A system of the present invention includes: a memory device which includes a first memory area for storing first information indicating that a first task acquires or attempts to acquire a lock, and a second memory area for storing second information indicating that a second task acquires or attempts to acquire the lock, and in which a time lag may occur between a time when the first task issues a writing instruction and a time when the written content is enabled to be referred to by the second task; a first acquisition section which reads the second memory area after issuing a writing instruction to write the first information to the first memory area in response to a request from the first task, and which makes a reply indicating a success of the lock acquisition on condition that the second information is not read; and a second acquisition section which writes the second information to the second memory area in response to a request from the second task, which enables the written content to be referred to by the first task, which thereafter executes a write-reflection process for enabling the content written in the first memory area by the first task to be referred to by the second task, which reads the first memory area after completion of the write-reflection process, and which makes a reply indicating a success of the lock acquisition on condition that the first information is not read from the first memory area.