reader.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  	"bufio"
     9  	"fmt"
    10  	"io"
    11  	"slices"
    12  	"strings"
    13  
    14  	"internal/trace/event/go122"
    15  	"internal/trace/internal/oldtrace"
    16  	"internal/trace/version"
    17  )
    18  
    19  // Reader reads a byte stream, validates it, and produces trace events.
    20  type Reader struct {
    21  	r           *bufio.Reader
    22  	lastTs      Time
    23  	gen         *generation
    24  	spill       *spilledBatch
    25  	spillErr    error // error from reading spill
    26  	frontier    []*batchCursor
    27  	cpuSamples  []cpuSample
    28  	order       ordering
    29  	emittedSync bool
    30  
    31  	go121Events *oldTraceConverter
    32  }
    33  
    34  // NewReader creates a new trace reader.
    35  func NewReader(r io.Reader) (*Reader, error) {
    36  	br := bufio.NewReader(r)
    37  	v, err := version.ReadHeader(br)
    38  	if err != nil {
    39  		return nil, err
    40  	}
    41  	switch v {
    42  	case version.Go111, version.Go119, version.Go121:
    43  		tr, err := oldtrace.Parse(br, v)
    44  		if err != nil {
    45  			return nil, err
    46  		}
    47  		return &Reader{
    48  			go121Events: convertOldFormat(tr),
    49  		}, nil
    50  	case version.Go122, version.Go123:
    51  		return &Reader{
    52  			r: br,
    53  			order: ordering{
    54  				mStates:     make(map[ThreadID]*mState),
    55  				pStates:     make(map[ProcID]*pState),
    56  				gStates:     make(map[GoID]*gState),
    57  				activeTasks: make(map[TaskID]taskState),
    58  			},
    59  			// Don't emit a sync event when we first go to emit events.
    60  			emittedSync: true,
    61  		}, nil
    62  	default:
    63  		return nil, fmt.Errorf("unknown or unsupported version go 1.%d", v)
    64  	}
    65  }
    66  
    67  // ReadEvent reads a single event from the stream.
    68  //
    69  // If the stream has been exhausted, it returns an invalid
    70  // event and io.EOF.
    71  func (r *Reader) ReadEvent() (e Event, err error) {
    72  	if r.go121Events != nil {
    73  		ev, err := r.go121Events.next()
    74  		if err != nil {
    75  			// XXX do we have to emit an EventSync when the trace is done?
    76  			return Event{}, err
    77  		}
    78  		return ev, nil
    79  	}
    80  
    81  	// Go 1.22+ trace parsing algorithm.
    82  	//
    83  	// (1) Read in all the batches for the next generation from the stream.
    84  	//   (a) Use the size field in the header to quickly find all batches.
    85  	// (2) Parse out the strings, stacks, CPU samples, and timestamp conversion data.
    86  	// (3) Group each event batch by M, sorted by timestamp. (batchCursor contains the groups.)
    87  	// (4) Organize batchCursors in a min-heap, ordered by the timestamp of the next event for each M.
    88  	// (5) Try to advance the next event for the M at the top of the min-heap.
    89  	//   (a) On success, select that M.
    90  	//   (b) On failure, sort the min-heap and try to advance other Ms. Select the first M that advances.
    91  	//   (c) If there's nothing left to advance, goto (1).
    92  	// (6) Select the latest event for the selected M and get it ready to be returned.
    93  	// (7) Read the next event for the selected M and update the min-heap.
    94  	// (8) Return the selected event, goto (5) on the next call.
    95  
    96  	// Set us up to track the last timestamp and fix up
    97  	// the timestamp of any event that comes through.
    98  	defer func() {
    99  		if err != nil {
   100  			return
   101  		}
   102  		if err = e.validateTableIDs(); err != nil {
   103  			return
   104  		}
   105  		if e.base.time <= r.lastTs {
   106  			e.base.time = r.lastTs + 1
   107  		}
   108  		r.lastTs = e.base.time
   109  	}()
   110  
   111  	// Consume any events in the ordering first.
   112  	if ev, ok := r.order.Next(); ok {
   113  		return ev, nil
   114  	}
   115  
   116  	// Check if we need to refresh the generation.
   117  	if len(r.frontier) == 0 && len(r.cpuSamples) == 0 {
   118  		if !r.emittedSync {
   119  			r.emittedSync = true
   120  			return syncEvent(r.gen.evTable, r.lastTs), nil
   121  		}
   122  		if r.spillErr != nil {
   123  			return Event{}, r.spillErr
   124  		}
   125  		if r.gen != nil && r.spill == nil {
   126  			// If we have a generation from the last read,
   127  			// and there's nothing left in the frontier, and
   128  			// there's no spilled batch, indicating that there's
   129  			// no further generation, it means we're done.
