batch.go

Documentation: internal/trace

     1  // Copyright 2023 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package trace
     6  
     7  import (
     8  	"bytes"
     9  	"encoding/binary"
    10  	"fmt"
    11  	"io"
    12  
    13  	"internal/trace/event"
    14  	"internal/trace/event/go122"
    15  )
    16  
    17  // timestamp is an unprocessed timestamp.
    18  type timestamp uint64
    19  
    20  // batch represents a batch of trace events.
    21  // It is unparsed except for its header.
    22  type batch struct {
    23  	m    ThreadID
    24  	time timestamp
    25  	data []byte
    26  	exp  event.Experiment
    27  }
    28  
    29  func (b *batch) isStringsBatch() bool {
    30  	return b.exp == event.NoExperiment && len(b.data) > 0 && event.Type(b.data[0]) == go122.EvStrings
    31  }
    32  
    33  func (b *batch) isStacksBatch() bool {
    34  	return b.exp == event.NoExperiment && len(b.data) > 0 && event.Type(b.data[0]) == go122.EvStacks
    35  }
    36  
    37  func (b *batch) isCPUSamplesBatch() bool {
    38  	return b.exp == event.NoExperiment && len(b.data) > 0 && event.Type(b.data[0]) == go122.EvCPUSamples
    39  }
    40  
    41  func (b *batch) isFreqBatch() bool {
    42  	return b.exp == event.NoExperiment && len(b.data) > 0 && event.Type(b.data[0]) == go122.EvFrequency
    43  }
    44  
    45  // readBatch reads the next full batch from r.
    46  func readBatch(r interface {
    47  	io.Reader
    48  	io.ByteReader
    49  }) (batch, uint64, error) {
    50  	// Read batch header byte.
    51  	b, err := r.ReadByte()
    52  	if err != nil {
    53  		return batch{}, 0, err
    54  	}
    55  	if typ := event.Type(b); typ != go122.EvEventBatch && typ != go122.EvExperimentalBatch {
    56  		return batch{}, 0, fmt.Errorf("expected batch event, got %s", go122.EventString(typ))
    57  	}
    58  
    59  	// Read the experiment of we have one.
    60  	exp := event.NoExperiment
    61  	if event.Type(b) == go122.EvExperimentalBatch {
    62  		e, err := r.ReadByte()
    63  		if err != nil {
    64  			return batch{}, 0, err
    65  		}
    66  		exp = event.Experiment(e)
    67  	}
    68  
    69  	// Read the batch header: gen (generation), thread (M) ID, base timestamp
    70  	// for the batch.
    71  	gen, err := binary.ReadUvarint(r)
    72  	if err != nil {
    73  		return batch{}, gen, fmt.Errorf("error reading batch gen: %w", err)
    74  	}
    75  	m, err := binary.ReadUvarint(r)
    76  	if err != nil {
    77  		return batch{}, gen, fmt.Errorf("error reading batch M ID: %w", err)
    78  	}
    79  	ts, err := binary.ReadUvarint(r)
    80  	if err != nil {
    81  		return batch{}, gen, fmt.Errorf("error reading batch timestamp: %w", err)
    82  	}
    83  
    84  	// Read in the size of the batch to follow.
    85  	size, err := binary.ReadUvarint(r)
    86  	if err != nil {
    87  		return batch{}, gen, fmt.Errorf("error reading batch size: %w", err)
    88  	}
    89  	if size > go122.MaxBatchSize {
    90  		return batch{}, gen, fmt.Errorf("invalid batch size %d, maximum is %d", size, go122.MaxBatchSize)
    91  	}
    92  
    93  	// Copy out the batch for later processing.
    94  	var data bytes.Buffer
    95  	data.Grow(int(size))
    96  	n, err := io.CopyN(&data, r, int64(size))
    97  	if n != int64(size) {
    98  		return batch{}, gen, fmt.Errorf("failed to read full batch: read %d but wanted %d", n, size)
    99  	}
   100  	if err != nil {
   101  		return batch{}, gen, fmt.Errorf("copying batch data: %w", err)
   102  	}
   103  
   104  	// Return the batch.
   105  	return batch{
   106  		m:    ThreadID(m),
   107  		time: timestamp(ts),
   108  		data: data.Bytes(),
   109  		exp:  exp,
   110  	}, gen, nil
   111  }
   112
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