Sample code for asynchronous programming in C

I need to program asynchronous ODBC driver,which need to handle user requested ODBC APIs in asynchronous way. I am desperate to know how to write an asynchronous program portable on all platforms. Can you please provide me a basic C code on how to right asynchronous code?

Thanks in advance.

2 Answers

tidy code for asynchronous IO is a good thread to start in.

Portable solutions don't really exist. It also differs for socket streams and files, on all platforms.

libevent is a good abstraction.

Writing ODBC is not for the faint hearted.

Take below as example, notice async mostly used in multi-thread,

// FILE NAME: a.c
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
typedef void (*pcb)(int a);
typedef struct parameter
{ int a; pcb callback;
} parameter;
void *callback_thread(void *p1)
{ //do something parameter *p = (parameter *)p1; while (1) { printf("GetCallBack print! \n"); sleep(3); //delay 3s p->callback(p->a); }
}
extern int SetCallBackFun(int a, pcb callback)
{ printf("SetCallBackFun print! \n"); parameter *p = malloc(sizeof(parameter)); p->a = 10; p->callback = callback; pthread_t thing1; pthread_create(&thing1, NULL, callback_thread, (void *)p); pthread_join(thing1, NULL);
}

// FILE NAME: b.c
#include "boo.c"
#include <stdio.h>
void fCallBack(int a)
{ //do something printf("a = %d\n",a); printf("fCallBack print! \n");
}
int main(void)
{ SetCallBackFun(4,fCallBack); return 0;
}

Output is below,

SetCallBackFun print!
GetCallBack print!
a = 10
fCallBack print!
GetCallBack print!
a = 10
fCallBack print!
GetCallBack print!
a = 10
fCallBack print!
GetCallBack print!
a = 10
fCallBack print!
GetCallBack print!
a = 10
fCallBack print!
GetCallBack print!

...

In terms of calling function, there are three types: sync, back, and async.

The tricky thing is the last two are highly correlated, why is that?

Perhaps a graph would make it clear, i.e.