library/cpp/actors/util/ticket_lock.h


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#pragma once 
 
#include "intrinsics.h" 
#include <util/system/guard.h> 
#include <util/system/yassert.h> 
 
class TTicketLock : TNonCopyable { 
    ui32 TicketIn; 
    ui32 TicketOut; 
 
public: 
    TTicketLock() 
        : TicketIn(0) 
        , TicketOut(0) 
    { 
    } 
 
    void Release() noexcept {
        AtomicUi32Increment(&TicketOut); 
    } 
 
    ui32 Acquire() noexcept {
        ui32 revolves = 0; 
        const ui32 ticket = AtomicUi32Increment(&TicketIn) - 1; 
        while (ticket != AtomicLoad(&TicketOut)) { 
            Y_VERIFY_DEBUG(ticket >= AtomicLoad(&TicketOut));
            SpinLockPause(); 
            ++revolves; 
        } 
        return revolves; 
    } 
 
    bool TryAcquire() noexcept {
        const ui32 x = AtomicLoad(&TicketOut); 
        if (x == AtomicLoad(&TicketIn) && AtomicUi32Cas(&TicketIn, x + 1, x)) 
            return true; 
        else 
            return false; 
    } 
 
    bool IsLocked() noexcept {
        const ui32 ticketIn = AtomicLoad(&TicketIn); 
        const ui32 ticketOut = AtomicLoad(&TicketOut); 
        return (ticketIn != ticketOut); 
    } 
 
    typedef ::TGuard<TTicketLock> TGuard; 
};