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/**
* @file coro_scheduler.h
* @author Nat Goodspeed
* @date 2024-08-05
* @brief Custom scheduler for viewer's Boost.Fibers (aka coroutines)
*
* $LicenseInfo:firstyear=2024&license=viewerlgpl$
* Copyright (c) 2024, Linden Research, Inc.
* $/LicenseInfo$
*/
#if ! defined(LL_CORO_SCHEDULER_H)
#define LL_CORO_SCHEDULER_H
#include "workqueue.h"
#include <boost/fiber/fiber.hpp>
#include <boost/fiber/algo/round_robin.hpp>
/**
* llcoro::scheduler is specifically intended for the viewer's main thread.
* Its role is to ensure that the main coroutine, responsible for UI
* operations and coordinating everything else, doesn't get starved by
* secondary coroutines -- however many of those there might be.
*
* The simple boost::fibers::algo::round_robin scheduler could result in
* arbitrary time lag between resumptions of the main coroutine. Of course
* every well-behaved viewer coroutine must be coded to yield before too much
* real time has elapsed, but sheer volume of secondary coroutines could still
* consume unreasonable real time before cycling back to the main coroutine.
*/
namespace llcoro
{
class scheduler: public boost::fibers::algo::round_robin
{
using super = boost::fibers::algo::round_robin;
public:
// If the main fiber is ready, and it's been at least this long since the
// main fiber last ran, jump the main fiber to the head of the queue.
static const F64 DEFAULT_TIMESLICE;
scheduler();
void awakened( boost::fibers::context*) noexcept override;
boost::fibers::context* pick_next() noexcept override;
static void use();
private:
LL::WorkQueue::ptr_t getWorkQueue();
// This is the fiber::id of the main fiber.
boost::fibers::fiber::id mMainID;
// This context* is nullptr while the main fiber is running or suspended,
// but is set to the main fiber's context each time the main fiber is ready.
boost::fibers::context* mMainCtx{};
// Remember the context returned by the previous pick_next() call.
boost::fibers::context* mPrevCtx{};
// If it's been at least this long since the last time the main fiber got
// control, jump it to the head of the queue.
F64 mTimeslice{ DEFAULT_TIMESLICE };
// Time when we resumed the most recently running fiber
F64 mResumeTime{ 0 };
// Timestamp as of the last time we suspended the main fiber.
F64 mMainLast{ 0 };
// Timestamp of start time
F64 mStart{ 0 };
// count context switches
U64 mSwitches{ 0 };
// WorkQueue for deferred logging
LL::WorkQueue::weak_t mQueue;
};
} // namespace llcoro
#endif /* ! defined(LL_CORO_SCHEDULER_H) */
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