github.com/pingcap/tiflow@v0.0.0-20240520035814-5bf52d54e205/pkg/p2p/server_stream_handle.go (about)

     1  // Copyright 2021 PingCAP, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package p2p
    15  
    16  import (
    17  	"context"
    18  	"sync"
    19  
    20  	"github.com/pingcap/tiflow/pkg/errors"
    21  	"github.com/pingcap/tiflow/proto/p2p"
    22  	"go.uber.org/atomic"
    23  )
    24  
    25  // streamHandle is used to provide the server a non-blocking handle of a stream.
    26  // It is needed because grpc-go does not provide a stream easily cancellable.
    27  // Since Go is not friendly with the receiver closing a channel, we need this
    28  // auxiliary data structure to make the stream cancellation more graceful.
    29  type streamHandle struct {
    30  	// mu protects sendCh. We should take the shared lock
    31  	// when sending and the exclusive lock when closing it.
    32  	// We consider Read to be anything except closing the channel,
    33  	// and close is Write in this definition.
    34  	// This definition provides an elegant solution for lock protecting Go channels.
    35  	mu     sync.RWMutex
    36  	sendCh chan<- p2p.SendMessageResponse
    37  
    38  	isClosed atomic.Bool
    39  	closeCh  chan struct{}
    40  
    41  	// read-only
    42  	streamMeta *p2p.StreamMeta
    43  }
    44  
    45  // newStreamHandle returns a new streamHandle.
    46  func newStreamHandle(meta *p2p.StreamMeta, sendCh chan<- p2p.SendMessageResponse) *streamHandle {
    47  	return &streamHandle{
    48  		sendCh:     sendCh,
    49  		closeCh:    make(chan struct{}),
    50  		streamMeta: meta,
    51  	}
    52  }
    53  
    54  // Send sends a message to the stream.
    55  // If called after Close, an error will be returned.
    56  func (s *streamHandle) Send(ctx context.Context, response p2p.SendMessageResponse) error {
    57  	s.mu.RLock()
    58  	defer s.mu.RUnlock()
    59  
    60  	// We need to read from isClosed while holding the lock.
    61  	// Otherwise, we risk the sendCh being closed after we have checked
    62  	// isClosed to be false. If this happens, we will try to send
    63  	// to a closed channel, which will panic.
    64  	if s.isClosed.Load() {
    65  		return errors.ErrPeerMessageInternalSenderClosed.GenWithStackByArgs()
    66  	}
    67  
    68  	select {
    69  	case <-ctx.Done():
    70  		return errors.Trace(ctx.Err())
    71  	case s.sendCh <- response:
    72  	case <-s.closeCh:
    73  		return errors.ErrPeerMessageInternalSenderClosed.GenWithStackByArgs()
    74  	}
    75  
    76  	return nil
    77  }
    78  
    79  // Close closes the stream handle.
    80  // We should not call Send after Close.
    81  func (s *streamHandle) Close() {
    82  	if s.isClosed.Swap(true) {
    83  		// already closed
    84  		return
    85  	}
    86  	// Must close `s.closeCh` while not holding `s.mu`.
    87  	close(s.closeCh)
    88  
    89  	s.mu.Lock()
    90  	defer s.mu.Unlock()
    91  
    92  	close(s.sendCh)
    93  }
    94  
    95  // GetStreamMeta returns the metadata associated with the stream.
    96  func (s *streamHandle) GetStreamMeta() *p2p.StreamMeta {
    97  	return s.streamMeta
    98  }