sprintf("received %d, want 1", v))
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}
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}()
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c1 := make(chan bool)
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c2 := make(chan bool)
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go func() {
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defer close(c2)
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if !s.Send(ctx, 1) {
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panic(fmt.Sprintf("Send failed unexpectedly"))
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}
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close(c1)
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if s.Send(ctx, 2) {
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panic(fmt.Sprintf("Send succeeded unexpectedly"))
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}
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}()
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<-c1
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// Force a garbage collection to try to get the finalizers to run.
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runtime.GC()
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select {
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case <-c2:
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case <-time.After(time.Minute):
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panic("_Ranger Send should have failed, but timed out")
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}
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}
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func main() {
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TestReadAll()
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TestMerge()
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TestFilter()
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TestSink()
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TestExclusive()
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TestExclusiveTry()
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TestRanger()
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}
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