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lib/mutex: add mutex with TryLock and update vendor

This commit is contained in:
Daniel Nephin 2020-12-04 18:56:03 -05:00
parent 08e8ed0a7e
commit 3685f39970
7 changed files with 372 additions and 14 deletions
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2
go.mod
View File

@ -84,7 +84,7 @@ require (
golang.org/x/crypto v0.0.0-20200930160638-afb6bcd081ae
golang.org/x/net v0.0.0-20200930145003-4acb6c075d10
golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45
golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a
golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9
golang.org/x/sys v0.0.0-20201024232916-9f70ab9862d5
golang.org/x/text v0.3.3 // indirect
golang.org/x/time v0.0.0-20200630173020-3af7569d3a1e

4
go.sum
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@ -583,8 +583,8 @@ golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJ
golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a h1:WXEvlFVvvGxCJLG6REjsT03iWnKLEWinaScsxF2Vm2o=
golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9 h1:SQFwaSi55rU7vdNs9Yr0Z324VNlrF+0wMqRXT4St8ck=
golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sys v0.0.0-20170830134202-bb24a47a89ea/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20180823144017-11551d06cbcc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

36
lib/mutex/mutex.go Normal file
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@ -0,0 +1,36 @@
/*
Package mutex implements the sync.Locker interface using x/sync/semaphore. It
may be used as a replacement for sync.Mutex when one or more goroutines need to
allow their calls to Lock to be cancelled by context cancellation.
*/
package mutex
import (
"context"
"golang.org/x/sync/semaphore"
)
type Mutex semaphore.Weighted
// New returns a Mutex that is ready for use.
func New() *Mutex {
return (*Mutex)(semaphore.NewWeighted(1))
}
func (m *Mutex) Lock() {
_ = (*semaphore.Weighted)(m).Acquire(context.Background(), 1)
}
func (m *Mutex) Unlock() {
(*semaphore.Weighted)(m).Release(1)
}
// TryLock acquires the mutex, blocking until resources are available or ctx is
// done. On success, returns nil. On failure, returns ctx.Err() and leaves the
// semaphore unchanged.
//
// If ctx is already done, Acquire may still succeed without blocking.
func (m *Mutex) TryLock(ctx context.Context) error {
return (*semaphore.Weighted)(m).Acquire(ctx, 1)
}

93
lib/mutex/mutex_test.go Normal file
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@ -0,0 +1,93 @@
package mutex
import (
"context"
"testing"
"time"
"github.com/stretchr/testify/require"
)
func TestMutex(t *testing.T) {
t.Run("starts unlocked", func(t *testing.T) {
m := New()
canLock(t, m)
})
t.Run("Lock blocks when locked", func(t *testing.T) {
m := New()
m.Lock()
lockIsBlocked(t, m)
})
t.Run("Unlock unblocks Lock", func(t *testing.T) {
m := New()
m.Lock()
m.Unlock() // nolint:staticcheck // SA2001 is not relevant here
canLock(t, m)
})
t.Run("TryLock acquires lock", func(t *testing.T) {
m := New()
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
t.Cleanup(cancel)
require.NoError(t, m.TryLock(ctx))
lockIsBlocked(t, m)
})
t.Run("TryLock blocks until timeout when locked", func(t *testing.T) {
m := New()
m.Lock()
ctx, cancel := context.WithTimeout(context.Background(), 20*time.Millisecond)
t.Cleanup(cancel)
err := m.TryLock(ctx)
require.Equal(t, err, context.DeadlineExceeded)
})
t.Run("TryLock acquires lock before timeout", func(t *testing.T) {
m := New()
m.Lock()
go func() {
time.Sleep(20 * time.Millisecond)
m.Unlock()
}()
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
t.Cleanup(cancel)
err := m.TryLock(ctx)
require.NoError(t, err)
})
}
func canLock(t *testing.T, m *Mutex) {
t.Helper()
chDone := make(chan struct{})
go func() {
m.Lock()
close(chDone)
}()
select {
case <-chDone:
case <-time.After(20 * time.Millisecond):
t.Fatal("failed to acquire lock before timeout")
}
}
func lockIsBlocked(t *testing.T, m *Mutex) {
t.Helper()
chDone := make(chan struct{})
go func() {
m.Lock()
close(chDone)
}()
select {
case <-chDone:
t.Fatal("expected Lock to block")
case <-time.After(20 * time.Millisecond):
}
}

