JPH07182186A - Effective using method for semaphore - Google Patents

Abstract

PURPOSE:To eliminate such processing that becomes impracticable due to a limited number of semaphores and also to know the occurrence of plural V operations (events) by a single P operation (cancle of waiting). CONSTITUTION:When plural V operations are carried out to a single semaphore 50, an event writing mechanism a20 is prepared to write a specific event into a prescribed storage area 60 for each V operation. Furthermore an event reading mechanism b20 is added to refer to the area 60 and to read a specific event out of the area 60 to which a V operation is carried out in response to a P operation, together with an event canceling mechanism b30 which finishes the processing against the read event and erases the contents of the relevant event written in the area 60. Therefore it is not needed to prepare the semaphores 50 for each event and a single semaphore 50 can be effectively used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for effectively using a semaphore in a computer system that executes a program or the like for notifying the occurrence of a plurality of events by using the semaphore.

[0002]

2. Description of the Related Art Generally, in a multiprocessor system or the like, a semaphore is used as a synchronization mechanism for controlling a plurality of processes. Two operations can be performed on a semaphore, a P operation or a V operation.

The P operation is an instruction for checking whether or not an event has occurred, and when an event has already occurred, it enters a waiting state. The V operation notifies the occurrence of a certain event, and releases the waiting of the partner who has performed the P operation. By using these two operations, the semaphore can be used for exclusive control of resources.

Performing a P operation means waiting for some event to occur and canceling the wait by the V operation when the event occurs.

In the following description, the events that need to be waited for in this P operation are shown as event X and event Y. Here, if the semaphore mechanism is such that only one V operation is valid even if the V operation is performed multiple times before the P operation is performed, or if one semaphore is used, When it is impossible to distinguish whether the operation is a V operation for an event, the following situation occurs (see FIG. 3).

If there is a V operation that wants to notify event X and a V operation that wants to notify event Y from process A to process B, if the V operation is notified only once, the wait state is set when event X occurs. It is impossible to distinguish the event of canceling and canceling the waiting state when the event Y occurs.

Therefore, it is necessary to separate the semaphores related to the event X and the event Y and perform the V operation and the P operation for each semaphore. As shown in FIG. 3, by separating the semaphores related to the event X and the event Y, it is possible to know whether the event X has occurred or the event X has occurred depending on which semaphore the wait has been released.

[0008]

If a plurality of V operations having different meanings may occur before the P operation, the V operation will be overwritten unless the semaphore is divided for each event. In order to avoid this, there is no problem if there are as many semaphores as the number of events as described above.

However, normally, the number of semaphores is limited in each system. Therefore, if the semaphore is divided for each event, there may be insufficient semaphores used in the system.

Further, for example, in order to know the occurrence of two events (V operation), it is necessary to wait (P operation) for each semaphore (that is, wait twice (P operation)).

The present invention has been made in consideration of the above circumstances, and eliminates inexecutable processing due to the limitation of the number of semaphores, and also allows a plurality of V operations (events) with one P operation (wait release). The purpose is to provide an effective use method of a semaphore capable of knowing the occurrence of.

[0012]

According to the present invention, when a plurality of V operations are performed on one semaphore, it is determined for each V operation which event it corresponds to, depending on each V operation for the semaphore. To a predetermined storage area, referring to the storage area according to the P operation for the semaphore, reading from the storage area which event the V operation was performed for, and processing relating to the read event And the step of erasing the contents of the writing of the related event in the storage area, there is no need to prepare a semaphore for each event, and one semaphore can be effectively used.

Further, it is characterized in that the contents of writing to the storage area corresponding to a plurality of V operations are read in response to one P operation for the semaphore.

Further, among the plurality of V operations, there are V operations for a plurality of the same events, or when there are a plurality of different events, a V operation for each event.
It is characterized by including an operation.

[0015]

According to such a method, when the number of semaphores is limited and a plurality of V operations are performed on one semaphore, each V operation is
The event for which the V operation was performed is written in the storage area. Therefore, even if the contents of the semaphore are overwritten by the V operation and only one V operation is valid, the occurrence of a plurality of V operations can be known by referring to the semaphore according to the P operation.

Further, for each V operation, the operation content for the semaphore is stored for each event, so P
When referring to the storage area according to the operation, by reading all the write contents, originally, only one V operation is valid for one semaphore. The content can be valid.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining an effective use method of a semaphore of the present invention. Here, it is assumed that there is a process A that performs V operation and a process B that performs P operation.

Process A is V operation mechanism a1.
0, the event writing mechanism A20. Further, the process B is assumed to have a V operation mechanism b10, an event writing mechanism b20, and an event canceling mechanism b30. The mechanisms provided in the processes A and B operate the semaphore 50 and the storage area 60.

