C++11 多執行緒下生產者消費者模型詳解
前面八章介紹了 C++11 併發程式設計的基礎(抱歉哈,第五章-第八章還在草稿中),本文將綜合運用 C++11 中的新的基礎設施(主要是多執行緒、鎖、條件變數)來闡述一個經典問題——生產者消費者模型,並給出完整的解決方案。
生產者消費者問題是多執行緒併發中一個非常經典的問題,相信學過作業系統課程的同學都清楚這個問題的根源。本文將就四種情況分析並介紹生產者和消費者問題,它們分別是:單生產者-單消費者模型,單生產者-多消費者模型,多生產者-單消費者模型,多生產者-多消費者模型,我會給出四種情況下的 C++11 併發解決方案,如果文中出現了錯誤或者你對程式碼有異議,歡迎交流 ;-)。
單生產者-單消費者模型
顧名思義,單生產者-單消費者模型中只有一個生產者和一個消費者,生產者不停地往產品庫中放入產品,消費者則從產品庫中取走產品,產品庫容積有限制,只能容納一定數目的產品,如果生產者生產產品的速度過快,則需要等待消費者取走產品之後,產品庫不為空才能繼續往產品庫中放置新的產品,相反,如果消費者取走產品的速度過快,則可能面臨產品庫中沒有產品可使用的情況,此時需要等待生產者放入一個產品後,消費者才能繼續工作。C++11實現單生產者單消費者模型的程式碼如下:
#include <unistd.h>
#include <cstdlib>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <thread>
static const int kItemRepositorySize = 10; // Item buffer size.
static const int kItemsToProduce = 1000; // How many items we plan to produce.
struct ItemRepository {
int item_buffer[kItemRepositorySize]; // 產品緩衝區, 配合 read_position 和 write_position 模型環形佇列.
size_t read_position; // 消費者讀取產品位置.
size_t write_position; // 生產者寫入產品位置.
std::mutex mtx; // 互斥量,保護產品緩衝區
std::condition_variable repo_not_full; // 條件變數, 指示產品緩衝區不為滿.
std::condition_variable repo_not_empty; // 條件變數, 指示產品緩衝區不為空.
} gItemRepository; // 產品庫全域性變數, 生產者和消費者操作該變數.
typedef struct ItemRepository ItemRepository;
void ProduceItem(ItemRepository *ir, int item)
{
std::unique_lock<std::mutex> lock(ir->mtx);
while(((ir->write_position + 1) % kItemRepositorySize)
== ir->read_position) { // item buffer is full, just wait here.
std::cout << "Producer is waiting for an empty slot...\n";
(ir->repo_not_full).wait(lock); // 生產者等待"產品庫緩衝區不為滿"這一條件發生.
}
(ir->item_buffer)[ir->write_position] = item; // 寫入產品.
(ir->write_position)++; // 寫入位置後移.
if (ir->write_position == kItemRepositorySize) // 寫入位置若是在佇列最後則重新設定為初始位置.
ir->write_position = 0;
(ir->repo_not_empty).notify_all(); // 通知消費者產品庫不為空.
lock.unlock(); // 解鎖.
}
int ConsumeItem(ItemRepository *ir)
{
int data;
std::unique_lock<std::mutex> lock(ir->mtx);
// item buffer is empty, just wait here.
while(ir->write_position == ir->read_position) {
std::cout << "Consumer is waiting for items...\n";
(ir->repo_not_empty).wait(lock); // 消費者等待"產品庫緩衝區不為空"這一條件發生.
}
data = (ir->item_buffer)[ir->read_position]; // 讀取某一產品
(ir->read_position)++; // 讀取位置後移
if (ir->read_position >= kItemRepositorySize) // 讀取位置若移到最後,則重新置位.
ir->read_position = 0;
(ir->repo_not_full).notify_all(); // 通知消費者產品庫不為滿.
lock.unlock(); // 解鎖.
return data; // 返回產品.
}
void ProducerTask() // 生產者任務
{
for (int i = 1; i <= kItemsToProduce; ++i) {
// sleep(1);
std::cout << "Produce the " << i << "^th item..." << std::endl;
ProduceItem(&gItemRepository, i); // 迴圈生產 kItemsToProduce 個產品.
}
}
void ConsumerTask() // 消費者任務
{
static int cnt = 0;
while(1) {
sleep(1);
int item = ConsumeItem(&gItemRepository); // 消費一個產品.
std::cout << "Consume the " << item << "^th item" << std::endl;
if (++cnt == kItemsToProduce) break; // 如果產品消費個數為 kItemsToProduce, 則退出.
}
}
void InitItemRepository(ItemRepository *ir)
{
ir->write_position = 0; // 初始化產品寫入位置.
ir->read_position = 0; // 初始化產品讀取位置.
}
int main()
{
InitItemRepository(&gItemRepository);
std::thread producer(ProducerTask); // 建立生產者執行緒.
std::thread consumer(ConsumerTask); // 建立消費之執行緒.
producer.join();
consumer.join();
}
單生產者-多消費者模型
與單生產者和單消費者模型不同的是,單生產者-多消費者模型中可以允許多個消費者同時從產品庫中取走產品。所以除了保護產品庫在多個讀寫執行緒下互斥之外,還需要維護消費者取走產品的計數器,程式碼如下:
#include <unistd.h>
#include <cstdlib>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <thread>
static const int kItemRepositorySize = 4; // Item buffer size.
static const int kItemsToProduce = 10; // How many items we plan to produce.
struct ItemRepository {
int item_buffer[kItemRepositorySize];
size_t read_position;
size_t write_position;
size_t item_counter;
std::mutex mtx;
std::mutex item_counter_mtx;
std::condition_variable repo_not_full;
std::condition_variable repo_not_empty;
} gItemRepository;
typedef struct ItemRepository ItemRepository;
void ProduceItem(ItemRepository *ir, int item)
{
std::unique_lock<std::mutex> lock(ir->mtx);
while(((ir->write_position + 1) % kItemRepositorySize)
== ir->read_position) { // item buffer is full, just wait here.
std::cout << "Producer is waiting for an empty slot...\n";
(ir->repo_not_full).wait(lock);
}
(ir->item_buffer)[ir->write_position] = item;
(ir->write_position)++;
if (ir->write_position == kItemRepositorySize)
ir->write_position = 0;
(ir->repo_not_empty).notify_all();
lock.unlock();
}
int ConsumeItem(ItemRepository *ir)
{
int data;
std::unique_lock<std::mutex> lock(ir->mtx);
// item buffer is empty, just wait here.
while(ir->write_position == ir->read_position) {
std::cout << "Consumer is waiting for items...\n";
(ir->repo_not_empty).wait(lock);
}
data = (ir->item_buffer)[ir->read_position];
(ir->read_position)++;
if (ir->read_position >= kItemRepositorySize)
ir->read_position = 0;
(ir->repo_not_full).notify_all();
lock.unlock();
return data;
}
void ProducerTask()
{
for (int i = 1; i <= kItemsToProduce; ++i) {
// sleep(1);
std::cout << "Producer thread " << std::this_thread::get_id()
<< " producing the " << i << "^th item..." << std::endl;
ProduceItem(&gItemRepository, i);
}
std::cout << "Producer thread " << std::this_thread::get_id()
<< " is exiting..." << std::endl;
}
void ConsumerTask()
{
bool ready_to_exit = false;
while(1) {
sleep(1);
std::unique_lock<std::mutex> lock(gItemRepository.item_counter_mtx);
if (gItemRepository.item_counter < kItemsToProduce) {
int item = ConsumeItem(&gItemRepository);
++(gItemRepository.item_counter);
std::cout << "Consumer thread " << std::this_thread::get_id()
<< " is consuming the " << item << "^th item" << std::endl;
} else ready_to_exit = true;
lock.unlock();
if (ready_to_exit == true) break;
}
std::cout << "Consumer thread " << std::this_thread::get_id()
<< " is exiting..." << std::endl;
}
void InitItemRepository(ItemRepository *ir)
{
ir->write_position = 0;
ir->read_position = 0;
ir->item_counter = 0;
}
int main()
{
InitItemRepository(&gItemRepository);
std::thread producer(ProducerTask);
std::thread consumer1(ConsumerTask);
std::thread consumer2(ConsumerTask);
std::thread consumer3(ConsumerTask);
std::thread consumer4(ConsumerTask);
producer.join();
consumer1.join();
consumer2.join();
consumer3.join();
consumer4.join();
}
多生產者-單消費者模型
與單生產者和單消費者模型不同的是,多生產者-單消費者模型中可以允許多個生產者同時向產品庫中放入產品。所以除了保護產品庫在多個讀寫執行緒下互斥之外,還需要維護生產者放入產品的計數器,程式碼如下:
#include <unistd.h>
#include <cstdlib>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <thread>
static const int kItemRepositorySize = 4; // Item buffer size.
