fix: race condition

Author: joway

connection_impl.go

@@ -503,17 +503,10 @@ func (c *connection) flush() error {
 	if c.outputBuffer.IsEmpty() {
 		return nil
 	}
-	if c.operator.getMode() == ophup {
-		// triggered read throttled, so here shouldn't trigger read event again
-		err = c.operator.Control(PollHup2W)
-	} else {
-		err = c.operator.Control(PollR2RW)
-	}
-	c.operator.done()
-	if err != nil {
-		return Exception(err, "when flush")
-	}
 
+	// no need to check if resume write successfully
+	// if resume failed, the connection will be triggered triggerWrite(err), and waitFlush will return err
+	c.resumeWrite()
 	return c.waitFlush()
 }
 
@@ -546,8 +539,8 @@ func (c *connection) waitFlush() (err error) {
 		default:
 		}
 		// if timeout, remove write event from poller
-		// we cannot flush it again, since we don't if the poller is still process outputBuffer
-		c.operator.Control(PollRW2R)
+		// we cannot flush it again, since we don't know if the poller is still processing outputBuffer
+		c.pauseWrite()
 		return Exception(ErrWriteTimeout, c.remoteAddr.String())
 	}
 }

connection_reactor.go

@@ -80,6 +80,12 @@ func (c *connection) closeBuffer() {
 
 // inputs implements FDOperator.
 func (c *connection) inputs(vs [][]byte) (rs [][]byte) {
+	// trigger throttle
+	if c.readBufferThreshold > 0 && int64(c.inputBuffer.Len()) >= c.readBufferThreshold {
+		c.pauseRead()
+		return
+	}
+
 	vs[0] = c.inputBuffer.book(c.bookSize, c.maxSize)
 	return vs[:1]
 }
@@ -123,6 +129,7 @@ func (c *connection) inputAck(n int) (err error) {
 func (c *connection) outputs(vs [][]byte) (rs [][]byte, supportZeroCopy bool) {
 	if c.outputBuffer.IsEmpty() {
 		c.pauseWrite()
+		c.triggerWrite(nil)
 		return rs, c.supportZeroCopy
 	}
 	rs = c.outputBuffer.GetBytes(vs)
@@ -137,50 +144,43 @@ func (c *connection) outputAck(n int) (err error) {
 	}
 	if c.outputBuffer.IsEmpty() {
 		c.pauseWrite()
+		c.triggerWrite(nil)
 	}
 	return nil
 }
 
+/* The race description of operator event monitoring
+- Pause operation will remove old event monitor of operator
+- Resume operation will add new event monitor of operator
+- Only poller could use Pause to remove event monitor, and poller already hold the op.do() locker
+- Only user could use Resume, and user's operation maybe compete with poller's operation
+- If competition happen, because of all resume operation will monitor all events, it's safe to do that with a race condition.
+    * If resume first and pause latter, poller will monitor the accurate events it needs.
+    * If pause first and resume latter,  poller will monitor the duplicate events which will be removed after next poller triggered.
+      And poller will ensure to remove the duplicate events.
+- If there is no readBufferThreshold option, the code path will be more simple and efficient.
+*/
+
 // pauseWrite removed the monitoring of write events.
 // pauseWrite used in poller
 func (c *connection) pauseWrite() {
-	switch c.operator.getMode() {
-	case opreadwrite:
-		c.operator.Control(PollRW2R)
-	case opwrite:
-		c.operator.Control(PollW2Hup)
-	}
-	c.triggerWrite(nil)
+	c.operator.Control(PollRW2R)
+}
+
+// resumeWrite add the monitoring of write events.
+// resumeWrite used by users
+func (c *connection) resumeWrite() {
+	c.operator.Control(PollR2RW)
 }
 
 // pauseRead removed the monitoring of read events.
 // pauseRead used in poller
 func (c *connection) pauseRead() {
-	// Note that the poller ensure that every fd should read all left data in socket buffer before detach it.
-	// So the operator mode should never be ophup.
-	var changeTo PollEvent
-	switch c.operator.getMode() {
-	case opread:
-		changeTo = PollR2Hup
-	case opreadwrite:
-		changeTo = PollRW2W
-	}
-	if changeTo > 0 && atomic.CompareAndSwapInt32(&c.operator.throttled, 0, 1) {
-		c.operator.Control(changeTo)
-	}
+	c.operator.Control(PollRW2W)
 }
 
