Task.WaitAll vs. Task.WhenAll: When Should I Use Which?

In-depth understanding of Task.WaitAll and Task.WhenAll

In asynchronous programming, developers often need to choose between Task.WaitAll and Task.WhenAll. These two methods each have their own characteristics and applicable scenarios.

Task.WaitAll

Task.WaitAll is a blocking method that pauses the execution of the current thread until all specified tasks are completed. This means that when using Task.WaitAll, other code and operations must wait for the task to complete before continuing. It is very useful in scenarios where synchronized behavior is required.

Task.WhenAll

Task.WhenAll is a non-blocking method. When called, it returns a task that represents the completion of all specified tasks. This allows code to continue executing while the task is still running. Once all tasks are completed, you can wait for the returned tasks to get the results.

Code Example

The following code snippet illustrates the difference between Task.WaitAll and Task.WhenAll:

Use Task.WaitAll blocking method:

Task task1 = Task.Run(() => { /* 任务 1 */ });
Task task2 = Task.Run(() => { /* 任务 2 */ });

Task.WaitAll(task1, task2);

// 代码在两个任务都完成后继续执行

Non-blocking way using Task.WhenAll:

Task task1 = Task.Run(() => { /* 任务 1 */ });
Task task2 = Task.Run(() => { /* 任务 2 */ });

Task whenAllTask = Task.WhenAll(task1, task2);

await whenAllTask; // 代码在 whenAllTask 完成后继续执行

In the first example, Task.WaitAll blocks the current thread until task1 and task2 complete. In the second example, Task.WhenAll returns a task (whenAllTask) that represents the completion of two tasks. This allows code to execute asynchronously while the task is still running. Once both tasks are completed, the code uses await to wait for whenAllTask to complete.

Choose the appropriate method

The choice of

Task.WaitAll and Task.WhenAll depends on the specific needs of the application. Task.WaitAll is suitable when synchronized behavior is required. Task.WhenAll is better when asynchronous execution is required, allowing the application to continue performing other tasks while waiting for the specified task to complete.

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