Managing access to a shared resource in a data processing system
Processes requiring access to shared resources are adapted to issue a reservation request, such that a place in a resource access queue, such as one administered by means of a semaphore system, can be reserved for the process. The reservation is issued by a Reservation Management module at a time calculated to ensure that the reservation reaches the head of the queue as closely as possible to the moment at which the process actually needs access to the resource. The calculation may be made on the basis of priority information concerning the process itself, and statistical information gathered concerning historical performance of the queue.
1. A system for obtaining access to a shared resource in a data processing system, the system comprising:
a computer comprising a processor; and
instructions which are executable, using the processor of the computer, to perform:
sending a reservation request from a process to an access queue manager that manages a queue of access requests for the shared resource, wherein:
the reservation request is adapted to notify the access queue manager as a foreshadowing of a forthcoming access request from the process that will request access to the shared resource; and
the reservation request is adapted to cause the access queue manager to calculate a queue entry cycle, the calculated queue entry cycle indicating when the access queue manager will subsequently queue the reservation request, on behalf of the process, in the queue of access requests;
sending the foreshadowed access request from the process to the access queue manager a predetermined time after sending the reservation request; and
accessing the shared resource by the process at a time of sending the foreshadowed access request, the reservation request having established an advance reservation in the queue that enables the process to obtain, at the predetermined time, a semaphore that allows the accessing.
2. The system of claim 1 , wherein the reservation request further comprises:
a time calculated by the process for queuing the reservation request onto the queue, wherein the queue controls access to the semaphoreand the time comprises an interval that corresponds to the predetermined time.
3. A non-transitory computer readable medium having encoded thereon a computer program for obtaining access to a shared resource in a data processing system, the computer program comprising instructions which, when executed by a computer, cause the computer to perform:
receiving a reservation request from a process at an access queue manager that manages a queue of access requests for the shared resource, the reservation request foreshadowing a forthcoming access request from the process for accessing the shared resource;
responsive to receiving the reservation request, calculating a queue entry cycle indicating when to subsequently queue the reservation request, on behalf of the process, in the queue of access requests;
responsive to reaching the calculated queue entry cycle, queuing the reservation request, on behalf of the process, in the queue of access requests;
receiving the foreshadowed access request at the access queue manager from the process a predetermined time after receiving the reservation request; and
accessing the shared resource by the process at a time of sending receiving the foreshadowed access request from the process, the reservation request having established an advance reservation in the queue that enables the process to obtain, at the predetermined time, a semaphore that allows the accessing.