如何在PHP中分配特定大小的内存块？

Question

我正在为我的分析代码编写单元测试。为此，我正在编写一些函数来分配内存并调用“睡眠”，以便生成可预测的内存和时间结果以供测试。

“分配内存”部分有点棘手。

如果没有“malloc”类型函数，我尝试附加到字符串： $myString .= 'x'; 并附加到数组： $myArray[] = null;

但我的结果表明这些结构不会按需线性分配内存。

感谢您的建议！

Answer 1

PHP 是一种高级语言。内存管理由引擎决定。您不能也不应该尝试解决此问题。

而是分析那些在 PHP 中实际上有用的东西，比如现实生活中字符串和数组的使用。

Answer 2

这是一个测试函数，它将内存分块分配到一系列数组中，直到总内存限制耗尽。也许您也可以使用类似的方法来根据需要分配内存。有点像 malloc() C 函数。

在我的网络服务器上，我得到以下结果：

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;
}