# dio_fcntl

(PHP 4 >= 4.2.0, PHP 5 < 5.1.0)

dio_fcntl — Performs a c library fcntl on fd

### 说明

dio_fcntl ( resource `$fd` , int `$cmd` [, mixed `$args` ] ) : mixed

The dio_fcntl() function performs the operation specified by `cmd` on the file descriptor `fd`. Some commands require additional arguments `args` to be supplied.

### 参数

`fd`

  The file descriptor returned by dio_open().

`cmd`

  Can be one of the following operations:

  - `F_SETLK` - Lock is set or cleared. If the lock is held by someone else dio_fcntl() returns -1.

  - `F_SETLKW` - like `F_SETLK`, but in case the lock is held by someone else, dio_fcntl() waits until the lock is released.

  - `F_GETLK` - dio_fcntl() returns an associative array (as described below) if someone else prevents lock. If there is no obstruction key "type" will set to `F_UNLCK`.

  - `F_DUPFD` - finds the lowest numbered available file descriptor greater than or equal to `args` and returns them.

  - `F_SETFL` - Sets the file descriptors flags to the value specified by `args`, which can be `O_APPEND`, `O_NONBLOCK` or `O_ASYNC`. To use `O_ASYNC` you will need to use the PCNTL extension.

`args`

  `args` is an associative array, when `cmd` is `F_SETLK` or `F_SETLLW`, with the following keys:

  - start - offset where lock begins

  - length - size of locked area. zero means to end of file

  - whence - Where l_start is relative to: can be `SEEK_SET`, `SEEK_END` and `SEEK_CUR`

  - type - type of lock: can be `F_RDLCK` (read lock), `F_WRLCK` (write lock) or `F_UNLCK` (unlock)

### 返回值

Returns the result of the C call.

### 范例

Example #1 Setting and clearing a lock

    <?php

    $fd = dio_open('/dev/ttyS0', O_RDWR);

    if (dio_fcntl($fd, F_SETLK, Array("type"=>F_WRLCK)) == -1) {
       // the file descriptor appears locked
       echo "The lock can not be cleared. It is held by someone else.";
    } else {
       echo "Lock successfully set/cleared";
    }

    dio_close($fd);
    ?>

### 注释

> Note: 此函数未在 Windows 平台下实现。