golang.org/x/exp@v0.0.0-20240506185415-9bf2ced13842/trace/testdata/generators/go122-create-syscall-reuse-thread-id.go (about)

     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  // Tests a G being created from within a syscall.
    10  //
    11  // Specifically, it tests a scenerio wherein a C
    12  // thread is calling into Go, creating a goroutine in
    13  // a syscall (in the tracer's model). The system is free
    14  // to reuse thread IDs, so first a thread ID is used to
    15  // call into Go, and then is used for a Go-created thread.
    16  //
    17  // This is a regression test. The trace parser didn't correctly
    18  // model GoDestroySyscall as dropping its P (even if the runtime
    19  // did). It turns out this is actually fine if all the threads
    20  // in the trace have unique IDs, since the P just stays associated
    21  // with an eternally dead thread, and it's stolen by some other
    22  // thread later. But if thread IDs are reused, then the tracer
    23  // gets confused when trying to advance events on the new thread.
    24  // The now-dead thread which exited on a GoDestroySyscall still has
    25  // its P associated and this transfers to the newly-live thread
    26  // in the parser's state because they share a thread ID.
    27  
    28  package main
    29  
    30  import (
    31  	"golang.org/x/exp/trace"
    32  	"golang.org/x/exp/trace/internal/event/go122"
    33  	testgen "golang.org/x/exp/trace/internal/testgen/go122"
    34  )
    35  
    36  func main() {
    37  	testgen.Main(gen)
    38  }
    39  
    40  func gen(t *testgen.Trace) {
    41  	g := t.Generation(1)
    42  
    43  	// A C thread calls into Go and acquires a P. It returns
    44  	// back to C, destroying the G.
    45  	b0 := g.Batch(trace.ThreadID(0), 0)
    46  	b0.Event("GoCreateSyscall", trace.GoID(4))
    47  	b0.Event("GoSyscallEndBlocked")
    48  	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcIdle)
    49  	b0.Event("ProcStart", trace.ProcID(0), testgen.Seq(1))
    50  	b0.Event("GoStatus", trace.GoID(4), trace.NoThread, go122.GoRunnable)
    51  	b0.Event("GoStart", trace.GoID(4), testgen.Seq(1))
    52  	b0.Event("GoSyscallBegin", testgen.Seq(2), testgen.NoStack)
    53  	b0.Event("GoDestroySyscall")
    54  
    55  	// A new Go-created thread with the same ID appears and
    56  	// starts running, then tries to steal the P from the
    57  	// first thread. The stealing is interesting because if
    58  	// the parser handles GoDestroySyscall wrong, then we
    59  	// have a self-steal here potentially that doesn't make
    60  	// sense.
    61  	b1 := g.Batch(trace.ThreadID(0), 0)
    62  	b1.Event("ProcStatus", trace.ProcID(1), go122.ProcIdle)
    63  	b1.Event("ProcStart", trace.ProcID(1), testgen.Seq(1))
    64  	b1.Event("ProcSteal", trace.ProcID(0), testgen.Seq(3), trace.ThreadID(0))
    65  }