using mkfifo to block on read until a write

Question

gcc (GCC) 4.7.2
c89

I am using pipes mkfifo. I have a reader and a writer.

I want the reader to block until there is something in the file.

There is a flag you can set O_NONBLOCK which is for non-blocking mode. So by default it should block on the read.

Writing to the file

int main(void)
{
    int fd;
    const char *pipe_file = "../../pipe_file/file";
    const char *pipe_msg = "PIPE Message";

    LOG_INFO("Start writer");

    /* Create the FIFO named pipe with read/write permissions */
    mkfifo(pipe_file, 0666);

    /* Write to the pipe */
    fd = open(pipe_file, O_WRONLY);
    write(fd, pipe_msg, strlen(pipe_msg) + 1);

    LOG_INFO("Terminate writer");

    return 0;
}

Reading from the file

int main(void)
{
    int fd = -1;
    const char *pipe_file = "../../pipe_file/file";
#define BUF_SIZE 1024
    char rd_buffer[BUF_SIZE];

    LOG_INFO("Start reader");

    fd = open(pipe_file, O_RDONLY);

    do {
        memset(rd_buffer, 0, sizeof(rd_buffer));
    /* I WANT IT TO BLOCK HERE, UNTIL THE FILE IS WRITTEN AGAIN */
        read(fd, rd_buffer, sizeof(rd_buffer));
        LOG_INFO("Contents of buffer [ %s ]", rd_buffer);
    /* NO NEED TO SLEEP AS THE FILE WILL DELAY WHEN BLOCKING, I THINK */
    } while(1);

    /* We're done clean up */
    close(fd);
    unlink(pipe_file);

    LOG_INFO("Terminate reader");

    return 0;
}

Answer 1

Your read() will return immediately in case of the other end of the fifo is not open in the write mode. Try to run your Write program first and see.

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