   130  			// Return io.EOF.
   131  			return Event{}, io.EOF
   132  		}
   133  		// Read the next generation.
   134  		var err error
   135  		r.gen, r.spill, err = readGeneration(r.r, r.spill)
   136  		if r.gen == nil {
   137  			return Event{}, err
   138  		}
   139  		r.spillErr = err
   140  
   141  		// Reset CPU samples cursor.
   142  		r.cpuSamples = r.gen.cpuSamples
   143  
   144  		// Reset frontier.
   145  		for m, batches := range r.gen.batches {
   146  			bc := &batchCursor{m: m}
   147  			ok, err := bc.nextEvent(batches, r.gen.freq)
   148  			if err != nil {
   149  				return Event{}, err
   150  			}
   151  			if !ok {
   152  				// Turns out there aren't actually any events in these batches.
   153  				continue
   154  			}
   155  			r.frontier = heapInsert(r.frontier, bc)
   156  		}
   157  
   158  		// Reset emittedSync.
   159  		r.emittedSync = false
   160  	}
   161  	tryAdvance := func(i int) (bool, error) {
   162  		bc := r.frontier[i]
   163  
   164  		if ok, err := r.order.Advance(&bc.ev, r.gen.evTable, bc.m, r.gen.gen); !ok || err != nil {
   165  			return ok, err
   166  		}
   167  
   168  		// Refresh the cursor's event.
   169  		ok, err := bc.nextEvent(r.gen.batches[bc.m], r.gen.freq)
   170  		if err != nil {
   171  			return false, err
   172  		}
   173  		if ok {
   174  			// If we successfully refreshed, update the heap.
   175  			heapUpdate(r.frontier, i)
   176  		} else {
   177  			// There's nothing else to read. Delete this cursor from the frontier.
   178  			r.frontier = heapRemove(r.frontier, i)
   179  		}
   180  		return true, nil
   181  	}
   182  	// Inject a CPU sample if it comes next.
   183  	if len(r.cpuSamples) != 0 {
   184  		if len(r.frontier) == 0 || r.cpuSamples[0].time < r.frontier[0].ev.time {
   185  			e := r.cpuSamples[0].asEvent(r.gen.evTable)
   186  			r.cpuSamples = r.cpuSamples[1:]
   187  			return e, nil
   188  		}
   189  	}
   190  	// Try to advance the head of the frontier, which should have the minimum timestamp.
   191  	// This should be by far the most common case
   192  	if len(r.frontier) == 0 {
   193  		return Event{}, fmt.Errorf("broken trace: frontier is empty:\n[gen=%d]\n\n%s\n%s\n", r.gen.gen, dumpFrontier(r.frontier), dumpOrdering(&r.order))
   194  	}
   195  	if ok, err := tryAdvance(0); err != nil {
   196  		return Event{}, err
   197  	} else if !ok {
   198  		// Try to advance the rest of the frontier, in timestamp order.
   199  		//
   200  		// To do this, sort the min-heap. A sorted min-heap is still a
   201  		// min-heap, but now we can iterate over the rest and try to
   202  		// advance in order. This path should be rare.
   203  		slices.SortFunc(r.frontier, (*batchCursor).compare)
   204  		success := false
   205  		for i := 1; i < len(r.frontier); i++ {
   206  			if ok, err = tryAdvance(i); err != nil {
   207  				return Event{}, err
   208  			} else if ok {
   209  				success = true
   210  				break
   211  			}
   212  		}
   213  		if !success {
   214  			return Event{}, fmt.Errorf("broken trace: failed to advance: frontier:\n[gen=%d]\n\n%s\n%s\n", r.gen.gen, dumpFrontier(r.frontier), dumpOrdering(&r.order))
   215  		}
   216  	}
   217  
   218  	// Pick off the next event on the queue. At this point, one must exist.
   219  	ev, ok := r.order.Next()
   220  	if !ok {
   221  		panic("invariant violation: advance successful, but queue is empty")
   222  	}
   223  	return ev, nil
   224  }
   225  
   226  func dumpFrontier(frontier []*batchCursor) string {
   227  	var sb strings.Builder
   228  	for _, bc := range frontier {
   229  		spec := go122.Specs()[bc.ev.typ]
   230  		fmt.Fprintf(&sb, "M %d [%s time=%d", bc.m, spec.Name, bc.ev.time)
   231  		for i, arg := range spec.Args[1:] {
   232  			fmt.Fprintf(&sb, " %s=%d", arg, bc.ev.args[i])
   233  		}
   234  		fmt.Fprintf(&sb, "]\n")
   235  	}
   236  	return sb.String()
   237  }
   238
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