[Scons-users] parallel invocation of SCons

Thu Feb 14 16:49:54 EST 2019

I agree that if you make your CI simpler that is the best way.

I disagree on the windows issue. the locking on a common PDB with build c++ is easy to correct with /Z7. I have not had issues with multiple independent builds on windows given they are in different directories, but maybe i have not had to build some certain case of something that does have an issue.

If I understand correctly there is one Sconstruct ( possibly copied for each repo) that builds different targets for different code bases?

GIven this I think it would be better to break up the Sconstruct to different scripts for each code base. Then have the final script look for the finial outputs to gather them up. These can all run independently ( minus the finial script and given they are in different directories or you redefine the db file) however this only makes sense if these code bases are independent from each other. If the code bases depend on the other code bases you will have a problem, and you might have to do as Bill suggest in having the CI block part of the pipeline from running at the same time.

I agree that it would be nice if we could get a better DB setup that would allow one to run in the same directory different variant builds at the same time without overwriting the DB. However that does not exist today. If you want to have a common DB for all the bits, you have to serialize the build targets on the CI, or you have to break up the build so it components are independent builds.

Jason
________________________________
From: Scons-users <scons-users-bounces at scons.org> on behalf of Damien <damien at khubla.com>
Sent: Thursday, February 14, 2019 11:09 AM
To: scons-users at scons.org
Subject: Re: [Scons-users] parallel invocation of SCons

We do this by having separate codebases for each build target, even though the codebase supports all the targets.  Each SCons is run in a separate process for each codebase.  We then have a final SCons pass that just does a set of env.Install('VariousVersionsOfBlahTarget') to collect everything together.  It sounds cumbersome, but it's very reliable, once you have the scripts set up it's straightforward.  Also, when one build breaks, only one is broken.

Damien

On 2/14/2019 9:57 AM, Bill Deegan wrote:
Jason,

Assuming the CI builds are building the same code, just changing the sconsign file won't be sufficient.
Especially if the builders are windows, with the joy of windows file locking...

Best way to solve this is:
1) fix the ci
2) cause SCons to wait until the other build is done before starting.

On Thu, Feb 14, 2019 at 7:06 AM Jason Kenny <dragon512 at live.com<mailto:dragon512 at live.com>> wrote:

Hi,

As I understand it, Scons will write most of the data at the end of the run. There is a race as it will write out the whole file with updated state from the current run. This leads to the race issue you are seeing as the state of one run will replace the data from a previous run, leading to bad states. I normally work around this via one of two ways:

1) run scons with two targets and a -j[n] option. This case normally solves the issue for me. it can however be hard to read output, or from your CI point of view not break up the tasks as you might like.
2) use the SConsignFile() in your different runs to use different DB files so there is no conflicts. This case may allow you to work around your issue as you can prevent the race condition on a common file.

Information about the SConsignFile below.

Jason

SConsignFile([file, dbm_module]) , env.SConsignFile([file, dbm_module])

This tells scons to store all file signatures in the specified database file. If the file name is omitted, .sconsign is used by default. (The actual file name(s) stored on disk may have an appropriated suffix appended by the dbm_module.) If file is not an absolute path name, the file is placed in the same directory as the top-level SConstruct file.

If file is None, then scons will store file signatures in a separate .sconsign file in each directory, not in one global database file. (This was the default behavior prior to SCons 0.96.91 and 0.97.)

The optional dbm_module argument can be used to specify which Python database module The default is to use a custom SCons.dblite module that uses pickled Python data structures, and which works on all Python versions.

Examples:

# Explicitly stores signatures in ".sconsign.dblite"
# in the top-level SConstruct directory (the
# default behavior).
SConsignFile()

# Stores signatures in the file "etc/scons-signatures"
# relative to the top-level SConstruct directory.
SConsignFile("etc/scons-signatures")

# Stores signatures in the specified absolute file name.
SConsignFile("/home/me/SCons/signatures")

# Stores signatures in a separate .sconsign file
# in each directory.
SConsignFile(None)

________________________________
From: Scons-users <scons-users-bounces at scons.org<mailto:scons-users-bounces at scons.org>> on behalf of Herzog, Tobias (CQSP) <tobias.herzog at carmeq.com<mailto:tobias.herzog at carmeq.com>>
Sent: Thursday, February 14, 2019 3:14 AM
To: Scons-users at scons.org<mailto:Scons-users at scons.org>
Subject: [Scons-users] parallel invocation of SCons

Hi SCons users,

due to a parallelization in a CI build pipeline, I have the use case, that SCons (possibly) is invoked concurrently in the same tree (i.e. using database) but with different build targets. I already noticed, that this can lead to a crashing SCons and/or corrupted database.
For me it would be sufficient, if SCons just waits until the other SCons process has finished. My Idea was, to acquire any kind of inter process lock right in the SConstruct, that is active until the process terminates. So my assumption here is, that database access takes place after the reading of SConstruct/SConscript is done.
Is this correct? Will this solution be safe? Has anyone solved this problem in another/better way?

Thanks an best regards,
Tobias
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