zmq4: add timeout support on send

Add internal/errgroup package to support cancellable error groups.

Fixes #147.

Authored-by: Sergey Egorov <[email protected]>

internal/errgroup/errgroup.go

@@ -0,0 +1,107 @@
+// Copyright 2023 The go-zeromq 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 errgroup is bit more advanced than golang.org/x/sync/errgroup.
+// Major difference is that when error group is created with WithContext
+// the parent context would implicitly cancel all functions called by Go method.
+package errgroup
+
+import (
+	"context"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// The Group is superior errgroup.Group which aborts whole group
+// execution when parent context is cancelled
+type Group struct {
+	grp *errgroup.Group
+	ctx context.Context
+}
+
+// WithContext creates Group and store inside parent context
+// so the Go method would respect parent context cancellation
+func WithContext(ctx context.Context) (*Group, context.Context) {
+	grp, child_ctx := errgroup.WithContext(ctx)
+	return &Group{grp: grp, ctx: ctx}, child_ctx
+}
+
+// Go runs the provided f function in a dedicated goroutine and waits for its
+// completion or for the parent context cancellation.
+func (g *Group) Go(f func() error) {
+	g.getErrGroup().Go(g.wrap(f))
+}
+
+// Wait blocks until all function calls from the Go method have returned, then
+// returns the first non-nil error (if any) from them.
+// If the error group was created via WithContext then the Wait returns error
+// of cancelled parent context prior any functions calls complete.
+func (g *Group) Wait() error {
+	return g.getErrGroup().Wait()
+}
+
+// SetLimit limits the number of active goroutines in this group to at most n.
+// A negative value indicates no limit.
+//
+// Any subsequent call to the Go method will block until it can add an active
+// goroutine without exceeding the configured limit.
+//
+// The limit must not be modified while any goroutines in the group are active.
+func (g *Group) SetLimit(n int) {
+	g.getErrGroup().SetLimit(n)
+}
+
+// TryGo calls the given function in a new goroutine only if the number of
+// active goroutines in the group is currently below the configured limit.
+//
+// The return value reports whether the goroutine was started.
+func (g *Group) TryGo(f func() error) bool {
+	return g.getErrGroup().TryGo(g.wrap(f))
+}
+
+func (g *Group) wrap(f func() error) func() error {
+	if g.ctx == nil {
+		return f
+	}
+
+	return func() error {
+		// If parent context is canceled,
+		// just return its error and do not call func f
+		select {
+		case <-g.ctx.Done():
+			return g.ctx.Err()
+		default:
+		}
+
+		// Create return channel and call func f
+		// Buffered channel is used as the following select
+		// may be exiting by context cancellation
+		// and in such case the write to channel can be block
+		// and cause the go routine leak
+		ch := make(chan error, 1)
+		go func() {
+			ch <- f()
+		}()
+
+		// Wait func f complete or
+		// parent context to be cancelled,
+		select {
+		case err := <-ch:
+			return err
+		case <-g.ctx.Done():
+			return g.ctx.Err()
+		}
+	}
+}
+
+// The getErrGroup returns actual x/sync/errgroup.Group.
+// If the group is not allocated it would implicitly allocate it.
+// Thats allows the internal/errgroup.Group be fully
+// compatible to x/sync/errgroup.Group
+func (g *Group) getErrGroup() *errgroup.Group {
+	if g.grp == nil {
+		g.grp = &errgroup.Group{}
+	}
+	return g.grp
+}

