Motivation:
If we don't need the scheduled future, then it will be one less complication when we change Netty Future to no longer extend JDK Future.
It would also result in fewer elements in our API.
Modification:
There was only one real use of ScheduledFuture in our code, in Cache.
This has been changed to wrap an ordinary future with a deadline for implementing the Delayed interface.
All other places were effectively overspecifying by relying on ScheduledFuture.
A few places were also specifying JDK Futures - these have been changed to specify Netty Futures.
Result:
Reduced dependency on the ScheduledFuture interfaces.
Motivation:
We should just add `executor()` to the `ChannelOutboundInvoker` interface and override this method in `Channel` to return `EventLoop`.
Modifications:
- Add `executor()` method to `ChannelOutboundInvoker`
- Let `Channel` override this method and return `EventLoop`.
- Adjust all usages of `eventLoop()`
- Add some default implementations
Result:
API cleanup
Motivation:
At the moment the outbound operations of ChannelHandler take a Promise as argument. This Promise needs to be carried forward to the next handler in the pipeline until it hits the transport. This is API choice has a few quirks which we should aim to remove:
- There is a difference between if you add a FutureListener to the Promise or the Future that is returned by the outbound method in terms of the ordering of execution of the listeners. Sometimes we add the listener to the promise while in reality we usually always want to add it to the future to ensure the listerns are executed in the "correct order".
- It is quite easy to "loose" a promise by forgetting to use the right method which also takes a promise
- We have no idea what EventExecutor is used for the passed in Promise which may invalid our assumption of threading.
While changing the method signature of the outbound operations of the ChannelHandler is a good step forward we should also take care of just remove all the methods from ChannelOutboundInvoker (and its sub-types) that take a Promise and just always use the methods that return a Future only.
Modifications:
- Change the signature of the methods that took a Promise to not take one anymore and just return a Future
- Remove all operations for ChannelOutboundInvoker that take a Promise.
- Adjust all code to cope with the API changes
Result:
Cleaner API which is easier to reason about and easier to use.
Motivation:
The generics for the existing futures, promises, and listeners are too complicated.
This complication comes from the existence of `ChannelPromise` and `ChannelFuture`, which forces listeners to care about the particular _type_ of future being listened on.
Modification:
* Add a `FutureContextListener` which can take a context object as an additional argument. This allows our listeners to have the channel piped through to them, so they don't need to rely on the `ChannelFuture.channel()` method.
* Make the `FutureListener`, along with the `FutureContextListener` sibling, the default listener API, retiring the `GenericFutureListener` since we no longer need to abstract over the type of the future.
* Change all uses of `ChannelPromise` to `Promise<Void>`.
* Change all uses of `ChannelFuture` to `Future<Void>`.
* Change all uses of `GenericFutureListener` to either `FutureListener` or `FutureContextListener` as needed.
* Remove `ChannelFutureListener` and `GenericFutureListener`.
* Introduce a `ChannelFutureListeners` enum to house the constants that previously lived in `ChannelFutureListener`. These constants now implement `FutureContextListener` and take the `Channel` as a context.
* Remove `ChannelPromise` and `ChannelFuture` — all usages now rely on the plain `Future` and `Promise` APIs.
* Add static factory methods to `DefaultPromise` that allow us to create promises that are initialised as successful or failed.
* Remove `CompleteFuture`, `SucceededFuture`, `FailedFuture`, `CompleteChannelFuture`, `SucceededChannelFuture`, and `FailedChannelFuture`.
* Remove `ChannelPromiseNotifier`.
Result:
Cleaner generics and more straight forward code.
Bootstrap methods now return Future<Channel> instead of ChannelFuture
Motivation:
In #8516 it was proposed to at some point remove the specialised ChannelFuture and ChannelPromise.
Or at least make them not extend Future and Promise, respectively.
One pain point encountered in this discussion is the need to get access to the channel object after it has been initialised, but without waiting for the channel registration to propagate through the pipeline.
Modification:
Add a Bootstrap.createUnregistered method, which will return a Channel directly.
All other Bootstrap methods that previously returned ChannelFuture now return Future<Channel>
Result:
It's now possible to obtain an initialised but unregistered channel from a bootstrap, without blocking.
And the other bootstrap methods now only release their channels through the result of their futures, preventing racy access to the channels.
Motivation:
At the moment all methods in `ChannelHandler` declare `throws Exception` as part of their method signature. While this is fine for methods that handle inbound events it is quite confusing for methods that handle outbound events. This comes due the fact that these methods also take a `ChannelPromise` which actually need to be fullfilled to signal back either success or failure. Define `throws...` for these methods is confusing at best. We should just always require the implementation to use the passed in promise to signal back success or failure. Doing so also clears up semantics in general. Due the fact that we can't "forbid" throwing `RuntimeException` we still need to handle this in some way tho. In this case we should just consider it a "bug" and so log it and close the `Channel` in question. The user should never have an exception "escape" their implementation and just use the promise. This also clears up the ownership of the passed in message etc.
As `flush(ChannelHandlerContext)` and `read(ChannelHandlerContext)` don't take a `ChannelPromise` as argument this also means that these methods can never produce an error. This makes kind of sense as these really are just "signals" for the underlying transports to do something. For `RuntimeException` the same rule is used as for other outbound event handling methods, which is logging and closing the `Channel`.
Motifications:
- Remove `throws Exception` from signature
- Adjust code to not throw and just notify the promise directly
- Adjust unit tests
Result:
Much cleaner API and semantics.
