feat(client): blocking LineSenderPool

README.md

@@ -80,15 +80,15 @@ To connect via TCP, set the configuration string to:
 **Warning: Experimental feature designed for use with HTTP senders ONLY**
 
 Version 3 of the client introduces a `LineSenderPool`, which provides a mechanism
-to cache previously-used `LineSender`s in memory so they can be reused without
-having to allocate and instantiate new senders.
+to pool previously-used `LineSender`s so they can be reused without having
+to allocate and instantiate new senders.
 
-A LineSenderPool is thread-safe and can be used to concurrently Acquire and Release senders
+A LineSenderPool is thread-safe and can be used to concurrently obtain senders
 across multiple goroutines.
 
 Since `LineSender`s must be used in a single-threaded context, a typical pattern is to Acquire
 a sender from a `LineSenderPool` at the beginning of a goroutine and use a deferred
-execution block to Release the sender at the end of the goroutine.
+execution block to Close the sender at the end of the goroutine.
 
 Here is an example of the `LineSenderPool` Acquire, Release, and Close semantics:
 
@@ -112,7 +112,7 @@ func main() {
 		}
 	}()
 
-	sender, err := pool.Acquire(ctx)
+	sender, err := pool.Sender(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -122,7 +122,8 @@ func main() {
 		Float64Column("price", 123.45).
 		AtNow(ctx)
 
-	if err := pool.Release(ctx, sender); err != nil {
+	// Close call returns the sender back to the pool
+	if err := sender.Close(ctx); err != nil {
 		panic(err)
 	}
 }

sender_pool.go

@@ -28,8 +28,11 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"math/big"
 	"strings"
 	"sync"
+	"sync/atomic"
+	"time"
 )
 
 // LineSenderPool wraps a mutex-protected slice of [LineSender]. It allows a goroutine to
@@ -38,12 +41,21 @@ import (
 // WARNING: This is an experimental API that is designed to work with HTTP senders ONLY.
 type LineSenderPool struct {
 	maxSenders int
+	numSenders int // number of used and free senders
 	conf       string
 
 	closed bool
 
-	senders []LineSender
-	mu      *sync.Mutex
+	freeSenders []*pooledSender
+	mu          *sync.Mutex
+	cond        sync.Cond // used to wake up free sender waiters
+}
+
+type pooledSender struct {
+	pool    *LineSenderPool
+	wrapped LineSender
+	dirty   bool   // set to true if any of the sender calls returned an error
+	tick    uint64 // even values stand for free sender, odd values mean in-use sender
 }
 
 // LineSenderPoolOption defines line sender pool config option.
@@ -61,11 +73,12 @@ func PoolFromConf(conf string, opts ...LineSenderPoolOption) (*LineSenderPool, e
 	}
 
 	pool := &LineSenderPool{
-		maxSenders: 64,
-		conf:       conf,
-		senders:    []LineSender{},
-		mu:         &sync.Mutex{},
+		maxSenders:  64,
+		conf:        conf,
+		freeSenders: make([]*pooledSender, 0, 64),
+		mu:          &sync.Mutex{},
 	}
+	pool.cond = *sync.NewCond(pool.mu)
 
 	for _, opt := range opts {
 		opt(pool)
@@ -82,50 +95,71 @@ func WithMaxSenders(count int) LineSenderPoolOption {
 	}
 }
 
-// Acquire obtains a LineSender from the pool. If the pool is empty, a new
+// Sender obtains a LineSender from the pool. If the pool is empty, a new
 // LineSender will be instantiated using the pool's config string.
-func (p *LineSenderPool) Acquire(ctx context.Context) (LineSender, error) {
+// If there is already maximum number of senders obtained from the pool,
+// this calls will block until one of the senders is returned back to
+// the pool by calling sender.Close().
+func (p *LineSenderPool) Sender(ctx context.Context) (LineSender, error) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
 	if p.closed {
-		return nil, fmt.Errorf("cannot Acquire a LineSender from a closed LineSenderPool")
+		return nil, errors.New("cannot Acquire a LineSender from a closed LineSenderPool")
+	}
+
+	// We may have to wait for a free sender
+	for len(p.freeSenders) == 0 && p.numSenders == p.maxSenders {
+		p.cond.Wait()
 	}
 
-	if len(p.senders) > 0 {
+	if len(p.freeSenders) > 0 {
 		// Pop sender off the slice and return it
-		s := p.senders[len(p.senders)-1]
-		p.senders = p.senders[0 : len(p.senders)-1]
+		s := p.freeSenders[len(p.freeSenders)-1]
+		atomic.AddUint64(&s.tick, 1)
+		p.freeSenders = p.freeSenders[0 : len(p.freeSenders)-1]
 		return s, nil
 	}
 
-	return LineSenderFromConf(ctx, p.conf)
+	s, err := LineSenderFromConf(ctx, p.conf)
+	if err != nil {
+		return nil, err
+	}
+	p.numSenders++
+	ps := &pooledSender{
+		pool:    p,
+		wrapped: s,
+	}
+	atomic.AddUint64(&ps.tick, 1)
+	return ps, nil
 }
 
