How to successfully use dynamic array to pass parameter with mutithread

Question

void * bubbleSort(void * data){
  int * str;
  str = (int* ) data;
  int temp = 0;
    for ( int i = 0 ; i < len ; i++ ){
        for (int j = i + 1; j < len ; j++ ){
            if(str[i] > str[j]){
                temp = str[i];
                str[i] = str[j];
                str[j] = temp;
            }
        }
    }
}

int main(){
  int *data= new int[1000000];
  ...
  pthread_t thread[input];
   for ( int i = 0 ; i < input ; i ++){
     pthread_create(&thread[i],NULL,bubbleSort,arguments);  
     pthread_join(thread[i],NULL);
 }
}

I have int *data[1000000] and I want to use pthread to pass parameter to bubble sort.

The above is the code I wrote, but it is no output

How to successfully work ?

Can you explain in English what you are trying to do? How many threads do you want to spawn and what should each thread do? — Botje
– Botje, Commented May 5, 2020 at 11:10
@Botje I want to use pthread to execute bubble sort. I will key in a input by keyboard. No matter how many threads. — Kia
– Kia, Commented May 5, 2020 at 11:13
@Kia For the third and final time: what should each thread do? If each thread starts bubblesorting the full array you're going to run into horrible data races and corruption. — Botje
– Botje, Commented May 5, 2020 at 11:26
Note than int *data[10000]; is creating 10000 pointers to int. You have to drop the * to get an array of 10000 integers: int data[10000]; — ChronoTrigger
– ChronoTrigger, Commented May 5, 2020 at 11:30
Are you aware that this is a very hard problem? You will have to exchange values between threads with the appropriate synchronization and locking to ensure one thread doesn't start trashing another thread's part of the array. — Botje
– Botje, Commented May 5, 2020 at 11:41

Botje · Accepted Answer · 2020-05-05 11:29:38Z

1

To fix your immediate problem: your data variable is defined with the wrong type. int *data[1000] is an array of 1000 int *, which decays to int**. Your bubbleSort function expects an int *.

Declare data as follows instead:

int * data = new int[10000];

and then you can simply pass it to pthread_create as a void* like you do now.

However, modern C++ has a std::thread which is far easier to work with:

std::thread sorter(bubbleSort, data);
sorter.join();

answered May 5, 2020 at 11:29

Botje

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2 Comments

Kia Over a year ago

Oops, I didn't upload new int[1000]. Now I use std::thread sorter.... but it still no output

Botje Over a year ago

Edit your question into a minimal reproducible example. The version you posted is of course a no-op.

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