static const int kItemsToProduce = 10; // How many items we plan to produce.
struct ItemRepository {
int item_buffer[kItemRepositorySize];
size_t read_position;
size_t write_position;
size_t item_counter;
std::mutex mtx;
std::mutex item_counter_mtx;
std::condition_variable repo_not_full;
std::condition_variable repo_not_empty;
} gItemRepository;
typedef struct ItemRepository ItemRepository;
void ProduceItem(ItemRepository *ir, int item)
{
std::unique_lock<std::mutex> lock(ir->mtx);
while(((ir->write_position + 1) % kItemRepositorySize)
== ir->read_position) { // item buffer is full, just wait here.
std::cout << "Producer is waiting for an empty slot...\n";
(ir->repo_not_full).wait(lock);
}
(ir->item_buffer)[ir->write_position] = item;
(ir->write_position)++;
if (ir->write_position == kItemRepositorySize)
ir->write_position = 0;
(ir->repo_not_empty).notify_all();
lock.unlock();
}
int ConsumeItem(ItemRepository *ir)
{
int data;
std::unique_lock<std::mutex> lock(ir->mtx);
// item buffer is empty, just wait here.
while(ir->write_position == ir->read_position) {
std::cout << "Consumer is waiting for items...\n";
(ir->repo_not_empty).wait(lock);
}
data = (ir->item_buffer)[ir->read_position];
(ir->read_position)++;
if (ir->read_position >= kItemRepositorySize)
ir->read_position = 0;
(ir->repo_not_full).notify_all();
lock.unlock();
return data;
}
void ProducerTask()
{
bool ready_to_exit = false;
while(1) {
sleep(1);
std::unique_lock<std::mutex> lock(gItemRepository.item_counter_mtx);
if (gItemRepository.item_counter < kItemsToProduce) {
++(gItemRepository.item_counter);
ProduceItem(&gItemRepository, gItemRepository.item_counter);
std::cout << "Producer thread " << std::this_thread::get_id()
<< " is producing the " << gItemRepository.item_counter
<< "^th item" << std::endl;
} else ready_to_exit = true;
lock.unlock();
if (ready_to_exit == true) break;
}
std::cout << "Producer thread " << std::this_thread::get_id()
<< " is exiting..." << std::endl;
}
void ConsumerTask()
{
static int item_consumed = 0;
while(1) {
sleep(1);
++item_consumed;
if (item_consumed <= kItemsToProduce) {
int item = ConsumeItem(&gItemRepository);
std::cout << "Consumer thread " << std::this_thread::get_id()
<< " is consuming the " << item << "^th item" << std::endl;
} else break;
}
std::cout << "Consumer thread " << std::this_thread::get_id()
<< " is exiting..." << std::endl;
}
void InitItemRepository(ItemRepository *ir)
{
ir->write_position = 0;
ir->read_position = 0;
ir->item_counter = 0;
}
int main()
{
InitItemRepository(&gItemRepository);
std::thread producer1(ProducerTask);
std::thread producer2(ProducerTask);
std::thread producer3(ProducerTask);
std::thread producer4(ProducerTask);
std::thread consumer(ConsumerTask);
producer1.join();
producer2.join();
producer3.join();
producer4.join();
consumer.join();
}
多生產者-多消費者模型
該模型可以說是前面兩種模型的綜合,程式需要維護兩個計數器,分別是生產者已生產產品的數目和消費者已取走產品的數目。另外也需要保護產品庫在多個生產者和多個消費者互斥地訪問。
程式碼如下:
#include <unistd.h>
#include <cstdlib>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <thread>
static const int kItemRepositorySize = 4; // Item buffer size.
