for 循环里面调用 defer cancel() 的调用导致内存泄露，程序OOM

[ymakedaq]

代码段 parser.go

	for {
		if p.cfg.StopNever {
			ctx = context.Background()
		} else {
			ctx, cancel = context.WithTimeout(context.Background(), 10*time.Second)
			defer cancel()  // 此处在 每次循环中并不会被调用 
		}
		// e, err := s.GetEvent(context.Background())
		e, err := s.GetEvent(ctx)
		if err != nil {
			// Try to output all left events
			// events := s.DumpEvents()
			// for _, e := range events {
			//  // e.Dump(os.Stdout)
			//  log.Info("===============")
			//  log.Info(e.Header.EventType)
			// }
			log.Errorf("Get event error: %v\n", err)
			break
		}

pprof head

` ``
go tool pprof http://127.0.0.1:9999/debug/pprof/heap
Fetching profile over HTTP from http://127.0.0.1:9999/debug/pprof/heap
Saved profile in /root/pprof/pprof.bingo2sql.alloc_objects.alloc_space.inuse_objects.inuse_space.019.pb.gz
File: bingo2sql
Type: inuse_space
Time: Jun 26, 2021 at 10:27am (UTC)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 2.99GB, 97.40% of 3.07GB total
Dropped 40 nodes (cum <= 0.02GB)
Showing top 10 nodes out of 28
flat flat% sum% cum cum%
1.04GB 33.82% 33.82% 1.11GB 36.04% context.WithDeadline
0.94GB 30.54% 64.36% 0.94GB 30.54% context.(*cancelCtx).Done.
0.76GB 24.77% 89.13% 0.76GB 24.77% runtime.systemstack.
0.06GB 1.94% 91.06% 0.07GB 2.22% time.AfterFunc
0.04GB 1.38% 92.45% 0.10GB 3.10% github.com/hanchuanchuan/go-mysql/replication.(*RowsEvent).Decode
0.04GB 1.32% 93.77% 0.16GB 5.10% github.com/hanchuanchuan/go-mysql/replication.(*BinlogParser).parseEvent
0.04GB 1.30% 95.07% 0.05GB 1.67% github.com/hanchuanchuan/go-mysql/packet.(*Conn).ReadPacket
0.03GB 1.06% 96.13% 0.03GB 1.06% time.goFunc
0.02GB 0.73% 96.86% 0.05GB 1.72% github.com/hanchuanchuan/go-mysql/replication.(*RowsEvent).decodeRows
0.02GB 0.54% 97.40% 0.02GB 0.54% github.com/hanchuanchuan/go-mysql/replication.(*BinlogParser).newRowsEvent

[ymakedaq]

可以改成以下方式

	var ctx context.Context
	var cancel context.CancelFunc
	for {
		if p.cfg.StopNever {
			ctx = context.Background()
		} else {
			ctx, cancel = context.WithTimeout(context.Background(), 10*time.Second)
			//defer cancel()
		}
		// e, err := s.GetEvent(context.Background())
		e, err := s.GetEvent(ctx)
		if err != nil {
			// Try to output all left events
			// events := s.DumpEvents()
			// for _, e := range events {
			//  // e.Dump(os.Stdout)
			//  log.Info("===============")
			//  log.Info(e.Header.EventType)
			// }
			cancel()
			log.Errorf("Get event error: %v\n", err)
			break
		}
		cancel()