php output_buffering cache usage introduction-PHP Tutorial-php.cn

php output_buffering cache usage introduction

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Release： 2016-07-25 08:55:20

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for($i=0; $i<10; $i++){
echo $i.'
';
sleep(2);
}
?>

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Running results: The output will not be output until all scripts are completed, because the data is not full of the size of a buffer.

Example 2, output_buffering=4096, output less data (less than one buffer), turn off output_buffering, modify output_buffering=0 in php.ini

for($i=0; $i<10; $i++){
echo $i.str_repeat(" ",500).'
'; / / The page will not be displayed until 256 (or more) bytes have been received, so some extra spaces must be sent to allow these browsers to display the page content.
flush();
sleep(1);
}
?>

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Run results: Because php buffering is disabled, there is no need to wait for the script to run before it can be output. The data does not stay in the php buffer, and you can see intermittent output. echo -> tcp buffer -> browser

Example 3, when output_buffering=4096, output larger data (larger than one buffer) without using ob_start()

for($i=0; $i<10; $i++){
echo file_get_contents('f.txt').$i.'
';
sleep (1);
}
?>

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Run the results: f.txt is a file larger than 4kb. Because it is larger than the default buffer value and the buffer space is not enough, it will be output every time the buffer is full, so you can see intermittent output.

Example 4, when output_buffering=4096, to output larger data (larger than one buffer), use ob_start()

ob_start();
for($i=0; $i<10; $i++){
echo file_get_contents('f.txt').$i.' sleep(1);
}
?>

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Run the results: Because ob_start() is used, a large enough space will be set for the buffer, so it will be saved until the script is executed and then output.

output_buffering method 1.ob_start Activate the output_buffering mechanism. Once activated, the script will no longer be output directly to the browser, but will be temporarily written to the php buffering area. It is not sent until the script has finished running.

2.ob_get_contents Get the data in php buffering. Note: it must be called before ob_end_clean(), otherwise you will only get null characters.

3.ob_end_flush and ob_end_clean ob_end_flush will output the data in php buffering, but will not clear it. ob_end_clean will not output, it will only clear the data in php buffering.

Note: The descriptions of ob_flush/flush in the manual all refresh the output buffer and need to be used together. In fact, the two of them operate on different objects. In some cases, flush does nothing at all.

ob_* series of functions operate the output buffer of PHP itself. So, ob_flush flushes PHP's own buffer.

And flush, strictly speaking, this only has practical effect when PHP is installed as an Apache Module (handler or filter). It is the buffer that refreshes WebServer (which can be considered specifically apache). Under the sapi of the apache module, flush will indirectly call the api of apache by calling the flush member function pointer of sapi_module: ap_rflush refreshes the output buffer of apache.

Some Apache modules, such as mod_gzip, may cache their own output, which will cause the results generated by the flush() function to not be sent to the client browser immediately. Even browsers cache received content before displaying it.

For example, the Netscape browser caches content until it receives a newline or the beginning of an html tag, and does not display the entire table until it receives a

tag. Some versions of Microsoft Internet Explorer will only start displaying the page after receiving 256 bytes, so some extra spaces must be sent for these browsers to display the page content.

The correct usage order is: ob_flush first, then flush. Of course, under other sapi, it is okay not to call flush, but in order to ensure the portability of the code, it is recommended to use it in conjunction with it.