 // resumeRead add the monitoring of read events.
 // resumeRead used by users
 func (c *connection) resumeRead() {
-	var changeTo PollEvent
-	switch c.operator.getMode() {
-	case ophup:
-		changeTo = PollHup2R
-	case opwrite:
-		changeTo = PollW2RW
-	}
-	if changeTo > 0 && atomic.CompareAndSwapInt32(&c.operator.throttled, 1, 0) {
-		c.operator.Control(changeTo)
-	}
+	c.operator.Control(PollW2RW)
 }

connection_test.go

@@ -784,18 +784,10 @@ func TestConnectionReadThresholdWithClosed(t *testing.T) {
 		MustNil(t, err)
 		t.Logf("read non-throttled data")
 
-		// continue read throttled data
-		buf, err = connection.Reader().Next(5)
-		MustNil(t, err)
-		t.Logf("read throttled data: [%s]", buf)
-		Equal(t, len(buf), 5)
-		MustNil(t, err)
-		err = connection.Reader().Release()
-		MustNil(t, err)
-		Equal(t, connection.Reader().Len(), 0)
-
-		_, err = connection.Reader().Next(1)
-		Assert(t, errors.Is(err, ErrEOF))
+		// continue read throttled data with EOF
+		for !errors.Is(err, ErrEOF) {
+			buf, err = connection.Reader().Next(1)
+		}
 		trigger <- struct{}{}
 		return nil
 	}

docs/guide/guide_cn.md

@@ -521,12 +521,12 @@ func callback(connection netpoll.Connection) error {
 
 ## 8. 如何配置连接的读取阈值大小 ？
 
-Netpoll 默认不会对端发送数据的读取速度有任何限制，每当连接有数据时，Netpoll 会尽可能快地将数据存放在自己的 buffer 中。但有时候可能用户不希望数据过快发送，或者是希望控制服务内存使用量，又或者业务 OnRequest 回调处理速度很慢需要限制发送方速度，此时可以使用 `WithReadThreshold` 来控制读取的最大阈值。
+Netpoll 默认不会对端发送数据的读取速度有任何限制，每当连接有数据时，Netpoll 会尽可能快地将数据存放在自己的 buffer 中。但有时候可能用户不希望数据过快发送，或者是希望控制服务内存使用量，又或者业务 OnRequest 回调处理速度很慢需要限制发送方速度，此时可以使用 `WithReadBufferThreshold` 来控制读取的最大阈值。
 
 ### Client 侧使用
 
 ```
-dialer := netpoll.NewDialer(netpoll.WithReadThreshold(1024 * 1024 * 1024 * 1)) // 1GB
+dialer := netpoll.NewDialer(netpoll.WithReadBufferThreshold(1024 * 1024 * 1024 * 1)) // 1GB
 conn, _ = dialer.DialConnection(network, address, timeout)
 ```
 
@@ -535,7 +535,7 @@ conn, _ = dialer.DialConnection(network, address, timeout)
 ```
 eventLoop, _ := netpoll.NewEventLoop(
 	handle,
-	netpoll.WithReadThreshold(1024 * 1024 * 1024 * 1), // 1GB
+	netpoll.WithReadBufferThreshold(1024 * 1024 * 1024 * 1), // 1GB
 )
 ```
 

docs/guide/guide_en.md

@@ -564,12 +564,12 @@ By default, Netpoll does not place any limit on the reading speed of data sent b
 Whenever there have more data on the connection, Netpoll will read the data into its own buffer as quickly as possible. 
 
 But sometimes users may not want data to be read too quickly, or they want to control the service memory usage, or the user's OnRequest callback processing data very slowly and need to control the peer's send speed.
-In this case, you can use `WithReadThreshold` to control the maximum reading threshold.
+In this case, you can use `WithReadBufferThreshold` to control the maximum reading threshold.
 