internal/errgroup/errgroup_test.go

@@ -0,0 +1,124 @@
+// Copyright 2023 The go-zeromq 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 errgroup
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// TestRegularErrGroupDoesNotRespectParentContext checks regular errgroup behavior
+// where errgroup.WithContext does not respect the parent context
+func TestRegularErrGroupDoesNotRespectParentContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	eg, _ := errgroup.WithContext(ctx)
+
+	what := fmt.Errorf("func generated error")
+	ch := make(chan error)
+	eg.Go(func() error { return <-ch })
+
+	cancel()   // abort parent context
+	ch <- what // signal the func in regular errgroup to fail
+	err := eg.Wait()
+
+	// The error shall be one returned by the function
+	// as regular errgroup.WithContext does not respect parent context
+	if err != what {
+		t.Errorf("invalid error. got=%+v, want=%+v", err, what)
+	}
+}
+
+// TestErrGroupWithContextCanCallFunctions checks the errgroup operations
+// are fine working and errgroup called function can return error
+func TestErrGroupWithContextCanCallFunctions(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	eg, _ := WithContext(ctx)
+
+	what := fmt.Errorf("func generated error")
+	ch := make(chan error)
+	eg.Go(func() error { return <-ch })
+
+	ch <- what       // signal the func in errgroup to fail
+	err := eg.Wait() // wait errgroup complete and read error
+
+	// The error shall be one returned by the function
+	if err != what {
+		t.Errorf("invalid error. got=%+v, want=%+v", err, what)
+	}
+}
+
+// TestErrGroupWithContextDoesRespectParentContext checks the errgroup operations
+// are cancellable by parent context
+func TestErrGroupWithContextDoesRespectParentContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	eg, _ := WithContext(ctx)
+
+	s1 := make(chan struct{})
+	s2 := make(chan struct{})
+	eg.Go(func() error {
+		s1 <- struct{}{}
+		<-s2
+		return fmt.Errorf("func generated error")
+	})
+
+	// We have no set limit to errgroup so
+	// shall be able to start function via TryGo
+	if ok := eg.TryGo(func() error { return nil }); !ok {
+		t.Errorf("Expected TryGo to be able start function!!!")
+	}
+
+	<-s1     // wait for function to start
+	cancel() // abort parent context
+
+	eg.Go(func() error {
+		t.Errorf("The parent context was already cancelled and this function shall not be called!!!")
+		return nil
+	})
+
+	s2 <- struct{}{} // signal the func in regular errgroup to fail
+	err := eg.Wait() // wait errgroup complete and read error
+
+	// The error shall be one returned by the function
+	// as regular errgroup.WithContext does not respect parent context
+	if err != context.Canceled {
+		t.Errorf("expected a context.Canceled error, got=%+v", err)
+	}
+}
+
+// TestErrGroupFallback tests fallback logic to be compatible with x/sync/errgroup
+func TestErrGroupFallback(t *testing.T) {
+	eg := Group{}
+	eg.SetLimit(2)
+
+	ch1 := make(chan error)
+	eg.Go(func() error { return <-ch1 })
+
+	ch2 := make(chan error)
+	ok := eg.TryGo(func() error { return <-ch2 })
+	if !ok {
+		t.Errorf("Expected errgroup.TryGo to success!!!")
+	}
+
+	// The limit set to 2, so 3rd function shall not be possible to call
+	ok = eg.TryGo(func() error {
+		t.Errorf("This function is unexpected to be called!!!")
+		return nil
+	})
+	if ok {
+		t.Errorf("Expected errgroup.TryGo to fail!!!")
+	}
+
+	ch1 <- nil
+	ch2 <- nil
+	err := eg.Wait()
+
+	if err != nil {
+		t.Errorf("expected a nil error, got=%+v", err)
+	}
+}

msgio.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"sync"
 
+	errgrp "github.com/go-zeromq/zmq4/internal/errgroup"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -63,11 +64,11 @@ func (q *qreader) Close() error {
 }
 
 func (q *qreader) addConn(r *Conn) {
-	go q.listen(q.ctx, r)
 	q.mu.Lock()
 	q.sem.enable()
 	q.rs = append(q.rs, r)
 	q.mu.Unlock()
+	go q.listen(q.ctx, r)
 }
 
 func (q *qreader) rmConn(r *Conn) {
@@ -167,7 +168,7 @@ func (mw *mwriter) rmConn(w *Conn) {
 
 func (w *mwriter) write(ctx context.Context, msg Msg) error {
 	w.sem.lock(ctx)
-	grp, _ := errgroup.WithContext(ctx)
+	grp, _ := errgrp.WithContext(ctx)
 	w.mu.Lock()
 	for i := range w.ws {
 		ww := w.ws[i]

options.go

@@ -44,6 +44,13 @@ func WithDialerTimeout(timeout time.Duration) Option {
 	}
 }
 
+// WithTimeout sets the timeout value for socket operations
+func WithTimeout(timeout time.Duration) Option {
+	return func(s *socket) {
+		s.timeout = timeout
+	}
+}
+
 // WithLogger sets a dedicated log.Logger for the socket.
 func WithLogger(msg *log.Logger) Option {
 	return func(s *socket) {

