"The global block is a global lock"
Ward, does wiki deliberately avoid global locks by design?
Clive, yes, wiki enables collective behavior without any synchronization at the application level.
The OCap object-capability model describes transferable rights to perform operations on an object:
An unforgeable reference that can be sent in messages, and,
a message that specifies the operation to be performed. wikipedia 
This very transaction, your question and my answer, are consistent with the OCap definition. The transferable object is the page title, the unforgeable reference is the site-slug from your site, and the specified operation is my delivery of an answer in the second paragraph above.
As I write this I am unsure you will ever read it. But, I expect this page to be read by many others who will gain insight from our possibly incomplete exchange.
Wiki lacks any mechanism where I can demand your attention. There will be no race condition where I compete for that attention with others. Hence no need for global locks. Still, interesting things can happen.
VIMEO 58291553 The collective behavior of the flock appears intentional.
Mark Miller draws much finer distinctions but quickly points out that "the agent's response to a message is only according to the agent's behavior which is to say all interaction is voluntary."
YOUTUBE 21R259Wei2w Published on Jan 28, 2017.
Wiki committer, Harlan Wood, suggests how wiki's goals can be extended without violating its decentralized autonomous foundation.
YOUTUBE V8B9dzyDIs0 Published on Jun 29, 2017.
We might consider how plugins could be designed that allow more synchronized structures to be built and shared as might be required by contracts in an economy.