worker.h

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#ifndef ZTH_WORKER_H
#define ZTH_WORKER_H
/*
 * Zth (libzth), a cooperative userspace multitasking library.
 * Copyright (C) 2019-2022  Jochem Rutgers
 *
 * 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 https://mozilla.org/MPL/2.0/.
 */
 
#ifdef __cplusplus
#       include <libzth/allocator.h>
#       include <libzth/config.h>
#       include <libzth/context.h>
#       include <libzth/fiber.h>
#       include <libzth/init.h>
#       include <libzth/list.h>
#       include <libzth/perf.h>
#       include <libzth/waiter.h>
 
#       include <cstring>
#       include <limits>
#       include <time.h>
 
namespace zth {
 
void sigchld_check();
 
class Worker;
 
class Worker
        : public UniqueID<Worker>
        , public ThreadLocalSingleton<Worker> {
        ZTH_CLASS_NEW_DELETE(Worker)
public:
        Worker()
                : UniqueID("Worker")
                , m_currentFiber()
                , m_workerFiber(&dummyWorkerEntry)
                , m_waiter(*this)
                , m_disableContextSwitch()
        {
                zth_init();
 
                int res = 0;
                zth_dbg(worker, "[%s] Created", id_str());
 
                if(instance() != this)
                        zth_abort("Only one worker allowed per thread");
 
                if((res = context_init()))
                        goto error;
 
                m_workerFiber.setName("zth::Worker");
                m_workerFiber.setStackSize(0); // no stack
                if((res = m_workerFiber.init()))
                        goto error;
 
                if((res = perf_init()))
                        goto error;
 
                zth_perf_event(m_workerFiber);
 
                if((res = waiter().run()))
                        goto error;
 
                return;
 
error:
                zth_abort("Cannot create Worker; %s", err(res).c_str());
        }
 
        virtual ~Worker() override
        {
                zth_dbg(worker, "[%s] Destruct", id_str());
 
                while(!m_suspendedQueue.empty()) {
                        Fiber& f = m_suspendedQueue.front();
                        resume(f);
                        f.kill();
                }
                while(!m_runnableQueue.empty()) {
                        m_runnableQueue.front().kill();
                        cleanup(m_runnableQueue.front());
                }
 
                perf_deinit();
                context_deinit();
        }
 
        Fiber* currentFiber() const noexcept
        {
                return m_currentFiber;
        }
 
        Waiter& waiter() noexcept
        {
                return m_waiter;
        }
 
        void add(Fiber* fiber) noexcept
        {
                zth_assert(fiber);
                zth_assert(fiber->state() != Fiber::Waiting); // We don't manage 'Waiting' here.
 
                if(unlikely(fiber->state() == Fiber::Suspended)) {
                        m_suspendedQueue.push_back(*fiber);
                        zth_dbg(worker, "[%s] Added suspended %s", id_str(), fiber->id_str());
                } else {
                        m_runnableQueue.push_front(*fiber);
                        zth_dbg(worker, "[%s] Added runnable %s", id_str(), fiber->id_str());
                }
 
                dbgStats();
        }
 
        Worker& operator<<(Fiber* fiber) noexcept
        {
                add(fiber);
                return *this;
        }
 
        void contextSwitchEnable(bool enable = true) noexcept
        {
                if(enable) {
                        zth_assert(m_disableContextSwitch > 0);
                        m_disableContextSwitch--;
                } else
                        m_disableContextSwitch++;
        }
 
        void contextSwitchDisable() noexcept
        {
                contextSwitchEnable(false);
        }
 
        bool contextSwitchEnabled() const noexcept
        {
                return m_disableContextSwitch == 0;
        }
 
        void release(Fiber& fiber) noexcept
        {
                if(unlikely(fiber.state() == Fiber::Suspended)) {
                        m_suspendedQueue.erase(fiber);
                        zth_dbg(worker, "[%s] Removed %s from suspended queue", id_str(),
                                fiber.id_str());
                } else {
                        if(&fiber == m_currentFiber)
                                m_runnableQueue.rotate(*fiber.listNext());
 
