docs: @Trivial
      private void decrementWithheldConcurrency() {
          int w;
          while ((w = withheldConcurrency.get()) > 0 && !withheldConcurrency.compareAndSet(w, w - 1));
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
              Tr.debug(this, tc, "withheld concurrency " + w + " --> " + (w == 0 ? 0 : (w - 1)));
      }