PHP cycle time control buffer method_PHP tutorial

for ($i=10; $i>0; $i--)

{ echo $i;

flush();

sleep(1); }

?>

According to the php manual

This function sends all the output of the program so far to the user's browser.

The above code should output $i every second. But this is not necessarily the case in practice. It is possible that after waiting for 10 seconds, all output is presented at the same time.

Okay, let’s change this code to

echo str_pad(" ", 256);

for ($i=10; $i>0; $i--)

{ echo $i;

flush();

sleep(1);

} ?>Hey, after adding this sentence ob_end_clean();, it is OK. In fact, it is also OK if we replace ob_end_clean() with ob_end_flush().

Note: IE needs to receive 256 bytes before starting to display.

Therefore, we need to add before: echo str_pad(" ", 256);

I'll change it again.

echo str_pad(" ", 256);

for ($i=10; $i>0; $i--)

{ echo $i;

ob_flush();//Modify part

flush();

sleep(1); } ?>Run it, do you find that $i is also output every second? Why is this?

Don't worry, let's take a look at php.ini.

Open php.ini, search for output_buffering, we will see a setting like this output_buffering = 4096. Just like its name output_buffering, the function of this setting is to buffer the output. The buffer size is 4096bytes.

In our first piece of code, the reason why the output is not as expected is precisely because this output_buffering buffers all the output. The output will not be sent before 4096 bytes is reached or the script ends.

The function of ob_end_clean() and ob_end_flush() in the second piece of code is to terminate the buffering. In this way, there is no need to wait until there is a buffer of 4096 bytes before being sent out.

In the third piece of code, ob_flush() is used. Its function is to send the buffered data, but it does not terminate the buffering, so it must be used before each flush().

If we don't want to use ob_end_clean(), ob_end_flush() and ob_flush(), we must set the output_buffering in php.ini small enough, for example, set to 0. It should be noted that if you plan to use ini_set("output_buffering", "0") to set it in a script, then please stop, this method will not work. Because at the beginning of the script, the buffering settings have been loaded, and then buffering begins.

You may ask, since ob_flush() sends the buffered data, why do you need to use flush()??? Can't you just use the following code? ?

echo str_pad(" ", 256);

for ($i=10; $i>0; $i--)

{ echo $i;

ob_flush();

sleep(1); } ?>Please note the difference between ob_flush() and flush(). The former is to release data from PHP's buffer, and the latter is to send data that is not in the buffer or has been released to the browser. So when the buffer exists, we must use ob_flush() and flush() at the same time.

So is flush() indispensable here? No, we have another method so that when data is output, it is immediately sent to the browser. The following two pieces of code do not need to use flush(). (When you set output_buffering to 0, even ob_flush() and ob_end_clean() are no longer needed)

ob_implicit_flush(true);

echo str_pad(" ", 256);

for ($i=10; $i>0; $i--)

{ echo $i;

ob_flush();

sleep(1); } ?>

ob_implicit_flush(true);

echo str_pad(" ", 256);

for ($i=10; $i>0; $i--)

{ echo $i;

sleep(1); }

?> Please note ob_implicit_flush(true) above. This function forces the output to be sent to the browser immediately whenever there is output. In this way, there is no need to use flush() to send it to the browser after each output (echo).

The above argument may not be true in some browsers. Because browsers also have their own rules. I used Firefox1.5, IE6, opera8.5 to test. Among them, opera cannot output normally, because it has a rule that if it does not encounter an HTML tag, it will never output unless the script ends. FireFox and IE are relatively normal.

Excerpted from: Lin Xi’s blog

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