136
vendor/golang.org/x/sync/semaphore/semaphore.go generated vendored Normal file
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@ -0,0 +1,136 @@
// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package semaphore provides a weighted semaphore implementation.
package semaphore // import "golang.org/x/sync/semaphore"
import (
"container/list"
"context"
"sync"
)
type waiter struct {
n int64
ready chan<- struct{} // Closed when semaphore acquired.
}
// NewWeighted creates a new weighted semaphore with the given
// maximum combined weight for concurrent access.
func NewWeighted(n int64) *Weighted {
w := &Weighted{size: n}
return w
}
// Weighted provides a way to bound concurrent access to a resource.
// The callers can request access with a given weight.
type Weighted struct {
size int64
cur int64
mu sync.Mutex
waiters list.List
}
// Acquire acquires the semaphore with a weight of n, blocking until resources
// are available or ctx is done. On success, returns nil. On failure, returns
// ctx.Err() and leaves the semaphore unchanged.
//
// If ctx is already done, Acquire may still succeed without blocking.
func (s *Weighted) Acquire(ctx context.Context, n int64) error {
s.mu.Lock()
if s.size-s.cur >= n && s.waiters.Len() == 0 {
s.cur += n
s.mu.Unlock()
return nil
}
if n > s.size {
// Don't make other Acquire calls block on one that's doomed to fail.
s.mu.Unlock()
<-ctx.Done()
return ctx.Err()
}
ready := make(chan struct{})
w := waiter{n: n, ready: ready}
elem := s.waiters.PushBack(w)
s.mu.Unlock()
select {
case <-ctx.Done():
err := ctx.Err()
s.mu.Lock()
select {
case <-ready:
// Acquired the semaphore after we were canceled. Rather than trying to
// fix up the queue, just pretend we didn't notice the cancelation.
err = nil
default:
isFront := s.waiters.Front() == elem
s.waiters.Remove(elem)
// If we're at the front and there're extra tokens left, notify other waiters.
if isFront && s.size > s.cur {
s.notifyWaiters()
}
}
s.mu.Unlock()
return err
case <-ready:
return nil
}
}
// TryAcquire acquires the semaphore with a weight of n without blocking.
// On success, returns true. On failure, returns false and leaves the semaphore unchanged.
func (s *Weighted) TryAcquire(n int64) bool {
s.mu.Lock()
success := s.size-s.cur >= n && s.waiters.Len() == 0
if success {
s.cur += n
}
s.mu.Unlock()
return success
}
// Release releases the semaphore with a weight of n.
func (s *Weighted) Release(n int64) {
s.mu.Lock()
s.cur -= n
if s.cur < 0 {
s.mu.Unlock()
panic("semaphore: released more than held")
}
s.notifyWaiters()
s.mu.Unlock()
}
func (s *Weighted) notifyWaiters() {
for {
next := s.waiters.Front()
if next == nil {
break // No more waiters blocked.
}
w := next.Value.(waiter)
if s.size-s.cur < w.n {
// Not enough tokens for the next waiter. We could keep going (to try to
// find a waiter with a smaller request), but under load that could cause
// starvation for large requests; instead, we leave all remaining waiters
// blocked.
//
// Consider a semaphore used as a read-write lock, with N tokens, N
// readers, and one writer. Each reader can Acquire(1) to obtain a read
// lock. The writer can Acquire(N) to obtain a write lock, excluding all
// of the readers. If we allow the readers to jump ahead in the queue,
// the writer will starve — there is always one token available for every
// reader.
break
}
s.cur += w.n
s.waiters.Remove(next)
close(w.ready)
}
}

