JPH06187175A - Exclusion control method for multi-task computing system - Google Patents

Abstract

PURPOSE:To execute a processing according to a priority order by a task even in the exclusion control method of a multi-task system in which the execution of the processing of the task is operated in the priority order by exclusively using a resource by operating the addition and subtraction of a counter value by a semaphore, and performing a lock operation and an un-lock operation. CONSTITUTION:When a task Tm 7 whose priority order is higher than a task Tn 8 occupying a semaphore 6 executes a P operation, the priority order is increased to the priority order which is the same as the task Tm 7. Then, when the task occupying the semaphore 6 executes a V operation, the priority order of the task is returned to the original order. Thus, the processing of the task Tn 8 occupying the semaphore can be prevented from being taken away by the task whose priority order is lower than the Tm 7 which is not related with the semaphore 6 and higher than the Tn 8, and the waiting task can start traveling according to the priority order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exclusive control system of an operating system (OS) for realizing multitask,
More specifically, it relates to an exclusive control method in a multi-task management system (data management, network management, etc.) that handles resources that must be exclusively controlled.

[0002]

2. Description of the Related Art In a multitasking system, when multiple tasks use resources that cannot be used simultaneously,
Check that it is not used by another task before using it. If another task is using it, it waits until the end of its use, and after the other task finishes its use and declares the release of resources, the waiting task becomes available. The logic that implements this operation is commonly called a semaphore. The semaphore is managed by the counter value, and two operations for it are functionally provided. One is P
It is called operation (lock operation), the counter value is decremented by 1, and if the result is positive (0 or more), the processing is continued,
It waits for the result to be negative. The other is called V operation (or unlock operation) and adds 1 to the counter value. At this time, if another task is waiting for the P operation, the P operation is repeated for that task.

FIG. 4 is a flowchart of resource exclusive control using a binary semaphore. Task A is executing the P operation. The semaphore counter only changes from the initial value of 1 to 0, and the task A continues processing as it is. Resources are exclusively used during this period. Even if the task B that wants to use the same resource executes the P operation during this period, the semaphore counter is already 0, so that the semaphore wait state is entered. This operation can prevent the same resource from being used twice. When task A executes V operation, the semaphore counter returns to 1 once, and immediately after task B
It returns to 0 again by P operation. At this point, the task B releases the wait for the semaphore and can use the resource as a result. When the task A executes the V operation, both the tasks A and B can be executed, but which task is executed depends on the priority order of the tasks.

FIG. 5 is a block diagram of a logic for realizing a semaphore. The semaphore management data 10 is composed of a link head 10a of a waiting task and a counter 10b.
Tasks (Tn, Tm, ...) Waiting for a semaphore are linked and monitored in order of priority. However, the task at the beginning of the link indicates the task that is occupying the semaphore. The priority of this task may be lower than the tasks linked to it thereafter. When the P operation is executed in this state,
The task is inserted at the position according to the priority of the semaphore waiting link sequence starting from the next link, excluding only the head as shown in. Further, the V operation is issued only from the task that is occupying the semaphore (the task at the head of the link sequence).
When the V operation is issued, the task at the beginning of the link sequence is removed from the link, and as a result, the task waiting at the beginning is released from the semaphore wait state and the task occupies the semaphore. Then it becomes possible to run.

[0005]

In the conventional exclusive control system, a task that waits for a semaphore creates a queue in the order of priority after a task that has already occupied the semaphore. In that case, the wait task unconditionally waits for the V operation of the semaphore, which causes a problem. FIG. 6 is a diagram for explaining the problem, and shows a state in which priority processing is blocked by the semaphore logic. The priority of task T _n that occupies a semaphore is n
And the priority of task T _m waiting for the release of the semaphore is m. Even if n <m, it is natural that the task T _m waits for the V operation of the task T _n .
If tasks that are higher in priority than n and lower than m and are not associated with a semaphore are running, T _n will be deprived of those tasks execution rights by the priority processing logic. As a result, T _m is weighted in a state of being lower than its own priority, and the processing logic of priority is broken at this point.

