Oddness regarding file locks in package.bbclass

[Peter Kjellerstedt <peter.kjellerstedt@axis.com>]

I just stumbled upon something odd in package.bbclass. In commit 
ede381d5 from January 2011 (the code hasn't changed since), the 
use of the ${PACKAGELOCK} lock file was changed to shared to 
improve parallelism. However, when looking at the actual change 
it becomes confusing. I have included it below for reference.

> commit ede381d56b180b384fdad98d445e5430819cfade
> Author: Richard Purdie <richard.purdie@linuxfoundation.org>
> Date:   Wed Jan 19 11:04:15 2011 +0000
> 
>     package.bbclass: Take a shared lock when reading to improve do_package parallelism
>     
>     Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
> 
> diff --git a/meta/classes/package.bbclass b/meta/classes/package.bbclass
> index d39c694de5..8e7fa26f72 100644
> --- a/meta/classes/package.bbclass
> +++ b/meta/classes/package.bbclass
> @@ -497,7 +497,8 @@ python emit_pkgdata() {
>  	pkgdest = bb.data.getVar('PKGDEST', d, 1)
>  	pkgdatadir = bb.data.getVar('PKGDESTWORK', d, True)
>  
> -	lf = bb.utils.lockfile(bb.data.expand("${PACKAGELOCK}", d))
> +	# Take shared lock since we're only reading, not writing
> +	lf = bb.utils.lockfile(bb.data.expand("${PACKAGELOCK}", d), True)

Here the lock is changed to shared as per the commit message.

>  
>  	data_file = pkgdatadir + bb.data.expand("/${PN}" , d)
>  	f = open(data_file, 'w')
> @@ -649,6 +650,7 @@ python package_do_shlibs() {
>  	shlibs_dir = bb.data.getVar('SHLIBSDIR', d, True)
>  	shlibswork_dir = bb.data.getVar('SHLIBSWORKDIR', d, True)
>  
> +	# Take shared lock since we're only reading, not writing
>  	lf = bb.utils.lockfile(bb.data.expand("${PACKAGELOCK}", d))

Here, however, it is not changed, even though a comment is added to 
say that it is. Was this intentional, or just an oversight?

>  
>  	def linux_so(root, path, file):
> @@ -878,6 +880,7 @@ python package_do_pkgconfig () {
>  							if hdr == 'Requires':
>  								pkgconfig_needed[pkg] += exp.replace(',', ' ').split()
>  
> +	# Take shared lock since we're only reading, not writing
>  	lf = bb.utils.lockfile(bb.data.expand("${PACKAGELOCK}", d))

Here again a comment is added, but the code is not changed to match.

>  
>  	for pkg in packages.split():

Also, what is the ${PACKAGELOCK} lock file actually protecting? With 
the exception of the two questionable cases above, I cannot see that 
the lock is taken privately anywhere else. And since it looks as the 
code in package_do_shlibs() and package_do_pkgconfig() is not what 
needs protection (based on the added comments above), what is?

//Peter