What exactly keeps the Glock's (or similar pistols) barrel in place during firing?

[:( I live in Cali :( :(]

Although I have a lot of experience with bolt action rifles, I know very little about pistols.

Since I am thinking of buying a Glock pistol or something similar to it at some point in the near future, I was browsing some youtube videos to see how to field strip various semi-auto pistols, to see which ones had the simplest takedown and reassembly.

Anyway, when I was watching a video on how to field strip a glock and put it back together, I noticed that the barrel seems to just sort of sit in place, without actually being held in place by anything.

When the guy shows how to take out the barrel during disassembly, he just pulls up and out, and when he puts it back in, he just sorta pushes it back in the reverse of how he took it out. There doesn't seem to be any actual thing locking it in place there, it seems as though if you fired it, it should just fly off or wiggle away or whatever the same way how you can easily just pull it out with your fingers during disassembly, I don't understand why it wouldn't do that when you fire the gun.

Am I missing something?

I assume there must be something which holds it in place somehow once the slide gets put back on or something, but, the way I see it it just doesn't make sense to me, I just don't understand what's keeping it locked in place there, it seems like it's just sitting there with nothing actually holding it there.

If someone could please explain/help me understand what it is that I'm missing/not understanding, I would much appreciate it, as I like the simplicity of the Glock a lot, and I think I will buy one as long as there is something actually keeping the barrel locked in place, which I assume there is and I just am missing something which someone who knows about these sorts of guns can explain to me. Thanks.

Here's the video I watched of it, the barrel removal is at about 2:10 into the video, and the putting the barrel back into place is a short while after:

http://www.youtube.com/watch?v=4vgXPK74nlI&hd=1

 

[Roughneck08]

The recoil spring locks it in place. No worries at all about it coming out or moving. It is secure. It has grooves in the lugs that the recoil spring reside in. It is a very secure system. The recoil spring securely holds the barrel to the slide.

http://www.rockyourglock.com/lube5.JPG

You see the grooves the allen wrench is pointing to? The recoil spring rests in there then you have to compress the recoil spring into the slide and lug. Easy enough. Wonderful design and above all, EASY field strip. Simple. Simple handgun.

 

[bigfatdave]

Well, that isn't such a bad video, really.
You can see all the components I'll talk about in it if you know what to look for, the "other step" on the underside of the barrel latches to the take-down catch, the spring goes into its step, the rear of the big hook assembly is what cams the barrel down, the chamber's square shape locks into the ejection port, etc etc.

http://www.genitron.com/glock23/intglock.html
http://www.genitron.com/Basics/Beretta92/New-Beretta-92.html
http://www.m1911.org/STI1911animation2.htm

There are animated cutaway images there, I'd suggest taking some time to study all of them, but the Glock is on top.
The 1911 is probably the most detailed, the Beretta has a good explanation of "dwell time", which is the reason all these guns don't have fixed barrels like a lower-pressure round would have, and is actually the reason we can have such powerful handguns that aren't revolvers.

Speaking generically about modern pistols utilizing a variation of the Browning recoil system ...

The barrel is housed in the slide and will lock into the slide and frame when fully forward, in most cases the locking is accomplished by the chamber area of the barrel locking into the slide's ejection port. In older designs the barrel would lock to the slide with lugs, the 1911 being the most common example of that system.
After firing, the barrel moves back and down, in most pistols there is a hook-like device on the underside that latches onto the assembly pin, slide stop pin, or a lug on the frame, and the barrel cams down at the rear. Again, the older design of the 1911 is a bit different, it uses a link to cam the chamber end of the barrel down, one end of the link is pinned to the barrel, the other is on the assembly pin which is also the slide stop lever.
Forward travel is limited by the disassembly latch in Glocks, (as far as I know) - you'll notice that once the striker and sear are no longer linked that there is little locking the slide and barrel in place other than the pin and rails. Pull the trigger on an empty chamber, pop the latch, and the upper assembly slides off the front of the gun.

Most of the complications in modern auto-loading pistols are from two design elements:
1 - dwell time must exist, and must be adequate with a variety of loads
2 - the fire control components in the frame and slide must interact but still allow simple disassembly

 

[Roughneck08]

Bigfatdave is the man. Thank you for a much more detailed and appropriate explanation than mine.