// Unless explicitly stated otherwise all files in this repository are licensed
// under the MIT/Apache-2.0 License, at your convenience
//
// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2020 Datadog, Inc.
//
use Debug;
use ;
/// The SharesManager allows the user to implement dynamic shares for a
/// [`TaskQueue`]
///
/// In terms of behavior, a [`TaskQueue`] with static shares is the same as a
/// `SharesManager` managed queue that always return the same value. However
/// this is a bit more expensive to compute because it needs to be reevaluated
/// constantly.
///
/// The difference is akin to a constant versus variable in your favorite
/// programming language.
///
/// [`TaskQueue`]: struct.Task.html#method.create_task_queue
/// Represents how many shares a [`TaskQueue`] should receive.
///
/// Glommio's scheduler doesn't work with priorities, but rather shares. That
/// means that if there is only one active task queue in the system, it will
/// always receive 100 % of the resources.
///
/// As soon as two or more task queues are active, resources will be split
/// between them proportionally to their shares: a queue with more shares will
/// receive more resources.
///
/// Be careful when trying to reason about percentages of utilization as they
/// will depend on the active task queues: The percentage of resources assigned
/// to a task queue should be close to `shares(i) / sum(shares(i) for i in t)`.
///
/// For example, if all task queues have 1000 shares (the default), when two of
/// them are active they will have each 50% of the resources. As soon as a third
/// one activates, each now has 33%.
///
/// This can be far off if there are other heavy processes competing for
/// resources with your application in a way that glommio can't see. For best
/// results you should consider dedicating CPUs and storage devices to your
/// application.
///
/// Shares are enforced by the system to be between 1 and 1000. So if all
/// [`TaskQueue`]s want maximum resources they should all get similar fractions.
/// It is not possible for a [`TaskQueue`] to say it wants to use more than the
/// others: it is only possible for the other task queues to say they are okay
/// with using less (by reducing their shares)
///
/// [`TaskQueue`]: struct.Task.html#method.create_task_queue