Method and apparatus for aligning the operation of a plurality of processors

A method of controlling a computer system comprising a plurality of processors, each processor processing a separate instruction stream, each instruction stream comprising instructions of a plurality of instruction types including an alignment request type, an alignment test type, and at least one other instruction type, and each instruction stream including at least one instruction of the alignment request type situated in the instruction stream to be executed at one point in time, at least one instruction of the alignment test type situated in the instruction stream to be executed at a later point in time than the instruction of the alignment request type, and at least some instruction streams having an instruction of another instruction type situated for execution at a point in time between execution of the instruction of the alignment request type and the instruction of the alignment test type, the method to bring said processors into alignment comprising the steps of:

• A. each of said processors upon execution of an instruction from its respective instruction stream of said alignment request type generating a request indication and thereafter continuing execution of instructions, from its respective instruction stream,
• B. each of said processors, upon execution of an instruction from its respective instruction stream of said alignment test type, being disabled from processing subsequent instructions in its instruction stream in the absence of an alignment indication;
• and
• C. generating said alignment indication when all of said processors have generated said request indication, thereby to enable said processors to execute instructions from their respective instruction streams following the instruction of said alignment test type.