f79810bac1
Taken from `Perl::Critic`:
A common idiom in perl for dealing with possible errors is to use `eval`
followed by a check of `$@`/`$EVAL_ERROR`:
eval {
...
};
if ($EVAL_ERROR) {
...
}
There's a problem with this: the value of `$EVAL_ERROR` (`$@`) can change
between the end of the `eval` and the `if` statement. The issue are object
destructors:
package Foo;
...
sub DESTROY {
...
eval { ... };
...
}
package main;
eval {
my $foo = Foo->new();
...
};
if ($EVAL_ERROR) {
...
}
Assuming there are no other references to `$foo` created, when the
`eval` block in `main` is exited, `Foo::DESTROY()` will be invoked,
regardless of whether the `eval` finished normally or not. If the `eval`
in `main` fails, but the `eval` in `Foo::DESTROY()` succeeds, then
`$EVAL_ERROR` will be empty by the time that the `if` is executed.
Additional issues arise if you depend upon the exact contents of
`$EVAL_ERROR` and both `eval`s fail, because the messages from both will
be concatenated.
Even if there isn't an `eval` directly in the `DESTROY()` method code,
it may invoke code that does use `eval` or otherwise affects
`$EVAL_ERROR`.
The solution is to ensure that, upon normal exit, an `eval` returns a
true value and to test that value:
# Constructors are no problem.
my $object = eval { Class->new() };
# To cover the possiblity that an operation may correctly return a
# false value, end the block with "1":
if ( eval { something(); 1 } ) {
...
}
eval {
...
1;
}
or do {
# Error handling here
};
Unfortunately, you can't use the `defined` function to test the result;
`eval` returns an empty string on failure.
Various modules have been written to take some of the pain out of
properly localizing and checking `$@`/`$EVAL_ERROR`. For example:
use Try::Tiny;
try {
...
} catch {
# Error handling here;
# The exception is in $_/$ARG, not $@/$EVAL_ERROR.
}; # Note semicolon.
"But we don't use DESTROY() anywhere in our code!" you say. That may be
the case, but do any of the third-party modules you use have them? What
about any you may use in the future or updated versions of the ones you
already use?
|
||
|---|---|---|
| .github/workflows | ||
| datadog | ||
| doc | ||
| examples | ||
| foreman | ||
| src | ||
| tests | ||
| .gitignore | ||
| bootstrap | ||
| configure.ac | ||
| COPYING | ||
| default.nix | ||
| flake.lock | ||
| flake.nix | ||
| hydra-api.yaml | ||
| hydra-module.nix | ||
| INSTALL | ||
| Makefile.am | ||
| Procfile | ||
| README.md | ||
| shell.nix | ||
| version | ||
Hydra
Hydra is a Continuous Integration service for Nix based projects.
Installation And Setup
Note: The instructions provided below are intended to enable new users to get a simple, local installation up and running. They are by no means sufficient for running a production server, let alone a public instance.
Enabling The Service
Running Hydra is currently only supported on NixOS. The hydra module allows for an easy setup. The following configuration can be used for a simple setup that performs all builds on localhost (Please refer to the Options page for all available options):
{
services.hydra = {
enable = true;
hydraURL = "http://localhost:3000";
notificationSender = "hydra@localhost";
buildMachinesFiles = [];
useSubstitutes = true;
};
}
Creating An Admin User
Once the Hydra service has been configured as above and activate you should already be able to access the UI interface at the specified URL. However some actions require an admin user which has to be created first:
$ su - hydra
$ hydra-create-user <USER> --full-name '<NAME>' \
--email-address '<EMAIL>' --password <PASSWORD> --role admin
Afterwards you should be able to log by clicking on "Sign In" on the top right of the web interface using the credentials specified by hydra-crate-user. Once you are logged in you can click "Admin -> Create Project" to configure your first project.
Creating A Simple Project And Jobset
In order to evaluate and build anything you need to crate projects that contain jobsets. Hydra supports imperative and declarative projects and many different configurations. The steps below will guide you through the required steps to creating a minimal imperative project configuration.
Creating A Project
Log in as adminstrator, click "Admin" and select "Create project". Fill the form as follows:
- Identifier:
hello - Display name:
hello - Description:
hello project
Click "Create project".
Creating A Jobset
After creating a project you are forwarded to the project page. Click "Actions" and choose "Create jobset". Fill the form with the following values:
- Identifier:
hello - Nix expression:
examples/hello.nixinhydra - Check interval: 60
- Scheduling shares: 1
We have to add two inputs for this jobset. One for nixpkgs and one for hydra (which we are referrencing in the Nix expression above):
-
Input name:
nixpkgs -
Type:
Git checkout -
Value:
https://github.com/nixos/nixpkgs-channels nixos-20.03 -
Input name:
hydra -
Type:
Git checkout -
Value:
https://github.com/nixos/hydra
Make sure State at the top of the page is set to "Enabled" and click on "Create jobset". This concludes the creation of a jobset that evaluates ./examples/hello.nix once a minute. Clicking "Evaluations" should list the first evaluation of the newly created jobset after a brief delay.
Building And Developing
Building Hydra
You can build Hydra via nix-build using the provided default.nix:
$ nix-build
Development Environment
You can use the provided shell.nix to get a working development environment:
$ nix-shell
$ ./bootstrap
$ configurePhase # NOTE: not ./configure
$ make
Executing Hydra During Development
When working on new features or bug fixes you need to be able to run Hydra from your working copy. This can be done using foreman:
$ nix-shell
$ # hack hack
$ make
$ foreman start
Have a look at the Procfile if you want to see how the processes are being started. In order to avoid conflicts with services that might be running on your host, hydra and postgress are started on custom ports:
- hydra-server: 63333
- postgresql: 64444
Note that this is only ever meant as an ad-hoc way of executing Hydra during development. Please make use of the NixOS module for actually running Hydra in production.
JSON API
You can also interface with Hydra through a JSON API. The API is defined in hydra-api.yaml and you can test and explore via the swagger editor
Additional Resources
- Hydra User's Guide
- Hydra on the NixOS Wiki
- hydra-cli
- Peter Simons - Hydra: Setting up your own build farm (NixOS)
License
Hydra is licensed under GPL-3.0
Icons provided free by EmojiOne.