device: use a waiting sync.Pool instead of a channel

Channels are FIFO which means we have guaranteed cache misses.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/pools.go

@@ -5,87 +5,80 @@
 
 package device
 
-import "sync"
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type WaitPool struct {
+	pool  sync.Pool
+	cond  sync.Cond
+	lock  sync.Mutex
+	count uint32
+	max   uint32
+}
+
+func NewWaitPool(max uint32, new func() interface{}) *WaitPool {
+	p := &WaitPool{pool: sync.Pool{New: new}, max: max}
+	p.cond = sync.Cond{L: &p.lock}
+	return p
+}
+
+func (p *WaitPool) Get() interface{} {
+	if p.max != 0 {
+		p.lock.Lock()
+		for atomic.LoadUint32(&p.count) >= p.max {
+			p.cond.Wait()
+		}
+		atomic.AddUint32(&p.count, 1)
+		p.lock.Unlock()
+	}
+	return p.pool.Get()
+}
+
+func (p *WaitPool) Put(x interface{}) {
+	p.pool.Put(x)
+	if p.max == 0 {
+		return
+	}
+	atomic.AddUint32(&p.count, ^uint32(0))
+	p.cond.Signal()
+}
 
 func (device *Device) PopulatePools() {
-	if PreallocatedBuffersPerPool == 0 {
-		device.pool.messageBufferPool = &sync.Pool{
-			New: func() interface{} {
-				return new([MaxMessageSize]byte)
-			},
-		}
-		device.pool.inboundElementPool = &sync.Pool{
-			New: func() interface{} {
-				return new(QueueInboundElement)
-			},
-		}
-		device.pool.outboundElementPool = &sync.Pool{
-			New: func() interface{} {
-				return new(QueueOutboundElement)
-			},
-		}
-	} else {
-		device.pool.messageBufferReuseChan = make(chan *[MaxMessageSize]byte, PreallocatedBuffersPerPool)
-		for i := 0; i < PreallocatedBuffersPerPool; i++ {
-			device.pool.messageBufferReuseChan <- new([MaxMessageSize]byte)
-		}
-		device.pool.inboundElementReuseChan = make(chan *QueueInboundElement, PreallocatedBuffersPerPool)
-		for i := 0; i < PreallocatedBuffersPerPool; i++ {
-			device.pool.inboundElementReuseChan <- new(QueueInboundElement)
-		}
-		device.pool.outboundElementReuseChan = make(chan *QueueOutboundElement, PreallocatedBuffersPerPool)
-		for i := 0; i < PreallocatedBuffersPerPool; i++ {
-			device.pool.outboundElementReuseChan <- new(QueueOutboundElement)
-		}
-	}
+	device.pool.messageBuffers = NewWaitPool(PreallocatedBuffersPerPool, func() interface{} {
+		return new([MaxMessageSize]byte)
+	})
+	device.pool.inboundElements = NewWaitPool(PreallocatedBuffersPerPool, func() interface{} {
+		return new(QueueInboundElement)
+	})
+	device.pool.outboundElements = NewWaitPool(PreallocatedBuffersPerPool, func() interface{} {
+		return new(QueueOutboundElement)
+	})
 }
 
 func (device *Device) GetMessageBuffer() *[MaxMessageSize]byte {
-	if PreallocatedBuffersPerPool == 0 {
-		return device.pool.messageBufferPool.Get().(*[MaxMessageSize]byte)
-	} else {
-		return <-device.pool.messageBufferReuseChan
-	}
+	return device.pool.messageBuffers.Get().(*[MaxMessageSize]byte)
 }
 
 func (device *Device) PutMessageBuffer(msg *[MaxMessageSize]byte) {
-	if PreallocatedBuffersPerPool == 0 {
-		device.pool.messageBufferPool.Put(msg)
-	} else {
-		device.pool.messageBufferReuseChan <- msg
-	}
+	device.pool.messageBuffers.Put(msg)
 }
 
 func (device *Device) GetInboundElement() *QueueInboundElement {
-	if PreallocatedBuffersPerPool == 0 {
-		return device.pool.inboundElementPool.Get().(*QueueInboundElement)
-	} else {
-		return <-device.pool.inboundElementReuseChan
-	}
+	return device.pool.inboundElements.Get().(*QueueInboundElement)
 }
 
 func (device *Device) PutInboundElement(elem *QueueInboundElement) {
 	elem.clearPointers()
-	if PreallocatedBuffersPerPool == 0 {
-		device.pool.inboundElementPool.Put(elem)
-	} else {
-		device.pool.inboundElementReuseChan <- elem
-	}
+	device.pool.inboundElements.Put(elem)
 }
 
 func (device *Device) GetOutboundElement() *QueueOutboundElement {
-	if PreallocatedBuffersPerPool == 0 {
-		return device.pool.outboundElementPool.Get().(*QueueOutboundElement)
-	} else {
-		return <-device.pool.outboundElementReuseChan
-	}
+	return device.pool.outboundElements.Get().(*QueueOutboundElement)
 }
 
 func (device *Device) PutOutboundElement(elem *QueueOutboundElement) {
 	elem.clearPointers()
-	if PreallocatedBuffersPerPool == 0 {
-		device.pool.outboundElementPool.Put(elem)
-	} else {
-		device.pool.outboundElementReuseChan <- elem
-	}
+	device.pool.outboundElements.Put(elem)
 }