是"deadlock"吗？如何在多线程中避免它？

我目前正在学习C++ 11的并发性。 我为课程作业写了一段代码。但是，代码不会完成运行。

我的环境：

系统： 视窗 10

编译器：mingw-w64x86_64-8.1.0-posix-she-rt_v6-rev0

更新：

我认为"加入"可以结束一个线程。感谢那些评论这个问题的好人，我明白"加入"不会"杀死"线程。它是线程执行完成后返回的函数。此外，我的代码中的问题可能是关于死锁。我已经尝试了一些方法来解决这个问题。但是，它都不起作用。

我尝试过的： 添加

if(ConsumerPtr->isConsumerDead()){
break;
}

在void Producer::prods();函数中。那行不通。 后来我又编辑了一些。我添加了一个新的全局变量来检查使用者是否已停止工作。另外，我还添加了更多if语句来检查void Buffer::put();周围的消费者。在那之后，我发现代码很少起作用，但在大多数时候都失败了。我试图编辑std::this_thread::sleep_for(std::chrono::milliseconds(60));单次消费/生产操作后的睡眠时间代码。我已经将 10 毫秒扩大到 60 毫秒。然后，代码工作得更好。现在，它很少失败。

我认为代码没有完成，因为运行过程中存在死锁。我发现了一个可能在 Wiki 上造成死锁的原因：当一个进程或线程进入等待状态时会发生死锁，因为请求的系统资源由另一个等待进程持有，而另一个等待进程又在等待另一个等待进程持有的另一个资源。如果一个进程由于请求的资源正被另一个等待进程使用而无法无限期地更改其状态，则称系统处于死锁状态。

那么，问题就变成了：这真的是一个僵局吗？如何避免死锁？我应该编辑什么以使我的代码更好？

以下是新代码：

#include <iostream>
#include <thread>
#include <mutex>          // std::mutex, std::unique_lock
#include <condition_variable> // std::condition_variable
using namespace std;
std::mutex mu; //mutex
//std::unique_lock<mutex> locker(mu); //unique_lock
std::condition_variable cond;
std::mutex m_mutex;
int consumerRunTurns = 0;
class Buffer {
public:
Buffer():count(0) {}
void put();
int get();
bool isBufferEmpty();
bool isBufferFull();
private:
int count;
}; //end class Buffer
//Thread Class and Functions inside:
class Consumer{
public:
Consumer(Buffer* cbptr);
void cons();
bool isConsumerDead();
private:
Buffer* BufferPtr;
};
class Producer{
public:
Producer(Buffer* pbptr, Consumer* coptr);
void prods();
private:
Buffer* BufferPtr;
Consumer* ConsumerPtr;
};
int main(){
Buffer* tc = new Buffer();
Consumer* cdtc = new Consumer(tc);
Producer* pdtc = new Producer(tc,cdtc);
std::thread t[5]; //declare an array of thread objects
int i = 0;
for(; i<3; ++i){
t[i]=std::thread(&Producer::prods,std::ref(pdtc));
}
for(; i<5; ++i){
t[i]=std::thread(&Consumer::cons,std::ref(cdtc));
}
cout << "Debug1" << endl;
cout << "Debug1" << endl;
cout << "Debug1" << endl;
for(i = 0; i<5; ++i){
t[i].join();
cout << "now i is :" << i << endl;
}
cout << "All threads terminated" << endl;
return 0;
}
void Buffer::put(){
std::unique_lock<mutex> locker(mu); //unique_lock
if(consumerRunTurns>=200){
cond.notify_one();
return;
}
while(isBufferFull()==1){
if(consumerRunTurns>=200){
cond.notify_one();
break;
}
cond.wait(locker);
}
if(consumerRunTurns>=200){
return;
}
if(isBufferFull()==0)
cond.notify_one();
++count;
std::cout << "producer thread" << this_thread::get_id() << ",count = " << count << endl;
}
int Buffer::get(){
std::unique_lock<mutex> locker(mu); //unique_lock
while(isBufferEmpty()==1){
cond.wait(locker);
}
if(isBufferEmpty()==0)
cond.notify_one();
--count;
std::cout << "consumer thread" << this_thread::get_id() << ",count = " << count << endl;
return count;
}
bool Buffer::isBufferEmpty(){
if(count <=0){
std::cout << "buffer is empty, consumer thread" << this_thread::get_id() << " is about to suspend." << endl;
return 1;
}
else
return 0;
}
bool Buffer::isBufferFull(){
if(count >=10){
std::cout << "buffer is full, producer thread" << this_thread::get_id() << " is about to suspend." << endl;
return 1;
}
else
return 0;
}
Consumer::Consumer(Buffer* cbptr):BufferPtr(cbptr){
}
bool Consumer::isConsumerDead(){
if(consumerRunTurns >= 200){
cout << "consumer Dead" << endl;
cout << "consumer Dead" << endl;
cout << "consumer Dead" << endl;
return 1;
}
else
return 0;
}
void Consumer::cons(){
for(int i = 0; i<100; ++i){
BufferPtr->get();
std::this_thread::sleep_for(std::chrono::milliseconds(60));
}
consumerRunTurns+=100;
}
Producer::Producer(Buffer* pbptr, Consumer* coptr):BufferPtr(pbptr), ConsumerPtr(coptr){}
void Producer::prods(){
for(int i = 0; i<100; ++i){
if(ConsumerPtr->isConsumerDead()){
break;
}
BufferPtr->put();
std::this_thread::sleep_for(std::chrono::milliseconds(60));
}
}

