Question

我已经包含了一个可以编译的源代码，并为自己查看问题。用g ++ -lpthread list-memchk.cpp -o list-memchk

编译

以此为例，./list-memchk 43000000 30000000 10

我已经包含了三个文件，第一个，

列表memchk.cpp

#include <cstdlib>
#include <iostream>
#include <pthread.h>


using namespace std;


 struct node
{
    public :
          unsigned int part1; // 4 bytes
          unsigned int part2; // 4 bytes
          node *next;         //pointer, 8 bytes on 64 bit system
      unsigned int read_part1();
 };


struct LinkedList
 {
     public:
     LinkedList();
          void insert(unsigned int data[], unsigned int data1);
          bool isEmpty() const;
          node* head;
 };

unsigned int node::read_part1() {
return part1;
}
 LinkedList::LinkedList():
 head(NULL)
{
}

bool LinkedList::isEmpty() const
{
  return (head == NULL);
}

  void LinkedList::insert(unsigned int data[], unsigned int data1)
 {



    node* oldHead = head;
    node* newHead = new node();
    newHead->part1 = data[0];
    newHead->part2 = data1;
    newHead->next = oldHead;
    head = newHead;

  }

unsigned int allocations = 300000000;
unsigned int index_size = 430000000;//index of lists, 430m,.
pthread_mutex_t mutex;
                    //will be creatad on heap
    LinkedList *list = NULL;



unsigned long node_count() {

 unsigned long numNodes = 0;


for (int i=0; i<index_size; i++)
{


  node* current = list[i].head;

// if root is null, the number of nodes is 0
if(current != NULL) {

// if root is not null, we have at least one node
    numNodes++;

// count all nodes
while(current->next != NULL) {
numNodes++;
current = current->next;
}

}

}

return numNodes;

}


#include "alloc_threads.cpp"










void start_threads(int thread_count) {

alloc_threads alloc_thr[thread_count];//thread objects
pthread_t threads[thread_count];

pthread_mutex_init(&mutex, NULL);

for (int i=0; i<thread_count; i++)
{

alloc_threads *rr;

rr = new alloc_threads(list, mutex, allocations);
alloc_thr[i] = *rr;

pthread_create(&threads[i], NULL, &alloc_threads::allocation_helper,&alloc_thr[i]);

delete rr;
}

for (int i=0; i<thread_count; i++)
pthread_join( threads[i], NULL);


}








int main(int argc, char *argv[])

{
if ( argc < 4 )
{
std::cout << "Missing paramaters. " << endl;
std::cout << "Please run me like this : <list-memchk> <index_size> <allocations_per_thread> <thread_count>" << endl;
return 1;
}


index_size = strtoul(argv[1], 0, 10);
allocations = strtoul(argv[2], 0, 10);
unsigned int thr_cnt = strtoul(argv[3], 0, 10);

LinkedList list_instance;

cout << "1 LinkedList instance takes [" << sizeof(list_instance) << "] bytes in memory!"<< endl;

node node_instance;

cout << "1 node instance takes [" << sizeof(node_instance) <<"] bytes in memory !"<< endl;


list = new (nothrow) LinkedList[index_size];
    if (!list)
    {
        cout << "Error allocating memory" << endl;
        return 1;
    }


unsigned int some_data[] = {00, 01};
unsigned int index;





cout << "Allocating ..." << endl;
start_threads(thr_cnt);


unsigned long sk = ((allocations * sizeof(node_instance) + index_size*sizeof(list_instance))) / (1024*1024*1024);

cout << "This process *should* consume around " << sk <<" GBytes of memory, but does it ?"<< endl;

cout << "Allocating done, *check the process size* ..." << endl;


cout << "Lets count `nodes` to see how many do we have; counting, please wait ..." << endl;

cout << "We have reached [" << node_count() << "] nodes, expected [" << allocations * thr_cnt << "] nodes. You may press any number key to exit." << endl;

string s;
getline(std::cin, s);



return 0;
}

然后， alloc_threads.cpp

#include "alloc_threads.h"
using namespace std;

alloc_threads::alloc_threads()
{
}

 void *alloc_threads::allocation_helper(void *context)
    {
        return ((alloc_threads *)context)->allocation();
    }

 alloc_threads::alloc_threads(LinkedList* x_list, pthread_mutex_t x_mutex, unsigned int x_allocations)


{
        list = x_list;
        mutex = x_mutex;
        allocations = x_allocations;
}

void * alloc_threads::allocation(void)
{

cout << "Thread started" << endl;
unsigned int some_data[] = {00, 01};
unsigned int index;
unsigned short inde;

LinkedList *list_instance2 = NULL;
for (int i=0; i<allocations; i++)
{

pthread_mutex_lock(&mutex);



index = rand();
inde = (unsigned short)index;
list_instance2 = &list[inde];

list_instance2->insert(some_data, some_data[1]);

pthread_mutex_unlock(&mutex);
}





cout << "Thread finished" << endl;
return 0;
}

alloc_threads::~alloc_threads()
{
}

最后， alloc_threads.h

class alloc_threads{
public:
    void *allocation(void);
    static void *allocation_helper(void *context);
    alloc_threads();
    alloc_threads(LinkedList *x_list, pthread_mutex_t x_mutex, unsigned int x_allocations);
    ~alloc_threads();
private:    
       pthread_mutex_t mutex;
       LinkedList* list;
       unsigned int allocations;

};

代码本身根本没有评论，但希望它并不难理解。我所做的，就是在多个并发线程中使用标准分配器分配内存，例如，10。在所有线程中完成分配后，我访问每个节点并在成功访问时递增numNodes。我通常得到的是，numNodes值比预期的更少/几百或几千。怎么了？并且，我已经用两个不同的分配器完成了这两个，它们都有相同的行为。

Answer 1

看来，我以错误的方式使用互斥锁 - 它不会阻止并发线程写入相同的内存。

我发现的solution是：在list-memchk.cpp中定义互斥变量并避免将其传递给线程但使用它as is。

list-memchk.cpp：用这个替换互斥锁定义，

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER ;

删除

pthread_mutex_init(&mutex, NULL);

alloc_threads.h：从此文件中删除互斥锁;

alloc_threads.cpp：删除mutex = x_mutex;

多数民众赞成。不再缺少节点。但是，分配速度很慢。看起来线程正在等待解锁互斥锁; cpu核心是空闲的，分配需要花费大量时间。

c ++链表在x64 linux上分配多个线程后缺少节点;为什么？

1 个答案: