Function has_span_db

src/brpc/span.cpp:510–510

// Can't use intrusive_ptr which has ctor/dtor issues.
static SpanDB* g_span_db = NULL;
bool has_span_db() { return !!g_span_db; }
bvar::CollectorSpeedLimit g_span_sl = BVAR_COLLECTOR_SPEED_LIMIT_INITIALIZER;
static bvar::DisplaySamplingRatio s_display_sampling_ratio(
    "rpcz_sampling_ratio", &g_span_sl);