commit 11b5e5c76a74a8f15cea07bc515b15c778bcf186
from: Stephen Day <stevvooe@users.noreply.github.com>
date: Wed May 25 21:10:48 2016 UTC

Merge pull request #15 from joushou/tagpool

Rework transport tag allocation logic

commit - a056819507b3f5113ef8b52f04e67dadf29d8927
commit + 11b5e5c76a74a8f15cea07bc515b15c778bcf186
blob - e17a6b70611d29e021f7791f0ef72032b4c16c27
blob + e7b76521e84d5fdbe9dc8059e923ee9cbd01f144
--- fcall.go
+++ fcall.go
@@ -111,11 +111,6 @@ type Fcall struct {
 }
 
 func newFcall(tag Tag, msg Message) *Fcall {
-	switch msg.Type() {
-	case Tversion, Rversion:
-		tag = NOTAG
-	}
-
 	return &Fcall{
 		Type:    msg.Type(),
 		Tag:     tag,
blob - 8a19e3836a0154314bf8f609fbf91e0ea0a29314
blob + 1b394d8df372ef32024ea6938f17be6116f6e493
--- transport.go
+++ transport.go
@@ -1,6 +1,7 @@
 package p9p
 
 import (
+	"errors"
 	"fmt"
 	"log"
 	"net"
@@ -95,6 +96,30 @@ func (t *transport) send(ctx context.Context, msg Mess
 	}
 }
 
+// allocateTag returns a valid tag given a tag pool map. It receives a hint as
+// to where to start the tag search. It returns an error if the allocation is
+// not possible. The provided map must not contain NOTAG as a key.
+func allocateTag(r *fcallRequest, m map[Tag]*fcallRequest, hint Tag) (Tag, error) {
+	// The tag pool is depleted if 65535 (0xFFFF) tags are taken.
+	if len(m) >= 0xFFFF {
+		return 0, errors.New("tag pool depleted")
+	}
+
+	// Look for the first tag that doesn't exist in the map and return it.
+	for i := 0; i < 0xFFFF; i++ {
+		hint++
+		if hint == NOTAG {
+			hint = 0
+		}
+
+		if _, exists := m[hint]; !exists {
+			return hint, nil
+		}
+	}
+
+	return 0, errors.New("allocateTag: unexpected error")
+}
+
 // handle takes messages off the wire and wakes up the waiting tag call.
 func (t *transport) handle() {
 	defer func() {
@@ -104,9 +129,9 @@ func (t *transport) handle() {
 	// the following variable block are protected components owned by this thread.
 	var (
 		responses = make(chan *Fcall)
-		tags      Tag
 		// outstanding provides a map of tags to outstanding requests.
 		outstanding = map[Tag]*fcallRequest{}
+		selected    Tag
 	)
 
 	// loop to read messages off of the connection
@@ -150,15 +175,17 @@ func (t *transport) handle() {
 	for {
 		select {
 		case req := <-t.requests:
-			// BUG(stevvooe): This is an awful tag allocation procedure.
-			// Replace this with something that let's us allocate tags and
-			// associate data with them, returning to them to a pool when
-			// complete. Such a system would provide a lot of information
-			// about outstanding requests.
-			tags++
-			fcall := newFcall(tags, req.message)
-			outstanding[fcall.Tag] = req
+			var err error
 
+			selected, err = allocateTag(req, outstanding, selected)
+			if err != nil {
+				req.err <- err
+				continue
+			}
+
+			outstanding[selected] = req
+			fcall := newFcall(selected, req.message)
+
 			// TODO(stevvooe): Consider the case of requests that never
 			// receive a response. We need to remove the fcall context from
 			// the tag map and dealloc the tag. We may also want to send a