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Package console-parallelization
Short Description Enables parallelization of Symfony Console commands
License MIT
Informations about the package console-parallelization
Parallelization for the Symfony Console
This library supports the parallelization of Symfony Console commands.
- How it works
- Installation
- Usage
- The API
- The ParallelCommand and the Parallelization trait
- Items
- Segments
- Batches
- Configuration
- Hooks
- Subscribed Services
- Differences with Amphp/ReactPHP
- Contribute
- Upgrade
- Authors
- License
How it works
When you launch a command with multiprocessing enabled, a main process fetches items and distributes them across the given number of child processes over the standard input. Child processes are killed after a fixed number of items (a segment) in order to prevent them from slowing down over time.
Optionally, the work of child processes can be split down into further chunks (batches). You can perform certain work before and after each of these batches (for example flushing changes to the database) in order to optimize the performance of your command.
Installation
Use Composer to install the package:
Usage
Add parallelization capabilities to your project, you can either extend the
ParallelCommand
class or use the Parallelization
trait:
You can run this command like a regular Symfony Console command:
Or, if you want, you can run the command using parallelization:
The API
The ParallelCommand and the Parallelization trait
This library offers a ParallelCommand
base class and a Parallelization
trait. If you are
looking for a basic usage, the ParallelCommand
should be simpler to use as it provides the
strictly required methods as abstract methods. All other hooks can be configured by
overriding the ::configureParallelExecutableFactory()
method.
The Parallelization
trait on the other hand implements all hooks by default, requiring a bit
less manual task. It does require to call ParallelizationInput::configureCommand()
to add the parallelization
related input arguments and options.
Items
The main process fetches all the items that need to be processed and passes them to the child processes through their Standard Input (STDIN). Hence, items must fulfill two requirements:
- Items must be strings
- Items must not contain newlines
Typically, you want to keep items small in order to offload processing from the main process to the child process. Some typical examples for items:
- The main process reads a file and passes the lines to the child processes
- The main processes fetches IDs of database rows that need to be updated and passes them to the child processes
Segments
When you run a command with multiprocessing enabled, the items returned by
fetchItems()
are split into segments of a fixed size. Each child processes
process a single segment and kills itself after that.
By default, the segment size is the same as the batch size (see below), but you
can try to tweak the performance of your command by choosing a different segment
size (ideally a multiple of the batch size). You can do so by overriding the
getSegmentSize()
method:
Batches
By default, the batch size and the segment size are the same. If desired, you can however choose a smaller batch size than the segment size and run custom code before or after each batch. You will typically do so in order to flush changes to the database or free resources that you don't need anymore.
To run code before/after each batch, override the hooks runBeforeBatch()
and
runAfterBatch()
:
You can customize the default batch size of 50 by overriding the getBatchSize()
method:
Configuration
The library offers a wide variety of configuration settings:
::getParallelExecutableFactory()
allows you to completely configure theParallelExecutorFactory
factory which goes from fragment, batch sizes, which PHP executable is used or any of the process handling hooks.::configureParallelExecutableFactory()
is a different, lighter extension point to configure theParallelExecutorFactory
factory.::getContainer()
allows you to configure which container is used. By default, it passes the application's kernel's container if there is one. This is used by the default error handler which resets the container in-between each item failure to avoid things such as a broken Doctrine entity manager. If you are not using a kernel (e.g. outside a Symfony application), no container will be returned by default.::createErrorHandler()
allows you to configure the error handler you want to use.::createLogger()
allows you to completely configure the logger you want.
Hooks
The library supports several process hooks which can be configured via
::configureParallelExecutableFactory()
:
Method* | Scope | Description |
---|---|---|
runBeforeFirstCommand($input, $output) |
Main process | Run before any child process is spawned |
runAfterLastCommand($input, $output) |
Main process | Run after all child processes have completed |
runBeforeBatch($input, $output, $items) |
Child process | Run before each batch in the child process (or main if no child process is spawned) |
runAfterBatch($input, $output, $items) |
Child process | Run after each batch in the child process (or main if no child process is spawned) |
*: When using the Parallelization
trait, those hooks can be directly configured by overriding the corresponding method.
Subscribed Services
You should be using subscribed services or proxies. Indeed, you may otherwise end up with the issue that the service
initially injected in the command may end up being different from the one used by the container. This is because upon
error, the ResetServiceErrorHandler
error handler is used which resets the container when an item fails. As a result,
if the service is not directly fetched from the container (to get a fresh instance if the container resets), you will
end up using an obsolete service.
A common symptom of this issue is to run into a closed entity manager issue.
Differences with Amphp/ReactPHP
If you came across this library and wonder what the differences are with Amphp or ReactPHP or other potential parallelization libraries, this section is to highlight a few differences.
The primary difference is the parallelization mechanism itself. Amphp or ReactPHP work by spawning a pool of workers and distributing the work to those. This library however, spawns a pool of processes. To be more specific, the differences lies in how the spawn processed are used:
- An Amphp/ReactPHP worker can share state; with this library however you cannot easily do so.
- A worker may handle multiple jobs, whereas with this library the process will be killed after each segment is completed. To bring it to a similar level, it would be somewhat equivalent to consider the work of handling a segment in this library as a Amphp/ReactPHP worker task, and that the worker is killed after handling a single task.
The other difference is that this library works with a command as its central point. This offers the following advantages:
- No additional context need to be provided: once in your child process, you are in your command as usual. No custom bootstrap is necessary.
- The command can be executed with and without parallelization seamlessly. It is also trivial to mimic the execution of
a child process as it is a matter of using the
--child
option and passing the child items via the STDIN. - It is easier to adapt the distribution of the load and memory leaks of the task by configuring the segment and batch sizes.
Contribute
Contributions to the package are always welcome!
- Report any bugs or issues you find on the issue tracker.
- You can grab the source code at the package's Git repository.
To run the CS fixer and tests you can use the command make
. More details
available with make help
.
Upgrade
See the upgrade guide.
Authors
License
All contents of this package are licensed under the MIT license.
All versions of console-parallelization with dependencies
fidry/cpu-core-counter Version ^0.5.0 || ^1.0
nikic/iter Version ^2.2
psr/log Version ^1.1 || ^2.0 || ^3.0
symfony/console Version ^6.4
symfony/dependency-injection Version ^6.4
symfony/deprecation-contracts Version ^2.5 || ^3.1
symfony/process Version ^6.4
symfony/service-contracts Version ^3.3
thecodingmachine/safe Version ^1.3.3 || ^2.4
webmozart/assert Version ^1.5