api: replaced Future.done with a sync.Cond

This commit reduces allocations.

Future.done allocation replaced with
- Future.cond (*sync.Cond)
- Future.finished (atomic.Bool)

Other code use Future.isDone() instead (Future.done == nil) check.

Added Future.finish() marks Future as done.
Future.WaitChan() now creates channel on demand.

Closes #496

Author: laines-it

CHANGELOG.md

@@ -12,6 +12,7 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 * New types for MessagePack extensions compatible with go-option (#459).
 * Added `box.MustNew` wrapper for `box.New` without an error (#448).
+* Added Future.cond (sync.Cond) and Future.finished bool. Added Future.finish() marks Future as done (#496). 
 
 ### Changed
 
@@ -23,8 +24,9 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 * Removed deprecated `box.session.push()` support: Future.AppendPush()
   and Future.GetIterator() methods, ResponseIterator and TimeoutResponseIterator types,
   Future.pushes[], Future.ready (#480, #497).
-* `LogAppendPushFailed` replaced with `LogBoxSessionPushUnsupported` (#480)
-* Removed deprecated `Connection` methods, related interfaces and tests are updated (#479)
+* `LogAppendPushFailed` replaced with `LogBoxSessionPushUnsupported` (#480).
+* Removed deprecated `Connection` methods, related interfaces and tests are updated (#479).
+* Future.done replaced with Future.cond (sync.Cond) + Future.finished bool (#496).
 
 ### Fixed
 

MIGRATION.md

@@ -15,6 +15,7 @@ TODO
 * Removed `box.session.push()` support: Future.AppendPush() and Future.GetIterator()
   methods, ResponseIterator and TimeoutResponseIterator types.
 * Removed deprecated `Connection` methods, related interfaces and tests are updated.
+
   *NOTE*: due to Future.GetTyped() doesn't decode SelectRequest into structure, substitute Connection.GetTyped() following the example:
   ```Go
   var singleTpl = Tuple{}
@@ -30,6 +31,7 @@ TODO
   ).GetTyped(&tpl)
   singleTpl := tpl[0]
   ```
+* Future.done replaced with Future.cond (sync.Cond) + Future.finished bool.
 
 ## Migration from v1.x.x to v2.x.x
 

connection.go

@@ -934,7 +934,7 @@ func (conn *Connection) newFuture(req Request) (fut *Future) {
 				ErrRateLimited,
 				"Request is rate limited on client",
 			}
-			fut.done = nil
+			fut.finish()
 			return
 		}
 	}
@@ -948,23 +948,23 @@ func (conn *Connection) newFuture(req Request) (fut *Future) {
 			ErrConnectionClosed,
 			"using closed connection",
 		}
-		fut.done = nil
+		fut.finish()
 		shard.rmut.Unlock()
 		return
 	case connDisconnected:
 		fut.err = ClientError{
 			ErrConnectionNotReady,
 			"client connection is not ready",
 		}
-		fut.done = nil
+		fut.finish()
 		shard.rmut.Unlock()
 		return
 	case connShutdown:
 		fut.err = ClientError{
 			ErrConnectionShutdown,
 			"server shutdown in progress",
 		}
-		fut.done = nil
+		fut.finish()
 		shard.rmut.Unlock()
 		return
 	}
@@ -993,7 +993,7 @@ func (conn *Connection) newFuture(req Request) (fut *Future) {
 			runtime.Gosched()
 			select {
 			case conn.rlimit <- struct{}{}:
-			case <-fut.done:
+			case <-fut.WaitChan():
 				if fut.err == nil {
 					panic("fut.done is closed, but err is nil")
 				}
@@ -1007,17 +1007,16 @@ func (conn *Connection) newFuture(req Request) (fut *Future) {
 // is "done" before the response is come.
 func (conn *Connection) contextWatchdog(fut *Future, ctx context.Context) {
 	select {
-	case <-fut.done:
+	case <-fut.WaitChan():
 	case <-ctx.Done():
 	}
 
