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60 lines
1.8 KiB
C++
60 lines
1.8 KiB
C++
/*! \file
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* \brief Contains the class Ticketlock
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*/
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#pragma once
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#include "../arch/core.h"
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#include "../arch/cache.h"
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/*! \brief Using Ticketlocks, it is possible to serialize blocks of code
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* that might otherwise run in parallel on multiple CPU cores,
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* or be interleaved due to interrupts or scheduling.
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*
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* \ingroup sync
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*
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* Synchronization is implemented using a lock and a ticket variable.
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* Once a thread tries to enter the critical area, it obtains a ticket by
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* atomically incrementing the ticket variable and waiting until the lock
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* counter reaches this ticket, if it is not there already.
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* When a thread leaves the critical area, it increments the lock variable by
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* one and thereby allows the next thread to enter the critical area.
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*
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* If you want that things just work, choose __ATOMIC_SEQ_CST as memorder.
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* This is not the most efficient memory order but works reasonably well.
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*
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* <a
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* href="https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html">Atomic
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* Builtins in GCC manual</a>
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*/
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class Ticketlock {
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// Prevent copies and assignments
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Ticketlock(const Ticketlock& copy) = delete;
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Ticketlock& operator=(const Ticketlock&) = delete;
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private:
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volatile uint64_t ticket_current;
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volatile uint64_t ticket_count;
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public:
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/*! \brief Constructor
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*
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* \todo(12) Complete Constructor (for \MPStuBS)
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*/
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consteval Ticketlock() : ticket_current(0), ticket_count(0) {}
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/*! \brief Enters the critical area. In case the area is already locked,
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* \ref lock() will actively wait until the area can be entered.
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*
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* \see \ref Core::pause()
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* \todo(12) Implement Method (for \MPStuBS)
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*/
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void lock();
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/*! \brief Unblocks the critical area.
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*
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* \todo(12) Implement Method (for \MPStuBS)
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*/
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void unlock();
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};
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