Remove the custom queue implementation. (#93)

Use mlink.Queue instead. It allocates a tiny bit more (because no freelist) but
not enough to worry about.

go.mod

@@ -6,6 +6,8 @@ require (
 	golang.org/x/sync v0.1.0
 )
 
+require github.com/creachadair/mds v0.0.0-20230313153906-9788b6f60568
+
 go 1.19
 
 // A bug in handler.New could panic a wrapped handler on pointer arguments.

go.sum

@@ -1,3 +1,5 @@
+github.com/creachadair/mds v0.0.0-20230313153906-9788b6f60568 h1:LzMDPh2FLXEHnQNTjGJT+vInPSDVOUTuzqE4GskHTNg=
+github.com/creachadair/mds v0.0.0-20230313153906-9788b6f60568/go.mod h1:caBACU+n1Q/rZ252FTzfnG0/H+ZUi+UnIQtEOraMv/g=
 github.com/fortytw2/leaktest v1.3.0 h1:u8491cBMTQ8ft8aeV+adlcytMZylmA5nnwwkRZjI8vw=
 github.com/fortytw2/leaktest v1.3.0/go.mod h1:jDsjWgpAGjm2CA7WthBh/CdZYEPF31XHquHwclZch5g=
 github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=

server.go

@@ -15,6 +15,7 @@ import (
 
 	"github.com/creachadair/jrpc2/channel"
 	"github.com/creachadair/jrpc2/code"
+	"github.com/creachadair/mds/mlink"
 	"golang.org/x/sync/semaphore"
 )
 
@@ -67,11 +68,11 @@ type Server struct {
 
 	mu *sync.Mutex // protects the fields below
 
-	nbar sync.WaitGroup  // notification barrier (see the dispatch method)
-	err  error           // error from a previous operation
-	work chan struct{}   // for signaling message availability
-	inq  *queue          // inbound requests awaiting processing
-	ch   channel.Channel // the channel to the client
+	nbar sync.WaitGroup          // notification barrier (see the dispatch method)
+	err  error                   // error from a previous operation
+	work chan struct{}           // for signaling message availability
+	inq  *mlink.Queue[jmessages] // inbound requests awaiting processing
+	ch   channel.Channel         // the channel to the client
 
 	// For each request ID currently in-flight, this map carries a cancel
 	// function attached to the context that was sent to the handler.
@@ -104,7 +105,7 @@ func NewServer(mux Assigner, opts *ServerOptions) *Server {
 		mu:      new(sync.Mutex),
 		start:   opts.startTime(),
 		builtin: opts.allowBuiltin(),
-		inq:     newQueue(),
+		inq:     mlink.NewQueue[jmessages](),
 		used:    make(map[string]context.CancelFunc),
 		call:    make(map[string]*Response),
 		callID:  1,
@@ -196,18 +197,18 @@ func (s *Server) signal() {
 func (s *Server) nextRequest() (func() error, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	for s.ch != nil && s.inq.isEmpty() {
+	for s.ch != nil && s.inq.IsEmpty() {
 		s.mu.Unlock()
 		<-s.work
 		s.mu.Lock()
 	}
-	if s.ch == nil && s.inq.isEmpty() {
+	if s.ch == nil && s.inq.IsEmpty() {
 		return nil, s.err
 	}
 	ch := s.ch // capture
 
-	next := s.inq.pop()
-	s.log("Dequeued request batch of length %d (qlen=%d)", len(next), s.inq.size())
+	next, _ := s.inq.Pop()
+	s.log("Dequeued request batch of length %d (qlen=%d)", len(next), s.inq.Len())
 
 	// Construct a dispatcher to run the handlers outside the lock.
 	return s.dispatch(next, ch), nil
@@ -553,7 +554,7 @@ func (s ServerStatus) Success() bool { return s.Err == nil }
 func (s *Server) WaitStatus() ServerStatus {
 	s.wg.Wait()
 	// Postcondition check.
-	if !s.inq.isEmpty() {
+	if !s.inq.IsEmpty() {
 		panic("s.inq is not empty at shutdown")
 	}
 	stat := ServerStatus{Err: s.err}
@@ -586,7 +587,7 @@ func (s *Server) stop(err error) {
 	//
 	// TODO(@creachadair): We need better tests for this behaviour.
 	var keep jmessages
-	s.inq.each(func(cur jmessages) {
+	s.inq.Each(func(cur jmessages) bool {
 		for _, req := range cur {
 			if req.isNotification() {
 				keep = append(keep, req)
@@ -595,10 +596,11 @@ func (s *Server) stop(err error) {
 				s.cancel(string(req.ID))
 			}
 		}
+		return true
 	})
-	s.inq.reset()
+	s.inq.Clear()
 	for _, elt := range keep {
-		s.inq.push(jmessages{elt})
+		s.inq.Add(jmessages{elt})
 	}
 	close(s.work)
 
@@ -653,9 +655,9 @@ func (s *Server) read(ch receiver) {
 			// was responses, so re-check the length after doing this.
 			keep := s.filterBatch(in)
 			if len(keep) != 0 {
-				s.log("Received request batch of size %d (qlen=%d)", len(keep), s.inq.size())
-				s.inq.push(keep)
-				if s.inq.size() == 1 { // the queue was empty
+				s.log("Received request batch of size %d (qlen=%d)", len(keep), s.inq.Len())
+				s.inq.Add(keep)
+				if s.inq.Len() == 1 { // the queue was empty
 					s.signal()
 				}
 			}