Is it possible to display progress of Asynchronous IO

Question

I am trying to implement file copy program with POSIX Asynchronous IO APIs in linux.

I tried this:

main() {
    char data[200];
    int fd = open("data.txt", O_RDONLY); // text file on the disk
    struct aiocb aio;

    aio.aio_fildes = fd;
    aio.aio_buf = data;
    aio.aio_nbytes = sizeof(data);
    aio.aio_offset = 0;

    memset(&aio, 0, sizeof(struct aiocb));
    aio_read(arg->aio_p);
    int counter = 0;
    while (aio_error(arg->aio_p) == EINPROGRESS) {
          printf("counter: %d\n", counter++);
    }

    int ret = aio_return(&aio);
    printf("ret value %d \n",ret);

    return 0;
}

But counter giving different results every time when I run

Is it possible to display progress of aio_read and aio_write functions?

Answer 1

You have different results because each different execution has its own context of execution that may differe from others (Do you always follow the exact same path to go from your house to the bank? Even if yes, elapsed time to reach the bank always exactly the same? Same task at the end - you're in the bank, different executions). What your program tries to measure is not I/O completion but the number of time it tests for completion of some async-I/O.

And no, there is no concept of percentage of completion of a given async-I/O.