Semaphore Reservation Clearing via Write Request Interception
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Solution Overview
Problem
Existing systems lack an efficient method to clear semaphore reservations in shared memory regions, leading to potential memory access issues and resource locking when a processor is interrupted before it can set the semaphore, resulting in obsolete reservations that must be manually cleared.
Innovation Solution
A method and processing system where a write request is transmitted to the semaphore memory region without actually writing to it, effectively clearing the reservation status and maintaining semaphore availability for other processors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a processor is interrupted before setting the semaphore, then the reservation remains uncleared causing resource locking issues, but manually clearing the reservation requires additional memory access steps and occupies additional memory
Solution Approach 1:
The patent merges the semaphore reservation clearing function with the existing semaphore memory region by using the same memory location for both purposes. The write request to the semaphore memory region serves dual purposes: it attempts to update the semaphore while simultaneously clearing the reservation status in the controller, eliminating the need for separate clearing operations and additional memory locations.
Solution Approach 2:
The semaphore memory region is given multi-functionality by serving both as the semaphore storage location and as the trigger mechanism for clearing reservations. A write request to this region universally handles both semaphore updates and reservation clearing, reducing system complexity and memory requirements.
2Productivity
If a write request is transmitted to clear the reservation, then the reservation is cleared efficiently, but data might be accidentally written to the semaphore memory region causing incorrect semaphore states
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of a memory controller that mediates between the write request and the semaphore memory region. The controller intercepts write requests destined for the semaphore memory region, clears the reservation status in response to the request, and then prevents the actual data from being written to the semaphore region, thus protecting semaphore state accuracy while enabling efficient reservation clearing.
Solution Approach 2:
The system uses the processor's own write request as the trigger for clearing the reservation, without requiring a separate clearing operation. The write request itself serves the dual purpose of attempting to update the semaphore and automatically clearing the reservation if the processor was interrupted, making the system self-correcting.
Data Source
AI summary
Semaphore operation manages exclusive access to a memory that is shared by a plurality of processing elements. Semaphore reservation status for exclusive access by a processing element is monitored by a memory controller. To clear an obsolete reservation status, a command signal is transmitted for a write operation to the memory while prohibiting update of the contents of a memory. The reservation status at the controller is changed from a reservation state to a non-reservation state in response to receipt of the command signal.