The V operation mechanism a10 is a module for executing a V operation on the semaphore 50. The P operation mechanism b10 is a module for executing a P operation on the semaphore 50.

The event writing mechanism a20 is a module for writing in the storage area 60 which event has occurred according to the V operation to the semaphore 50 by the V operation mechanism a10.

The event reading mechanism b20 is a module for reading which event has occurred from the storage area 60 in accordance with the P operation for the semaphore 50 by the P operation mechanism b10.

The event canceling mechanism b30 is a module for erasing the memory of the memory area 60 in preparation for the next V operation when the processing for the notified event is completed.

In FIG. 1, reference numeral a01 is a V operation, reference numeral b01 is a P operation, reference numeral a02 is a write to the storage area 60, reference numeral b02 is a read from the storage area 60, and reference numeral b03 is a storage erase of the storage area 60. It shows the operation of.

In FIG. 1, process A to process B
It shows an example when there is a notification of an event to process B
When there is an event to notify the process A from the process A, it is sufficient that the processes A and B have the configuration of each process.

Next, the operation of this embodiment will be described.
Conventionally, if the V operation is performed many times before the P operation, the contents of the operation by the V operation are overwritten on the semaphore, so that it is effective only once.

Therefore, in the present invention, when there are V operations of different events that occur at the same time, which event has occurred is stored in the storage area 60, and V operations of what events have been performed in the past. By holding the data, it is possible to know all the past occurrences of V operations by one V operation.

Usually, when the events are different, it is necessary to separate the semaphores, but in the case of this mechanism, it is possible to know which event among a plurality of events has occurred with one semaphore.

Here, an example of a case where it is necessary to notify a plurality of events from the process A to the process B will be described. First, the process A includes the V operation mechanism a10.
Performs V operation to notify that event X has occurred. Further, the process A writes in the storage area 60 that the V operation of the event X has been executed by the event writing mechanism a20. This state is shown in FIG. The fact that the V operation of the event X has been performed is shown by turning on the bit of the area X. The storage method does not matter.

Next, the process A performs the V operation for notifying that the event Y has occurred by the V operation mechanism a10. At this time, for the semaphore 50, the previously operated V operation contents are overwritten. Further, the process A is the event writing mechanism a.
At 20, the fact that the V operation of event Y has been executed is written in the storage area 60. This state is shown in Fig. 2 (2).
Is shown in.

Next, the process B performs the P operation on the semaphore 50 by the P operation mechanism b10. Here, since the V operation has already been performed, the wait is released.

Originally, since the semaphore 50 has been overwritten, only the subsequent V operation (event Y) is valid, and only one V operation is notified, but the process B is notified by the event writing mechanism b20. The storage area 60 is referenced based on the notification. This allows
It can be seen that the process B has performed the V operation of the event X and the V operation of the event Y so far.
This state is shown in FIG.

Process B performs a relational process regarding event X. Then, when the related processing regarding the event X is completed, the process B erases the notification of the storage area 60 of the event X by the event canceling mechanism b30 in preparation for the next V operation.

Further, the process B performs a related process regarding the event Y. Then, when the related process for the event Y is completed, the process B prepares for the next V operation by the event canceling mechanism b30 and stores the storage area 6 of the event Y.
Clear notifications of 0. This state is shown in FIG.

In the above embodiment, the events that occur are described as two events, X and Y. However, in the case of three or more events, the contents corresponding to each event are stored in the storage area 60. By storing it, it can be realized in the same manner.

[0035]

As described above, according to the present invention, by effectively utilizing semaphores, it is possible to enable processing that was impossible due to the limitation of the number of semaphores, and to perform P operation (wait release) once. Since the occurrence of a plurality of V operations (events) can be known, efficient and effective control can be performed.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an effective use method of a semaphore according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of this embodiment.

FIG. 3 is a diagram for explaining a conventional method of using a semaphore.

[Explanation of symbols]

a10 ... V operation mechanism, a20 ... event writing mechanism, b10 ... P operation mechanism, b20 ... event reading mechanism, b30 ... event canceling mechanism, 50 ... semaphore,
60 ... Storage area.

Claims (3)

[Claims] 1. When a plurality of V operations are performed on one semaphore, which event is written to a predetermined storage area for each V operation according to each V operation for the semaphore, In response to the P operation for the semaphore, the storage area is referred to, the event for which the V operation is performed is read from the storage area, the processing related to the read event is completed, and the related event is stored in the storage area. Efficient use of semaphores characterized by erasing written contents. 2. The method for effectively using a semaphore according to claim 1, wherein the contents of writing to the storage area corresponding to a plurality of V operations are read in response to one P operation for the semaphore. 3. The effective semaphore according to claim 1, wherein the plurality of V operations include V operations for a plurality of same events or V operations for a plurality of different events when there are a plurality of different events. How to Use.