go122-confuse-seq-across-generations.go

     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"
    26  	"internal/trace/internal/testgen"
    27  	"internal/trace/tracev2"
    28  	"internal/trace/version"
    29  )
    30  
    31  func main() {
    32  	testgen.Main(version.Go122, gen)
    33  }
    34  
    35  func gen(t *testgen.Trace) {
    36  	g1 := t.Generation(1)
    37  
    38  	// A running goroutine blocks.
    39  	b10 := g1.Batch(trace.ThreadID(0), 0)
    40  	b10.Event("ProcStatus", trace.ProcID(0), tracev2.ProcRunning)
    41  	b10.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), tracev2.GoRunning)
    42  	b10.Event("GoStop", "whatever", testgen.NoStack)
    43  
    44  	// The running goroutine gets unblocked.
    45  	b11 := g1.Batch(trace.ThreadID(1), 0)
    46  	b11.Event("ProcStatus", trace.ProcID(1), tracev2.ProcRunning)
    47  	b11.Event("GoStart", trace.GoID(1), testgen.Seq(1))
    48  	b11.Event("GoStop", "whatever", testgen.NoStack)
    49  
    50  	g2 := t.Generation(2)
    51  
    52  	// Start running the goroutine, but later.
    53  	b21 := g2.Batch(trace.ThreadID(1), 3)
    54  	b21.Event("ProcStatus", trace.ProcID(1), tracev2.ProcRunning)
    55  	b21.Event("GoStart", trace.GoID(1), testgen.Seq(2))
    56  
    57  	// The goroutine starts running, then stops, then starts again.
    58  	b20 := g2.Batch(trace.ThreadID(0), 5)
    59  	b20.Event("ProcStatus", trace.ProcID(0), tracev2.ProcRunning)
    60  	b20.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), tracev2.GoRunnable)
    61  	b20.Event("GoStart", trace.GoID(1), testgen.Seq(1))
    62  	b20.Event("GoStop", "whatever", testgen.NoStack)
    63  }
    64
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