以前的代码：

#include <iostream>
#include <thread>
#include <mutex>          // std::mutex, std::unique_lock
#include <condition_variable> // std::condition_variable
using namespace std;
std::mutex mu; //mutex
//std::unique_lock<mutex> locker(mu); //unique_lock
std::condition_variable cond;
std::mutex m_mutex;
class Buffer {
public:
Buffer():count(0) {}
void put();
int get();
bool isBufferEmpty();
bool isBufferFull();
private:
int count;
}; //end class Buffer
//Thread Class and Functions inside:
class Consumer{
public:
Consumer(Buffer* cbptr);
void cons();
bool isConsumerDead();
private:
Buffer* BufferPtr;
int consumerDeadFlag;
};
class Producer{
public:
Producer(Buffer* pbptr, Consumer* coptr);
void prods();
private:
Buffer* BufferPtr;
Consumer* ConsumerPtr;
};
int main(){
Buffer* tc = new Buffer();
Consumer* cdtc = new Consumer(tc);
Producer* pdtc = new Producer(tc,cdtc);
std::thread t[5]; //declare an array of thread objects
int i = 0;
for(; i<3; ++i){
t[i]=std::thread(&Producer::prods,std::ref(pdtc));
}
for(; i<5; ++i){
t[i]=std::thread(&Consumer::cons,std::ref(cdtc));
}
cout << "Debug1" << endl;
cout << "Debug1" << endl;
cout << "Debug1" << endl;
for(i = 0; i<5; ++i){
t[i].join();
cout << "now i is :" << i << endl;
}
cout << "All threads terminated" << endl;
return 0;
}
void Buffer::put(){
std::unique_lock<mutex> locker(mu); //unique_lock
while(isBufferFull()==1){
cond.wait(locker);
}
if(isBufferFull()==0)
cond.notify_one();
++count;
std::cout << "producer thread" << this_thread::get_id() << ",count = " << count << endl;
}
int Buffer::get(){
std::unique_lock<mutex> locker(mu); //unique_lock
while(isBufferEmpty()==1){
cond.wait(locker);
}
if(isBufferEmpty()==0)
cond.notify_one();
--count;
std::cout << "consumer thread" << this_thread::get_id() << ",count = " << count << endl;
return count;
}
bool Buffer::isBufferEmpty(){
if(count <=0){
std::cout << "buffer is empty, consumer thread" << this_thread::get_id() << " is about to suspend." << endl;
return 1;
}
else
return 0;
}
bool Buffer::isBufferFull(){
if(count >=10){
std::cout << "buffer is full, producer thread" << this_thread::get_id() << " is about to suspend." << endl;
return 1;
}
else
return 0;
}
Consumer::Consumer(Buffer* cbptr):BufferPtr(cbptr){
consumerDeadFlag = 0;
}
bool Consumer::isConsumerDead(){
if(consumerDeadFlag > 1){
cout << "consumer Dead" << endl;
cout << "consumer Dead" << endl;
cout << "consumer Dead" << endl;
return 1;
}
else
return 0;
}
void Consumer::cons(){
for(int i = 0; i<100; ++i){
BufferPtr->get();
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
++consumerDeadFlag;
}
Producer::Producer(Buffer* pbptr, Consumer* coptr):BufferPtr(pbptr), ConsumerPtr(coptr){}
void Producer::prods(){
for(int i = 0; i<100; ++i){
if(ConsumerPtr->isConsumerDead()){
break;
}
BufferPtr->put();
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
}

输出：

producer threadDebug12,count = 1
producer thread4,count = 2
producer thread3,count = 3
Debug1
Debug1
consumer thread5,count = 2
consumer thread6,count = 1
producer thread2,count = 2
consumer thread5,count = 1
producer thread4,count = 2
producer thread3,count = 3
consumer thread6,count = 2
producer thread2,count = 3
producer thread4,count = 4
producer thread3,count = 5
consumer thread5,count = 4
consumer thread6,count = 3
producer thread2,count = 4
producer thread4,count = 5
consumer thread5,count = 4
producer thread3,count = 5
consumer thread6,count = 4
producer thread2,count = 5
consumer thread5,count = 4
producer thread4,count = 5
producer thread3,count = 6
consumer thread6,count = 5
producer thread2,count = 6
producer thread4,count = 7
producer thread3,count = 8
consumer thread5,count = 7
consumer thread6,count = 6
producer thread2,count = 7
consumer thread5,count = 6
producer thread4,count = 7
producer thread3,count = 8
consumer thread6,count = 7
producer thread2,count = 8
consumer thread5,count = 7
producer thread4,count = 8
producer thread3,count = 9
consumer thread6,count = 8
producer thread2,count = 9
producer thread4,count = 10
consumer thread5,count = 9
producer thread3,count = 10
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
buffer is full, producer thread4 is about to suspend.
consumer thread5,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread2 is about to suspend.
consumer thread6,count = 9
producer thread4,count = 10
buffer is full, producer thread2 is about to suspend.
consumer thread5,count = 9
producer thread2,count = 10
buffer is full, producer thread3 is about to suspend.
consumer thread6,count = 9
producer thread3,count = 10
buffer is full, producer thread4 is about to suspend.
buffer is full, producer thread2 is about to suspend.

等(由于字数限制(

consumer Dead
consumer Dead
consumer Dead