-// Release flushes the LineSender and returns it back to the pool. If the pool
-// is full, the sender is closed and discarded. In cases where the sender's
-// flush fails, it is not added back to the pool.
-func (p *LineSenderPool) Release(ctx context.Context, s LineSender) error {
-	// If there is an error on flush, do not add the sender back to the pool
-	if err := s.Flush(ctx); err != nil {
-		return err
+func (p *LineSenderPool) free(ctx context.Context, ps *pooledSender) error {
+	var flushErr error
+
+	if ps.dirty {
+		flushErr = ps.Flush(ctx)
 	}
 
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
-	for i := range p.senders {
-		if p.senders[i] == s {
-			return fmt.Errorf("LineSender %p has already been released back to the pool", s)
-		}
+	if flushErr != nil {
+		// Failed to flush, close and call it a day
+		p.numSenders--
+		closeErr := ps.wrapped.Close(ctx)
+		return fmt.Errorf("%s %w", flushErr, closeErr)
 	}
 
-	if p.closed || len(p.senders) >= p.maxSenders {
-		return s.Close(ctx)
+	if ps.dirty || p.closed {
+		// Previous error or closed pool, close and call it a day
+		p.numSenders--
+		return ps.wrapped.Close(ctx)
 	}
 
-	p.senders = append(p.senders, s)
-
+	p.freeSenders = append(p.freeSenders, ps)
+	// Notify free sender waiters, if any
+	p.cond.Broadcast()
 	return nil
 }
 
@@ -135,23 +169,28 @@ func (p *LineSenderPool) Close(ctx context.Context) error {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
+	if p.closed {
+		// Already closed
+		return nil
+	}
 	p.closed = true
 
 	var senderErrors []error
 
-	for _, s := range p.senders {
-		senderErr := s.Close(ctx)
+	for _, ps := range p.freeSenders {
+		senderErr := ps.wrapped.Close(ctx)
 		if senderErr != nil {
 			senderErrors = append(senderErrors, senderErr)
-
 		}
 	}
+	p.numSenders -= len(p.freeSenders)
+	p.freeSenders = []*pooledSender{}
 
 	if len(senderErrors) == 0 {
 		return nil
 	}
 
-	err := fmt.Errorf("error closing one or more LineSenders in the pool")
+	err := errors.New("error closing one or more LineSenders in the pool")
 	for _, senderErr := range senderErrors {
 		err = fmt.Errorf("%s %w", err, senderErr)
 	}
@@ -170,10 +209,81 @@ func (p *LineSenderPool) IsClosed() bool {
 	return p.closed
 }
 
-// Len returns the numbers of cached LineSenders in the pool.
+// Len returns the number of LineSenders in the pool.
 func (p *LineSenderPool) Len() int {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
-	return len(p.senders)
+	return p.numSenders
+}
+
+func (ps *pooledSender) Table(name string) LineSender {
+	ps.wrapped.Table(name)
+	return ps
+}
+
+func (ps *pooledSender) Symbol(name, val string) LineSender {
+	ps.wrapped.Symbol(name, val)
+	return ps
+}
+
+func (ps *pooledSender) Int64Column(name string, val int64) LineSender {
+	ps.wrapped.Int64Column(name, val)
+	return ps
+}
+
+func (ps *pooledSender) Long256Column(name string, val *big.Int) LineSender {
+	ps.wrapped.Long256Column(name, val)
+	return ps
+}
+
+func (ps *pooledSender) TimestampColumn(name string, ts time.Time) LineSender {
+	ps.wrapped.TimestampColumn(name, ts)
+	return ps
+}
+
+func (ps *pooledSender) Float64Column(name string, val float64) LineSender {
+	ps.wrapped.Float64Column(name, val)
+	return ps
+}
+
+func (ps *pooledSender) StringColumn(name, val string) LineSender {
+	ps.wrapped.StringColumn(name, val)
+	return ps
+}
+
+func (ps *pooledSender) BoolColumn(name string, val bool) LineSender {
+	ps.wrapped.BoolColumn(name, val)
+	return ps
+}
+
+func (ps *pooledSender) AtNow(ctx context.Context) error {
+	err := ps.wrapped.AtNow(ctx)
+	if err != nil {
+		ps.dirty = true
+	}
+	return err
+}
+
+func (ps *pooledSender) At(ctx context.Context, ts time.Time) error {
+	err := ps.wrapped.At(ctx, ts)
+	if err != nil {
+		ps.dirty = true
+	}
+	return err
+}
+
+func (ps *pooledSender) Flush(ctx context.Context) error {
+	err := ps.wrapped.Flush(ctx)
+	if err != nil {
+		ps.dirty = true
+	}
+	return err
+}
+
+func (ps *pooledSender) Close(ctx context.Context) error {
+	if atomic.AddUint64(&ps.tick, 1)&1 == 1 {
+		return errors.New("double sender close")
+	}
+	return ps.pool.free(ctx, ps)
 }