84 lines
2.1 KiB
C++
84 lines
2.1 KiB
C++
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#include <iostream>
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#include <QSemaphore>
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#include <QThread>
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#include <QCoreApplication>
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/*
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* Barlas Chpt 3 Ex 12:
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Create three threads, each printing out the letters A, B, and C.
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The printing must adhere to these rules:
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• The total number of Bs and Cs that have been output at any
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point in the output string cannot exceed the total number
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of As that have been output at that point.
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• After a C has been output, another C cannot be output until
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one or more Bs have been output.
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Use semaphores to solve the problem.
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*/
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class Printer {
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private:
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QSemaphore &lockBC_;
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QSemaphore &lockC_;
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QString name_;
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public:
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explicit Printer(QSemaphore &lockBC, QSemaphore &lockC, QString name) : lockBC_(lockBC), lockC_(lockC),
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name_(name) {};
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void printA() {
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this->lockBC_.release(1);
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std::cout << name_.toStdString() << " A\n";
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}
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void printB() {
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if (this->lockBC_.tryAcquire(1, 10000)) {
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if (this->lockC_.available() == 0) {
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this->lockC_.release(1);
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}
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std::cout << name_.toStdString() << " B\n";
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}
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}
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void printC() {
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if (this->lockBC_.tryAcquire(1, 10000)) {
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if (this->lockC_.tryAcquire(1, 10000)) {
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std::cout << name_.toStdString() << " C\n";
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} else {
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this->lockBC_.release(1);
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}
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}
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}
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};
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class Worker : public QThread {
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private:
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Printer printer_;
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public:
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Worker(QSemaphore &lockBC, QSemaphore &lockC, QString tname) : printer_(lockBC, lockC, tname) {};
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protected:
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void run() {
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printer_.printA();
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printer_.printB();
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printer_.printC();
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}
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};
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int main(int argc, char *argv[]) {
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QCoreApplication app(argc, argv);
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QSemaphore lockC(1);
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QSemaphore lockBC(0);
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int N = 3;
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Worker *workers[N];
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for (int i = 0; i < N; i++) {
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workers[i] = new Worker(lockBC, lockC, QString("Thread %1").arg(i));
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workers[i]->start();
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}
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return app.exec();
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}
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