                        m_runnableQueue.erase(fiber);
                        zth_dbg(worker, "[%s] Removed %s from runnable queue", id_str(),
                                fiber.id_str());
                }
                dbgStats();
        }
 
        bool schedule(Fiber* preferFiber = nullptr, Timestamp const& now = Timestamp::now())
        {
                if(unlikely(!contextSwitchEnabled()))
                        // Don't switch, immediately continue.
                        return true;
 
                if(preferFiber)
                        zth_dbg(worker, "[%s] Schedule to %s", id_str(), preferFiber->id_str());
                else
                        zth_dbg(worker, "[%s] Schedule", id_str());
 
                dbgStats();
 
                // Check if fiber is within the runnable queue.
                zth_assert(
                        !preferFiber || preferFiber == &m_workerFiber
                        || m_runnableQueue.contains(*preferFiber));
 
                if(unlikely(!runEnd().isNull() && runEnd().isBefore(now))) {
                        // Stop worker and return to its run1() call.
                        zth_dbg(worker, "[%s] Time is up", id_str());
                        preferFiber = &m_workerFiber;
                }
 
                Fiber* nextFiber = preferFiber;
                bool didSchedule = false;
reschedule:
                if(likely(!nextFiber)) {
                        if(likely(!m_runnableQueue.empty()))
                                // Use first of the queue.
                                nextFiber = &m_runnableQueue.front();
                        else
                                // No fiber to switch to.
                                nextFiber = &m_workerFiber;
                }
 
                zth_assert(nextFiber == &m_workerFiber || nextFiber->listPrev());
                zth_assert(nextFiber == &m_workerFiber || nextFiber->listNext());
 
                {
                        // NOLINTNEXTLINE(clang-analyzer-cplusplus.NewDelete)
                        Fiber* prevFiber = m_currentFiber;
                        m_currentFiber = nextFiber;
 
                        if(unlikely(nextFiber != &m_workerFiber))
                                m_runnableQueue.rotate(*nextFiber->listNext());
 
                        int res =
                                nextFiber->run(likely(prevFiber) ? *prevFiber : m_workerFiber, now);
                        // Warning! When res == 0, fiber might already have been deleted.
                        m_currentFiber = prevFiber;
 
                        switch(res) {
                        case 0:
                                // Ok, just returned to this fiber. Continue execution.
                                return true;
                        case EAGAIN:
                                // Switching to the same fiber.
                                return didSchedule;
                        case EPERM:
                                // fiber just died.
                                cleanup(*nextFiber);
                                // Retry to find a fiber.
                                nextFiber = nullptr;
                                didSchedule = true;
                                goto reschedule;
                        default:
                                zth_abort("Unhandled Fiber::run() error: %s", err(res).c_str());
                        }
                }
        }
 
        void cleanup(Fiber& fiber)
        {
                zth_assert(fiber.state() == Fiber::Dead);
 
                if(unlikely(m_currentFiber == &fiber)) {
                        // It seems that the current fiber is dead.
                        // In this case, we cannot delete the fiber and its context,
                        // as that is the context we are currently using.
                        // Return to the worker's context and sort it out from there.
 
                        zth_dbg(worker, "[%s] Current fiber %s just died; switch to worker",
                                id_str(), fiber.id_str());
                        zth_assert(contextSwitchEnabled());
                        schedule(&m_workerFiber);
 
