# eio_readahead

(PECL eio >= 0.0.1dev)

eio_readahead — Perform file readahead into page cache

### 说明

eio_readahead ( mixed `$fd` , int `$offset` , int `$length` [, int `$pri` = EIO_PRI_DEFAULT [, callable `$callback` = NULL [, mixed `$data` = NULL ]]] ) : resource

eio_readahead() populates the page cache with data from a file so that subsequent reads from that file will not block on disk I/O. See READAHEAD(2) man page for details.

### 参数

`fd`

  Stream, Socket resource, or numeric file descriptor

`offset`

  Starting point from which data is to be read.

`length`

  Number of bytes to be read.

`pri`

  请求的优先级：`EIO_PRI_DEFAULT`，`EIO_PRI_MIN`，`EIO_PRI_MAX` 或 `NULL`。如果是 `NULL`，`pri` 将设为 `EIO_PRI_DEFAULT`。

`callback`

  `callback` 函数在请求完成时被调用。其应匹配一下原型：

      void callback(mixed $data, int $result[, resource $req]);

  `data`

    传递给请求的用户数据。

  `result`

    针对请求的结果的值。通常是相应的系统调用返回的值。

  `req`

    可选的请求资源，可被 eio_get_last_error() 之类的函数使用。

`data`

  Arbitrary variable passed to `callback`.

### 返回值

eio_readahead() returns request resource on success or `FALSE` on error.