[Omake] OMake locking

[Aleksey Nogin]

On 17.01.2007 08:38, Jared C. Davis wrote:

> I'm wondering if there's a way to make OMake's locking mechanism less 
> severe.
> 
> My project has a few long-running files take over an hour to build
> apiece.  When I start building one of these files, I can't use OMake
> at all on other parts of the project

Jared,

This is not really about locking - the basic assumption of OMake is that 
it does the global dependency analysis on the whole project, so in 
general you can not really have more than one instance of OMake running 
on the same project, without loosing some of the reliability guarantees 
that OMake is designed to provide. Also, there is a global per-project 
"build state" database (.omakedb) that is not designed for parallel 
access. The locking is there just to remind you of this limitation.

Basically, if you do want to run more than one copy of OMake, you need 
to have more than one project. Different projects are allowed to share 
[sub]directories (although, OMake running on one project will not 
"trust" what another copy of OMake did, so they might end up "fighting" 
in those directories). From the OMake's point of view, projects are 
different if they have different "project root" directory(*).

Basically, if you want a separate project that shares all the 
directories with an existing one, create a fresh directory and copy the 
OMakeroot file from the original project to the new directory. Next, 
replace the ".SUBDIRS: ." line with ".SUBDIRS: 
path/to/original/project/root". Now you should be able to run omake in 
the new project root directory, even if you already have one running in 
the original one.

Note:
  - You do not have to point the ".SUBDIRS" line to the original root, 
often it is sufficient to point it to a subdirectory. In that case, you 
can just use that subdirectory as the root of the new project, copy the 
OMakeroot there and keep the ".SUBDIRS: ." line.
  - As I said before, one instance of omake will not in general 
"recognize" the progress made by another (as you will end up having two 
completely separate .omakedb databases - this is the database that, 
among other things, records which files have been successfully built - 
omake, contrary to how make does it, does not trust file time stamps).
  - It is up to you to make sure that the two instances of OMake do not 
end up "fighting" (e.g., many strange things might happen if both try to 
build the same file at the same time), Well, I guess this is no worse 
that what you'd get if you tried to do this with make.

Aleksey

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(*) May be we should allow different projects to share a root directory, 
but this never came up before.