Task.WaitAll 会阻塞当前线程，直到所有其他任务完成执行。
Task.WhenAll 方法用于创建一个当且仅当所有其他任务都完成时，该任务才会完成。在第一个示例中，我们可以看到，使用 Task.WhenAll 时，任务完成会在其他任务完成之前执行。这意味着 Task.WhenAll 不会阻止执行。在第二个示例中，我们可以看到，当使用 Task.WaitAll 时，任务完成仅在所有其他任务完成后才执行。这意味着 Task.WaitAll 会阻止执行。
示例
static void Main(string[] args){
Task task1 = new Task(() =>{
for (var i = 0; i < 5; i++){
Console.WriteLine("Task 1 - iteration {0}", i);
Task.Delay(1000);
}
Console.WriteLine("Task 1 complete");
});
Task task2 = new Task(() =>{
for (var i = 0; i < 5; i++){
Console.WriteLine("Task 2 - iteration {0}", i);
Task.Delay(1000);
}
Console.WriteLine("Task 2 complete");
});
task1.Start();
task2.Start();
Console.WriteLine("Waiting for tasks to complete.");
Task.WhenAll(task1, task2);
Console.WriteLine("Both Tasks Completed.");
Console.ReadLine();
}输出
Waiting for tasks to complete. Both Tasks Completed. Task 1 - iteration 0 Task 2 - iteration 0 Task 2 - iteration 1 Task 2 - iteration 2 Task 2 - iteration 3 Task 1 - iteration 1 Task 1 - iteration 2 Task 1 - iteration 3 Task 1 - iteration 4 Task 1 complete Task 2 - iteration 4 Task 2 complete
示例
static void Main(string[] args){
Task task1 = new Task(() =>{
for (var i = 0; i < 5; i++){
Console.WriteLine("Task 1 - iteration {0}", i);
Task.Delay(1000);
}
Console.WriteLine("Task 1 complete");
});
Task task2 = new Task(() =>{
for (var i = 0; i < 5; i++){
Console.WriteLine("Task 2 - iteration {0}", i);
Task.Delay(1000);
}
Console.WriteLine("Task 2 complete");
});
task1.Start();
task2.Start();
Console.WriteLine("Waiting for tasks to complete.");
Task.WaitAll(task1, task2);
Console.WriteLine("Both Tasks Completed.");
Console.ReadLine();
}输出
Waiting for tasks to complete. Task 1 - iteration 0 Task 2 - iteration 0 Task 1 - iteration 1 Task 1 - iteration 2 Task 1 - iteration 3 Task 1 - iteration 4 Task 1 complete Task 2 - iteration 1 Task 2 - iteration 2 Task 2 - iteration 3 Task 2 - iteration 4 Task 2 complete Both Tasks Completed
