Spawn compute

These spawn functions give maximum control over spawning remote compute.

spawn(lf, *, dst[, context, distributed, ...])	Spawn a remote query and await it asynchronously.
spawn_blocking(lf, *, dst[, context, ...])	Spawn a remote query and block the thread until the result is ready.
spawn_many(lf, *, dst[, context, ...])	Spawn a multiple remote queries and await it asynchronously.
spawn_many_blocking(lf, *, dst[, context, ...])	Spawn a multiple remote queries and await it asynchronously.