我正在处理Producer Consumer（多线程）问题，我遇到了死锁。我的问题是如何？
我有多个生产者创建n个产品，并将它们放在全局队列中。如果队列中没有空间，则生产者必须等待。
我的消费者正在使用First Come First Serve访问队列。如果队列中没有任何内容，则消费者必须等待。消费者将使用产品的PART，并且只有在完全消耗产品时才会从队列中删除产品。当没有更多的产品需要消费时，消费者将停止消费。
当第一个项目被消耗时，我得到了死锁。我正在使用互斥锁来锁定队列，2个条件变量用于在项目被添加或移除到队列时发出信号，以及信号量用于跟踪正在消耗的项目。
知道为什么它可能会陷入僵局吗？
输入：2（生产者）3（消费者）5（生产项目）2（队列大小）0（N / A）50（量子）1（种子）
制片：
#include <pthread.h>
#include <semaphore.h>
#include "producerConsumer.h"
#include <iostream>
#include <sys/time.h>
void* producer(void* args)
{
tProducer producer = *((tProducer*) args);
tProduct products[producer.products];
unsigned int queueMax = producer.queueMax;
timeval time;
std::string output;
for(int i = 0; i < producer.products; i++)
{
//Create item
products[i].productId = i;
products[i].life = producer.lifeOfProduct;
gettimeofday(&time, NULL);
products[i].timestamp = time.tv_sec;
//Lock and add to queue
pthread_mutex_lock(&queueLock);
//Queue is full and must wait
if(queue.size() >= queueMax)
{
output = "Producer: " + std::to_string(producer.id) + " is waiting\n";
std::cout << output;
pthread_cond_wait(&removeSignal, &queueLock);
}
//Debug message
output = "Producer: " + std::to_string(producer.id) + " is producing.\n";
std::cout << output;
//Add item to queue and signal
queue.push(products[i]);
pthread_cond_signal(&addSignal);
pthread_mutex_unlock(&queueLock);
//pthread_cond_signal(&addSignal);
//Debug message
output = "Producer: " + std::to_string(producer.id) + " just produced.\n";
std::cout << output;
}
pthread_exit(NULL);
}
消费者：
#include <pthread.h>
#include <semaphore.h>
#include "producerConsumer.h"
#include <iostream>
void* consumer(void* args)
{
tConsumer consumer = *((tConsumer*) args);
int id = consumer.id;
int quantum = consumer.quantum;
std::string output;
while(true)
{
//Exit when nothing else is being created
if(sem_trywait(&totalProductsLeft) < 0)
{
break;
}
//Subtract life from product, and remove from queue if done
pthread_mutex_lock(&queueLock);
//Wait until item is in queue
if(queue.size() <= 0)
{
//Debug message
output = "Consumer: " + std::to_string(id) + " is waiting.\n";
std::cout << output;
pthread_cond_wait(&addSignal, &queueLock);
}
//Debug message
output = "Consumer: " + std::to_string(id) + " is ready.\n";
std::cout << output;
tProduct& product = queue.front();
product.life -= quantum;
//Item is done being consumed
if(product.life <= 0)
{
//Debug message
output = "Product: " + std::to_string(product.productId) + " is dead.\n";
std::cout << output;
//Remove a spot
queue.pop();
pthread_cond_signal(&removeSignal);
sem_wait(&totalProductsLeft);
}
else
{
//Debug message
output = "Product: " + std::to_string(product.life) + "hp is not done.\n";
std::cout << output;
}
pthread_mutex_unlock(&queueLock);
}
//May need to broadcast
pthread_exit(NULL);
}
Main（只是为了展示我如何初始化所有内容）：
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <pthread.h>
#include <semaphore.h>
#include "producerConsumer.h"
std::queue<tProduct> queue;
pthread_cond_t addSignal;
pthread_cond_t removeSignal;
sem_t totalProductsLeft;
pthread_mutex_t queueLock;
int main(int argc, char** argv)
{
//Handle input
const int NUM_INPUTS = 8;
int numberProducers;
int numberConsumers;
int numberOfProducts;
int queueSize;
int scheduleType;
int quantum;
int seed;
//Error check for input
if(argc != NUM_INPUTS)
{
std::cout << "Invalid number of arguments.\n";
return -1;
}
//Grab arguments
numberProducers = atoi(argv[1]);
numberConsumers = atoi(argv[2]);
numberOfProducts = atoi(argv[3]);
queueSize = atoi(argv[4]);
scheduleType = atoi(argv[5]);
quantum = atoi(argv[6]);
seed = atoi(argv[7]);
//Get rid of warnings for now
std::cout << numberOfProducts << std::endl;
std::cout << queueSize << std::endl;
std::cout << quantum << std::endl;
std::cout << seed << std::endl;
std::cout << scheduleType << std::endl;
//Create threads
pthread_t producerThreads[numberProducers];
pthread_t consumerThreads[numberConsumers];
tProducer producerArgs[numberProducers];
tConsumer consumerArgs[numberConsumers];
//Initialize global
pthread_mutex_init(&queueLock, NULL);
pthread_cond_init(&addSignal, NULL);
pthread_cond_init(&removeSignal, NULL);
std::cout << "Total Items: " << (numberProducers * numberOfProducts) << std::endl;
sem_init(&totalProductsLeft, 0, numberProducers * numberOfProducts);
//Start threads
srand(seed);
for(int i = 0; i < numberProducers; i++)
{
producerArgs[i].id = i;
producerArgs[i].products = numberOfProducts;
producerArgs[i].lifeOfProduct = rand() % 1024;
producerArgs[i].queueMax = queueSize;
pthread_create(&(producerThreads[i]), 0, producer, &producerArgs[i]);
}
for(int i = 0; i < numberConsumers; i++)
{
consumerArgs[i].id = i;
consumerArgs[i].quantum = quantum;
pthread_create(&(consumerThreads[i]), 0, consumer, &consumerArgs[i]);
}
//Wait for threads to end
for(int i = 0; i < numberProducers; i++)
{
pthread_join(producerThreads[i], NULL);
}
for(int i = 0; i < numberConsumers; i++)
{
pthread_join(consumerThreads[i], NULL);
}
return 0;
}
答案 0 :(得分：1)
我最终搞清楚了。在我的消费者中，sem_trywait在没有消耗物品时递减。然后我的消费者中的sem_wait被阻止，因为没有剩下的项目。