-	select {
-	case <-fut.done:
+	if fut.isDone() {
 		return
-	default:
-		conn.cancelFuture(fut, fmt.Errorf("context is done (request ID %d): %w",
-			fut.requestId, context.Cause(ctx)))
 	}
+
+	conn.cancelFuture(fut, fmt.Errorf("context is done (request ID %d): %w",
+		fut.requestId, context.Cause(ctx)))
 }
 
 func (conn *Connection) incrementRequestCnt() {
@@ -1034,7 +1033,7 @@ func (conn *Connection) send(req Request, streamId uint64) *Future {
 	conn.incrementRequestCnt()
 
 	fut := conn.newFuture(req)
-	if fut.done == nil {
+	if fut.isDone() {
 		conn.decrementRequestCnt()
 		return fut
 	}
@@ -1057,12 +1056,12 @@ func (conn *Connection) putFuture(fut *Future, req Request, streamId uint64) {
 	shardn := fut.requestId & (conn.opts.Concurrency - 1)
 	shard := &conn.shard[shardn]
 	shard.bufmut.Lock()
-	select {
-	case <-fut.done:
+
+	if fut.isDone() {
 		shard.bufmut.Unlock()
 		return
-	default:
 	}
+
 	firstWritten := shard.buf.Len() == 0
 	if shard.buf.Cap() == 0 {
 		shard.buf.b = make([]byte, 0, 128)

future.go

@@ -3,6 +3,7 @@ package tarantool
 import (
 	"io"
 	"sync"
+	"sync/atomic"
 	"time"
 )
 
@@ -15,32 +16,43 @@ type Future struct {
 	mutex     sync.Mutex
 	resp      Response
 	err       error
+	cond      sync.Cond
+	finished  atomic.Bool
 	done      chan struct{}
 }
 
 func (fut *Future) wait() {
-	if fut.done == nil {
-		return
+	fut.mutex.Lock()
+	defer fut.mutex.Unlock()
+
+	for !fut.isDone() {
+		fut.cond.Wait()
 	}
-	<-fut.done
 }
 
 func (fut *Future) isDone() bool {
-	if fut.done == nil {
-		return true
-	}
-	select {
-	case <-fut.done:
-		return true
-	default:
-		return false
+	return fut.finished.Load()
+}
+
+func (fut *Future) finish() {
+	fut.mutex.Lock()
+	defer fut.mutex.Unlock()
+
+	fut.finished.Store(true)
+
+	if fut.done != nil {
+		close(fut.done)
 	}
+
+	fut.cond.Broadcast()
 }
 
 // NewFuture creates a new empty Future for a given Request.
 func NewFuture(req Request) (fut *Future) {
 	fut = &Future{}
-	fut.done = make(chan struct{})
+	fut.done = nil
+	fut.finished.Store(false)
+	fut.cond = *sync.NewCond(&fut.mutex)
 	fut.req = req
 	return fut
 }
@@ -60,7 +72,14 @@ func (fut *Future) SetResponse(header Header, body io.Reader) error {
 	}
 	fut.resp = resp
 
-	close(fut.done)
+	fut.finished.Store(true)
+
+	if fut.done != nil {
+		close(fut.done)
+	}
+
+	fut.cond.Broadcast()
+
 	return nil
 }
 
@@ -74,7 +93,13 @@ func (fut *Future) SetError(err error) {
 	}
 	fut.err = err
 
-	close(fut.done)
+	fut.finished.Store(true)
+
+	if fut.done != nil {
+		close(fut.done)
+	}
+
+	fut.cond.Broadcast()
 }
 
 // GetResponse waits for Future to be filled and returns Response and error.
@@ -122,8 +147,16 @@ func init() {
 
 // WaitChan returns channel which becomes closed when response arrived or error occurred.
 func (fut *Future) WaitChan() <-chan struct{} {
-	if fut.done == nil {
+	fut.mutex.Lock()
+	defer fut.mutex.Unlock()
+
+	if fut.isDone() {
 		return closedChan
 	}
+
+	if fut.done == nil {
+		fut.done = make(chan struct{})
+	}
+
 	return fut.done
 }