feat: context with timeout

For context with external time context with timeouts can be used.

Author: ohlsont

pkg/clock/clock.go

@@ -2,6 +2,7 @@
 package clock
 
 import (
+	"context"
 	"time"
 
 	"google.golang.org/protobuf/types/known/timestamppb"
@@ -12,6 +13,9 @@ type Clock interface {
 	// After waits for the duration to elapse and then sends the current time on the returned channel.
 	After(duration time.Duration) <-chan time.Time
 
+	// AfterFunc waits for the duration to elapse and then calls the function f given to it.
+	AfterFunc(d time.Duration, f func()) Timer
+
 	// NewTicker returns a new Ticker.
 	NewTicker(d time.Duration) Ticker
 
@@ -37,3 +41,19 @@ type Ticker interface {
 	// Stop the Ticker.
 	Stop()
 }
+
+type Timer interface {
+	// C returns the channel on which the timer is going to be triggered.
+	C() <-chan time.Time
+
+	// Stop the Timer.
+	Stop() bool
+}
+
+// ContextCtrl is clocked by an external interface.
+type ContextCtrl interface {
+	WithTimeout(
+		parent context.Context,
+		timeout time.Duration,
+	) (context.Context, context.CancelFunc)
+}

pkg/clock/system.go

@@ -39,10 +39,22 @@ func (c systemClock) Sleep(d time.Duration) {
 	time.Sleep(d)
 }
 
+func (c systemClock) AfterFunc(d time.Duration, f func()) Timer {
+	return &systemTimer{Timer: time.AfterFunc(d, f)}
+}
+
 type systemTicker struct {
 	time.Ticker
 }
 
 func (t systemTicker) C() <-chan time.Time {
 	return t.Ticker.C
 }
+
+type systemTimer struct {
+	*time.Timer
+}
+
+func (t systemTimer) C() <-chan time.Time {
+	return t.Timer.C
+}

