code: private boolean tryRelease(long c, WorkQueue v, long inc) {
          int sp = (int)c, ns = sp & ~UNSIGNALLED;
          if (v != null) {
              int vs = v.scanState;
              long nc = (v.stackPred & SP_MASK) | (UC_MASK & (c + inc));
              if (sp == vs && U.compareAndSwapLong(this, CTL, c, nc)) {
                  v.scanState = ns;
                  LockSupport.unpark(v.parker);
                  return true;
              }
          }
          return false;
      }
docs: Signals and releases worker v if it is top of idle worker
  stack.  This performs a one-shot version of signalWork only if
  there is (apparently) at least one idle worker.
  
  @param c incoming ctl value
  @param v if non-null, a worker
  @param inc the increment to active count (zero when compensating)
  @return true if successful