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# QLock Class Reference

The QLock class is a wrapper for a System V shared semaphore. More...

`#include <qlock_qws.h>`

List of all member functions.

## Public Members

- QLock ( const QString & filename, char id, bool create = FALSE )
- ~QLock ()
- enum Type { Read, Write }
- bool isValid () const
- void lock ( Type t )
- void unlock ()
- bool locked () const

## Detailed Description

The QLock class is a wrapper for a System V shared semaphore.

It is used by Qt/Embedded for synchronizing access to the graphics card and shared memory region between processes.

See also Input/Output and Networking and Qt/Embedded.

## Member Type Documentation

### QLock::Type

- `QLock::Read`
- `QLock::Write`

## Member Function Documentation

### QLock::QLock ( const QString & filename, char id, bool create = FALSE )

Creates a lock. filename is the file path of the Unix-domain socket the Qt/Embedded client is using. id is the name of the particular lock to be created on that socket. If create is TRUE the lock is to be created (as the Qt/Embedded server does); if create is FALSE the lock should exist already (as the Qt/Embedded client expects).

### QLock::~QLock ()

Destroys a lock

### bool QLock::isValid () const

Returns TRUE if the lock constructor was succesful; returns FALSE if the lock could not be created or was not available to connect to.

### void QLock::lock ( Type t )

Locks the semaphore with a lock of type t. Locks can either be Read or Write. If a lock is Read, attempts by other processes to obtain Read locks will succeed, and Write attempts will block until the lock is unlocked. If locked as Write, all attempts to lock by other processes will block until the lock is unlocked. Locks are stacked: i.e. a given QLock can be locked multiple times by the same process without blocking, and will only be unlocked after a corresponding number of unlock() calls.

### bool QLock::locked () const

Returns TRUE if the lock is currently held by the current process; otherwise returns FALSE.

### void QLock::unlock ()

Unlocks the semaphore. If other processes were blocking waiting to lock() the semaphore, one of them will wake up and succeed in lock()ing.

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