library/cpp/messagebus/actor/tasks.h


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#pragma once

#include <util/system/atomic.h>
#include <util/system/yassert.h>

namespace NActor {
    class TTasks { 
        enum { 
            // order of values is important 
            E_WAITING, 
            E_RUNNING_NO_TASKS, 
            E_RUNNING_GOT_TASKS, 
        }; 

    private: 
        TAtomic State; 

    public: 
        TTasks() 
            : State(E_WAITING) 
        { 
        }

        // @return true iff caller have to either schedule task or execute it 
        bool AddTask() { 
            // High contention case optimization: AtomicGet is cheaper than AtomicSwap. 
            if (E_RUNNING_GOT_TASKS == AtomicGet(State)) { 
                return false; 
            } 

            TAtomicBase oldState = AtomicSwap(&State, E_RUNNING_GOT_TASKS); 
            return oldState == E_WAITING; 
        }

        // called by executor 
        // @return true iff we have to recheck queues 
        bool FetchTask() { 
            TAtomicBase newState = AtomicDecrement(State); 
            if (newState == E_RUNNING_NO_TASKS) { 
                return true; 
            } else if (newState == E_WAITING) { 
                return false; 
            } 
            Y_FAIL("unknown"); 
        } 
    }; 

}