Linux跨C连接到同一sockaddr线程

Question

I'm trying to get multiple sockets connecting to the same address and port in multiple threads by sharing a const struct sockaddr_in passed to connect() . But the connection cannot be established.

My code is like this:

#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pthread.h>

void* foo(void* sa) {
  struct sockaddr_in* server_address = (struct sockaddr_in*) sa;
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (connect(sockfd, (struct sockaddr*)&server_address, sizeof(server_address)) != 0) {
    perror("Cannot connect in foo\n");
    exit(1);
  }
  // do something...
  return NULL;
}

int main(int argc, char* argv[]) {
  const struct sockaddr_in server_address = {
    .sin_addr = inet_addr("127.0.0.1"),
    .sin_port = htons(80),
    .sin_family = AF_INET
  };
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (connect(sockfd, (struct sockaddr*)&server_address, sizeof(server_address)) != 0) {
    perror("Cannot connect in main\n");
    exit(1);
  } else {
    printf("It works in main\n");
  }
  pthread_t t;
  pthread_create(&t, NULL, foo, (void*)&server_address);
  pthread_join(t, NULL);
}

and output like this

It works in main
Cannot connect in foo
: Invalid argument

I can write and read the socket in main , but fail in foo.

What's wrong with the sockaddr_in ?

Now I have to recreate the same sockaddr_in in every thread every time to connect. Is there any efficient way to avoid these overhead?

I am on Ubuntu 16.04, with gcc 5.4.1 compiled and ran with

$ gcc myconnect.c -lpthread && ./a.out

Answer 1

sizeof(server_address) in function foo is the size of a struct sockaddr_in pointer and not the size of struct sockaddr_in as it needs to be. Similar (struct sockaddr*)&server_address is not a pointer to the struct sockaddr_in but a pointer to the pointer:

void* foo(void* sa) {
  struct sockaddr_in* server_address = (struct sockaddr_in*) sa;
  ...
  if (connect(sockfd, (struct sockaddr*)&server_address, sizeof(server_address)) != 0) {

This should work instead:

if (connect(sockfd, (struct sockaddr*)server_address, sizeof(*server_address)) != 0) {