FIG. 7 is a diagram showing an example of the execution order of processing. T _n is deprived of the execution right by the tasks T _{n1 to} T _{ni which} are not related to the semaphore and have higher priority than themselves. At this time T _n1 ~
There is no guarantee that T _ni has higher priority than T _m . T _n1
It is quite possible that ~ T _ni is a task of higher priority than T _{n and} lower than T _m . In that case T _m is T
Execution is hindered not only by _n but also by an unspecified number of T _{n1 to} T _ni , which obviously hinders priority processing. Generally, in computer processing, such a resource wait time is extremely long as compared with processing execution using a CPU as shown in FIG. Therefore, even if the CPU usage is controlled to be in the order of priority, there are many cases where the priority is not followed.
Actually, the processing according to the priority order cannot be performed. An object of the present invention is to solve the above-mentioned problem and to reduce the possibility that a task violates the principle of traveling according to the priority order, and to execute the task in the priority order surely by exclusive control. To provide a method.

[0007]

In order to achieve the above object, an exclusive control method of a multitask computing system according to the present invention performs a lock operation on a semaphore when a task executes a process according to a priority order. By using the resource exclusively, and when the task finishes the processing execution, the release of the use of the resource is declared by performing the unlock operation to the semaphore, and then the plurality of waiting tasks It enables processing execution by using the resources according to the priority. In this exclusive control method, when a task (T _n ) performs a lock operation and exclusively uses a resource, the task (T _n )
_(n ) When the task (T _m ) having a higher priority is locked, the task (T _m ) is placed in the wait state and the priority of the task (T _n ) is raised from (n) to (m). When the task (T _n ) performs a V operation on the semaphore, the task (T _n ) is returned to the original priority (n).

[0008]

According to the above configuration, the system can execute the processing in which the priority of the task is faithfully reflected even while waiting for the resource, and the waiting task can be executed by the task having the priority lower than itself. You will not be deprived of the right to execute.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining an embodiment of an exclusive control system for a multitask computing system according to the present invention. In FIG. 1A, the multi-task computing system is composed of a control means 1 by a CPU, a data / program storage means 2, an input device 3, an output device 4 and a display means 5. This system performs data management, network management, etc. The task management program is read from the data / program storage means, and under the control of the control means 1, task generation processing, system resource allocation, task selection to be executed,
Performs monitoring of the execution status, task disappearance processing, etc. The generated task is processed by the CPU, according to the assigned priority.
Processing is executed using resources such as data, programs, input device 3, output device 4, and the like. Since a plurality of tasks cannot use the same resource at the same time, the semaphore counter 6 is used exclusively during the execution of processing.

Now, a task (T _n ) 8 of priority n for forming a network and receiving data is generated,
It is assumed that the semaphore counter 6 is occupied and the input device 3 is used to display the received data on the display means 5 and store the received data in the memory. In this state, the task (T
_a task (T _m ) 7 having a higher priority than _n ) 8 occurs,
It is assumed that the P operation is performed to execute the process using the same input device 3. Then, it is assumed that the tasks (T _{n1 to} T _ni ) 9 having the priorities between n and m occur during the execution of the processing of the task (T _n ) 8. In such a case, the P operation of the task (T _m ) 7 causes the priority of the task (T _n ) to be the same as that of the task (T _m ) 7 under the control of the control means 1 as shown in FIG. Be raised to. As a result, the priority of the task (T _n ) 8 becomes higher than that of the tasks (T _{n1 to} T _ni ) 9, so that the priority of the task (T _m ) 7 is not hindered. Then, by the V operation of the task (T _n ) 8 after the end of the current processing, the priority of the task (T _n ) 8 is returned to the original priority _n under the control of the control means 1.

