PURPOSE: To decrease the number of steps when the exclusive execution right is secured and to carry out the exclusive control between the calculation processing units at a high speed by realizing an exclusive control mechanism with the use of an inseparable comparison/ exchange instruction in terms of a user task.

CONSTITUTION: A discriminating variable which shows the presence or absence of the exclusive execution right is shared with a variable which shows the head of the queue structure used for the temporary interruption/restart of the calculation processing units. These two variables are inseparably converted for execution of the exclusive control of the calculation processing units. In such condition, the data structure is called as a queue structure. Meanwhile a flag showing the presence or absence of the exclusive execution right and serving also as a head pointer of a queue is secured at every section/area which performs the exclusive control to a memory area common to the tasks. An inseparable comparison/exchange instruction performs the inseparable comparison/exchange of the memory contents. Then the memory value, the comparison value and the exchange value are read and sent to an arithmetic processor. The memory value is compared with the comparison value. If both values are equal to each other, the memory value can be exchanged with the exchange value. If not, nothing is carried out.