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Performs a c library fcntl on fd (PHP 4 >= 4.2.0, PHP 5 <= 5.0.5)
mixed dio_fcntl ( resource fd, int cmd [, mixed args] )

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


This function is not implemented on Windows platforms.



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 above) 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

  • "wenth" - 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 499. 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 succesfully set/cleared";