go122-confuse-seq-across-generations.go

Documentation: internal/trace/v2/testdata/generators

     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  // Regression test for an issue found in development.
     6  //
     7  // The core of the issue is that if generation counters
     8  // aren't considered as part of sequence numbers, then
     9  // it's possible to accidentally advance without a
    10  // GoStatus event.
    11  //
    12  // The situation is one in which it just so happens that
    13  // an event on the frontier for a following generation
    14  // has a sequence number exactly one higher than the last
    15  // sequence number for e.g. a goroutine in the previous
    16  // generation. The parser should wait to find a GoStatus
    17  // event before advancing into the next generation at all.
    18  // It turns out this situation is pretty rare; the GoStatus
    19  // event almost always shows up first in practice. But it
    20  // can and did happen.
    21  
    22  package main
    23  
    24  import (
    25  	"internal/trace/v2"
    26  	"internal/trace/v2/event/go122"
    27  	testgen "internal/trace/v2/internal/testgen/go122"
    28  )
    29  
    30  func main() {
    31  	testgen.Main(gen)
    32  }
    33  
    34  func gen(t *testgen.Trace) {
    35  	g1 := t.Generation(1)
    36  
    37  	// A running goroutine blocks.
    38  	b10 := g1.Batch(trace.ThreadID(0), 0)
    39  	b10.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
    40  	b10.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
    41  	b10.Event("GoStop", "whatever", testgen.NoStack)
    42  
    43  	// The running goroutine gets unblocked.
    44  	b11 := g1.Batch(trace.ThreadID(1), 0)
    45  	b11.Event("ProcStatus", trace.ProcID(1), go122.ProcRunning)
    46  	b11.Event("GoStart", trace.GoID(1), testgen.Seq(1))
    47  	b11.Event("GoStop", "whatever", testgen.NoStack)
    48  
    49  	g2 := t.Generation(2)
    50  
    51  	// Start running the goroutine, but later.
    52  	b21 := g2.Batch(trace.ThreadID(1), 3)
    53  	b21.Event("ProcStatus", trace.ProcID(1), go122.ProcRunning)
    54  	b21.Event("GoStart", trace.GoID(1), testgen.Seq(2))
    55  
    56  	// The goroutine starts running, then stops, then starts again.
    57  	b20 := g2.Batch(trace.ThreadID(0), 5)
    58  	b20.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
    59  	b20.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunnable)
    60  	b20.Event("GoStart", trace.GoID(1), testgen.Seq(1))
    61  	b20.Event("GoStop", "whatever", testgen.NoStack)
    62  }
    63
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