Decryption of the underlying development principles of PHP7: Exploring PHP memory management strategies and technologies

Decryption of the underlying development principles of PHP7: Exploring the strategies and technologies of PHP memory management

In recent years, the performance of PHP7 has been significantly improved, mainly due to Its improved underlying development principles. Among them, PHP memory management has become an important focus, which plays a vital role in the execution efficiency and performance of PHP scripts. This article will reveal the strategies and techniques of PHP memory management and explain them in detail with code examples.

In the era of PHP5, PHP adopted the reference counting (Reference Counting) memory management method. Simply put, reference counting records the number of times each variable refers to the memory block to determine whether it needs to be recycled. However, the reference counting method is prone to problems in handling circular references, leading to memory leaks. In order to solve this problem, PHP7 introduced the garbage collector (Garbage Collector).

The principle of the garbage collector is to find memory blocks that are no longer referenced and release them. In PHP7, the garbage collector uses the Mark and Sweep algorithm. Specifically, the garbage collector starts from the global root, scans all memory blocks step by step, and marks the referenced memory blocks. After the scan is completed, unmarked memory blocks are considered garbage and released.

Below we use a simple code example to illustrate the working principle of the garbage collector in PHP7:

<?php
class MyClass {
  public $otherObject;
}

$object1 = new MyClass();
$object2 = new MyClass();

$object1->otherObject = $object2;
$object2->otherObject = $object1;

unset($object1);
unset($object2);
?>

In this example, we created two MyClass objects $object1 and $object2 , and let them reference each other. Then, we delete the references of $object1 and $object2 through the unset() function. Since these two objects are referenced nowhere else, they will be considered garbage by the garbage collector and released.

In addition to the garbage collector, PHP7 also introduced the memory pool (Memory Pool) to improve the efficiency of memory allocation. In PHP5, every time it needs to allocate memory, PHP will call the memory allocation function provided by the operating system, such as malloc(). However, this approach will bring significant performance overhead when memory is allocated and released frequently.

In order to solve this problem, PHP7 introduced the concept of memory pool. The memory pool is a pre-allocated memory area, and PHP will allocate temporary memory from this memory pool. In this way, frequent calls to the operating system's memory allocation function are avoided, thereby improving the efficiency of memory allocation.

The following is a simple sample code that demonstrates the use of memory pools in PHP7:

<?php
$memoryPoolSize = 1024 * 1024; // 1MB
$memoryPool = new SplFixedArray($memoryPoolSize);

function allocateMemory($size) {
  global $memoryPool, $memoryPoolSize;

  for ($i = 0; $i < $memoryPoolSize; $i++) {
    if ($memoryPool[$i] === null) {
      $memoryPool[$i] = str_repeat(' ', $size);
      return $memoryPool[$i];
    }
  }

  return null; // 内存池已满，无法分配
}

$myMemory = allocateMemory(100);
if ($myMemory === null) {
  echo '内存分配失败';
} else {
  echo '成功分配了100字节的内存';
}

unset($myMemory);
?>

In this example, we first create a 1MB size memory pool and use SplFixedArray to represent it. Then, we define an allocateMemory() function, which is used to allocate memory of a specified size from the memory pool. In this way, we can avoid frequent calls to the operating system's memory allocation function.

To sum up, in the underlying development principles of PHP7, memory management is an important link. By introducing the garbage collector and memory pool, PHP7 greatly improves the efficiency and performance of memory management. We hope that through the introduction and sample code of this article, readers will have a deeper understanding of the underlying development principles of PHP7 and be able to rationally utilize these features in actual development to optimize the execution efficiency and performance of PHP scripts.

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