gecko-dev/build/unix
Gregory Szorc 8922082362 Bug 1460777 - Taskgraph tasks for retrieving remote content; r=dustin, glandium
Currently, many tasks fetch content from the Internets. A problem with
that is fetching from the Internets is unreliable: servers may have
outages or be slow; content may disappear or change out from under us.

The unreliability of 3rd party services poses a risk to Firefox CI.
If services aren't available, we could potentially not run some CI tasks.
In the worst case, we might not be able to release Firefox. That would
be bad. In fact, as I write this, gmplib.org has been unavailable for
~24 hours and Firefox CI is unable to retrieve the GMP source code.
As a result, building GCC toolchains is failing.

A solution to this is to make tasks more hermetic by depending on
fewer network services (which by definition aren't reliable over time
and therefore introduce instability).

This commit attempts to mitigate some external service dependencies
by introducing the *fetch* task kind.

The primary goal of the *fetch* kind is to obtain remote content and
re-expose it as a task artifact. By making external content available
as a cached task artifact, we allow dependent tasks to consume this
content without touching the service originally providing that
content, thus eliminating a run-time dependency and making tasks more
hermetic and reproducible over time.

We introduce a single "fetch-url" "using" flavor to define tasks that
fetch single URLs and then re-expose that URL as an artifact. Powering
this is a new, minimal "fetch" Docker image that contains a
"fetch-content" Python script that does the work for us.

We have added tasks to fetch source archives used to build the GCC
toolchains.

Fetching remote content and re-exposing it as an artifact is not
very useful by itself: the value is in having tasks use those
artifacts.

We introduce a taskgraph transform that allows tasks to define an
array of "fetches." Each entry corresponds to the name of a "fetch"
task kind. When present, the corresponding "fetch" task is added as a
dependency. And the task ID and artifact path from that "fetch" task
is added to the MOZ_FETCHES environment variable of the task depending
on it. Our "fetch-content" script has a "task-artifacts"
sub-command that tasks can execute to perform retrieval of all
artifacts listed in MOZ_FETCHES.

To prove all of this works, the code for fetching dependencies when
building GCC toolchains has been updated to use `fetch-content`. The
now-unused legacy code has been deleted.

This commit improves the reliability and efficiency of GCC toolchain
tasks. Dependencies now all come from task artifacts and should always
be available in the common case. In addition, `fetch-content` downloads
and extracts files concurrently. This makes it faster than the serial
application which we were previously using.

There are some things I don't like about this commit.

First, a new Docker image and Python script for downloading URLs feels
a bit heavyweight. The Docker image is definitely overkill as things
stand. I can eventually justify it because I want to implement support
for fetching and repackaging VCS repositories and for caching Debian
packages. These will require more packages than what I'm comfortable
installing on the base Debian image, therefore justifying a dedicated
image.

The `fetch-content static-url` sub-command could definitely be
implemented as a shell script. But Python is readily available and
is more pleasant to maintain than shell, so I wrote it in Python.

`fetch-content task-artifacts` is more advanced and writing it in
Python is more justified, IMO. FWIW, the script is Python 3 only,
which conveniently gives us access to `concurrent.futures`, which
facilitates concurrent download.

`fetch-content` also duplicates functionality found elsewhere.
generic-worker's task payload supports a "mounts" feature which
facilitates downloading remote content, including from a task
artifact. However, this feature doesn't exist on docker-worker.
So we have to implement downloading inside the task rather than
at the worker level. I concede that if all workers had generic-worker's
"mounts" feature and supported concurrent download, `fetch-content`
wouldn't need to exist.

`fetch-content` also duplicates functionality of
`mach artifact toolchain`. I probably could have used
`mach artifact toolchain` instead of writing
`fetch-content task-artifacts`. However, I didn't want to introduce
the requirement of a VCS checkout. `mach artifact toolchain` has its
origins in providing a feature to the build system. And "fetching
artifacts from tasks" is a more generic feature than that. I think
it should be implemented as a generic feature and not something that is
"toolchain" specific.

I think the best place for a generic "fetch content" feature is in
the worker, where content can be defined in the task payload. But as
explained above, that feature isn't universally available. The next
best place is probably run-task. run-task already performs generic,
very-early task preparation steps, such as performing a VCS checkout.
I would like to fold `fetch-content` into run-task and make it all
driven by environment variables. But run-task is currently Python 2
and achieving concurrency would involve a bit of programming (or
adding package dependencies). I may very well port run-task to Python
3 and then fold fetch-content into it. Or maybe we leave
`fetch-content` as a standalone script.

MozReview-Commit-ID: AGuTcwNcNJR

--HG--
extra : source : 0b941cbdca76fb2fbb98dc5bbc1a0237c69954d0
extra : histedit_source : a3e43bdd8a9a58550bef02fec3be832ca304ea93
2018-06-06 14:37:49 -07:00
..
build-binutils Bug 1466060 - Upgrade to binutils 2.28.1. r=nalexander 2018-06-01 17:48:41 +09:00
build-gcc Bug 1460777 - Taskgraph tasks for retrieving remote content; r=dustin, glandium 2018-06-06 14:37:49 -07:00
build-hfsplus Bug 1436800: Update fedora source URL; r=glandium 2018-02-08 12:26:08 -07:00
elfhack Bug 1457482 Correct elfhack's LTO detection to handle -flto=thin r=glandium 2018-06-01 10:10:16 -05:00
stdc++compat Bug 1464084 - Don't export std:🧵:_M_start_thread symbols with --enable-stdcxx-compat. r=froydnj 2018-06-01 08:10:25 +09:00
aix.exp
moz.build Bug 1333003 part 4 - Package the binary of llvm-symbolizer also on Windows. r=ted 2017-03-10 12:24:02 +08:00
mozconfig.asan Bug 1421728 - Add a macosx64 fuzzing-asan build. r=dustin,froydnj 2018-02-08 17:16:41 -05:00
mozconfig.linux Bug 1446809 - Remove some b2g leftover in the build r=glandium 2018-03-20 10:46:23 +01:00
mozconfig.linux32 Bug 1431251 - Remove PKG_CONFIG_LIBDIR from mozconfigs. r=rillian 2018-01-27 11:49:23 +09:00
mozconfig.lto Bug 1457482 Add an LTO Build Target r=glandium 2018-05-30 12:27:25 -05:00
mozconfig.stdcxx Bug 1427339 - Make mozconfig.stdcxx work with both CentOS and Debian-built GCCs. r=gps 2018-01-06 14:19:30 +09:00
mozconfig.tsan
mozilla.in
print-failed-commands.sh
print-non-newline.sh
rewrite_asan_dylib.py bug 1463425 - Fix flake8/pep8 issue by hand in build/ r=gps 2018-05-21 23:58:19 +02:00
run-gprof.sh
run-hiprof.sh
run-mozilla.sh Bug 1407211 - Fix typo in build/unix/run-mozilla.sh from bug 1403366. r=glandium 2017-10-12 07:28:20 +09:00
run-third.sh