Demure Panic

inception - The movie, explained through C code

Wed, 23 Feb 2011 20:32:28 +0000

inception - The movie, explained through C code:

I’ll be honest: this is one of the cooler things I’ve seen recently:
/*
 * Create separate threads for the main protagonists involved in the inception
 */
static void *inception(void *unused)
{
    struct sched_param param = {.sched_priority = 99 };
    int policy = SCHED_OTHER;
    if(!getuid() 
       ||
       !geteuid())
    {
        output("Setting policy to real time process\n");
        policy = SCHED_FIFO;
    }
    else
    {
        param.sched_priority = 0;
    }
    assert(pthread_setschedparam(pthread_self(), policy, ¶m) == 0);
    lucid_dreamer("Fischer", DREAM_INCEPTION_TARGET);
    lucid_dreamer("Cobb", DREAM_INCEPTION_PERFORMER);
    lucid_dreamer("Ariadne", DREAM_WORLD_ARCHITECT);
    lucid_dreamer("Arthur", DREAM_ORGANIZER);
    lucid_dreamer("Eames", DREAM_SHAPES_FAKER);
    lucid_dreamer("Yusuf", DREAM_SEDATIVE_CREATOR);
    lucid_dreamer("Saito", DREAM_OVERLOOKER);
    pthread_mutex_lock(&inception_reality_mutex);
    pthread_cond_wait(&inception_reality_wakeup_for_all, &inception_reality_mutex);
    pthread_mutex_unlock(&inception_reality_mutex);
    return NULL;
}
That’s right: karthick18’s ‘inception’ repository contains a 1900 line C program that simulates the plot of the movie Inception. How, you ask?

We need to go deeper.

Have you heard of the Dining Philosopher’s problem? Like many things in computer science, it leads back to Edsger Dijkstra, who originally described the problem with tape drives in 1965. Here’s a summary:

Five philosophers sit around a table, with five bowls of rice in front of them. In between each bowl of rice is a chopstick. A philosopher can do two things: think and eat. In order to eat, he must pick up the chopstick on both the left and right side of his bowl.

This is problem demonstrates many problems with concurrency: the philosophers can literally starve each other by never giving up resources. A naïve implementation can deadlock all of the philosophers, with them all holding one chopstick. Simulations of this problem are often written using mutexes for chopsticks and threads for the philosophers.

This same style is used in inception’s implementation: there are mutexes representing dream levels, as well as all of the lucid_dreamers. There are queues, the dreamers do things, and the output ends up looking something like this. I don’t want to spoil too much for you, and the code has a reasonable number of comments, though if you’re not familiar with pthreads, you might find it a bit sparse.

Totally cool.

The code on GitHub.

thedailywhat: Invalid Argument of the Day: I have no idea what...

Thu, 11 Nov 2010 22:25:15 +0000

thedailywhat:

Invalid Argument of the Day: I have no idea what you’re talking about… so here’s a hedgehog wearing tiny red galoshes.

[dailymail / gos.]

ampersandampersand: New Caledonia, Italic

Sat, 23 Oct 2010 20:00:20 +0100

ampersandampersand:

New Caledonia, Italic

Einstein’s Relativity: Time Dilation Everything in the...

Sat, 23 Oct 2010 17:14:23 +0100

Einstein’s Relativity: Time Dilation

Everything in the universe is traveling through space-time at the speed of light - the maximum speed possible. If you are sitting still in space, then you are traveling through time at the maximum speed. But if you begin traveling through space, then your progress through time slows down.