File Locking

[Arne Babenhauserheide]

Am Donnerstag 16 Oktober 2008 11:51:28 schrieb Alpár Jüttner:
> Therefore locking is inherently impossible in DVC. If you really need it
> (in most cases you don't), you must use a system where the commit and
> the push operation is strictly tied together, like SVN.

That's only true when you judge DVCS while thinking in the centralized 
paradigm. 

What a commit in SVN does is two things: Store a current state of the repo and 
publicize it. A lock therefore prevents publication of a modified file by 
preventing the saving of its state. 

In Mercurial these two things are seperated, so preventing the publication of 
a modified file can be done without having to disallow people to save its 
state locally. 

So the "disallow publication" aspect of locking is completely possible in a 
DVCS: Just don't accept any changesets which modify locked files. 

And the "disallow saving the modified state" aspect is an inherently flawed 
idea, since it poses unnecessary restrictions on the individual developer even 
though his actions don't affect others if he doesn't publicize his changes. 


In short: With Mercurial you can do the good aspect of file locking: Keep 
people from disturbing the work of others by pushing changes to a locked file 
to a reference repository. But you can't do the bad part of locking: Disturb 
the private work of people. 


Besides: That bad part (discrupting the work of individuals by forbidding them 
to save the state of a locked file) also offers no security, since locking a 
file in SVN doesn't keep people from spreading a modified version, it just 
keeps them from saving its state inside SVN. 

Best wishes, 
Arne
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