US 5,317,749 A · Method and apparatus for controlling access by a plurality of processors to a shared resource

Abstract

A latch manager enabling multiple processors in a multiprocessor system to gain access to a shared resource. Resource access is controlled by the use of a latch-control word. There is one latch-control word associated with each of the shared resources in the system. The latch-control word can reside either in the shared resource itself or in a separate common area of the system to which each of the processors has access. The latch-control word is captured by the requesting processor and its contents are modified to indicate that the requesting processor owns the latch (either in a shared or exclusive state) or that it is making a request to own the latch at the first opportunity. If the processor was not able to gain ownership of the latch upon its initial capture, the denied processor will wait and monitor the latch until it has been promoted to ownership of the latch. Optionally, the processor can back out of the request and continue processing.

Claims15

Dependent claims

A method of controlling access by a plurality of processors to a shared resource, said method comprising the steps of:

reading a latch-control word from a memory location in response to an access request by a first processor, said access request reflecting said first processor's desire for access to said shared resource, said latch-control word indicating an access status of said shared resource;
reading a held-exclusive flag and a held-shared flag from said latch-control word;
granting said first processor access to said shared resource and setting one of said held flags if said held flags indicate said shared resource is not held;
setting one of two waiting flags in said latch-control word if said held flags indicate said shared resource is already held and said one of two waiting flags is not already set, said waiting flags denoting that at least one of said plurality of processors is waiting for access to said resource;
and
writing said latch-control word back to said memory location.

3 more elements

An apparatus for controlling access by a plurality of processors to a shared resource comprising:

a latch-control word residing in a memory accessible by said plurality of processors, said latch-control word indicating an access status of said share resource;
a held-exclusive flag in said latch-control word, said held-exclusive flag indicating that said shared resource is held exclusively by one of said plurality of processors;
a held-shared flag in said latch-control word, said held-shared flag indicting that said shared resource is held shared by one or more of said plurality of processors;
an exclusive-waiting flag in said latch-control word, said exclusive-waiting flag indicating that at least one of said plurality of processors is waiting for exclusive access to said shared resource;
a shared-waiting flag in said latch-control word, said shared-waiting flag indicating that at least one of said plurality of processors is waiting for shared access to said shared resource;
a means for granting access to a requesting processor if said held flags indicate said shared resource is not held;
and
a means for setting one of said waiting flags if said shared resource is held.

5 more elements

Dependencies are inferred from the claim text.

Method and apparatus for controlling access by a plurality of processors to a shared resource

Life of this patent

Method and apparatus for controlling access by a plurality of processors to a shared resource

Life of this patent

Abstract

Claims15