Understanding Asynchronous Network Requests in iOS
The Problem of Overwhelming the System with Concurrent Calls
As a developer, we have all faced the challenge of dealing with asynchronous network requests in our apps. When these requests are made concurrently, it can lead to issues such as slow performance, crashes, or even an entire system being overwhelmed. In this article, we will delve into the world of asynchronous network requests and explore ways to mitigate these problems.
The Problem Statement
The problem at hand is that when making multiple asynchronous network requests simultaneously, our app becomes unresponsive. Specifically, it seems that the uploads are causing issues, even though they don’t do anything but make a normal HTTP request. On top of this, the keyboard lag is also a significant problem.
Understanding iOS’s Networking Architecture
Before we dive into the solution, let’s take a look at how iOS handles networking requests.
iOS uses NSURLConnection and AFNetworking to handle network requests. When an app makes an asynchronous request, it creates a connection with the server, sends the request, and waits for the response.
## Creating a Connection
To create a connection, we use `NSURLRequest` and pass it to `[NSURLConnection sendAsynchronousRequest:request queue:queueTwo completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){ ...}]`.
### The Issue with Concurrent Requests
The problem arises when multiple requests are made concurrently. iOS has a limit on the number of concurrent connections that can be established at any given time.
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## Limitations of Concurrent Connections
According to Apple's documentation, there is a maximum limit on the number of concurrent connections you can make. The actual limit depends on several factors, including the type of request and the network conditions.
In our case, we're dealing with uploads which are more resource-intensive than GET requests. This means that even if we're not uploading any data, making multiple concurrent uploads could still lead to issues.
### Using NSOperationQueue for Better Management
One solution to this problem is to use `NSOperationQueue` (more on this later) and make our app more efficient with networking.
```markdown
## Introduction to NSOperationQueue
An `NSOperationQueue` is a powerful tool that allows us to manage a queue of operations. By default, the number of concurrent operations is limited by the system, but we can override this limit or specify a custom value depending on the requirements of our app.
In the context of networking, an `NSOperationQueue` can be used to keep track of ongoing requests and ensure that no new requests are made until the current ones have completed.
### How NSOperationQueue Works
Here's how it works in more detail:
- We create an instance of `NSOperationQueue`.
- We add our network request operations to this queue.
- The operation is executed when it reaches the front of the queue.
- If there are ongoing requests, new ones will wait until those have completed.
By using `NSOperationQueue`, we can ensure that our app doesn't become overwhelmed with concurrent connections and maintain a better user experience.
### AFNetworking's NSOperationQueues
Another popular networking library for iOS is `AFNetworking`. It also includes an `NSOperationQueue` feature to manage batched network calls.
```markdown
## EnqueueBatchOfHTTPRequestOperationsWithRequests
In AFNetworking, you can use the `enqueueBatchOfHTTPRequestOperationsWithRequests:progressBlock:completionBlock:` method to make a batch of HTTP requests concurrently.
This is particularly useful when dealing with multiple uploads or downloads. The progress block is used to display the current status of the operations, while the completion block handles any necessary cleanup after all operations have completed.
Here's an example:
```markdown
## Example Using AFNetworking's NSOperationQueue
[client enqueueBatchOfHTTPRequestOperationsWithRequests:urlRequests progressBlock:^(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations) {
NSLog(@"%d / %d", numberOfFinishedOperations, totalNumberOfOperations);
} completionBlock:^(NSArray *operations) {
NSLog(@"All Done!");
}];
Managing Operations with a Custom Queue
In certain situations, you might need to have more control over the number of concurrent operations. In this case, you can create your own NSOperationQueue instance and use it for managing your network calls.
## Custom NSOperationQueue
Create an instance of `NSOperationQueue` with a custom maximum concurrency value:
```markdown
// Create an instance of NSOperationQueue
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 5; // Set to your desired value
// Add network request operations to the queue
[client enqueueBatchOfHTTPRequestOperationsWithRequests:urlRequests progressBlock:^(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations) {
NSLog(@"%d / %d", numberOfFinishedOperations, totalNumberOfOperations);
} completionBlock:^(NSArray *operations) {
NSLog(@"All Done!");
}];
Best Practices for Managing Concurrent Connections
To ensure that your app handles concurrent connections effectively:
- Avoid making too many requests at once: Keep the number of concurrent connections under control by limiting the maximum concurrency value or using a custom queue.
- Use batching techniques: When possible, make batches of multiple requests to reduce the overhead and optimize performance.
- Implement progress blocks and completion blocks: Keep users informed about the status of their network operations.
By applying these best practices, you can create an efficient networking architecture for your app that handles concurrent connections effectively and maintains a smooth user experience.
Last modified on 2024-06-30