Preemptive (swim-concurrent 4.0.0 API)

```
public interface Preemptive
```
Function interface that callers can optionally invoke concurrently.

Method Summary

All Methods Instance Methods Default Methods
Modifier and Type	Method	Description
`default boolean`	`isPreemptive()`	Returns `true` if callers can safely invoke this function object concurrently.

- Method Detail
  - isPreemptive
```
default boolean isPreemptive()
```
    Returns true if callers can safely invoke this function object concurrently. Returns false if this function object is not thread safe. Returns false by default.