解释Under a synchronous model of computation, every eligible process executes a step in each round, and the messages reach their destinations before the next round begins. So, it takes at most (n − 1) rounds for the algorithm to terminate. This is because, by Lemma 10.1, once D(parent(i)) attains its correct value, it takes one more round for D(i) to become correct. Since (1) D(0) is always correct, (2) the paths are acyclic, and (3) there are n nodes, it may take at most (n − 1) rounds for every D to be correct and the algorithm to terminate. Since in every round every edge carries a message, the message complexity is (n−1)⋅|E|, i.e., O(|V|⋅|E|).

在同步计算模型下，每个合法的进程在每一轮中都会执行一步操作，并且消息在下一轮开始之前到达其目的地。因此，该算法最多需要 (n-1) 轮才能终止。这是因为根据引理10.1，一旦 D(parent(i)) 达到正确的值，再经过一轮 D(i) 就会变得正确。由于 (1) D(0) 总是正确的，(2) 路径是无环的，(3) 有 n 个节点，因此可能需要最多 (n-1) 轮才能使每个 D 变得正确并且算法终止。由于在每一轮中每条边都携带一条消息，因此消息复杂度为 (n-1) * |E|，即 O(|V| * |E|)。

相关问题

A listener indicated an asynchronous response by returning true, but the message channel closed before a response was received

When a listener returns `true` to indicate an asynchronous response, it means that the response will be sent at a later time. However, if the message channel is closed before the response is received, it can lead to issues as the response will not reach the intended recipient.

To address this problem, you can consider implementing a mechanism to handle such scenarios. One approach is to use a callback function or a promise to handle the asynchronous response. The listener can return a unique identifier or a reference to the callback function/promise, which allows the recipient to track the response even if the message channel is closed temporarily.

Here's a general example of using a callback function:

function sendMessage(message, callback) {
  // Send message to the recipient
  // ...

  // When the response is received
  const response = receivedResponse();

  // Invoke the callback function with the response
  callback(response);
}

function handleMessage(message) {
  // Check if it's an asynchronous response
  if (isAsynchronousResponse(message)) {
    // Get the callback function reference from the message
    const callback = getCallbackFromMessage(message);

    // Call the callback function with the received response
    callback(receivedResponse());
  } else {
    // Handle other types of messages
    // ...
  }
}

By using this approach, the recipient can handle both synchronous and asynchronous responses appropriately, even if the message channel closes temporarily.

Ajax.html:35 [Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of it...

这个警告是由浏览器发出的，它告诉你同步 XMLHttpRequest 是过时的，因为它会阻塞主线程，导致用户体验不佳。建议使用异步 XMLHttpRequest 代替。你可以在代码中改为使用异步的 XMLHttpRequest，例如：

var xhr = new XMLHttpRequest();
xhr.open('GET', '/my/url', true); // 第三个参数指示是否使用异步，默认为 true
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        console.log(xhr.responseText);
    }
};
xhr.send();

这样就可以避免警告了。