112
vendor/golang.org/x/sync/singleflight/singleflight.go generated vendored
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@ -6,7 +6,42 @@
// mechanism.
package singleflight // import "golang.org/x/sync/singleflight"
import "sync"
import (
"bytes"
"errors"
"fmt"
"runtime"
"runtime/debug"
"sync"
)
// errGoexit indicates the runtime.Goexit was called in
// the user given function.
var errGoexit = errors.New("runtime.Goexit was called")
// A panicError is an arbitrary value recovered from a panic
// with the stack trace during the execution of given function.
type panicError struct {
value interface{}
stack []byte
}
// Error implements error interface.
func (p *panicError) Error() string {
return fmt.Sprintf("%v\n\n%s", p.value, p.stack)
}
func newPanicError(v interface{}) error {
stack := debug.Stack()
// The first line of the stack trace is of the form "goroutine N [status]:"
// but by the time the panic reaches Do the goroutine may no longer exist
// and its status will have changed. Trim out the misleading line.
if line := bytes.IndexByte(stack[:], '\n'); line >= 0 {
stack = stack[line+1:]
}
return &panicError{value: v, stack: stack}
}
// call is an in-flight or completed singleflight.Do call
type call struct {
@ -57,6 +92,12 @@ func (g *Group) Do(key string, fn func() (interface{}, error)) (v interface{}, e
c.dups++
g.mu.Unlock()
c.wg.Wait()
if e, ok := c.err.(*panicError); ok {
panic(e)
} else if c.err == errGoexit {
runtime.Goexit()
}
return c.val, c.err, true
}
c := new(call)
@ -70,6 +111,8 @@ func (g *Group) Do(key string, fn func() (interface{}, error)) (v interface{}, e
// DoChan is like Do but returns a channel that will receive the
// results when they are ready.
//
// The returned channel will not be closed.
func (g *Group) DoChan(key string, fn func() (interface{}, error)) <-chan Result {
ch := make(chan Result, 1)
g.mu.Lock()
@ -94,17 +137,66 @@ func (g *Group) DoChan(key string, fn func() (interface{}, error)) <-chan Result
// doCall handles the single call for a key.
func (g *Group) doCall(c *call, key string, fn func() (interface{}, error)) {
c.val, c.err = fn()
c.wg.Done()
normalReturn := false
recovered := false
g.mu.Lock()
if !c.forgotten {
delete(g.m, key)
// use double-defer to distinguish panic from runtime.Goexit,
// more details see https://golang.org/cl/134395
defer func() {
// the given function invoked runtime.Goexit
if !normalReturn && !recovered {
c.err = errGoexit
}
c.wg.Done()
g.mu.Lock()
defer g.mu.Unlock()
if !c.forgotten {
delete(g.m, key)
}
if e, ok := c.err.(*panicError); ok {
// In order to prevent the waiting channels from being blocked forever,
// needs to ensure that this panic cannot be recovered.
if len(c.chans) > 0 {
go panic(e)
select {} // Keep this goroutine around so that it will appear in the crash dump.
} else {
panic(e)
}
} else if c.err == errGoexit {
// Already in the process of goexit, no need to call again
} else {
// Normal return
for _, ch := range c.chans {
ch <- Result{c.val, c.err, c.dups > 0}
}
}
}()
func() {
defer func() {
if !normalReturn {
// Ideally, we would wait to take a stack trace until we've determined
// whether this is a panic or a runtime.Goexit.
//
// Unfortunately, the only way we can distinguish the two is to see
// whether the recover stopped the goroutine from terminating, and by
// the time we know that, the part of the stack trace relevant to the
// panic has been discarded.
if r := recover(); r != nil {
c.err = newPanicError(r)
}
}
}()
c.val, c.err = fn()
normalReturn = true
}()
if !normalReturn {
recovered = true
}
for _, ch := range c.chans {
ch <- Result{c.val, c.err, c.dups > 0}
}
g.mu.Unlock()
}
// Forget tells the singleflight to forget about a key. Future calls

3
vendor/modules.txt vendored
View File

@ -505,8 +505,9 @@ golang.org/x/oauth2/google
golang.org/x/oauth2/internal
golang.org/x/oauth2/jws
golang.org/x/oauth2/jwt
# golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a
# golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9
golang.org/x/sync/errgroup
golang.org/x/sync/semaphore
golang.org/x/sync/singleflight
# golang.org/x/sys v0.0.0-20201024232916-9f70ab9862d5
golang.org/x/sys/cpu