C++中的生产者-消费者

Question

这是我第一次尝试生产者-消费者问题(以及一般的线程操作)，所以任何关于禁忌和修复的反馈都是非常感谢的！

#include <condition_variable>
std::condition_variable cv;

#include <iostream>
#include <random>

#include <mutex>
std::mutex mtx;

#include <thread>

// standard in all of my programs
void panic(const std::string &msg) {
    throw std::runtime_error("Error: " + msg + "\n");
}

int count = 0, buff_size = 0;
char* buff;

int random_int(int lower_bound) {
    std::random_device seed;
    std::mt19937 generator(seed());
    std::uniform_int_distribution<int> dist(lower_bound, std::nextafter(26, DBL_MAX));

    return dist(generator);
}

char random_char(int lower_bound) {
    return 'A' + (random_int(lower_bound) % 26);
}

/* Consumer

Reads characters from the buffer and prints them.

*/
void consume(int job) {
    std::unique_lock<std::mutex> lck(mtx);

    while (count == 0) {
        cv.wait(lck);
    }

    /*
    job + 1 = Running
    job = Ready
    */
    for (int i = 0; i < buff_size; i++) {
        std::cout << buff[i] << std::endl;
    }

    count--;
}

/* Producer

Randomly generates letters at (pos > buff_size & pos <= 26),
inserts them at the next available position in the buffer,
and then prints out the lowercase form of the inputted letter.

*/
void produce(int job) {
    std::unique_lock<std::mutex> lck(mtx);

    for (int i = 0; i < buff_size; i++) {
        buff[i] = random_char(buff_size);
        std::cout << static_cast<char>(tolower(buff[i])) << std::endl;
    }

    count++;
    cv.notify_one();
}

int main() {
    int buf_size = 0;

    std::cout << "The Producer-Consumer Problem (in C++11!)" << std::endl << "Enter the buffer size: ";
    std::cin >> buf_size;

    if (buf_size > 0 && buf_size <= 26) {
        // set the buffer size
        buff_size = buf_size;
        buff = new char[buff_size];
    }
    else {
        // rage quit
        panic("The range must be > 0 and <= 26.");
    }

    std::thread production[10], processed[10];

    /* Initialize the arrays */
    for (int order = 0; order < buff_size; order++) {
        production[order] = std::thread(produce, order);
        processed[order] = std::thread(consume, order);
    }

    /* Join the threads to the main threads */
    for (int order = 0; order < buff_size; order++) {
        processed[order].join();
        production[order].join();
    }
}

Answer 1

我从@Mat的答案中修改的代码：

#include <condition_variable>
#include <iostream>
#include <random>
#include <mutex>
#include <thread>
#include <vector>

// global variables
std::condition_variable cv;
std::mutex mtx;
std::vector<char> data;

int count = 0, buff_size = 0;

char random_char() {
    thread_local std::random_device seed;
    thread_local std::mt19937 generator(seed());
    thread_local std::uniform_int_distribution<int> dist('A', 'Z');

    return static_cast<char>(dist(generator));
}

/* Consumer

Prints out the contents of the shared buffer.

*/
void consume() {
    std::unique_lock<std::mutex> lck(mtx);

    while (count == 0) {
        cv.wait(lck);
    }

    for (const auto& it : data) {
        std::cout << it << std::endl;
    }

    count--;
}

/* Producer

Randomly generates capital letters in the range of A to Z,
prints out those letters in lowercase, and then
inserts them into the shared buffer.

*/
void produce() {
    std::unique_lock<std::mutex> lck(mtx);

    char c = random_char();
    std::cout << " " << static_cast<char>(tolower(c)) << std::endl;
    data.push_back(c);

    count++;
    cv.notify_one();
}

int main() {
    std::cout << "The Producer-Consumer Problem (in C++11!)" << std::endl << "Enter the buffer size: ";
    std::cin >> buff_size;

    // keep the buffer in-range of the alphabet
    if (buff_size < 0) {
        buff_size = 0;
    }
    else if (buff_size > 26) {
        buff_size = 26;
    }

    std::thread production[26], processed[26];

    // initialize the arrays
    for (int order = 0; order < buff_size; order++) {
        production[order] = std::thread(produce);
        processed[order] = std::thread(consume);
    }

    // join the threads to the main threads
    for (int order = 0; order < buff_size; order++) {
        processed[order].join();
        production[order].join();
    }

    std::cout << "Succeeded with a shared buffer of " << data.size() << " letters!";
}