Introduction to plugins🔗
Plugins contain the implementations of vAccel operations. While the vAccel library itself is the only requirement to compile a vAccel application, you need to use a plugin for the application to actually do something useful.
The use of plugins can become clearer by revisiting the image classification example from Running the examples.
As we have already shown, to specify a backend plugin you have to set the VACCEL_PLUGINS environment variable.
Ensure VACCEL_PLUGINS is not set in the environment while keeping debug logging enabled:
If you run the example, there will be no errors concerning the binaries themselves (ie. undefined symbols) but the operation will fail at runtime:
$ classify /usr/local/share/vaccel/images/example.jpg 1
2025.04.05-19:25:04.80 - <debug> Initializing vAccel
2025.04.05-19:25:04.80 - <info> vAccel 0.6.1-194-19056528
2025.04.05-19:25:04.80 - <debug> Config:
2025.04.05-19:25:04.80 - <debug> plugins = (null)
2025.04.05-19:25:04.80 - <debug> log_level = debug
2025.04.05-19:25:04.80 - <debug> log_file = (null)
2025.04.05-19:25:04.80 - <debug> profiling_enabled = false
2025.04.05-19:25:04.80 - <debug> version_ignore = false
2025.04.05-19:25:04.80 - <debug> Created top-level rundir: /run/user/1002/vaccel/k0R150
2025.04.05-19:25:04.80 - <debug> New rundir for session 1: /run/user/1002/vaccel/k0R150/session.1
2025.04.05-19:25:04.80 - <debug> Initialized session 1
Initialized session with id: 1
2025.04.05-19:25:04.80 - <debug> session:1 Looking for plugin implementing VACCEL_OP_IMAGE_CLASSIFY
2025.04.05-19:25:04.80 - <warn> None of the loaded plugins implement VACCEL_OP_IMAGE_CLASSIFY
Could not run op: 95
2025.04.05-19:25:04.80 - <debug> Released session 1
2025.04.05-19:25:04.80 - <debug> Cleaning up vAccel
2025.04.05-19:25:04.80 - <debug> Cleaning up sessions
2025.04.05-19:25:04.80 - <debug> Cleaning up resources
2025.04.05-19:25:04.80 - <debug> Cleaning up plugins
It is clear from the output that no implementation is found for the VACCEL_OP_IMAGE_CLASSIFY operation. By comparing the output with classify from the previous document, you can see that the reason is that no plugin has been loaded.
You can find out more about the available plugins and their usage in the Plugins section.
Using a plugin from a non-standard library path🔗
It is recommended that vAccel and the vAccel plugins are installed in the standard library search paths for ease of use (ie. /usr/lib, /usr/local/lib etc.). If this is not possible or desirable there are two ways to use the plugins:
- Assuming vAccel is installed in a standard path, use the full path to specify the plugin. For example, if the
NoOpplugin is installed in/opt/noop/lib:
or,
- Add the vAccel/plugin library paths to the library search paths and specify the plugin as usual. For example, if vAccel and the
NoOpplugin are installed in/opt/vaccel/lib: