March brings us a new Conan release but sadly it also brought us the notice of having to postpone ConanDays due to growing concerns about the Coronavirus. This was a hard decision to make for the safety and well being of all of you, but we hope it will make possible for an even greater meeting of the Conan community soon. But let’s focus on the good news and see what comes with Conan 1.23.

Parallel binary downloads

As you know, we have been doing a great effort to speed-up several Conan commands to make the CI faster. We already implemented some cool features in Conan 1.21 and 1.22:

  • Parallel uploads: since Conan 1.21, it is possible to upload Conan packages to remotes faster thanks to the use of multiple threads. To activate this feature, add the --parallel argument to the conan upload command. Parallel uploads can achieve an increase in speed for around 400% depending on the situation.

  • Download cache: in Conan 1.22 we introduced a download cache that can be concurrently used by several Conan instances using different CONAN_USER_HOME folders. This cache can be shared between different simultaneous CI jobs, so if the files were previously downloaded, they will be reused from the cache without the need to download them again. Use this feature setting storage.download_cache="path/to/the/cache" in conan.conf.

Now, as the icing on the cake in Conan 1.23, we are providing the possibility to download binaries in parallel. To use it, set general.parallel_download in conan_conf. This parameter has to be set to the number of threads you want to use for downloading and will speed-up. This setting will be used when dependencies are installed (conan install, conan create) and when multiple binaries for the same package are retrieved via conan download command.

Let’s see an example of how much time we could save using this feature if we need, for example, to download a package for lots of configurations. We will download zlib/1.2.11 for all the 82 different configurations available in Conan-Center Index. Doing this would typically take around 3 minutes for a conventional Internet connection.

We will set the number of download threads to 8 but feel free to play with this setting depending on your machine.

➜ conan config set general.parallel_download=8
➜ time conan download zlib/1.2.11
Downloading conanmanifest.txt completed [0.29k]
Downloading conanfile.py completed [7.59k]
Downloading conan_export.tgz completed [0.23k]
Decompressing conan_export.tgz completed [0.00k]
Downloading conan_sources.tgz completed [6.91k]
Decompressing conan_sources.tgz completed [0.00k]
...
Downloading conaninfo.txt completed [0.46k]
Downloading conan_package.tgz completed [88.12k]
Decompressing conan_package.tgz completed [0.00k]
zlib/1.2.11: Package installed c83d8b197f1a331ca3b55943846d427ad4f7f8e1
conan download zlib/1.2.11@ -r conan-center  4.23s user 0.96s system 16% cpu
30.536 total

As you can see it just took around 30 seconds to download all the binaries what means an improvement of around a 600% in time.

If you try this feature you may experience some message overlaps in the command line output. We have prioritized the feature over a clean output but will solve these output problems shortly.

Use all of these features in combination or separate and please tell us if they are making your CI’s faster.

CONAN_V2_MODE to start testing features that will deprecate when Conan v2 is released

Although we still have plenty of time and work ahead before Conan 2.0 we would like to start testing the deprecation of features for Conan 2.0. We have introduced the CONAN_V2_MODE environment variable that activates some behaviors and defaults that are intended to be in the next major release.

Some of the most important default behaviors for Conan 2.0 will be:

  • Revisions are enabled by default (adds revisions_enabled=1 to conan.conf).
  • No hooks activated by default.
  • SCM data will be stored into conandata.yml.
  • GCC >= 5 autodetected profile will use libstdc++11.

We will be adding behaviors to this mode as we progress in the roadmap to Conan v2 so stay updated in the documentation.

Our objective is to minimize the impact on existing recipes when Conan 2.0 is released and start gathering feedback about the new configuration and behavior. Be advised that this mode is only for experimenting, please do not activate this mode in a production environment!

Other cool things

  • clean-modified subcommand for graph command. When a package of a dependency graph is going to be re-built, using a given lockfile, it is desired to finish the build knowing which packages of the graph have been rebuilt as a result of the last command. This command will clean all the previously existing “modified” flags before such build, so after the build, the “modified” are only those that have been built now. https://docs.conan.io/en/latest/reference/commands/misc/graph.html#conan-graph-clean-modified
  • full_transitive_package_id can now be activated in conan.conf to include transitive dependencies even when the direct dependencies remove them, for example when depending on a header-only library that depends on a static library. Read more about this here.



Have a look at the full list of features and fixes in the changelog.

Please, report any bug or share your feedback opening a new issue in our issue tracker and don’t forget to update.