A method for storing into a non-EX cache line in a multiprocessor system. Upon a store into a non-EX line the instruction execution and the processing of subsequent instructions will continue. The results of the current instruction, however, and any subsequent instruction whose decode and execution depends upon the result of the current instruction or that requires operand fetches, will not be released until the processing of the current instruction is resolved. The request to store into the non-EX line is simultaneously sent to the SCE to obtain the EX state for the line. The SCE serializes storage requests. When a request for EX state is processed, certain XI actions (e.g. XI-invalidates) may be invoked. Any instruction using fetched data XI-invalidated before the resolution of a preceding store at the same CP is considered likely to be invalid, and redone.

The present invention is a method of allocating memory storage in a memory storage space commonly shared by multiple processors. The method allocates a minimum apparent memory storage space equal to one cache line and in response to storing an object, said object occupying a memory storage space equal to less than one cache line, the method determines the value of a variable. The method then allocates said memory storage space for said object based on the value of said variable and updates said variable.

This invention is directed to a memory system that determines which blocks of a set of associative blocks in cache memory are unavailable for replacement. This is accomplished by operating the memory system to maintain a duplicate set of tags which track block ownership for this cache pursuant to a "snoopy" protocol. In addition, the cache system maintains a bit associated with each memory address to indicate whether any data blocks resident in it have been locked. The interlock status of the data blocks in the cache is not communicated to the memory system. Once a block is locked, it cannot be allocated for replacement until it is unlocked. When the cache system encounters a locked block, it skips over that block and allocates the next block of the associative blocks. From this, the memory system infers, by means of a replacement algorithm, that block is being locked and, therefore, cannot be replaced. This enables the memory system to implement an irregular replacement policy for this cache when the block to be replaced is owned and locked.

An apparatus, program product, and method of processing a request to create an immutable object reuse an existing immutable object in appropriate circumstances to represent redundant data without the necessity for creating an additional immutable object. Prior to creating a new object in response to a request to create an immutable object, a determination is made as to whether a matching immutable object already exists that has the same contents as the requested immutable object. If so, creation of a new object is inhibited, and a reference to the matching immutable object is returned in response to the request.

Apparatus and method for insuring data cache content integrity among parallel processors is provided. Each processor has a data cache to store intermediate calculations. The data cache of each processor is synchronized with each other through the use of synchronization intervals. During entry of a synchronization interval, modified data variables contained in an individual cache are written back to a shared memory. The unmodified data contained in a data cache is flushed from memory. During exiting of a synchronization interval, data variables which were not modified since entry into the synchronization interval are also flushed. By retaining modified data cache values in the individual processors which computed the modified values, unnecessary access to shared memory is avoided.