pub.go

@@ -39,7 +39,7 @@ func (pub *pubSocket) Close() error {
 // Send puts the message on the outbound send queue.
 // Send blocks until the message can be queued or the send deadline expires.
 func (pub *pubSocket) Send(msg Msg) error {
-	ctx, cancel := context.WithTimeout(pub.sck.ctx, pub.sck.timeout())
+	ctx, cancel := context.WithTimeout(pub.sck.ctx, pub.sck.Timeout())
 	defer cancel()
 	return pub.sck.w.write(ctx, msg)
 }
@@ -49,7 +49,7 @@ func (pub *pubSocket) Send(msg Msg) error {
 // The message will be sent as a multipart message.
 func (pub *pubSocket) SendMulti(msg Msg) error {
 	msg.multipart = true
-	ctx, cancel := context.WithTimeout(pub.sck.ctx, pub.sck.timeout())
+	ctx, cancel := context.WithTimeout(pub.sck.ctx, pub.sck.Timeout())
 	defer cancel()
 	return pub.sck.w.write(ctx, msg)
 }
@@ -149,11 +149,11 @@ func (q *pubQReader) Close() error {
 }
 
 func (q *pubQReader) addConn(r *Conn) {
-	go q.listen(q.ctx, r)
 	q.mu.Lock()
 	q.sem.enable()
 	q.rs = append(q.rs, r)
 	q.mu.Unlock()
+	go q.listen(q.ctx, r)
 }
 
 func (q *pubQReader) rmConn(r *Conn) {

rep.go

@@ -34,7 +34,7 @@ func (rep *repSocket) Close() error {
 // Send puts the message on the outbound send queue.
 // Send blocks until the message can be queued or the send deadline expires.
 func (rep *repSocket) Send(msg Msg) error {
-	ctx, cancel := context.WithTimeout(rep.sck.ctx, rep.sck.timeout())
+	ctx, cancel := context.WithTimeout(rep.sck.ctx, rep.sck.Timeout())
 	defer cancel()
 	return rep.sck.w.write(ctx, msg)
 }
@@ -44,7 +44,7 @@ func (rep *repSocket) Send(msg Msg) error {
 // The message will be sent as a multipart message.
 func (rep *repSocket) SendMulti(msg Msg) error {
 	msg.multipart = true
-	ctx, cancel := context.WithTimeout(rep.sck.ctx, rep.sck.timeout())
+	ctx, cancel := context.WithTimeout(rep.sck.ctx, rep.sck.Timeout())
 	defer cancel()
 	return rep.sck.w.write(ctx, msg)
 }

rep_test.go

@@ -134,6 +134,7 @@ func TestCancellation(t *testing.T) {
 
 		defer wg.Done()
 		repCtx, cancel := context.WithCancel(context.Background())
+		defer cancel()
 		rep := zmq4.NewRep(repCtx)
 		defer rep.Close()
 

req.go

@@ -35,7 +35,7 @@ func (req *reqSocket) Close() error {
 // Send puts the message on the outbound send queue.
 // Send blocks until the message can be queued or the send deadline expires.
 func (req *reqSocket) Send(msg Msg) error {
-	ctx, cancel := context.WithTimeout(req.sck.ctx, req.sck.timeout())
+	ctx, cancel := context.WithTimeout(req.sck.ctx, req.sck.Timeout())
 	defer cancel()
 	return req.sck.w.write(ctx, msg)
 }
@@ -45,7 +45,7 @@ func (req *reqSocket) Send(msg Msg) error {
 // The message will be sent as a multipart message.
 func (req *reqSocket) SendMulti(msg Msg) error {
 	msg.multipart = true
-	ctx, cancel := context.WithTimeout(req.sck.ctx, req.sck.timeout())
+	ctx, cancel := context.WithTimeout(req.sck.ctx, req.sck.Timeout())
 	defer cancel()
 	return req.sck.w.write(ctx, msg)
 }

router.go

@@ -35,7 +35,7 @@ func (router *routerSocket) Close() error {
 // Send puts the message on the outbound send queue.
 // Send blocks until the message can be queued or the send deadline expires.
 func (router *routerSocket) Send(msg Msg) error {
-	ctx, cancel := context.WithTimeout(router.sck.ctx, router.sck.timeout())
+	ctx, cancel := context.WithTimeout(router.sck.ctx, router.sck.Timeout())
 	defer cancel()
 	return router.sck.w.write(ctx, msg)
 }
@@ -119,11 +119,11 @@ func (q *routerQReader) Close() error {
 }
 
 func (q *routerQReader) addConn(r *Conn) {
-	go q.listen(q.ctx, r)
 	q.mu.Lock()
 	q.sem.enable()
 	q.rs = append(q.rs, r)
 	q.mu.Unlock()
+	go q.listen(q.ctx, r)
 }
 
 func (q *routerQReader) rmConn(r *Conn) {