php操作共享内存shmop类如何使用

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SimpleSHM 是一个较小的抽象层，用于使用 PHP 操作共享内存，支持以一种面向对象的方式轻松操作内存段。在编写使用共享内存进行存储的小型应用程序时，这个库可帮助创建非常简洁的代码。可以使用 3 个方法进行处理：读、写和删除。从该类中简单地实例化一个对象，可以控制打开的共享内存段。

类对象和测试代码

<?php
//类对象
namespace Simple\SHM;
class Block
{
    /**
     * Holds the system id for the shared memory block
     *
     * @var int
     * @access protected
     */
    protected $id;
    /**
     * Holds the shared memory block id returned by shmop_open
     *
     * @var int
     * @access protected
     */
    protected $shmid;
    /**
     * Holds the default permission (octal) that will be used in created memory blocks
     *
     * @var int
     * @access protected
     */
    protected $perms = 0644;
    /**
     * Shared memory block instantiation
     *
     * In the constructor we'll check if the block we're going to manipulate
     * already exists or needs to be created. If it exists, let's open it.
     *
     * @access public
     * @param string $id (optional) ID of the shared memory block you want to manipulate
     */
    public function __construct($id = null)
    {
        if($id === null) {
            $this->id = $this->generateID();
        } else {
            $this->id = $id;
        }
        if($this->exists($this->id)) {
            $this->shmid = shmop_open($this->id, "w", 0, 0);
        }
    }
    /**
     * Generates a random ID for a shared memory block
     *
     * @access protected
     * @return int System V IPC key generated from pathname and a project identifier
     */
    protected function generateID()
    {
        $id = ftok(__FILE__, "b");
        return $id;
    }
    /**
     * Checks if a shared memory block with the provided id exists or not
     *
     * In order to check for shared memory existance, we have to open it with
     * reading access. If it doesn't exist, warnings will be cast, therefore we
     * suppress those with the @ operator.
     *
     * @access public
     * @param string $id ID of the shared memory block you want to check
     * @return boolean True if the block exists, false if it doesn't
     */
    public function exists($id)
    {
        $status = @shmop_open($id, "a", 0, 0);
        return $status;
    }
    /**
     * Writes on a shared memory block
     *
     * First we check for the block existance, and if it doesn't, we'll create it. Now, if the
     * block already exists, we need to delete it and create it again with a new byte allocation that
     * matches the size of the data that we want to write there. We mark for deletion,  close the semaphore
     * and create it again.
     *
     * @access public
     * @param string $data The data that you wan't to write into the shared memory block
     */
    public function write($data)
    {
        $size = mb_strlen($data, 'UTF-8');
        if($this->exists($this->id)) {
            shmop_delete($this->shmid);
            shmop_close($this->shmid);
            $this->shmid = shmop_open($this->id, "c", $this->perms, $size);
            shmop_write($this->shmid, $data, 0);
        } else {
            $this->shmid = shmop_open($this->id, "c", $this->perms, $size);
            shmop_write($this->shmid, $data, 0);
        }
    }
    /**
     * Reads from a shared memory block
     *
     * @access public
     * @return string The data read from the shared memory block
     */
    public function read()
    {
        $size = shmop_size($this->shmid);
        $data = shmop_read($this->shmid, 0, $size);
        return $data;
    }
    /**
     * Mark a shared memory block for deletion
     *
     * @access public
     */
    public function delete()
    {
        shmop_delete($this->shmid);
    }
    /**
     * Gets the current shared memory block id
     *
     * @access public
     */
    public function getId()
    {
        return $this->id;
    }
    /**
     * Gets the current shared memory block permissions
     *
     * @access public
     */
    public function getPermissions()
    {
        return $this->perms;
    }
    /**
     * Sets the default permission (octal) that will be used in created memory blocks
     *
     * @access public
     * @param string $perms Permissions, in octal form
     */
    public function setPermissions($perms)
    {
        $this->perms = $perms;
    }
    /**
     * Closes the shared memory block and stops manipulation
     *
     * @access public
     */
    public function __destruct()
    {
        shmop_close($this->shmid);
    }
}

<?php
//测试使用代码
namespace Simple\SHM\Test;
use Simple\SHM\Block;
class BlockTest extends \PHPUnit_Framework_TestCase
{
    public function testIsCreatingNewBlock()
    {
        $memory = new Block;
        $this->assertInstanceOf('Simple\\SHM\\Block', $memory);
        $memory->write('Sample');
        $data = $memory->read();
        $this->assertEquals('Sample', $data);
    }
    public function testIsCreatingNewBlockWithId()
    {
        $memory = new Block(897);
        $this->assertInstanceOf('Simple\\SHM\\Block', $memory);
        $this->assertEquals(897, $memory->getId());
        $memory->write('Sample 2');
        $data = $memory->read();
        $this->assertEquals('Sample 2', $data);
    }
    public function testIsMarkingBlockForDeletion()
    {
        $memory = new Block(897);
        $memory->delete();
        $data = $memory->read();
        $this->assertEquals('Sample 2', $data);
    }
    public function testIsPersistingNewBlockWithoutId()
    {
        $memory = new Block;
        $this->assertInstanceOf('Simple\\SHM\\Block', $memory);
        $memory->write('Sample 3');
        unset($memory);
        $memory = new Block;
        $data = $memory->read();
        $this->assertEquals('Sample 3', $data);
    }
}

额外说明

<?php
 
$memory = new SimpleSHM;
$memory->write('Sample');
echo $memory->read();
 
?>

请注意，上面代码里没有为该类传递一个 ID。如果没有传递 ID，它将随机选择一个编号并打开该编号的新内存段。我们可以以参数的形式传递一个编号，供构造函数打开现有的内存段，或者创建一个具有特定 ID 的内存段，如下

<?php
 
$new = new SimpleSHM(897);
$new->write('Sample');
echo $new->read();
 
?>

神奇的方法 __destructor 负责在该内存段上调用 shmop_close 来取消设置对象，以与该内存段分离。我们将这称为 “SimpleSHM 101”。现在让我们将此方法用于更高级的用途：使用共享内存作为存储。存储数据集需要序列化，因为数组或对象无法存储在内存中。尽管这里使用了 JSON 来序列化，但任何其他方法（比如 XML 或内置的 PHP 序列化功能）也已足够。如下

<?php
 
require('SimpleSHM.class.php');
 
$results = array(
    'user' => 'John',
    'password' => '123456',
    'posts' => array('My name is John', 'My name is not John')
);
 
$data = json_encode($results);
 
$memory = new SimpleSHM;
$memory->write($data);
$storedarray = json_decode($memory->read());
 
print_r($storedarray);
 
?>

我们成功地将一个数组序列化为一个 JSON 字符串，将它存储在共享内存块中，从中读取数据，去序列化 JSON 字符串，并显示存储的数组。这看起来很简单，但请想象一下这个代码片段带来的可能性。您可以使用它存储 Web 服务请求、数据库查询或者甚至模板引擎缓存的结果。在内存中读取和写入将带来比在磁盘中读取和写入更高的性能。

使用此存储技术不仅对缓存有用，也对应用程序之间的数据交换也有用，只要数据以两端都可读的格式存储。不要低估共享内存在 Web 应用程序中的力量。可采用许多不同的方式来巧妙地实现这种存储，惟一的限制是开发人员的创造力和技能。

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