C语言 创建线程 - 传递参数
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create thread - passing arguments
提问by Mankarse
I am attempting on creating multiple threads that each thread calculates a prime. I am trying to pass a second argument to a function using thread create. It keeps throwing up errors.
我正在尝试创建多个线程，每个线程计算一个素数。我正在尝试使用线程创建将第二个参数传递给函数。它不断抛出错误。
void* compute_prime (void* arg, void* arg2)
{
here is my main() with the create thread. &primeArray[i] after &max_prime is giving me the errors.
这是我的 main() 与创建线程。&max_prime 之后的 &primeArray[i] 给了我错误。
for(i=0; i< num_threads; i++)
{
primeArray[i]=0;
printf("creating threads: \n");
pthread_create(&primes[i],NULL, compute_prime, &max_prime, &primeArray[i]);
thread_number = i;
//pthread_create(&primes[i],NULL, compPrime, &max_prime);
}
/* join threads */
for(i=0; i< num_threads; i++)
{
pthread_join(primes[i], NULL);
//pthread_join(primes[i], (void*) &prime);
//pthread_join(primes[i],NULL);
//printf("\nThread %d produced: %d primes\n",i, prime);
printf("\nThread %d produced: %d primes\n",i, primeArray[i]);
sleep(1);
}
the error i get is:
我得到的错误是：
myprime.c: In function amaina:
myprime.c:123: warning: passing argument 3 of apthread_createa from incompatible pointer type
/usr/include/pthread.h:227: note: expected avoid * (*)(void *)a but argument is of type avoid * (*)(void *, void *)a
myprime.c:123: error: too many arguments to function apthread_createa
It works fine if i take out the second argument.
如果我去掉第二个参数，它工作正常。
回答by Mankarse
You can only pass a single argument to the function that you are calling in the new thread. Create a struct to hold both of the values and send the address of the struct.
您只能将一个参数传递给您在新线程中调用的函数。创建一个结构来保存这两个值并发送结构的地址。
#include <pthread.h>
#include <stdlib.h>
typedef struct {
//Or whatever information that you need
int *max_prime;
int *ith_prime;
} compute_prime_struct;
void *compute_prime (void *args) {
compute_prime_struct *actual_args = args;
//...
free(actual_args);
return 0;
}
#define num_threads 10
int main() {
int max_prime = 0;
int primeArray[num_threads];
pthread_t primes[num_threads];
for (int i = 0; i < num_threads; ++i) {
compute_prime_struct *args = malloc(sizeof *args);
args->max_prime = &max_prime;
args->ith_prime = &primeArray[i];
if(pthread_create(&primes[i], NULL, compute_prime, args)) {
free(args);
//goto error_handler;
}
}
return 0;
}
回答by Varun Vijaykumar
In case of std::thread, the user can pass arguments to the thread function in the following method
在 std::thread 的情况下，用户可以通过以下方法将参数传递给线程函数
std::thread(funcName,arg1,arg2);
std::thread(funcName,arg1,arg2);
for instance,
例如，
//for a thread function,
void threadFunction(int x,int y){
std::cout << x << y << std::endl;
}
// u can pass x and y values as below
std::thread mTimerThread;
mTimerThread = std::thread(threadFunction,1,12);
回答by Милош Ве?кови?
This is the code of Manakarse, everything is really good but you need a
这是Manakarse的代码，一切都很好，但你需要一个
pthread_join(thread[i],NULL)
pthread_join（线程[i]，NULL）
just to be sure all of threads will successfully execute before end of main thread("main will "waiting" while all of threads aren't finished yet) ;
只是为了确保所有线程都将在主线程结束之前成功执行（“主线程将“等待”而所有线程尚未完成）；
