text: /*
   * Copyright (c) Meta Platforms, Inc. and affiliates.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #pragma once
  
  #include <folly/Executor.h>
  
  namespace folly {
  
  // `SoftRealTimeExecutor` is an executor that performs some priority-based
  // scheduling with a deadline assigned to each task. __Soft__ real-time
  // means that not every deadline is guaranteed to be met.
  class SoftRealTimeExecutor : public virtual Executor {
   public:
    void add(Func) override = 0;
  
    // Add a task with an assigned abstract deadline.
    //
    // NOTE: The type of `deadline` was chosen to be an integral rather than
    // a typed time point or duration (e.g., `std::chrono::time_point`) to allow
    // for flexibility. While the deadline for a task may be a time point,
    // it could also be a duration or the size of the task, which emulates
    // rate-monotonic scheduling that prioritizes small tasks. It also enables
    // for example, tiered scheduling (strictly prioritizing a category of tasks)
    // by assigning the high-bit of the deadline.
    virtual void add(Func, uint64_t deadline) = 0;
  };
  
  } // namespace folly
  