3

When I use file_get_contents and pass it as a parameter to another function, without assigning it to a variable, does that memory get released before the script execution finishes?

For Example:

preg_match($pattern, file_get_contents('http://domain.tld/path/to/file.ext'), $matches);

Will the memory used by file_get_contents be released before the script finishes?

UnkwnTech
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4 Answers4

11

The temporary string created to hold the file contents will be destroyed. Without delving into the sources to confirm, here's a couple of ways you can test that a temporary value created as a function parameter gets destroyed:

Method 1: a class which reports its destruction

This demonstrates lifetime by using a class which reports on its own demise:

class lifetime
{
    public function __construct()
    {
         echo "construct\n";
    }
    public function __destruct()
    {
         echo "destruct\n";
    }


}

function getTestObject()
{
   return new lifetime();
}


function foo($obj)
{
   echo "inside foo\n";
}




echo "Calling foo\n";
foo(getTestObject());
echo "foo complete\n";

This outputs

Calling foo
construct
inside foo
destruct
foo complete

Which indicates that the implied temporary variable is destroyed right after the foo function call.

Method 2: measure memory usage

Here's another method which offers further confirmation using memory_get_usage to measure how much we've consumed. 

function foo($str)
{
   $length=strlen($str);

   echo "in foo: data is $length, memory usage=".memory_get_usage()."\n";
}

echo "start: ".memory_get_usage()."\n";
foo(file_get_contents('/tmp/three_megabyte_file'));
echo "end: ".memory_get_usage()."\n";

This outputs

start: 50672
in foo: data is 2999384, memory usage=3050884
end: 51544
Paul Dixon
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0

In following code memory usage = 6493720

start: 1050504

end: 6492344

echo "start: ".memory_get_usage()."\n";
$data = file_get_contents("/six_megabyte_file");
echo "end: ".memory_get_usage()."\n";

but memory usage in following code = 1049680

start = 1050504

end = 1050976

echo "start: ".memory_get_usage()."\n";
file_get_contents("/six_megabyte_file");
echo "end: ".memory_get_usage()."\n";

Note: in first code file stores in a variable.

Hossein
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0

If you think this will help in avoiding insufficient memory errors you are wrong. Your code (bytes_format):

<?php
$url = 'http://speedtest.netcologne.de/test_10mb.bin';
echo 'Before: ' . bytes_format(memory_get_usage()) . PHP_EOL;
preg_match('~~', file_get_contents($url), $matches);
echo 'After: ' . bytes_format(memory_get_usage()) . PHP_EOL;
echo 'Peak: ' . bytes_format(memory_get_peak_usage(true)) . PHP_EOL;
?>

uses 10.5 MB:

Before: 215.41 KB
After: 218.41 KB
Peak: 10.5 MB

and this code:

<?php
$url = 'http://speedtest.netcologne.de/test_10mb.bin';
echo 'Before: ' . bytes_format(memory_get_usage()) . PHP_EOL;
$contents = file_get_contents($url);
preg_match('~~', $contents, $matches);
unset($contents);
echo 'After: ' . bytes_format(memory_get_usage()) . PHP_EOL;
echo 'Peak: ' . bytes_format(memory_get_peak_usage(true)) . PHP_EOL;
?>

uses 10.5 MB as well:

Before: 215.13 KB
After: 217.64 KB
Peak: 10.5 MB

If you like to guard your script you need to use the $length parameter or read the file in chunks.

Community
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mgutt
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0

In your example the memory will be released when $matches goes out of scope.
If you weren't storing the result of the match the memory would be released immediately

meouw
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