Trying to figure how will my Async calls to Third Party Libs get offloaded to OS,
Netty has Boss threads that are used to accept incoming connections but the processing of a connection is handed off to a worker thread (i.e. IO-threads). The threads that are used by the EventLoopGroup are "IO-threads", these threads IO-threads will handle 0-n Channels. As I understand, Netty has an event cycle, so whenever you call any Async IO function the request gets pushed down to the o/s level, and it uses epoll and waits for an event to send back to netty and the IO-threads are free to serve request on other channels, When the operating system generates an event that netty subscribed to, netty then has an event loop that gets triggered. Further, You should not block (sleep in) these IO threads otherwise your clients will be waiting for a response and you will also waste a thread that could have been used to process another request, if you want to ensure a ChannelHandler will be offloaded from the IO-thread you would usually create a DefaultEventExecutorGroup and specify it when you add the ChannelHandler.
Now as per my understanding, a channelPipelineFactory is used to create a ChannelPipeline, each time a request is received by the server. A ChannelPipeline contains a series of ChannelHandlers that process the request. Now the question I have is, If a few of the handlers in my pipeline need to fetch data from a cache like Redis and Aerospike, this is Blocking IO. The processing of the request is blocked by that IOThread until the IO is completed. My understanding of event-driven async I/O coming from NodeJS is that there is one event loop and there are a series of callback functions registered for blocking I/O operations, and these get invoked whenever the I/O is complete. How do I achieve the same in Netty? In, NodeJs I could call the Async functions of Redis & Aerospike Client Libraries. The Async functions returned promise and the callback function passed in Async Call would be called when the IO completes(i.e. Data is Fetched from Caches). NodeJs knows some IO is going so it frees the Request Processing pipeline and handles other Requests. How do I signal Netty that free the IO-threads so that they can process other Requests of my HTTP Server and push the request down to OS level and wait for the event from OS, I could use ExecutorGroup and do the function call in a separate Thread but that would defeat the purpose as it is not EventDriven.
This is what i got from Chat GPT , not sure if this is correct
Instantiating an asynchronous operation on an Executor and obtaining a Future does not automatically free the Executor thread. The Executor thread will continue to be occupied until the asynchronous operation associated with the Future is completed.
When you submit an asynchronous task to an Executor, it typically executes the task in a separate thread. The Executor thread is responsible for executing the task and monitoring its progress. When you obtain a Future representing the result of the task, it allows you to check the completion status, retrieve the result, or perform other actions based on the task's completion.
However, it's important to note that the Future itself does not have control over the lifecycle of the Executor thread. The Executor thread will be released and made available for other tasks only when the associated asynchronous operation completes.
Here's an example to illustrate this behavior:
Executor executor = ...; // Get an Executor
Future<String> future = executor.submit(() -> {
// Perform asynchronous task
return "Result";
});
// The Executor thread is still occupied until the task completes
// Wait for the task to complete and retrieve the result
String result = future.get();
// The Executor thread is released at this point
In the above example, the Executor thread is occupied while the asynchronous task is being executed. The get() method on the Future blocks until the task completes, and only after that, the Executor thread is released and becomes available for other tasks.
If you want to free the Executor thread without blocking, you can use non-blocking techniques such as callbacks or attaching listeners to the Future object. By providing a callback or listener, you can asynchronously handle the completion of the operation without blocking the Executor thread.
executor.submit(() -> {
// Perform asynchronous task
return "Result";
}).addListener((FutureListener<String>) future -> {
// Handle completion asynchronously
if (future.isSuccess()) {
String result = future.get();
// Process the result
} else {
Throwable cause = future.cause();
// Handle the failure
}
});
In this case, the addListener() method allows you to attach a listener to the Future object, which will be invoked asynchronously when the operation completes. This approach allows the Executor thread to be released immediately after the task is submitted, without blocking it until the task completes.
So, to summarize, instantiating an asynchronous operation on an Executor and obtaining a Future does not automatically free the Executor thread. The thread will be occupied until the associated asynchronous operation completes. To free the Executor thread without blocking, you can use non-blocking techniques such as callbacks or attaching listeners to the Future object.