为什么PHP会一次性发送所有内容？ [重复]

Question

Possible Duplicate:
what is output buffering?

I have some content that takes a while to be generated by PHP. Meanwhile I would like to use this simple JS trick to display a "Loading..." message. The message would disappear as soon as the output is generated.

<p id="loading_msg">Loading...</p>

<h1>Hello</h1>
<?php
    sleep(2); // This is the greedy function call
    print '<p>This content definitely took a while to be generated !.</p>';
?>

<script type="text/javascript">
    var e = document.getElementById("loading_msg");
    e.style.display = "none";
</script>

The problem is, instead of sending everything up to sleep(2); then blocking, it will wait before all the page is generated, and then, send it all at once. It obviously breaks the purpose of my "Loading..." message, because it doesn't appear before the 2 seconds have elapsed. Any ideas of why, and how I could work around this ?

Answer 1

By default, PHP will buffer your output and send a fewer number of larger chunks to the user. You can use flush to send the contents of write buffer to the user immediately:

<p id="loading_msg">Loading...</p>

<h1>Hello</h1>
<?php
    flush();
    sleep(2);

This won't work if you've previously enabled output buffering by calling ob_start or the php.ini directive output_buffering to 1.