Abstract: A data processing apparatus has processing circuitry for processing threads using resources accessible to the processing circuitry. Thread handling circuitry handles pending threads which are waiting for resources required for processing. When a request is made for a resource which is not available, a lock is set to ensure that once the resource becomes available, the resource remains available until the lock is removed. This prevents other threads reallocating the resource. When a subsequent pending thread requests access to the same locked unavailable resource, the lock is transferred to that subsequent thread so that the latest thread accessing that resource is considered the lock owning thread. The lock is removed once the lock owning thread is ready for processing.