// Copyright 2023 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Tests a G being created from within a syscall. // // Specifically, it tests a scenario wherein a C // thread is calling into Go, creating a goroutine in // a syscall (in the tracer's model). The system is free // to reuse thread IDs, so first a thread ID is used to // call into Go, and then is used for a Go-created thread. // // This is a regression test. The trace parser didn't correctly // model GoDestroySyscall as dropping its P (even if the runtime // did). It turns out this is actually fine if all the threads // in the trace have unique IDs, since the P just stays associated // with an eternally dead thread, and it's stolen by some other // thread later. But if thread IDs are reused, then the tracer // gets confused when trying to advance events on the new thread. // The now-dead thread which exited on a GoDestroySyscall still has // its P associated and this transfers to the newly-live thread // in the parser's state because they share a thread ID. package main import ( "internal/trace" "internal/trace/event/go122" testgen "internal/trace/internal/testgen/go122" ) func main() { testgen.Main(gen) } func gen(t *testgen.Trace) { g := t.Generation(1) // A C thread calls into Go and acquires a P. It returns // back to C, destroying the G. b0 := g.Batch(trace.ThreadID(0), 0) b0.Event("GoCreateSyscall", trace.GoID(4)) b0.Event("GoSyscallEndBlocked") b0.Event("ProcStatus", trace.ProcID(0), go122.ProcIdle) b0.Event("ProcStart", trace.ProcID(0), testgen.Seq(1)) b0.Event("GoStatus", trace.GoID(4), trace.NoThread, go122.GoRunnable) b0.Event("GoStart", trace.GoID(4), testgen.Seq(1)) b0.Event("GoSyscallBegin", testgen.Seq(2), testgen.NoStack) b0.Event("GoDestroySyscall") // A new Go-created thread with the same ID appears and // starts running, then tries to steal the P from the // first thread. The stealing is interesting because if // the parser handles GoDestroySyscall wrong, then we // have a self-steal here potentially that doesn't make // sense. b1 := g.Batch(trace.ThreadID(0), 0) b1.Event("ProcStatus", trace.ProcID(1), go122.ProcIdle) b1.Event("ProcStart", trace.ProcID(1), testgen.Seq(1)) b1.Event("ProcSteal", trace.ProcID(0), testgen.Seq(3), trace.ThreadID(0)) }