54 lines
1.3 KiB
C++
54 lines
1.3 KiB
C++
#pragma once
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#include "../object/queue.h"
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#include "../types.h"
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/*! \file
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* \brief \ref Semaphore for synchronization of threads.
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*/
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/*!
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* \defgroup ipc Inter-Process Communication
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* \brief Communication between threads
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*/
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// Forward declarations to break cyclic includes
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struct Vault;
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class Thread;
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/*! \brief Semaphore used for synchronization of threads.
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* \ingroup ipc
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*
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* The class Semaphore implements the concept of counting semaphores.
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* Waiting threads are parked inside a \ref Queue.
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*/
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class Semaphore {
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// Prevent copies and assignments
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Semaphore(const Semaphore&) = delete;
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Semaphore& operator=(const Semaphore&) = delete;
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Queue<Thread> waiting;
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public:
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/*! \brief Constructor; initialized the counter with provided value `c`
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* \param c Initial counter value
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*/
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explicit Semaphore(unsigned c = 0) : counter(c) {}
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unsigned counter;
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bool used;
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/*! \brief Wait for access to the critical area.
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*
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* Enter/decrement/wait operation: If the counter is greater than 0, then
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* it is decremented by one. Otherwise the calling thread will be enqueued
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* to wait until it can do that.
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*
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*/
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void p(Vault& vault);
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/*! \brief Leave the critical area.
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*
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* Leave/increment operation: If there are threads waiting, wake the
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* first one; otherwise increment the counter by one.
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*
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*/
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void v(Vault& vault);
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};
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