关于php:PHP-FFI-实现list

本文通过 PHP FFI 个性初步实现了 list 链表

<?php
// php 字符串转 C char 指针
function stringToCharPtr(string $str)
{$strChar = str_split($str);

    $c = FFI::new('char[' . count($strChar) . ']', false);
    foreach ($strChar as $i => $char) {$c[$i] = $char;
    }
    return FFI::cast(FFI::type('char *'), $c);
}


class FFIHelper
{
    private static $ffi;
    public static function create()
    {if (empty(self::$ffi)) {self::$ffi = \FFI::load("./test.h");
        }
        return self::$ffi;
    }
}

class StringArray
{
    private $char;
    private $capacity;
    private $length;

    public function __construct(int $capacity = 0)
    {if ($capacity > 0) {$this->create($capacity);
        }
    }

    /**
     * 创立 list
     */
    public function create(int $capacity)
    {if (!is_numeric($capacity) || $capacity <= 0) {throw new \Exception("list 长度不能够为 0");
        }
        $this->char                = \FFI::new ('char*[' . ($capacity) . ']', false, true);
        $this->capacity = $capacity;
    }

    public function append($string)
    {
        $postion = $this->length;
        if ($postion >= $this->capacity) {$this->grow($this->capacity * 2);
        }
        $this->char[$postion] = stringToCharPtr($string . "\0");
        $this->length++;
    }

    public function get($postion)
    {return $this->ArrayList->data;}

    public function delete($postion)
    {if ($postion < 0) {throw new \Exception("删除地位不能够小于 0");
        }
        if ($postion > $this->ArrayList->length) {throw new \Exception("删除地位大于 list 长度");
        }
    
    }

    public function length()
    {return $this->length;}

    /**
     * 减少数组长度
     */
    public function grow($size)
    {if ($size < $this->capacity) {throw new \Exception("无需减少 list 容量");
        }
        $oldData = $this->char;
        $newData = \FFI::new ('char*[' . ($size) . ']', false, true);
        \FFI::memcpy($newData, $this->char, \FFI::sizeof($oldData) * $this->length);
        $this->char                = $newData;
        $this->capacity = $size;
        \FFI::free($oldData);
    }

    public function getList()
    {return $this->char;}

    public function __destruct()
    {}}
$star_memory = memory_get_usage();
$start       = microtime(true);

$list = new StringArray(2000000);


$i    = 0;
$data = [];
while (true) {$list->append("hello 你好");
    //$data[] = "aaas 你好" . $i;
    $i++;
    if ($i > 1000000) {break;}
}
//var_dump(FFI::string($list->get(0)));
$end_memory = memory_get_usage();
$elapsed    = microtime(true) - $start;

echo "That took $elapsed seconds.\n";

var_dump((($end_memory - $star_memory) / 1024 / 1024) . "M");

因为 PHP 底层字符串做了解决，雷同字符串会只存一次，通过计数器的形式来示意援用的次数，而本文中实现的字符串并未进行认为解决。因此，每次都会从新创立新的字符串。

通过文中代码测试，发现即便为对字符串进行解决，内存占用状况也会至多优化 3 倍以上，当然目前美中不足的是，字符串转为 char 指针耗时比拟久，扔须要优化。