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

dio_fcntlPerforms a c library fcntl on fd


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.



The file descriptor returned by dio_open().


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 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)

Return Values

Returns the result of the C call.


Example #1 Setting and clearing a lock


= 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 {
"Lock successfully set/cleared";



Note: This function is not implemented on Windows platforms.

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User Contributed Notes 1 note

Guillermo Prandi
11 years ago
Actually, there's a small typo in the above docs. The parameter for where l_start is relative to is actually "whence" and not "wenth" like stated.
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