Motivation:
Sometime in the past we introduced the concept of Void*Promise. As it turned out this was not a good idea at all as basically each handler in the pipeline need to be very careful to correctly handle this. We should better just remove this "optimization".
Modifications:
- Remove Void*Promise and all the related APIs
- Remove tests which were related to Void*Promise
Result:
Less error-prone API
Motivation:
HTTP is a plaintext protocol which means that someone may be able
to eavesdrop the data. To prevent this, HTTPS should be used whenever
possible. However, maintaining using https:// in all URLs may be
difficult. The nohttp tool can help here. The tool scans all the files
in a repository and reports where http:// is used.
Modifications:
- Added nohttp (via checkstyle) into the build process.
- Suppressed findings for the websites
that don't support HTTPS or that are not reachable
Result:
- Prevent using HTTP in the future.
- Encourage users to use HTTPS when they follow the links they found in
the code.
Motivation:
The wakeup logic in EpollEventLoop is overly complex
Modification:
* Simplify the race to wakeup the loop
* Dont let the event loop wake up itself (it's already awake!)
* Make event loop check if there are any more tasks after preparing to
sleep. There is small window where the non-eventloop writers can issue
eventfd writes here, but that is okay.
Result:
Cleaner wakeup logic.
Benchmarks:
```
BEFORE
Benchmark Mode Cnt Score Error Units
EpollSocketChannelBenchmark.executeMulti thrpt 20 408381.411 ± 2857.498 ops/s
EpollSocketChannelBenchmark.executeSingle thrpt 20 157022.360 ± 1240.573 ops/s
EpollSocketChannelBenchmark.pingPong thrpt 20 60571.704 ± 331.125 ops/s
Benchmark Mode Cnt Score Error Units
EpollSocketChannelBenchmark.executeMulti thrpt 20 440546.953 ± 1652.823 ops/s
EpollSocketChannelBenchmark.executeSingle thrpt 20 168114.751 ± 1176.609 ops/s
EpollSocketChannelBenchmark.pingPong thrpt 20 61231.878 ± 520.108 ops/s
```
Motivation:
In 42742e233f we already added default methods to Channel*Handler and deprecated the Adapter classes to simplify the class hierarchy. With this change we go even further and merge everything into just ChannelHandler. This simplifies things even more in terms of class-hierarchy.
Modifications:
- Merge ChannelInboundHandler | ChannelOutboundHandler into ChannelHandler
- Adjust code to just use ChannelHandler
- Deprecate old interfaces.
Result:
Cleaner and simpler code in terms of class-hierarchy.
Motivation:
We can use lambdas now as we use Java8.
Modification:
use lambda function for all package, #8751 only migrate transport package.
Result:
Code cleanup.
* Decouble EventLoop details from the IO handling for each transport to allow easy re-use of code and customization
Motiviation:
As today extending EventLoop implementations to add custom logic / metrics / instrumentations is only possible in a very limited way if at all. This is due the fact that most implementations are final or even package-private. That said even if these would be public there are the ability to do something useful with these is very limited as the IO processing and task processing are very tightly coupled. All of the mentioned things are a big pain point in netty 4.x and need improvement.
Modifications:
This changeset decoubled the IO processing logic from the task processing logic for the main transport (NIO, Epoll, KQueue) by introducing the concept of an IoHandler. The IoHandler itself is responsible to wait for IO readiness and process these IO events. The execution of the IoHandler itself is done by the SingleThreadEventLoop as part of its EventLoop processing. This allows to use the same EventLoopGroup (MultiThreadEventLoupGroup) for all the mentioned transports by just specify a different IoHandlerFactory during construction.
Beside this core API change this changeset also allows to easily extend SingleThreadEventExecutor / SingleThreadEventLoop to add custom logic to it which then can be reused by all the transports. The ideas are very similar to what is provided by ScheduledThreadPoolExecutor (that is part of the JDK). This allows for example things like:
* Adding instrumentation / metrics:
* how many Channels are registered on an SingleThreadEventLoop
* how many Channels were handled during the IO processing in an EventLoop run
* how many task were handled during the last EventLoop / EventExecutor run
* how many outstanding tasks we have
...
...
* Implementing custom strategies for choosing the next EventExecutor / EventLoop to use based on these metrics.
* Use different Promise / Future / ScheduledFuture implementations
* decorate Runnable / Callables when submitted to the EventExecutor / EventLoop
As a lot of functionalities are folded into the MultiThreadEventLoopGroup and SingleThreadEventLoopGroup this changeset also removes:
* AbstractEventLoop
* AbstractEventLoopGroup
* EventExecutorChooser
* EventExecutorChooserFactory
* DefaultEventLoopGroup
* DefaultEventExecutor
* DefaultEventExecutorGroup
Result:
Fixes https://github.com/netty/netty/issues/8514 .
Motivation:
Optimizing the Epoll channel needs an objective measure of how fast
it is.
Modification:
Add a simple, closed loop, ping-pong benchmark.
Result:
Benchmark can be used to measure #7816
Initial numbers:
```
Result "io.netty.microbench.channel.epoll.EpollSocketChannelBenchmark.pingPong":
22614.403 ±(99.9%) 797.263 ops/s [Average]
(min, avg, max) = (21093.160, 22614.403, 24977.387), stdev = 918.130
CI (99.9%): [21817.140, 23411.666] (assumes normal distribution)
Benchmark Mode Cnt Score Error Units
EpollSocketChannelBenchmark.pingPong thrpt 20 22614.403 ± 797.263 ops/s
```
