Struct Shard 

struct Shard {
    queue: VecDeque<Task>,
    sealed: bool,
}

Fields

queue: VecDeque<Task>

sealed: bool

Set (under the shard’s lock) when the shard is drained for shutdown; pushes to a sealed shard are rejected. This is what guarantees that a spawner racing with shutdown cannot leave a task behind: a push either loses (rejected, task is shut down) or wins, in which case the sealer that later drains this shard collects the task.