/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

include protocol PBackground;
using mozilla::TimeDuration from "mozilla/TimeStamp.h";
[MoveOnly] using base::SharedMemoryHandle from "base/shared_memory.h";
namespace mozilla {
namespace ipc {

/**
 * PIdleScheduler is the protocol for cross-process idle scheduling.
 * Only child processes participate in the scheduling and parent process
 * can run its idle tasks whenever it needs to.
 *
 * The scheduler keeps track of the following things.
 * - Activity of the main thread of each child process. A process is active
 *   when it is running tasks. Because of performance cross-process
 *   counters in shared memory are used for the activity tracking. There is
 *   one counter counting the activity state of all the processes and one
 *   counter for each process. This way if a child process crashes, the global
 *   counter can be updated by decrementing the per process counter from it.
 * - Child processes running prioritized operation. Top level page loads is an
 *   example of a prioritized operation. When such is ongoing, idle tasks are
 *   less likely to run.
 * - Idle requests. When a child process locally has idle tasks to run, it
 *   requests idle time from the scheduler. Initially requests go to a wait list
 *   and the scheduler runs and if there are free logical cores for the child
 *   processes, idle time is given to the child process, and the process goes to
 *   the idle list. Once idle time has been consumed or there are no tasks to
 *   process, child process informs the scheduler and the process is moved back
 *   to the default queue.
 */
async protocol PIdleScheduler
{
  manager PBackground;

child:
  async IdleTime(uint64_t id, TimeDuration budget);

parent:
  async InitForIdleUse() returns (SharedMemoryHandle? state, uint32_t childId);
  async RequestIdleTime(uint64_t id, TimeDuration budget);
  async IdleTimeUsed(uint64_t id);

  // Child can send explicit Schedule message to parent if it thinks parent process
  // might be able to let some other process to use idle time.
  async Schedule();

  // Note, these two messages can be sent even before InitForIdleUse.
  async RunningPrioritizedOperation();
  async PrioritizedOperationDone();

  // Ask if now would be a good time to GC
  async RequestGC() returns (bool may_gc);

  // Let the parent know when we start a GC without asking first.
  async StartedGC();

  // Called for ending any kind of GC.
  async DoneGC();

  // This message is never sent. Each PIdleScheduler actor will stay alive as long as
  // its PBackground manager.
  async __delete__();
};

} // namespace ipc
} // namespace mozilla