Release list fixes & broader use

rpc/answer.go

@@ -183,17 +183,17 @@ func (ans *answer) setBootstrap(c capnp.Client) error {
 //
 // The caller MUST NOT hold ans.c.lk.
 func (ans *answer) Return(e error) {
+	rl := &releaseList{}
+	defer rl.Release()
+
 	ans.c.lk.Lock()
 	if e != nil {
-		rl := &releaseList{}
 		ans.sendException(rl, e)
 		ans.c.lk.Unlock()
-		rl.Release()
 		ans.pcalls.Wait()
 		ans.c.tasks.Done() // added by handleCall
 		return
 	}
-	rl := &releaseList{}
 	if err := ans.sendReturn(rl); err != nil {
 		select {
 		case <-ans.c.bgctx.Done():
@@ -204,13 +204,11 @@ func (ans *answer) Return(e error) {
 			}
 
 			ans.c.lk.Unlock()
-			rl.Release()
 			ans.pcalls.Wait()
 			return
 		}
 	}
 	ans.c.lk.Unlock()
-	rl.Release()
 	ans.pcalls.Wait()
 	ans.c.tasks.Done() // added by handleCall
 }

rpc/releaselist.go

@@ -4,11 +4,12 @@ import "capnproto.org/go/capnp/v3"
 
 type releaseList []capnp.ReleaseFunc
 
-func (rl releaseList) Release() {
-	for i, r := range rl {
+func (rl *releaseList) Release() {
+	funcs := *rl
+	for i, r := range funcs {
 		if r != nil {
 			r()
-			rl[i] = nil
+			funcs[i] = nil
 		}
 	}
 }

rpc/rpc.go

@@ -658,6 +658,9 @@ func (c *Conn) handleBootstrap(ctx context.Context, id answerID) error {
 }
 
 func (c *Conn) handleCall(ctx context.Context, call rpccp.Call, releaseCall capnp.ReleaseFunc) error {
+	rl := &releaseList{}
+	defer rl.Release()
+
 	id := answerID(call.QuestionId())
 
 	// TODO(3rd-party handshake): support sending results to 3rd party vat
@@ -722,11 +725,9 @@ func (c *Conn) handleCall(ctx context.Context, call rpccp.Call, releaseCall capn
 	c.lk.answers[id] = ans
 	if parseErr != nil {
 		parseErr = rpcerr.Annotate(parseErr, "incoming call")
-		rl := &releaseList{}
 		ans.sendException(rl, parseErr)
 		c.lk.Unlock()
 		c.er.ReportError(parseErr)
-		rl.Release()
 		releaseCall()
 		return nil
 	}
@@ -778,10 +779,8 @@ func (c *Conn) handleCall(ctx context.Context, call rpccp.Call, releaseCall capn
 		}
 		if tgtAns.flags.Contains(resultsReady) {
 			if tgtAns.err != nil {
-				rl := &releaseList{}
 				ans.sendException(rl, tgtAns.err)
 				c.lk.Unlock()
-				rl.Release()
 				releaseCall()
 				return nil
 			}
@@ -792,21 +791,17 @@ func (c *Conn) handleCall(ctx context.Context, call rpccp.Call, releaseCall capn
 			content, err := tgtAns.results.Content()
 			if err != nil {
 				err = rpcerr.Failedf("incoming call: read results from target answer: %w", err)
-				rl := &releaseList{}
 				ans.sendException(rl, err)
 				c.lk.Unlock()
-				rl.Release()
 				releaseCall()
 				c.er.ReportError(err)
 				return nil
 			}
 			sub, err := capnp.Transform(content, p.target.transform)
 			if err != nil {
 				// Not reporting, as this is the caller's fault.
-				rl := &releaseList{}
 				ans.sendException(rl, err)
 				c.lk.Unlock()
-				rl.Release()
 				releaseCall()
 				return nil
 			}
@@ -1116,14 +1111,16 @@ type parsedReturn struct {
 }
 
 func (c *Conn) handleFinish(ctx context.Context, id answerID, releaseResultCaps bool) error {
+	rl := &releaseList{}
+	defer rl.Release()
 	c.lk.Lock()
+	defer c.lk.Unlock()
+
 	ans := c.lk.answers[id]
 	if ans == nil {
-		c.lk.Unlock()
 		return rpcerr.Failedf("incoming finish: unknown answer ID %d", id)
 	}
 	if ans.flags.Contains(finishReceived) {
-		c.lk.Unlock()
 		return rpcerr.Failedf("incoming finish: answer ID %d already received finish", id)
 	}
 	ans.flags |= finishReceived
@@ -1134,15 +1131,11 @@ func (c *Conn) handleFinish(ctx context.Context, id answerID, releaseResultCaps
 		ans.cancel()
 	}
 	if !ans.flags.Contains(returnSent) {
-		c.lk.Unlock()
 		return nil
 	}
 
 	// Return sent and finish received: time to destroy answer.
-	rl := &releaseList{}
 	err := ans.destroy(rl)
-	c.lk.Unlock()
-	rl.Release()
 	if err != nil {
 		return rpcerr.Annotate(err, "incoming finish: release result caps")
 	}