pkg/contextctrl/context.go

@@ -0,0 +1,265 @@
+package contextctrl
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/einride/clock-go/pkg/clock"
+)
+
+// newCancelCtx returns an initialized cancelCtx.
+func newCancelCtx(parent context.Context) cancelCtx {
+	return cancelCtx{Context: parent}
+}
+
+// goroutines counts the number of goroutines ever created; for testing.
+var goroutines int32 //nolint:gochecknoglobals
+
+// propagateCancel arranges for child to be canceled when parent is.
+func propagateCancel(parent context.Context, child canceler) {
+	done := parent.Done() //nolint:ifshort
+	if done == nil {
+		return // parent is never canceled
+	}
+
+	select {
+	case <-done:
+		// parent is already canceled
+		child.cancel(false, parent.Err())
+		return
+	default:
+	}
+
+	if p, ok := parentCancelCtx(parent); ok {
+		p.mu.Lock()
+		if p.err != nil {
+			// parent has already been canceled
+			child.cancel(false, p.err)
+		} else {
+			if p.children == nil {
+				p.children = make(map[canceler]struct{})
+			}
+			p.children[child] = struct{}{}
+		}
+		p.mu.Unlock()
+	} else {
+		atomic.AddInt32(&goroutines, +1)
+		go func() {
+			select {
+			case <-parent.Done():
+				child.cancel(false, parent.Err())
+			case <-child.Done():
+			}
+		}()
+	}
+}
+
+// &cancelCtxKey is the key that a cancelCtx returns itself for.
+var cancelCtxKey int //nolint:gochecknoglobals
+
+// parentCancelCtx returns the underlying *cancelCtx for parent.
+// It does this by looking up parent.Value(&cancelCtxKey) to find
+// the innermost enclosing *cancelCtx and then checking whether
+// parent.Done() matches that *cancelCtx. (If not, the *cancelCtx
+// has been wrapped in a custom implementation providing a
+// different done channel, in which case we should not bypass it.)
+func parentCancelCtx(parent context.Context) (*cancelCtx, bool) {
+	done := parent.Done()
+	if done == closedchan || done == nil {
+		return nil, false
+	}
+	p, ok := parent.Value(&cancelCtxKey).(*cancelCtx)
+	if !ok {
+		return nil, false
+	}
+	pdone, _ := p.done.Load().(chan struct{})
+	if pdone != done {
+		return nil, false
+	}
+	return p, true
+}
+
+// removeChild removes a context from its parent.
+func removeChild(parent context.Context, child canceler) {
+	p, ok := parentCancelCtx(parent)
+	if !ok {
+		return
+	}
+	p.mu.Lock()
+	if p.children != nil {
+		delete(p.children, child)
+	}
+	p.mu.Unlock()
+}
+
+// A canceler is a context type that can be canceled directly. The
+// implementations are *cancelCtx and *timerCtx.
+type canceler interface {
+	cancel(removeFromParent bool, err error)
+	Done() <-chan struct{}
+}
+
+// closedchan is a reusable closed channel.
+var closedchan = make(chan struct{}) //nolint:gochecknoglobals
+
+func init() { //nolint:gochecknoinits
+	close(closedchan)
+}
+
+// A cancelCtx can be canceled. When canceled, it also cancels any children
+// that implement canceler.
+type cancelCtx struct {
+	context.Context
+
+	mu       sync.Mutex            // protects following fields
+	done     atomic.Value          // of chan struct{}, created lazily, closed by first cancel call
+	children map[canceler]struct{} // set to nil by the first cancel call
+	err      error                 // set to non-nil by the first cancel call
+}
+
+func (c *cancelCtx) Value(key interface{}) interface{} {
+	if key == &cancelCtxKey {
+		return c
+	}
+	return c.Context.Value(key)
+}
+
+func (c *cancelCtx) Done() <-chan struct{} {
+	d := c.done.Load()
+	if d != nil {
+		return d.(chan struct{})
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	d = c.done.Load()
+	if d == nil {
+		d = make(chan struct{})
+		c.done.Store(d)
+	}
+	return d.(chan struct{})
+}
+
+func (c *cancelCtx) Err() error {
+	c.mu.Lock()
+	err := c.err
+	c.mu.Unlock()
+	return err
+}
+
+// cancel closes C.done, cancels each of C's children, and, if
+// removeFromParent is true, removes C from its parent's children.
+func (c *cancelCtx) cancel(removeFromParent bool, err error) {
+	if err == nil {
+		panic("context: internal error: missing cancel error")
+	}
+	c.mu.Lock()
+	if c.err != nil {
+		c.mu.Unlock()
+		return // already canceled
+	}
+	c.err = err
+	d, _ := c.done.Load().(chan struct{})
+	if d == nil {
+		c.done.Store(closedchan)
+	} else {
+		close(d)
+	}
+	for child := range c.children {
+		// NOTE: acquiring the child's lock while holding parent's lock.
+		child.cancel(false, err)
+	}
+	c.children = nil
+	c.mu.Unlock()
+	if removeFromParent {
+		removeChild(c.Context, c)
+	}
+}
+
+// WithDeadline returns a copy of the parent context with the deadline adjusted
+// to be no later than d. If the parent's deadline is already earlier than d,
+// WithDeadline(parent, d) is semantically equivalent to parent. The returned
+// context's Done channel is closed when the deadline expires, when the returned
+// cancel function is called, or when the parent context's Done channel is
+// closed, whichever happens first.
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this Context complete.
+func (g *ExternalContext) WithDeadline(parent context.Context, d time.Time) (context.Context, context.CancelFunc) {
+	if parent == nil {
+		panic("cannot create context from nil parent")
+	}
+	if cur, ok := parent.Deadline(); ok && cur.Before(d) {
+		// The current deadline is already sooner than the new one.
+		return context.WithCancel(parent)
+	}
+	c := &timerCtx{
+		cancelCtx: newCancelCtx(parent),
+		deadline:  d,
+	}
+	propagateCancel(parent, c)
+	dur := d.Sub(g.C.Now())
+	if dur <= 0 {
+		c.cancel(true, context.DeadlineExceeded) // deadline has already passed
+		return c, func() { c.cancel(false, context.Canceled) }
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.err == nil {
+		c.timer = g.C.AfterFunc(dur, func() {
+			c.cancel(true, context.DeadlineExceeded)
+		})
+	}
+	return c, func() { c.cancel(true, context.Canceled) }
+}
+
+// A timerCtx carries a Timer and a deadline. It embeds a cancelCtx to
+// implement Done and Err. It implements cancel by stopping its Timer then
+// delegating to cancelCtx.cancel.
+type timerCtx struct {
+	cancelCtx
+	timer clock.Timer // Under cancelCtx.mu.
+
+	deadline time.Time
+}
+
+func (c *timerCtx) Deadline() (deadline time.Time, ok bool) {
+	return c.deadline, true
+}
+
+func (c *timerCtx) cancel(removeFromParent bool, err error) {
+	c.cancelCtx.cancel(false, err)
+	if removeFromParent {
+		// Remove this timerCtx from its parent cancelCtx's children.
+		removeChild(c.cancelCtx.Context, c)
+	}
+	// C.mu.Lock() // removed from original code in context
+	if c.timer != nil {
+		tim := c.timer
+		c.timer = nil
+		tim.Stop()
+	}
+	// C.mu.Unlock() // removed from original code in context
+}
+
+// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this Context complete:
+//
+// 	func slowOperationWithTimeout(ctx context.Context) (Result, error) {
+// 		ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
+// 		defer cancel()  // releases resources if slowOperation completes before timeout elapses
+// 		return slowOperation(ctx)
+// 	}
+func (g *ExternalContext) WithTimeout(
+	parent context.Context,
+	timeout time.Duration,
+) (context.Context, context.CancelFunc) {
+	return g.WithDeadline(parent, g.C.Now().Add(timeout))
+}
+
+type ExternalContext struct {
+	C clock.Clock
+}