                        // We should not get here, as we are dead.
                        zth_abort("[Worker %p] Failed to switch to worker", this);
                }
 
                zth_dbg(worker, "[%s] Fiber %s is dead; cleanup", id_str(), fiber.id_str());
                // Remove from runnable queue
                m_runnableQueue.erase(fiber);
                zth_assert(&fiber != &m_workerFiber);
                // NOLINTNEXTLINE(clang-analyzer-cplusplus.NewDelete)
                delete &fiber;
 
                sigchld_check();
        }
 
        void suspend(Fiber& fiber)
        {
                switch(fiber.state()) {
                case Fiber::New:
                case Fiber::Ready:
                        release(fiber);
                        fiber.suspend();
                        add(&fiber);
                        break;
                case Fiber::Running:
                        release(fiber);
                        fiber.suspend();
                        add(&fiber);
                        zth_assert(currentFiber() == &fiber);
                        zth_assert(contextSwitchEnabled());
                        // Current fiber suspended, immediate reschedule.
                        schedule();
                        break;
                case Fiber::Waiting:
                        // Not on my queue...
                        fiber.suspend();
                        break;
                default:; // Ignore.
                }
        }
 
        void resume(Fiber& fiber) noexcept
        {
                if(fiber.state() != Fiber::Suspended)
                        return;
 
                release(fiber);
                fiber.resume();
                add(&fiber);
        }
 
        Timestamp const& runEnd() const noexcept
        {
                return m_end;
        }
 
        void run(TimeInterval const& duration = TimeInterval())
        {
                if(duration <= 0) {
                        zth_dbg(worker, "[%s] Run", id_str());
                        m_end = Timestamp::null();
                } else {
                        zth_dbg(worker, "[%s] Run for %s", id_str(), duration.str().c_str());
                        m_end = Timestamp::now() + duration;
                }
 
                while(!m_runnableQueue.empty()
                      && (runEnd().isNull() || Timestamp::now() < runEnd())) {
                        schedule();
                        zth_assert(!currentFiber());
                }
 
                sigchld_check();
                zth_dbg(worker, "[%s] Stopped", id_str());
        }
 
        typedef Load<> Load_type;
 
        Load_type& load() noexcept
        {
                return m_load;
        }
 
        Load_type const& load() const noexcept
        {
                return m_load;
        }
 
protected:
        static void dummyWorkerEntry(void*)
        {
                zth_abort("The worker fiber should not be executed.");
        }
 
        bool isInWorkerContext() const noexcept
        {
                return m_currentFiber == nullptr || m_currentFiber == &m_workerFiber;
        }
 
        void dbgStats() noexcept
        {
                if(!Config::SupportDebugPrint || !Config::Print_worker)
                        return;
 
                zth_dbg(list, "[%s] Run queue:", id_str());
                if(m_runnableQueue.empty())
                        zth_dbg(list, "[%s]   <empty>", id_str());
                else
                        for(decltype(m_runnableQueue.begin()) it = m_runnableQueue.begin();
                            it != m_runnableQueue.end(); ++it)
                                zth_dbg(list, "[%s]   %s", id_str(), it->str().c_str());
 
                zth_dbg(list, "[%s] Suspended queue:", id_str());
                if(m_suspendedQueue.empty())
                        zth_dbg(list, "[%s]   <empty>", id_str());
                else
                        for(decltype(m_suspendedQueue.begin()) it = m_suspendedQueue.begin();
                            it != m_suspendedQueue.end(); ++it)
                                zth_dbg(list, "[%s]   %s", id_str(), it->str().c_str());
        }
 
private:
        Fiber* m_currentFiber;
        List<Fiber> m_runnableQueue;
        List<Fiber> m_suspendedQueue;
        Fiber m_workerFiber;
        Waiter m_waiter;
        Timestamp m_end;
        int m_disableContextSwitch;
        Load_type m_load;
 
        friend void worker_global_init();
};
 
ZTH_EXPORT __attribute__((pure)) inline Worker& currentWorker() noexcept
{
        // Dereference is guarded by the safe_ptr.
        return *Worker::instance();
}
 
ZTH_EXPORT __attribute__((pure)) inline Fiber& currentFiber() noexcept
{
        Worker const& w = currentWorker();
        Fiber* f = w.currentFiber();
        zth_assert(f);
        // cppcheck-suppress nullPointerRedundantCheck
        return *f;
}
 
