102 lines
3.8 KiB
C++
102 lines
3.8 KiB
C++
/// Fig. 17.7: SynchronizedBuffer.h
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// SynchronizedBuffer maintains synchronized access to a shared mutable
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// integer that is accessed by a producer thread and a consumer thread.
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#pragma once
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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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using namespace std::string_literals;
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class SynchronizedBuffer {
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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 (m_occupied) {
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std::cout << fmt::format(
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"Producer tries to write.\n{:<40}{}\t\t{}\n\n",
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"Buffer full. Producer waits.", m_buffer, m_occupied);
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// wait on condition variable m_cv; the lambda in the second
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// argument ensures that if the thread gets the processor
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// before m_occupied is false, the thread continues waiting
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m_cv.wait(dataLock, [&]() {return !m_occupied; });
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}
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// write to m_buffer
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m_buffer = value;
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m_occupied = true;
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std::cout << fmt::format("{:<40}{}\t\t{}\n\n",
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"Producer writes "s + std::to_string(value),
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m_buffer, m_occupied);
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} // dataLock's destructor releases the lock on m_mutex
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// if consumer is waiting, notify it that it can now read
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m_cv.notify_one();
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}
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// return value from m_buffer
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int get() {
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int value; // will store the value returned by get
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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 read from m_buffer
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std::unique_lock dataLock{m_mutex};
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if (!m_occupied) {
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std::cout << fmt::format(
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"Consumer tries to read.\n{:<40}{}\t\t{}\n\n",
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"Buffer empty. Consumer waits.", m_buffer, m_occupied);
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// wait on condition variable m_cv; the lambda in the second
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// argument ensures that if the thread gets the processor
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// before m_occupied is true, the thread continues waiting
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m_cv.wait(dataLock, [&]() {return m_occupied; });
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}
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value = m_buffer;
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m_occupied = false;
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std::cout << fmt::format("{:<40}{}\t\t{}\n{}\n",
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"Consumer reads "s + std::to_string(m_buffer),
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m_buffer, m_occupied, std::string(64, '-'));
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} // dataLock's destructor releases the lock on m_mutex
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// if producer is waiting, notify it that it can now write
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m_cv.notify_one();
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return value;
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}
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private:
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int m_buffer{-1}; // shared by producer and consumer threads
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bool m_occupied{false};
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std::condition_variable m_cv;
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std::mutex m_mutex;
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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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***********************************************************************/
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