How can I allocate a block of memory of a specific size in PHP?

I am writing a unit test for my profiling code. In order to do so, I am writing some functions that will allocate memory and call 'sleep' in order to generate predictable memory and time results that I can test against.

The "allocate memory" part is turning out to be a bit tricky.

Without a 'malloc' type function, I have tried appending to a string: $myString .= 'x'; and appending to an array: $myArray[] = null;

But my results show that these structures do not allocate memory linearly开发者_高级运维 on demand.

Your suggestions are appreciated!

PHP is a high-level language. Memory management is left up to the engine. You cannot and should not attempt to work around this.

Instead profile things that are actually useful to profile in PHP, like real-life use of strings and arrays of stuff.

Here is a test function that allocates memory in chunks into an a series of arrays until total memory limit is exhausted. Perhaps you can use a similar method to allocate memory as you like as well. Sort of like a mallaoc() C function...

On my web server I get these results...

Memory Test

Memory Limit: 536870912 
Initial memory usage: 637448 

Allocate 1 million single character elements to myArray0 
Current memory usage: 97026784 
Allocate 1 million single character elements to myArray1 
Current memory usage: 193415768 
Allocate 1 million single character elements to myArray2 
Current memory usage: 289804704 
Allocate 1 million single character elements to myArray3 
Current memory usage: 386193640 
Allocate 1 million single character elements to myArray4 
Current memory usage: 482582576 
Memory Test Complete

Total memory used: 482582576 
Average memory used per array in each of 5 arrays: 96389025 
Average memory used per character in each of 5 arrays: 96 
Remaining memory: 54288336

// This routine demonstrates how to get and use PHP memory_limit, memory_get_usage, variable array names, and array_fill
// to allocate large blocks of memory without exceeding php.ini total available memory
echo "<h2>Memory Test</h2>";

// Get total memory available to script
$memory_limit = get_memory_limit();
echo "Memory Limit: $memory_limit <br />";
$initMemory = $currentMemory = memory_get_usage();
echo "Initial memory usage: $initMemory <br /><br />";

// Start consuming memory by stuffing multiple arrays with an arbitrary character
$i =0;
while ( $currentMemory + ($currentMemory - $initMemory)/($i+1) <= $memory_limit) 
{       
    echo "Allocate 1 million single character elements to myArray$i <br />";
    ${myArray.$i} = array_fill(0, 1000000, "z");
    $currentMemory = memory_get_usage();
    echo "Current memory usage: $currentMemory <br />";
    $i++;
}
echo "<h2>Memory Test Complete</h2>";
echo "Total memory used: $currentMemory <br />";
$aveMemoryPerArray = (int)(($currentMemory - $initMemory)/$i);
echo "Average memory used per array in each of " .$i . " arrays: " . $aveMemoryPerArray . " <br />";    
echo "Average memory used per character in each of " . $i . " arrays: " . (int)($aveMemoryPerArray/1000000) . " <br />";
echo "Remaning memory: " . ($memory_limit - $currentMemory) . "<br />";

// Utility to convert php.ini memory_limit text string into an integer value in bytes
// Reference: http://stackoverflow.com/questions/10208698/checking-memory-limit-in-php
function get_memory_limit()
{
    $memory_limit = ini_get('memory_limit');
    if (preg_match('/^(\d+)(.)$/', $memory_limit, $matches)) {
        if ($matches[2] == 'M') {
            $memory_limit = $matches[1] * 1024 * 1024; // nnnM -> nnn MB
        } else if ($matches[2] == 'K') {
            $memory_limit = $matches[1] * 1024; // nnnK -> nnn KB
        }
    }
    return $memory_limit;
}