Spawns a Fiber to compute &block in the background after delay has elapsed. Access to get is synchronized between fibers, and returns the block value after the &block completes. &block is only called once. get may be called multiple times, and returns the block's return value or re-raises any unrescued Exception. May be canceled before &block is called by calling cancel. Calling get before the delay has elapsed results in the call waiting for the delay to fully elapse and compute to next finish, then the value is returned.

d = delay(1) { Process.signal(Signal::KILL, Process.pid) }
# ... long operations ...
d.cancel

Spawns a Fiber to compute &block in the background. Access to get is synchronized between fibers, and returns the block value after the &block completes. &block is only called once. get may be called multiple times, and returns the block's return value or re-raises any unrescued Exception.

f = future { `echo hello` }
# ... other actions ...
f.get # => "hello\n"

Conditionally spawns a Fiber to run &block in the background. Access to get is synchronized between fibers, and returns the block value after the &block completes. &block is only called once. get may be called multiple times, and returns the block's return value or re-raises any unrescued Exception. &block doesn't run by default, only when get is called.

l = lazy { expensive_computation }
spawn { maybe_use_computation(l) }
spawn { maybe_use_computation(l) }