// N.B. Only one GC can be running at a time, so this is naturally
	// serialized by the caller.
	trace.seqGC++
}

// STWStart traces a STWBegin event.
func (tl traceLocker) STWStart(reason stwReason) {
	// Although the current P may be in _Pgcstop here, we model the P as running during the STW. This deviates from the

	//
	// N.B. This will also emit a status event for this goroutine.
	tl := traceAcquire()
	tl.Gomaxprocs(gomaxprocs)  // Get this as early in the trace as possible. See comment in traceAdvance.
	tl.STWStart(stwStartTrace) // We didn't trace this above, so trace it now.

	// Record the fact that a GC is active, if applicable.
	if gcphase == _GCmark || gcphase == _GCmarktermination {
		tl.GCActive()
	}