Re: [ANNOUNCE] CGit v0.1-pre

On Mon, 11 Dec 2006, Lars Hjemli wrote:

Your pseudo-algorithm is dubious:

		name = generate_cache_name(request);
	top:
		if (!exists(name)) {
			if (lock_cache(name)) {
				generate_cache(request, name);
				unlock_cache(name);
			} else {
				sched_yield();
				goto top;
			}
		} else if (expired(name)) {
			if (lock_cache(name)) {
				generate_cache(request, name);
				unlock_cache(name);
			}
		}
		print_file(name);

You really should have:

	if (!exists) {
		if (!lock)
			delay-and-repeat;
		/* RETEST exists _after_ getting the lock */
		if (!exists) {
			generate into lock-file
			mv lockfile exists;
		} else {
			rm lockfile
		}
	}

because you really want to re-check the existence after you got the lock, otherwise you would race with somebody else that got the lock, generated the data, and then unlocked (and you got the lock _after_ the data was generated, so now you generate it unnecessarily).

As a side note: how do you release your caches?