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3 - 3 Program Attributes

Programs that are executed by a computer have several properties. Depending on the property of the program that is executed, the method of operation is different. It is necessary to pay attention to this point.

(1) Relocatable program

A relocatable program is a program that can be read into memory by a loader and executed at any address. It is sometimes called a relocation program. The program is made executable by actions including correction of the address information corresponding to the load position. Furthermore, programs for which the address can be changed even during execution are called dynamic relocatable programs.

(2) Reusable program

A reusable program can be used any number of times. Normally, a program must be reloaded into main memory for each execution. (This is called a reload.) However, a reusable program does not require any reloads and can be used repeatedly once it is loaded. When the execution of a reusable program starts, actions including the initialization of variables are performed to maintain process consistency. Therefore, it cannot be used for multiple tasks at the same time.

(3) Reentrant program

A reentrant program allows the correct result to be obtained even if it is used in multiple tasks simultaneously. A reentrant program is divided into a variable part and a procedure part, and implements concurrent processing by allocating a variable part to each task while only the procedure part is shared. In order to be used in multiple tasks simultaneously, a reentrant program requires the properties of reusable programs that can be used repeatedly without reloading. · 1 question

(4) Recursive program

A recursive program is a program that can call itself during program execution. It can return to the state immediately prior to execution by recording the states during processing with the LIFO (Last-In First Out) method. However, even if the program is able to call itself, there is no guarantee that it can also be called from another task, so it is not necessarily a reentrant program.