reader.go

Documentation: golang.org/x/exp/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  // Code generated by "gen.bash" from internal/trace/v2; DO NOT EDIT.
     6  
     7  //go:build go1.21
     8  
     9  package trace
    10  
    11  import (
    12  	"bufio"
    13  	"fmt"
    14  	"io"
    15  	"slices"
    16  	"strings"
    17  
    18  	"golang.org/x/exp/trace/internal/event/go122"
    19  	"golang.org/x/exp/trace/internal/oldtrace"
    20  	"golang.org/x/exp/trace/internal/version"
    21  )
    22  
    23  // Reader reads a byte stream, validates it, and produces trace events.
    24  type Reader struct {
    25  	r           *bufio.Reader
    26  	lastTs      Time
    27  	gen         *generation
    28  	spill       *spilledBatch
    29  	frontier    []*batchCursor
    30  	cpuSamples  []cpuSample
    31  	order       ordering
    32  	emittedSync bool
    33  
    34  	go121Events *oldTraceConverter
    35  }
    36  
    37  // NewReader creates a new trace reader.
    38  func NewReader(r io.Reader) (*Reader, error) {
    39  	br := bufio.NewReader(r)
    40  	v, err := version.ReadHeader(br)
    41  	if err != nil {
    42  		return nil, err
    43  	}
    44  	switch v {
    45  	case version.Go111, version.Go119, version.Go121:
    46  		tr, err := oldtrace.Parse(br, v)
    47  		if err != nil {
    48  			return nil, err
    49  		}
    50  		return &Reader{
    51  			go121Events: convertOldFormat(tr),
    52  		}, nil
    53  	case version.Go122, version.Go123:
    54  		return &Reader{
    55  			r: br,
    56  			order: ordering{
    57  				mStates:     make(map[ThreadID]*mState),
    58  				pStates:     make(map[ProcID]*pState),
    59  				gStates:     make(map[GoID]*gState),
    60  				activeTasks: make(map[TaskID]taskState),
    61  			},
    62  			// Don't emit a sync event when we first go to emit events.
    63  			emittedSync: true,
    64  		}, nil
    65  	default:
    66  		return nil, fmt.Errorf("unknown or unsupported version go 1.%d", v)
    67  	}
    68  }
    69  
    70  // ReadEvent reads a single event from the stream.
    71  //
    72  // If the stream has been exhausted, it returns an invalid
    73  // event and io.EOF.
    74  func (r *Reader) ReadEvent() (e Event, err error) {
    75  	if r.go121Events != nil {
    76  		ev, err := r.go121Events.next()
    77  		if err != nil {
    78  			// XXX do we have to emit an EventSync when the trace is done?
    79  			return Event{}, err
    80  		}
    81  		return ev, nil
    82  	}
    83  
    84  	// Go 1.22+ trace parsing algorithm.
    85  	//
    86  	// (1) Read in all the batches for the next generation from the stream.
    87  	//   (a) Use the size field in the header to quickly find all batches.
    88  	// (2) Parse out the strings, stacks, CPU samples, and timestamp conversion data.
    89  	// (3) Group each event batch by M, sorted by timestamp. (batchCursor contains the groups.)
    90  	// (4) Organize batchCursors in a min-heap, ordered by the timestamp of the next event for each M.
    91  	// (5) Try to advance the next event for the M at the top of the min-heap.
    92  	//   (a) On success, select that M.
    93  	//   (b) On failure, sort the min-heap and try to advance other Ms. Select the first M that advances.
    94  	//   (c) If there's nothing left to advance, goto (1).
    95  	// (6) Select the latest event for the selected M and get it ready to be returned.
    96  	// (7) Read the next event for the selected M and update the min-heap.
    97  	// (8) Return the selected event, goto (5) on the next call.
    98  
    99  	// Set us up to track the last timestamp and fix up
   100  	// the timestamp of any event that comes through.
   101  	defer func() {
   102  		if err != nil {
   103  			return
   104  		}
   105  		if err = e.validateTableIDs(); err != nil {
   106  			return
   107  		}
   108  		if e.base.time <= r.lastTs {
   109  			e.base.time = r.lastTs + 1
   110  		}
   111  		r.lastTs = e.base.time
   112  	}()
   113  
   114  	// Consume any events in the ordering first.
