#include <stdio.h>
#include <stdlib.h>
#include <sys/msg.h>
#include <time.h>

typedef struct _MESSAGE  {
    long nMsgType;
    char sText[ 30 ];
} MESSAGE, *PMESSAGE;

#define MAX_MESSAGE	sizeof( MESSAGE ) 
#define MSGKEY		100

void Child( int nMessages );
void Parent( int nMessages );
void MilliSleep( int nMilliSec );

int g_msgid;

int main( int argc, char* argv[] )
{
    int nMessages = 100;

    g_msgid = msgget( MSGKEY, 0644 | IPC_CREAT );

    if ( -1 == g_msgid )  {
        perror( "msgget" );
        exit( EXIT_FAILURE );
    }

    if ( argc > 1 )  {
        nMessages = atoi( argv[ 1 ] );

        if ( nMessages < 1 )
            nMessages = 1;
    }

    setbuf( stdout, NULL );

    if ( 0 == fork() )
        Child( nMessages );
    else  {
        Parent( nMessages );
        wait( 0 );

        /* remove the queue from the system */
        if ( -1 == msgctl( g_msgid, IPC_RMID, NULL ) )
            perror( "msgctl" );
    }
 
    return 0;
}

void Child( int nMessages )
{
    MESSAGE msg;
    int     i;

    msg.nMsgType = 1;

    for ( i = 1; i <= nMessages; ++i )  {
        sprintf( msg.sText, "Line number %d", i );
        printf( "Child sending '%s'\n", msg.sText );

        if ( -1 == msgsnd( g_msgid, &msg, MAX_MESSAGE, 0 ) )
            perror( "child message send" );

        /* sleep now and then */
        if ( 0 == ( i % 25 ) )
            MilliSleep( rand() % 1000 );
    }
}

void Parent( int nMessages )
{
    MESSAGE msg;
    int     i;

    msg.nMsgType = 0;

    for ( i = 0; i < nMessages; ++i )  {
        if ( -1 != msgrcv( g_msgid, &msg, MAX_MESSAGE, 0, 0 ) )
            printf( "Parent got '%s'\n", msg.sText );
        else
            perror( "parent msg receive" );

        /* sleep now and then */
        if ( 0 == ( i % 20 ) )
            MilliSleep( rand() % 500 );
    }
}

void MilliSleep( int nMilliSec )
{
    struct timespec ts;

    ts.tv_sec  = nMilliSec / 1000000;
    ts.tv_nsec = ( nMilliSec % 1000 ) * 1000000;

    nanosleep( &ts, NULL );
}