public Long getCas() {
    if (cas == null) {
      try {
        get();
      } catch (InterruptedException e) {
        status = new OperationStatus(false, "Interrupted", StatusCode.INTERRUPTED);
      } catch (ExecutionException e) {
        getLogger().warn("Error getting cas of operation", e);
      }
    }
    if (cas == null && status.isSuccess()) {
      throw new UnsupportedOperationException("This operation doesn't return"
          + "a cas value.");
    }
    return cas;
  }
Get the CAS for this operation.

The interrupted status of the current thread is cleared by this method.
Inspect the returned OperationStatus to check whether an interruption has taken place.

@throws UnsupportedOperationException If this is for an ASCII protocol
configured client.
@return the CAS for this operation or null if unsuccessful.
src/main/java/net/spy/memcached/internal/OperationFuture.java