.NET Best Practices: Avoid Abuse

In C#,It is a common method used to perform asynchronous tasks in background threads.

It is very suitable for scenarios that require parallel processing.But if not used with caution, may result in additional thread pool scheduling, which in turn affects the performance of the program.

What is a thread pool?

Thread pooling is an optimization mechanism in .NET that reduces the overhead of thread creation and destruction by reusing a fixed number of threads.

Threads in thread pool are forHandle short-term tasksDesigned, it does not require frequent creation and destruction, so it can significantly improve performance.

The mechanism behind it

The function of the method is to queue the specified delegate to the thread pool for execution.

This sounds handy because it allows you to easily perform tasks in the background thread. However, its use is not always the best choice, especially in certain specific cases.

Unnecessary thread pool scheduling

Normally, when you callWhen , the system will arrange tasks to be executed in the thread pool, which is already optimized and suitable for handling concurrent tasks.

But if you have already run the code on a thread pool thread, use againpossibleCause unnecessaryadditional scheduling.

Suppose we have an asynchronous method that is already running in the worker thread, as follows:

public async Task ProcessDataAsync()
 {
     // Do some operations
     await (1000); // Simulate some asynchronous operations

     // At this time, it is already running on a thread pool thread
     // Calling again will result in unnecessary extra thread pool scheduling
     await (() => ProcessMoreData());
 }

In this example,ProcessDataAsyncIn-houseawait (1000)The current thread will be returned to the thread pool and wait for the asynchronous operation to complete.

And inWhen called, the system will redirect theProcessMoreDataMethods are submitted to thread pool. This leads to an unnecessary thread pool scheduling: the task could have been executed directly on the current thread, rather than starting a new thread pool thread.

Why isn't this a good practice?

Additional thread pool scheduling: Thread pool scheduling is not free. Each time a task is scheduled to a thread pool, the system needs to do some work to select an idle thread to handle the task, and this process is overhead. If you have already executed code on a thread pool thread, continuing to execute tasks directly will save unnecessary overhead.

Thread pool resource consumption: The size of the thread pool is limited. Too much thread pool scheduling may lead to the exhaustion of thread pool threads, which affects the application's responsiveness. When the thread pool thread is exhausted, new tasks will have to queue for idle threads, which can cause delays.

Context Switching: Multiple scheduling tasks will result in frequent context switches, and each context switch has performance costs. Under high load conditions, this cost can be very obvious, affecting the overall performance of the program.

How to optimize?

Avoid unnecessary: Avoid using it again if the task is already executed on a thread pool thread. Call the method directly, or useasyncandawaitContinue to follow-up tasks.

Use asynchronous operations: When possible, try to use itasyncandawaitto handle asynchronous operations, so that the system will automatically manage thread scheduling instead of explicitly creating new tasks. For example, in the above example, follow-up operations should be performed directly:

public async Task ProcessDataAsync()
 {
     // Do some operations
     await (1000); // Simulate some asynchronous operations

     // Perform subsequent operations directly, rather than using
     ProcessMoreData();
 }

Reasonable use: Use if the task is a compute-intensive operation, or other reasons that need to be executed in a background thread (such as avoiding blocking UI threads). For I/O intensive or other asynchronous tasks, try to use itasyncandawait。

Summarize

It is a powerful tool, but in some scenarios, overuse of it can bring unnecessary performance overhead.

Especially when it is already running in the background thread, callThis may result in additional thread pool scheduling and unnecessary resource consumption.

In order to optimize program performance, you should choose and use it reasonably according to the nature of the taskOr a way to perform tasks directly.