FIG. 2 is a flow chart showing the processing of the P operation of the exclusive control method of the multitask computing system according to the present invention. The control means 1 first checks whether the semaphore is occupied (step (hereinafter "S
"T") 1). If it is not occupied, the process proceeds to ST2, the data for managing the corresponding task is linked to the head of the semaphore management data, and the semaphore counter is decremented by 1 (ST3). On the other hand, if it is occupied, proceed to ST4,
Compare the priority of the occupying task with that of the requesting task. As a result, if the priority of the dedicated task is low, the priority is raised to the priority of the task waiting for the semaphore (ST5). If there is already a task waiting for a semaphore and the priority of the dedicated task has not been changed by that task, that is, if the priority of the dedicated task is changed for the first time, the priority of the original low priority is stored. Keep it. Then, the requested task is inserted into the semaphore-waiting task link sequence at a position according to the priority order, and the semaphore-waiting state is set (ST6).

FIG. 3 is a flowchart showing the process of the V operation of the exclusive control system of the multitask computing system according to the present invention. First, set the semaphore counter +
Add 1 (ST1), and remove the data that manages the task that occupied the first semaphore from the link string (ST
2). Then, the stored priority is changed to the original priority (ST3). Next, it is determined whether or not there is a task waiting for the semaphore (ST4). If there is a task waiting for the semaphore, the semaphore counter is decremented by 1 and the waiting state of the task at the head of the link is released (ST5). This task is guaranteed to have the highest priority among the waiting tasks (links waiting for a semaphore are created in order of highest priority), so run at your own priority. To start. At this time, which of the task that has executed the V operation and the task that has been released from the waiting state actually starts running is determined by the mutual priority order, and the higher one starts execution.

[0013]

As described above, in the exclusive control method according to the present invention, while a task that is occupying a semaphore is being processed, a task having a higher priority than the task that is occupying the semaphore performs a P operation and is in a wait state. When the semaphore is occupied, the priority of the task that is occupying the semaphore is raised to the same priority as the task in the wait state, and when the task that is occupying the semaphore finishes its processing and performs a V operation, it is returned to the original priority. Therefore, even if a task that has a higher priority than a task that is occupying a semaphore during the wait state and a lower priority than a task that is in the wait state occurs that is not related to the semaphore, the priority execution right of the task in the wait state is It will not be robbed. Therefore, the task is much less likely to break the principle of running according to priority. As a result, the task can faithfully execute the processing in the priority order, and it is more certain that the CPU executes the processing in order from the higher priority order.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of an exclusive control system of a multi-task computing system according to the present invention.

FIG. 2 is a flowchart showing a P operation process in the exclusive control method of the multi-task computing system according to the present invention.

FIG. 3 is a flowchart showing a V operation process in the exclusive control method of the multi-task computing system according to the present invention.

FIG. 4 is a flowchart of exclusive control of resources using a binary semaphore.

FIG. 5 is a configuration diagram of a logic that realizes a semaphore.

FIG. 6 is a diagram for explaining a state in which priority processing is blocked by a semaphore logic.

FIG. 7 is a diagram illustrating an example of an execution order of processing.

FIG. 8 is a diagram for explaining that a resource wait time is very long in computer processing.

[Explanation of symbols]

1 control means 2 data / program storage means 3 input device 4 output device 5 display means 6 semaphore counter 7 task T _m 8 task T _n 10 semaphore management data 10a link header 10b semaphore counter

Claims (1)

[Claims] 1. In a multi-task computing system, when a task executes a process according to a priority order, a resource is exclusively used by performing a lock operation on a semaphore, and the task ends the process execution. At this time, an exclusive control that enables release of the use of the resource by performing an unlock operation on the semaphore and then enables execution of processing by using the resource according to the priority of a plurality of waiting tasks In the method, when a task (T _n ) performs a lock operation and exclusively uses a resource, if a task (T _m ) having a higher priority than the task (T _n ) performs a lock operation, that task (T _n ). T
_m ) is placed in a wait state and the task (T _n )
A means for raising the priority from (n) to (m) of, when the task (T _n) has a V operation on a semaphore, a means for returning to the task (T _n) of the original priority (n) An exclusive control method for a multi-task computing system characterized by the above.