// Need to keep a reference so that the cached value can be re-evaluated on mutation, but
                // use a soft reference to allow the state to be GCed
                //
                // Also keep a soft reference to try to avoid recreating the state when it is queried during

	},
	EvGCBegin: event.Spec{
		Name:         "GCBegin",
		Args:         []string{"dt", "gc_seq", "stack"},
		IsTimedEvent: true,
		StackIDs:     []int{2},
	},
	EvGCEnd: event.Spec{
		Name:         "GCEnd",
		Args:         []string{"dt", "gc_seq"},
		StartEv:      EvGCBegin,
		IsTimedEvent: true,
	},
	EvGCSweepActive: event.Spec{
		Name:         "GCSweepActive",
		Args:         []string{"dt", "p"},

        captureOutput.flush()
        super.flush()
    }

    fun stop() = safely {
        isCapturing!!.remove()
        // Give a chance for other threads' weak references to the local to be GCed if any
        isCapturing = null
    }

    private
    fun safely(block: () -> Unit) =
        try {
            synchronized(this, block)
        } catch (ex: InterruptedException) {

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

// GCDone traces a GCEnd event.
//
// Must be emitted by an actively running goroutine on an active P. This restriction can be changed
// easily and only depends on where it's currently called.
func (tl traceLocker) GCDone() {