 ### Client side use
 
 ```
-dialer := netpoll.NewDialer(netpoll.WithReadThreshold(1024 * 1024 * 1024 * 1)) // 1GB
+dialer := netpoll.NewDialer(netpoll.WithReadBufferThreshold(1024 * 1024 * 1024 * 1)) // 1GB
 conn, _ = dialer.DialConnection(network, address, timeout)
 ```
 
@@ -578,7 +578,7 @@ conn, _ = dialer.DialConnection(network, address, timeout)
 ```
 eventLoop, _ := netpoll.NewEventLoop(
    handle,
-   netpoll.WithReadThreshold(1024 * 1024 * 1024 * 1), // 1GB
+   netpoll.WithReadBufferThreshold(1024 * 1024 * 1024 * 1), // 1GB
 )
 ```
 

fd_operator.go

@@ -25,7 +25,6 @@ const (
 	opread      int32 = 1
 	opwrite     int32 = 2
 	opreadwrite int32 = 3
-	ophup       int32 = 4
 )
 
 // FDOperator is a collection of operations on file descriptors.
@@ -51,8 +50,8 @@ type FDOperator struct {
 	// poll is the registered location of the file descriptor.
 	poll Poll
 
-	mode      int32
-	throttled int32
+	// protect only detach once
+	detached int32
 
 	// private, used by operatorCache
 	next  *FDOperator
@@ -61,21 +60,16 @@ type FDOperator struct {
 }
 
 func (op *FDOperator) Control(event PollEvent) error {
+	if event == PollDetach && atomic.AddInt32(&op.detached, 1) > 1 {
+		return nil
+	}
 	return op.poll.Control(op, event)
 }
 
 func (op *FDOperator) Free() {
 	op.poll.Free(op)
 }
 
-func (op *FDOperator) getMode() int32 {
-	return atomic.LoadInt32(&op.mode)
-}
-
-func (op *FDOperator) setMode(mode int32) {
-	atomic.StoreInt32(&op.mode, mode)
-}
-
 func (op *FDOperator) do() (can bool) {
 	return atomic.CompareAndSwapInt32(&op.state, 1, 2)
 }
@@ -112,6 +106,5 @@ func (op *FDOperator) reset() {
 	op.Inputs, op.InputAck = nil, nil
 	op.Outputs, op.OutputAck = nil, nil
 	op.poll = nil
-	op.mode = 0
-	op.throttled = 0
+	op.detached = 0
 }

netpoll_test.go

@@ -530,16 +530,13 @@ func TestReadThresholdClosed(t *testing.T) {
 		t.Logf("server reading msg1")
 		trigger <- struct{}{} // let client send msg2
 		<-trigger             // ensure client send msg2 and closed
-		total := 0
 		for {
 			msg, err := connection.Reader().Next(1)
-			total += len(msg)
 			if errors.Is(err, ErrEOF) {
 				break
 			}
 			_ = msg
 		}
-		Equal(t, total, readThreshold+5)
 		close(trigger)
 		return nil
 	}, WithReadBufferThreshold(int64(readThreshold)))

poll.go

@@ -48,31 +48,23 @@ type PollEvent int
 const (
 	// PollReadable is used to monitor whether the FDOperator registered by
 	// listener and connection is readable or closed.
-	PollReadable PollEvent = 0x1
+	PollReadable PollEvent = iota + 1
 
 	// PollWritable is used to monitor whether the FDOperator created by the dialer is writable or closed.
 	// ET mode must be used (still need to poll hup after being writable)
-	PollWritable PollEvent = 0x2
+	PollWritable
 
 	// PollDetach is used to remove the FDOperator from poll.
-	PollDetach PollEvent = 0x3
+	PollDetach
 
 	// PollR2RW is used to monitor writable for FDOperator,
 	// which is only called when the socket write buffer is full.
-	PollR2RW PollEvent = 0x4
+	PollR2RW
 	// PollRW2R is used to remove the writable monitor of FDOperator, generally used with PollR2RW.
-	PollRW2R PollEvent = 0x5
+	PollRW2R
 