static const int kItemsToProduce = 10; // How many items we plan to produce.
struct ItemRepository {
int item_buffer[kItemRepositorySize];
size_t read_position;
size_t write_position;
size_t produced_item_counter;
size_t consumed_item_counter;
std::mutex mtx;
std::mutex produced_item_counter_mtx;
std::mutex consumed_item_counter_mtx;
std::condition_variable repo_not_full;
std::condition_variable repo_not_empty;
} gItemRepository;
typedef struct ItemRepository ItemRepository;
void ProduceItem(ItemRepository *ir, int item)
{
std::unique_lock<std::mutex> lock(ir->mtx);
while(((ir->write_position + 1) % kItemRepositorySize)
== ir->read_position) { // item buffer is full, just wait here.
std::cout << "Producer is waiting for an empty slot...\n";
(ir->repo_not_full).wait(lock);
}
(ir->item_buffer)[ir->write_position] = item;
(ir->write_position)++;
if (ir->write_position == kItemRepositorySize)
ir->write_position = 0;
(ir->repo_not_empty).notify_all();
lock.unlock();
}
int ConsumeItem(ItemRepository *ir)
{
int data;
std::unique_lock<std::mutex> lock(ir->mtx);
// item buffer is empty, just wait here.
while(ir->write_position == ir->read_position) {
std::cout << "Consumer is waiting for items...\n";
(ir->repo_not_empty).wait(lock);
}
data = (ir->item_buffer)[ir->read_position];
(ir->read_position)++;
if (ir->read_position >= kItemRepositorySize)
ir->read_position = 0;
(ir->repo_not_full).notify_all();
lock.unlock();
return data;
}
void ProducerTask()
{
bool ready_to_exit = false;
while(1) {
sleep(1);
std::unique_lock<std::mutex> lock(gItemRepository.produced_item_counter_mtx);
if (gItemRepository.produced_item_counter < kItemsToProduce) {
++(gItemRepository.produced_item_counter);
ProduceItem(&gItemRepository, gItemRepository.produced_item_counter);
std::cout << "Producer thread " << std::this_thread::get_id()
<< " is producing the " << gItemRepository.produced_item_counter
<< "^th item" << std::endl;
} else ready_to_exit = true;
lock.unlock();
if (ready_to_exit == true) break;
}
std::cout << "Producer thread " << std::this_thread::get_id()
<< " is exiting..." << std::endl;
}
void ConsumerTask()
{
bool ready_to_exit = false;
while(1) {
sleep(1);
std::unique_lock<std::mutex> lock(gItemRepository.consumed_item_counter_mtx);
if (gItemRepository.consumed_item_counter < kItemsToProduce) {
int item = ConsumeItem(&gItemRepository);
++(gItemRepository.consumed_item_counter);
std::cout << "Consumer thread " << std::this_thread::get_id()
<< " is consuming the " << item << "^th item" << std::endl;
} else ready_to_exit = true;
lock.unlock();
if (ready_to_exit == true) break;
}
std::cout << "Consumer thread " << std::this_thread::get_id()
<< " is exiting..." << std::endl;
}
void InitItemRepository(ItemRepository *ir)
{
ir->write_position = 0;
ir->read_position = 0;
ir->produced_item_counter = 0;
ir->consumed_item_counter = 0;
}
int main()
{
InitItemRepository(&gItemRepository);
std::thread producer1(ProducerTask);
std::thread producer2(ProducerTask);
std::thread producer3(ProducerTask);
std::thread producer4(ProducerTask);
std::thread consumer1(ConsumerTask);
std::thread consumer2(ConsumerTask);
std::thread consumer3(ConsumerTask);
std::thread consumer4(ConsumerTask);
producer1.join();
producer2.join();
producer3.join();
producer4.join();
consumer1.join();
consumer2.join();
consumer3.join();
consumer4.join();
}