Libcurl

Question

我正在尝试了解 curl_multi_perform 的工作原理。文档说：

This function performs transfers on all the added handles that need attention in an non-blocking fashion. The easy handles have previously been added to the multi handle with curl_multi_add_handle.

When an application has found out there's data available for the multi_handle or a timeout has elapsed, the application should call this function to read/write whatever there is to read or write right now etc.

问题一：“应用程序应该调用”是什么意思？应用程序如何导致某些事情？您是说程序员应该调用吗？

好的，我找到了两个简单的用法示例 - "curl_multi_perform":

1 - https://everything.curl.dev/libcurl/drive/multi

int transfers_running;
do {
   curl_multi_wait ( multi_handle, NULL, 0, 1000, NULL);
   curl_multi_perform ( multi_handle, &transfers_running );
} while (transfers_running);

2 - enter link description here

int still_running;
do {
  CURLMcode mc = curl_multi_perform(multi_handle, &still_running);
 
  if(!mc && still_running)
    /* wait for activity, timeout or "nothing" */
    mc = curl_multi_poll(multi_handle, NULL, 0, 1000, NULL);
 
  if(mc) {
    fprintf(stderr, "curl_multi_poll() failed, code %d.\n", (int)mc);
    break;
  }
 
/* if there are still transfers, loop! */
} while(still_running);

-首先：

在第一个示例中 curl_multi_perform 在 curl_multi_wait 之后调用。
在第二个例子中 curl_multi_perform 在 curl_multi_wait 之前被调用。

什么都不清楚。

其次：

为什么我需要循环调用 curl_multi_perform ??没看懂。

为什么一次调用不够？

Answer 1

Question 1: What does the "application should call" mean? How can an application cause something? Did you mean the programmer should call ?

程序员不调用函数。程序员编写告诉计算机做什么的程序。所以这意味着程序员应该编写告诉应用程序调用函数的代码。

in the first example curl_multi_perform is called after curl_multi_wait.

in the second example curl_multi_perform is called before curl_multi_wait.

两种顺序都行。正如文档所说：

This function does not require that there actually is any data available for reading or that data can be written, it can be called just in case.

如果没有可用的，它会立即return，更新transfers_running。

Why do I need to call curl_multi_perform in a loop ?? I do not understand.

因为正在进行多项传输。 curl_multi_wait() returns 一旦有任何数据可用。处理完该数据后，您需要继续等待其他传输。

此外，这不会等待传输完成，它会在数据到达时处理部分数据。所以你必须一直调用它，直到你发送或接收所有内容。

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