NET Framework, many objects that establish connections to external resources are created by using static factory methods of other classes that manage these connections. Holding an open database connection that is not required may prevent other concurrent users from gaining access to the database. Some resource types are scarce and should not be held onto. Set such properties once (for example, during startup), and create separate instances if you need to configure different settings. For example, setting DefaultRequestHeaders on the HttpClient class before each request can create a race condition. The HttpClient class is designed to be used in this manner, but other classes might not support concurrent requests, so check the available documentation.īe careful about setting properties on shared objects, as this can lead to race conditions. Objects that you share across multiple requests must be thread-safe. Other objects might support pooling, enabling the system to spread the workload across multiple instances. The HttpClient class is designed to be shared rather than pooled. The type of shared resource might dictate whether you should use a singleton or create a pool. If a class is not shareable (not thread-safe), then this antipattern does not apply. The key element of this antipattern is repeatedly creating and destroying instances of a shareable object. This method uses the shared instance of HttpClient for every call to GetProductAsync. Static SingleHttpClientInstanceController() Private static readonly HttpClient httpClient public class SingleHttpClientInstanceController : ApiController
The following example uses a static HttpClient instance, thus sharing the connection across all requests. If the class that wraps the external resource is shareable and thread-safe, create a shared singleton instance or a pool of reusable instances of the class.
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How to fix improper instantiation antipattern Simulate delay due to setup and configuration of ExpensiveToCreateService Return await expensiveToCreateService.GetProductByIdAsync(id) Var expensiveToCreateService = new ExpensiveToCreateService() public class NewServiceInstancePerRequestController : ApiController Continually creating and destroying instances of this class might adversely affect the scalability of the system. Here the issue is not necessarily socket exhaustion, but simply how long it takes to create each instance. The following example creates an instance of the ExpensiveToCreateService class. Other classes that wrap resources or are expensive to create might cause similar issues. This problem is not restricted to the HttpClient class. Under heavy load, the web server may exhaust the number of available sockets, resulting in SocketException errors. A new HttpClient object is created for each user request. In a web application, this technique is not scalable.
Var result = await httpClient.GetStringAsync(string.Format(" hostName)) Using (var httpClient = new HttpClient()) Public async Task GetProductAsync(string id) This method creates a new instance of HttpClient and disposes it for every call to GetProductAsync. public class NewHttpClientInstancePerRequestController : ApiController NET.) The following ASP.NET example creates an instance of HttpClient to communicate with a remote service. NET libraries, but the pattern is not unique to. However, it's a common misunderstanding that these classes should be acquired only as necessary and released quickly. These classes are intended to be instantiated once and reused throughout the lifetime of an application. Connects to Redis, including Azure Cache for Redis. Posts and receives messages to a Service Bus queue. Communicates with a web service using HTTP. Here are some examples of broker classes that are relevant to Azure applications: Internally, these classes typically manage their own connections to the resource, acting as brokers that clients can use to access the resource. Many libraries provide abstractions of external resources. An antipattern is a common response to a recurring problem that is usually ineffective and may even be counter-productive. This behavior can hurt performance, and is called an improper instantiation antipattern. Sometimes new instances of a class are continually created, when it is meant to be created once and then shared.