Programming

#define SIGBUF_SIZE 1024

typedef struct sigdata
{
        int a;
        int b;
} sigdata;

struct
{
        unsigned int rdpos, wrpos;
        sigdata buffer[SIGBUF_SIZE];
} sigbuf={ 0, 0 };

int put_value(sigdata val)
{
        unsigned int wrpos=__sync_fetch_and_add(&sigbuf.wrpos, 1);
        unsigned int rdpos=__sync_fetch_and_add(&sigbuf.rdpos, 0);
        // Compare this way, to prevent integer wraparound problems!
        unsigned int off=(wrpos-rdpos);

        if(off >= SIGBUF_SIZE)
        {
                __sync_fetch_and_sub(&sigbuf.wrpos, 1);
                return(-1);
        }

        sigbuf.buffer[wrpos % SIGBUF_SIZE]=val;
        return(0);
}

// use like:
//         sigdata d;
//         get_value(&d);
int get_value(sigdata *val)
{
        unsigned int wrpos=__sync_fetch_and_add(&sigbuf.wrpos, 0);
        // Do NOT add here!  If a signal happens, it may see a 'free'
        // element even though there's not.  Only add once we're sure
        // there's anything to read.
        unsigned int rdpos=__sync_fetch_and_add(&sigbuf.rdpos, 0);
        unsigned int off=(wrpos-rdpos);

        if(off == 0)    // Empty buffer
                return(-1);

        (*val)=sigbuf.buffer[__sync_fetch_and_add(&sigbuf.rdpos, 1)%SIGBUF_SIZE]);
        return(0);
}