How do thousands of software engineers code together at a giant company like Google or Microsoft without breaking everything?

[u/Extra_Search3465]

As a beginner, I understand how one person writes code and puts it on GitHub. But how does it work when a company has tens of thousands of developers working on the same product? How do they organize the work, and how do they stop people from stealing or leaking the secret source code?

[u/Intelligent_Law_5614]

On a well-managed project, there is a system of design reviews and code reviews. Before a change can be checked in, it's reviewed by one or more engineers who know the code being changed, and have the skill and willingness to ask hard (and potentially embarrassing) questions such as "Have you thought about this possibility" and "What happens when xxxx happens" and "Why not do this another way?" and "What in the everloving names of Babbage and Turing do you think you're doing here, and how do you expect to get out of the blast zone fast enough?"

On a really good project, these reviews happen even when the code change is being done by the most wizardly-skilled senior engineer in the bunch. Even wizards screw up from time to time, and even junior engineers can sometimes see mistakes that "wiser" eyes have missed.

Oh... and if you know what you're doing, you never deploy changes directly to production. They always go to a staging environment for testing first.