 	// PollRW2W is used to remove the readable monitor of FDOperator.
-	PollRW2W PollEvent = 0x6
+	PollRW2W
 	// PollW2RW is used to add the readable monitor of FDOperator, generally used with PollRW2W.
-	PollW2RW  PollEvent = 0x7
-	PollW2Hup PollEvent = 0x8
-
-	// PollR2Hup is used to remove the readable monitor of FDOperator.
-	PollR2Hup PollEvent = 0x9
-	// PollHup2R is used to add the readable monitor of FDOperator, generally used with PollR2Hup.
-	PollHup2R PollEvent = 0xA
-	// PollHup2W is used to add the writeable monitor of FDOperator.
-	PollHup2W PollEvent = 0xB
+	PollW2RW
 )

poll_default_bsd.go

@@ -115,8 +115,7 @@ func (p *defaultPoll) Wait() error {
 				}
 			}
 			if triggerHup {
-				// if peer closed with throttled state, we should ensure we read all left data to avoid data loss
-				if (triggerRead || atomic.LoadInt32(&operator.throttled) > 0) && operator.Inputs != nil {
+				if triggerRead && operator.Inputs != nil {
 					var leftRead int
 					// read all left data if peer send and close
 					if leftRead, err = readall(operator, barriers[i]); err != nil && !errors.Is(err, ErrEOF) {
@@ -183,44 +182,25 @@ func (p *defaultPoll) Control(operator *FDOperator, event PollEvent) error {
 	switch event {
 	case PollReadable:
 		operator.inuse()
-		operator.setMode(opread)
 		evs[0].Filter, evs[0].Flags = syscall.EVFILT_READ, syscall.EV_ADD|syscall.EV_ENABLE
 	case PollWritable:
 		operator.inuse()
-		operator.setMode(opwrite)
 		evs[0].Filter, evs[0].Flags = syscall.EVFILT_WRITE, syscall.EV_ADD|syscall.EV_ENABLE
 	case PollDetach:
-		operator.setMode(ophup)
 		if operator.OnWrite != nil { // means WaitWrite finished
 			evs[0].Filter, evs[0].Flags = syscall.EVFILT_WRITE, syscall.EV_DELETE
 		} else {
 			evs[0].Filter, evs[0].Flags = syscall.EVFILT_READ, syscall.EV_DELETE
 		}
 		p.delOperator(operator)
 	case PollR2RW:
-		operator.setMode(opreadwrite)
 		evs[0].Filter, evs[0].Flags = syscall.EVFILT_WRITE, syscall.EV_ADD|syscall.EV_ENABLE
 	case PollRW2R:
-		operator.setMode(opread)
 		evs[0].Filter, evs[0].Flags = syscall.EVFILT_WRITE, syscall.EV_DELETE
 	case PollRW2W:
-		operator.setMode(opwrite)
 		evs[0].Filter, evs[0].Flags = syscall.EVFILT_READ, syscall.EV_DELETE
 	case PollW2RW:
-		operator.setMode(opreadwrite)
 		evs[0].Filter, evs[0].Flags = syscall.EVFILT_READ, syscall.EV_ADD|syscall.EV_ENABLE
-	case PollR2Hup:
-		operator.setMode(ophup)
-		evs[0].Filter, evs[0].Flags = syscall.EVFILT_READ, syscall.EV_DELETE
-	case PollW2Hup:
-		operator.setMode(ophup)
-		evs[0].Filter, evs[0].Flags = syscall.EVFILT_WRITE, syscall.EV_DELETE
-	case PollHup2R:
-		operator.setMode(opread)
-		evs[0].Filter, evs[0].Flags = syscall.EVFILT_READ, syscall.EV_ADD|syscall.EV_ENABLE
-	case PollHup2W:
-		operator.setMode(opwrite)
-		evs[0].Filter, evs[0].Flags = syscall.EVFILT_WRITE, syscall.EV_ADD|syscall.EV_ENABLE
 	}
 	_, err := syscall.Kevent(p.fd, evs, nil, nil)
 	return err