extern thread_local ThreadStatus * current_thread;

class ThreadStatus : public boost::noncopyable
{
public:
    /// Linux's PID (or TGID) (the same id is shown by ps util)
    const UInt64 thread_id = 0;

    MemoryTracker memory_tracker{VariableContext::Thread};

    /// Small amount of untracked memory (per thread atomic-less counter)
    Int64 untracked_memory = 0;
    /// Each thread could new/delete memory in range of (-untracked_memory_limit, untracked_memory_limit) without access to common counters.
    Int64 untracked_memory_limit = 4 * 1024 * 1024;

protected:
    ThreadGroupStatusPtr thread_group;
……