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Diffstat (limited to 'indra/llcommon/coro_scheduler.cpp')
| -rw-r--r-- | indra/llcommon/coro_scheduler.cpp | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/indra/llcommon/coro_scheduler.cpp b/indra/llcommon/coro_scheduler.cpp new file mode 100644 index 0000000000..337162cbd5 --- /dev/null +++ b/indra/llcommon/coro_scheduler.cpp @@ -0,0 +1,164 @@ +/** + * @file coro_scheduler.cpp + * @author Nat Goodspeed + * @date 2024-08-05 + * @brief Implementation for llcoro::scheduler. + * + * $LicenseInfo:firstyear=2024&license=viewerlgpl$ + * Copyright (c) 2024, Linden Research, Inc. + * $/LicenseInfo$ + */ + +// Precompiled header +#include "linden_common.h" +// associated header +#include "coro_scheduler.h" +// STL headers +// std headers +#include <iomanip> +// external library headers +#include <boost/fiber/operations.hpp> +// other Linden headers +#include "llcallbacklist.h" +#include "lldate.h" +#include "llerror.h" + +namespace llcoro +{ + +const F32 scheduler::DEFAULT_TIMESLICE{ LL::Timers::DEFAULT_TIMESLICE }; + +const std::string qname("General"); + +scheduler::scheduler(): + // Since use_scheduling_algorithm() must be called before any other + // Boost.Fibers operations, we can assume that the calling fiber is in + // fact the main fiber. + mMainID(boost::this_fiber::get_id()), + mStart(LLDate::now().secondsSinceEpoch()), + mQueue(LL::WorkQueue::getInstance(qname)) +{} + +void scheduler::awakened( boost::fibers::context* ctx) noexcept +{ + if (ctx->get_id() == mMainID) + { + // If the fiber that just came ready is the main fiber, record its + // pointer. + llassert(! mMainCtx); + mMainCtx = ctx; + } + // Delegate to round_robin::awakened() as usual, even for the main fiber. + // This way, as long as other fibers don't take too long, we can just let + // normal round_robin processing pass control to the main fiber. + super::awakened(ctx); +} + +boost::fibers::context* scheduler::pick_next() noexcept +{ + // count calls to pick_next() + ++mSwitches; + // pick_next() is called when the previous fiber has suspended, and we + // need to pick another. Did the previous pick_next() call pick the main + // fiber? If so, it's the main fiber that just suspended. + auto now = LLDate::now().secondsSinceEpoch(); + if (mMainRunning) + { + mMainRunning = false; + mMainLast = now; + } + + boost::fibers::context* next; + + // When the main fiber is ready, and it's been more than mTimeslice since + // the main fiber last ran, it's time to intervene. + F32 elapsed(now - mMainLast); + if (mMainCtx && elapsed > mTimeslice) + { + // We claim that the main fiber is not only stored in mMainCtx, but is + // also queued (somewhere) in our ready list. + llassert(mMainCtx->ready_is_linked()); + // The usefulness of a doubly-linked list is that, given only a + // pointer to an item, we can unlink it. + mMainCtx->ready_unlink(); + // Instead of delegating to round_robin::pick_next() to pop the head + // of the queue, override by returning mMainCtx. + next = mMainCtx; + + /*------------------------- logging stuff --------------------------*/ + // Unless this log tag is enabled, don't even bother posting. + LL_DEBUGS("LLCoros.scheduler"); + // This feature is inherently hard to verify. The logging in the + // lambda below seems useful, but also seems like a lot of overhead + // for a coroutine context switch. Try posting the logging lambda to a + // ThreadPool to offload that overhead. However, if this is still + // taking an unreasonable amount of context-switch time, this whole + // passage could be skipped. + + // Record this event for logging, but push it off to a thread pool to + // perform that work. Presumably std::weak_ptr::lock() is cheaper than + // WorkQueue::getInstance(). + LL::WorkQueue::ptr_t queue{ mQueue.lock() }; + // We probably started before the relevant WorkQueue was created. + if (! queue) + { + // Try again to locate the specified WorkQueue. + queue = LL::WorkQueue::getInstance(qname); + mQueue = queue; + } + // Both the lock() call and the getInstance() call might have failed. + if (queue) + { + // Bind values. Do NOT bind 'this' to avoid cross-thread access! + // It would be interesting to know from what queue position we + // unlinked the main fiber, out of how many in the ready list. + // Unfortunately round_robin::rqueue_ is private, not protected, + // so we have no access. + queue->post( + [switches=mSwitches, start=mStart, elapsed, now] + () + { + U32 runtime(U32(now) - U32(start)); + U32 minutes(runtime / 60u); + U32 seconds(runtime % 60u); + // use stringize to avoid lasting side effects to the + // logging ostream + LL_DEBUGS("LLCoros.scheduler") + << "At time " + << stringize(minutes, ":", std::setw(2), std::setfill('0'), seconds) + << " (" << switches << " switches), coroutines took " + << stringize(std::setprecision(4), elapsed) + << " sec, main coroutine jumped queue" + << LL_ENDL; + }); + } + LL_ENDL; + /*----------------------- end logging stuff ------------------------*/ + } + else + { + // Either the main fiber isn't yet ready, or it hasn't yet been + // mTimeslice seconds since the last time the main fiber ran. Business + // as usual. + next = super::pick_next(); + } + + // super::pick_next() could also have returned the main fiber, which is + // why this is a separate test instead of being folded into the override + // case above. + if (next && next->get_id() == mMainID) + { + // we're about to resume the main fiber: it's no longer "ready" + mMainCtx = nullptr; + // instead, it's "running" + mMainRunning = true; + } + return next; +} + +void scheduler::use() +{ + boost::fibers::use_scheduling_algorithm<scheduler>(); +} + +} // namespace llcoro |