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");
        }
    };
 
}