future-blog-post-13

future4.go

// Interface represents a future. No concrete implementation is
// exposed; all access to a future is via this interface.
type Interface interface {
    // Get returns the values calculated by the future. It will pause until
    // the value is calculated.
    //
    // If Get is invoked multiple times, the same value will be returned each time.
    // Subsequent calls to Get will return instantaneously.
    //
    // When the future is cancelled, nil is returned for both the value and the error.
    Get() (interface{}, error)

    // GetUntil waits for up to Duration d for the future to complete. If the
    // future completes before the Duration completes, the value and error are returned
    // and timeout is returned as false. If the Duration completes before the future
    // returns, nil is returned for the value and the error and timeout is returned
    // as true.
    //
    // When the future is cancelled, nil is returned for both the value and the error.
    GetUntil(d time.Duration) (interface{}, bool, error)

    // Then allows multiple function calls to be chained together into a
    // single future.
    //
    // Each call is run in order, with the output of the previous call passed into
    // the next function in the chain. If an error occurs at any step in the chain,
    // processing ceases and the error is returned via Get or GetUntil.
    Then(Step) Interface

    // Cancel prevents a future that hasn’t completed from returning a
    // value. Any current or future calls to Get or GetUntil will return
    // immediately.
    //
    // If the future has already completed or has already been
    // cancelled, calling Cancel will do nothing.
    // After a successful cancel, IsCancelled returns true.
    //
    // Calling Cancel on a future that has not completed does not stop the
    // currently running function. However, any chained functions will not
    // be run and the values returned by the current function are not accessible.
    Cancel()

    // IsCancelled indicates if a future terminated due to cancellation.
    // If Cancel was called and the future’s work was not completed, IsCancelled
    // returns true. Otherwise, it returns false
    IsCancelled() bool
}