   115  	if ev, ok := r.order.Next(); ok {
   116  		return ev, nil
   117  	}
   118  
   119  	// Check if we need to refresh the generation.
   120  	if len(r.frontier) == 0 && len(r.cpuSamples) == 0 {
   121  		if !r.emittedSync {
   122  			r.emittedSync = true
   123  			return syncEvent(r.gen.evTable, r.lastTs), nil
   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  		r.gen, r.spill, err = readGeneration(r.r, r.spill)
   135  		if err != nil {
   136  			return Event{}, err
   137  		}
   138  
   139  		// Reset CPU samples cursor.
   140  		r.cpuSamples = r.gen.cpuSamples
   141  
   142  		// Reset frontier.
   143  		for m, batches := range r.gen.batches {
   144  			bc := &batchCursor{m: m}
   145  			ok, err := bc.nextEvent(batches, r.gen.freq)
   146  			if err != nil {
   147  				return Event{}, err
   148  			}
   149  			if !ok {
   150  				// Turns out there aren't actually any events in these batches.
   151  				continue
   152  			}
   153  			r.frontier = heapInsert(r.frontier, bc)
   154  		}
   155  
   156  		// Reset emittedSync.
   157  		r.emittedSync = false
   158  	}
   159  	tryAdvance := func(i int) (bool, error) {
   160  		bc := r.frontier[i]
   161  
   162  		if ok, err := r.order.Advance(&bc.ev, r.gen.evTable, bc.m, r.gen.gen); !ok || err != nil {
   163  			return ok, err
   164  		}
   165  
   166  		// Refresh the cursor's event.
   167  		ok, err := bc.nextEvent(r.gen.batches[bc.m], r.gen.freq)
   168  		if err != nil {
   169  			return false, err
   170  		}
   171  		if ok {
   172  			// If we successfully refreshed, update the heap.
   173  			heapUpdate(r.frontier, i)
   174  		} else {
   175  			// There's nothing else to read. Delete this cursor from the frontier.
   176  			r.frontier = heapRemove(r.frontier, i)
   177  		}
   178  		return true, nil
   179  	}
   180  	// Inject a CPU sample if it comes next.
   181  	if len(r.cpuSamples) != 0 {
   182  		if len(r.frontier) == 0 || r.cpuSamples[0].time < r.frontier[0].ev.time {
   183  			e := r.cpuSamples[0].asEvent(r.gen.evTable)
   184  			r.cpuSamples = r.cpuSamples[1:]
   185  			return e, nil
   186  		}
   187  	}
   188  	// Try to advance the head of the frontier, which should have the minimum timestamp.
   189  	// This should be by far the most common case
   190  	if len(r.frontier) == 0 {
   191  		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))
   192  	}
   193  	if ok, err := tryAdvance(0); err != nil {
   194  		return Event{}, err
   195  	} else if !ok {
   196  		// Try to advance the rest of the frontier, in timestamp order.
   197  		//
   198  		// To do this, sort the min-heap. A sorted min-heap is still a
   199  		// min-heap, but now we can iterate over the rest and try to
   200  		// advance in order. This path should be rare.
   201  		slices.SortFunc(r.frontier, (*batchCursor).compare)
   202  		success := false
   203  		for i := 1; i < len(r.frontier); i++ {
   204  			if ok, err = tryAdvance(i); err != nil {
   205  				return Event{}, err
   206  			} else if ok {
   207  				success = true
   208  				break
   209  			}
   210  		}
   211  		if !success {
   212  			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))
   213  		}
   214  	}
   215  
   216  	// Pick off the next event on the queue. At this point, one must exist.
   217  	ev, ok := r.order.Next()
   218  	if !ok {
   219  		panic("invariant violation: advance successful, but queue is empty")
   220  	}
   221  	return ev, nil
   222  }
   223  
   224  func dumpFrontier(frontier []*batchCursor) string {
   225  	var sb strings.Builder
   226  	for _, bc := range frontier {
   227  		spec := go122.Specs()[bc.ev.typ]
   228  		fmt.Fprintf(&sb, "M %d [%s time=%d", bc.m, spec.Name, bc.ev.time)
   229  		for i, arg := range spec.Args[1:] {
   230  			fmt.Fprintf(&sb, " %s=%d", arg, bc.ev.args[i])
   231  		}
   232  		fmt.Fprintf(&sb, "]\n")
   233  	}
   234  	return sb.String()
   235  }
   236
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