__attribute__((pure)) inline UniqueID<Fiber> const& currentFiberID() noexcept
{
        return currentFiber();
}
 
inline void getContext(Worker** worker, Fiber** fiber) noexcept
{
        Worker& current_worker = currentWorker();
        if(likely(worker))
                *worker = &current_worker;
 
        if(likely(fiber)) {
                Fiber* currentFiber_ = *fiber = current_worker.currentFiber();
                if(unlikely(!currentFiber_))
                        zth_abort("Not within fiber context");
        }
}
 
ZTH_EXPORT inline void
yield(Fiber* preferFiber = nullptr, bool alwaysYield = false,
      Timestamp const& now = Timestamp::now())
{
        Fiber const& f = currentFiber();
 
        perf_syscall("yield()", now);
        if(unlikely(!alwaysYield && !f.allowYield(now)))
                return;
 
        currentWorker().schedule(preferFiber, now);
}
 
ZTH_EXPORT inline void outOfWork()
{
        yield(nullptr, true);
}
 
inline void suspend()
{
        Worker* worker = nullptr;
        Fiber* f = nullptr;
        getContext(&worker, &f);
        worker->suspend(*f);
}
 
inline void resume(Fiber& fiber)
{
        Worker* worker = nullptr;
        getContext(&worker, nullptr);
        worker->resume(fiber);
}
 
int startWorkerThread(void (*f)(), size_t stack = 0, char const* name = nullptr);
int execlp(char const* file, char const* arg, ... /*, nullptr */);
int execvp(char const* file, char* const arg[]);
 
} // namespace zth
 
EXTERN_C ZTH_EXPORT ZTH_INLINE void zth_yield() noexcept
{
        zth::yield();
}
 
EXTERN_C ZTH_EXPORT ZTH_INLINE void zth_outOfWork() noexcept
{
        zth::outOfWork();
}
 
EXTERN_C ZTH_EXPORT ZTH_INLINE int zth_worker_create() noexcept
{
        if(!zth::Worker::instance())
                return EINVAL;
 
        try {
                new zth::Worker();
                return 0;
        } catch(std::bad_alloc const&) {
                return ENOMEM;
        } catch(...) {
        }
        return EAGAIN;
}
 
EXTERN_C ZTH_EXPORT ZTH_INLINE void zth_worker_run(struct timespec const* ts = nullptr) noexcept
{
        zth::Worker* w = zth::Worker::instance();
        if(unlikely(!w))
                return;
 
        w->run(ts ? zth::TimeInterval(ts->tv_sec, ts->tv_nsec) : zth::TimeInterval());
}
 
EXTERN_C ZTH_EXPORT ZTH_INLINE void zth_worker_destroy() noexcept
{
        zth::Worker* w = zth::Worker::instance();
        if(unlikely(!w))
                return;
        delete w;
}
 
EXTERN_C ZTH_EXPORT ZTH_INLINE int
zth_startWorkerThread(void (*f)(), size_t stack = 0, char const* name = nullptr) noexcept
{
        return zth::startWorkerThread(f, stack, name);
}
 
EXTERN_C ZTH_EXPORT ZTH_INLINE int zth_execvp(char const* file, char* const arg[]) noexcept
{
        return zth::execvp(file, arg);
}
 
#else // !__cplusplus
 
#       include <time.h>
 
ZTH_EXPORT void zth_yield();
ZTH_EXPORT void zth_outOfWork();
 
ZTH_EXPORT int zth_worker_create();
ZTH_EXPORT void zth_worker_run(struct timespec const* ts);
ZTH_EXPORT int zth_worker_destroy();
 
ZTH_EXPORT int zth_startWorkerThread(void (*f)(), size_t stack, char const* name);
ZTH_EXPORT int zth_execvp(char const* file, char* const arg[]);
 
#endif // __cplusplus
#endif // ZTH_WORKER_H