摘要：是一個(gè)較小的抽象層，用于使用操作共享內(nèi)存，支持以一種面向?qū)ο蟮姆绞捷p松操作內(nèi)存段。在編寫(xiě)使用共享內(nèi)存進(jìn)行存儲(chǔ)的小型應(yīng)用程序時(shí)，這個(gè)庫(kù)可幫助創(chuàng)建非常簡(jiǎn)潔的代碼。不要低估共享內(nèi)存在應(yīng)用程序中的力量。

SimpleSHM 是一個(gè)較小的抽象層，用于使用 PHP 操作共享內(nèi)存，支持以一種面向?qū)ο蟮姆绞捷p松操作內(nèi)存段。在編寫(xiě)使用共享內(nèi)存進(jìn)行存儲(chǔ)的小型應(yīng)用程序時(shí)，這個(gè)庫(kù)可幫助創(chuàng)建非常簡(jiǎn)潔的代碼。可以使用 3 個(gè)方法進(jìn)行處理：讀、寫(xiě)和刪除。從該類(lèi)中簡(jiǎn)單地實(shí)例化一個(gè)對(duì)象，可以控制打開(kāi)的共享內(nèi)存段。

類(lèi)對(duì)象和測(cè)試代碼

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);
    }
}

assertInstanceOf("SimpleSHMBlock", $memory);

        $memory->write("Sample");
        $data = $memory->read();
        $this->assertEquals("Sample", $data);
    }

    public function testIsCreatingNewBlockWithId()
    {
        $memory = new Block(897);
        $this->assertInstanceOf("SimpleSHMBlock", $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("SimpleSHMBlock", $memory);
        $memory->write("Sample 3");
        unset($memory);

        $memory = new Block;
        $data = $memory->read();
        $this->assertEquals("Sample 3", $data);
    }
}

額外說(shuō)明

write("Sample");
echo $memory->read();
 
?>

請(qǐng)注意，上面代碼里沒(méi)有為該類(lèi)傳遞一個(gè) ID。如果沒(méi)有傳遞 ID，它將隨機(jī)選擇一個(gè)編號(hào)并打開(kāi)該編號(hào)的新內(nèi)存段。我們可以以參數(shù)的形式傳遞一個(gè)編號(hào)，供構(gòu)造函數(shù)打開(kāi)現(xiàn)有的內(nèi)存段，或者創(chuàng)建一個(gè)具有特定 ID 的內(nèi)存段，如下

write("Sample");
echo $new->read();
 
?>

神奇的方法 __destructor 負(fù)責(zé)在該內(nèi)存段上調(diào)用 shmop_close 來(lái)取消設(shè)置對(duì)象，以與該內(nèi)存段分離。我們將這稱(chēng)為 “SimpleSHM 101”。現(xiàn)在讓我們將此方法用于更高級(jí)的用途：使用共享內(nèi)存作為存儲(chǔ)。存儲(chǔ)數(shù)據(jù)集需要序列化，因?yàn)閿?shù)組或?qū)ο鬅o(wú)法存儲(chǔ)在內(nèi)存中。盡管這里使用了 JSON 來(lái)序列化，但任何其他方法（比如 XML 或內(nèi)置的 PHP 序列化功能）也已足夠。如下

 "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);
 
?>

我們成功地將一個(gè)數(shù)組序列化為一個(gè) JSON 字符串，將它存儲(chǔ)在共享內(nèi)存塊中，從中讀取數(shù)據(jù)，去序列化 JSON 字符串，并顯示存儲(chǔ)的數(shù)組。這看起來(lái)很簡(jiǎn)單，但請(qǐng)想象一下這個(gè)代碼片段帶來(lái)的可能性。您可以使用它存儲(chǔ) Web 服務(wù)請(qǐng)求、數(shù)據(jù)庫(kù)查詢或者甚至模板引擎緩存的結(jié)果。在內(nèi)存中讀取和寫(xiě)入將帶來(lái)比在磁盤(pán)中讀取和寫(xiě)入更高的性能。

使用此存儲(chǔ)技術(shù)不僅對(duì)緩存有用，也對(duì)應(yīng)用程序之間的數(shù)據(jù)交換也有用，只要數(shù)據(jù)以兩端都可讀的格式存儲(chǔ)。不要低估共享內(nèi)存在 Web 應(yīng)用程序中的力量。可采用許多不同的方式來(lái)巧妙地實(shí)現(xiàn)這種存儲(chǔ)，惟一的限制是開(kāi)發(fā)人員的創(chuàng)造力和技能。