創建N個線程

Question

我寫了下面的代碼來創建N個線程並打印每個線程的線程ID。

#include<stdio.h> 
#include<pthread.h> 
#include <stdlib.h> 
#include <sys/types.h> 
#include <sys/syscall.h> 
#include <unistd.h> 


void *threadFunction (void *); 

int main (void) 
{ 

    int n=0,i=0,retVal=0; 
    pthread_t *thread; 

    printf("Enter the number for threads you want to create between 1 to 100 \n"); 
    scanf("%d",&n); 

    thread = (pthread_t *) malloc (n*sizeof(pthread_t)); 

    for (i=0;i<n;i++){ 
     retVal=pthread_create(&thread[i],NULL,threadFunction,(void *)&i); 
     if(retVal!=0){ 
      printf("pthread_create failed in %d_th pass\n",i); 
      exit(EXIT_FAILURE);   
     } 
    } 

    for(i=0;i<n;i++){ 
     retVal=pthread_join(thread[i],NULL); 
      if(retVal!=0){ 
       printf("pthread_join failed in %d_th pass\n",i); 
       exit(EXIT_FAILURE);   
      } 
    } 

} 

void *threadFunction (void *arg) 
{ 
    int threadNum = *((int*) arg); 

    pid_t tid = syscall(SYS_gettid); 

    printf("I am in thread no : %d with Thread ID : %d\n",threadNum,(int)tid); 


} 

爭我傳遞給每個線程是一個計數器i從0到n-1遞增爲每個新的線程。 雖然在輸出我看到我的價值爲零的所有線程，無法undestand，請有人請解釋。

Enter the number for threads you want to create between 1 to 100 
    5 
    I am in thread no : 0 with Thread ID : 11098 
    I am in thread no : 0 with Thread ID : 11097 
    I am in thread no : 0 with Thread ID : 11096 
    I am in thread no : 0 with Thread ID : 11095 
    I am in thread no : 0 with Thread ID : 11094 

Answer 1

問題在於以下行：

retVal=pthread_create(&thread[i],NULL,threadFunction,(void *)&i); 

不通過的i的地址，i保持在主函數變化。相反，在線程函數中使用並傳遞我的值和類型轉換。

對於實施例，傳遞值象下面這樣：

retVal=pthread_create(&thread[i],NULL,threadFunction,(void *)i); 

在如下線程功能的訪問：

void *threadFunction (void *arg) 
{ 
    int threadNum = (int)arg; 

    pid_t tid = syscall(SYS_gettid); 

    printf("I am in thread no : %d with Thread ID : %d\n",threadNum,(int)tid); 


}