126 lines
4.8 KiB
C++
126 lines
4.8 KiB
C++
// Fig. 17.9: CircularBuffer.h
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// Synchronizing access to a shared three-element circular buffer.
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#pragma once
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#include <array>
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#include <condition_variable>
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#include <fmt/format.h>
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#include <mutex>
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#include <iostream>
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#include <string>
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#include <string_view>
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using namespace std::string_literals;
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class CircularBuffer {
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public:
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// place value into m_buffer
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void put(int value) {
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// critical section that requires a lock to modify shared data
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{
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// lock on m_mutex to be able to write to m_buffer
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std::unique_lock dataLock{m_mutex};
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// if no empty locations, wait on condition variable m_cv
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if (m_occupiedCells == m_buffer.size()) {
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std::cout << "Buffer is full. Producer waits.\n\n";
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// wait on the condition variable; the lambda argument
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// ensures that if the thread gets the processor before
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// the m_buffer has open cells, the thread continues waiting
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m_cv.wait(dataLock,
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[&] {return m_occupiedCells < m_buffer.size(); });
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}
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m_buffer[m_writeIndex] = value; // write to m_buffer
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++m_occupiedCells; // one more m_buffer cell is occupied
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m_writeIndex = (m_writeIndex + 1) % m_buffer.size();
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displayState(fmt::format("Producer writes {}", value));
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} // dataLock's destructor releases the lock on m_mutex here
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m_cv.notify_one(); // notify threads waiting to read from m_buffer
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}
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// return value from m_buffer
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int get() {
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int readValue; // will temporarily hold the next value read
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// critical section that requires a lock to modify shared data
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{
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// lock on m_mutex to be able to write to m_buffer
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std::unique_lock dataLock{m_mutex};
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// if no data to read, place thread in waiting state
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if (m_occupiedCells == 0) {
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std::cout << "Buffer is empty. Consumer waits.\n\n";
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// wait on the condition variable; the lambda argument
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// ensures that if the thread gets the processor before
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// there is data in the m_buffer, the thread continues waiting
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m_cv.wait(dataLock, [&]() {return m_occupiedCells > 0; });
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}
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readValue = m_buffer[m_readIndex]; // read value from m_buffer
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m_readIndex = (m_readIndex + 1) % m_buffer.size();
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--m_occupiedCells; // one fewer m_buffer cells is occupied
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displayState(fmt::format("Consumer reads {}", readValue));
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} // dataLock's destructor releases the lock on m_mutex here
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m_cv.notify_one(); // notify threads waiting to write to m_buffer
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return readValue;
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}
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// display current operation and m_buffer state
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void displayState(std::string_view operation) const {
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std::string s;
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// add operation argument and number of occupied m_buffer cells
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s += fmt::format("{} (buffer cells occupied: {})\n{:<15}",
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operation, m_occupiedCells, "buffer cells:");
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// add values in m_buffer
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for (int value : m_buffer) {
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s += fmt::format(" {:2d} ", value);
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}
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s += fmt::format("\n{:<15}", ""); // padding
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// add underlines
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for (int i{0}; i < m_buffer.size(); ++i) {
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s += "---- "s;
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}
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s += fmt::format("\n{:<15}", ""); // padding
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for (int i{0}; i < m_buffer.size(); ++i) {
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s += fmt::format(" {}{} ",
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(i == m_writeIndex ? 'W' : ' '),
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(i == m_readIndex ? 'R' : ' '));
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}
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s += "\n\n";
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std::cout << s; // display the state string
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}
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private:
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std::condition_variable m_cv;
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std::mutex m_mutex;
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std::array<int, 3> m_buffer{-1, -1, -1}; // shared m_buffer
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int m_occupiedCells{0}; // count number of buffers used
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int m_writeIndex{0}; // index of next element to write to
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int m_readIndex{0}; // index of next element to read
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};
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/************************************************************************
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* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The *
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* authors and publisher shall not be liable in any event for *
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* incidental or consequential damages in connection with, or arising *
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* out of, the furnishing, performance, or use of these programs. *
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***********************************************************************/ |