JPH0478932A - Shared resource exclusion control system - Google Patents

Abstract

PURPOSE:To improve the use efficiency of shared resources by permitting a fact that a lock request task outruns in a shared mode, only in the case the number of shared mode lock request tasks which outrun the task for waiting for a lock in an exclusion mode is less than the maximum outrunning task number. CONSTITUTION:A shared resource exclusion control function 9 consists of a lock request processing part 6, an unlock request processing part 7 and an exclusion control table 8. In such a state, in the case resources are not locked against a lock request of a shared mode, the lock right is given to a task 10 which outputs a request, and in the case of the resources are locked in the shared mode, the lock right is given to the task 10 of the request unless there is a lock waiting task in an exclusion mode. Also, in the case there is the lock waiting task in the exclusion mode, and in any case of lock waiting, the number (the number of outrunning tasks) of shared mode lock request tasks which outrun the request sequence of the lock request in the exclusion mode is less than the maximum outrunning task number, the lock right is given to the task 10 which outputs the request. In such a way, by preventing generation of a permanent blockage, resources can be used efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coexisting resource exclusive control method in a computer system.

[Conventional technology]

Exclusive control is required for resources used by multiple tasks in a computer system in order to serialize access to them. For such exclusive control, computer systems are equipped with basic functions called lock/afrost and enqueue/dequeue, and there are usually two types of lock requests: exclusive mode and shared mode.

The basic operation of conventional exclusive control is as follows.

That is, when a certain task issues a lock request, the lock right is immediately granted if the resource to which the lock request is made is not locked by another task. However, if the resource is already locked by another task and the mode in which the resource is locked or the lock request mode of the requesting task is in exclusive mode, the task waits for a lock. If the mode in which the resource is locked and the lock request mode of the task that issued the request are both shared mode, (1) If there is no task waiting for the lock, the task that issued the request is given the lock right, and If there is a waiting task, the task that issued the request is made to wait for a lock.

(2) Immediately grant lock rights to the task that issued the request.

Either of the following methods may be used.

Further, if the task that has locked the resource issues an unlotter request, the exercise of the locking right by this task ends.

At this time, if there is no other task holding the lock and there is a task waiting for the lock, if the request mode of the task that requested the lock earliest among them is exclusive mode,
If the lock is granted only to this task, and if it is in shared mode, then (1) it will wait for a lock in shared mode earlier than any task that is currently waiting for a lock in exclusive mode, corresponding to (1) and (2) above. Give lock rights to all tasks that are currently in the list.

(2) Give lock rights to all tasks currently waiting for a lock in shared mode.

Either of the following methods may be used.

[Problem to be solved by the invention]

In the conventional shared resource exclusive control method that adopts method (1) above, the task that issued the shared mode lock request cannot overtake and lock the task that issued the exclusive mode lock request under any circumstances. unlocked,
When granting the lock right to the next task waiting for a lock, if the lock mode of the task waiting for the lock is shared mode, if there is a task waiting for the lock in exclusive mode, the task that is waiting for the lock in shared mode after that Lock rights are not granted and resources cannot be used efficiently.

In addition, in the conventional shared resource exclusive control method that adopts method (2) above, if shared mode lock requests are made more frequently than exclusive mode lock requests, the task that requested the lock will be locked in exclusive mode forever. The disadvantage is that a situation in which rights are not granted, that is, a permanent blockade occurs.

[Means to solve the problem]

The shared resource exclusive control method of the present invention is a shared resource exclusive control method for a computer system in which, in response to a shared mode lock request, if the resource is not locked, the task that issued the request is given the locking right, and the resource is locked. is locked in shared mode, if there is no task waiting for a lock in exclusive mode, the lock right is given to the task that issued the request, and if there is a task waiting for a lock in exclusive mode, that If the number of shared mode lock requesting tasks that have overtaken the request order of the exclusive mode lock request (hereinafter referred to as the "overtaking task number") is less than the maximum overtaking task number N, the locking right is given to the task that issued the above request, and the maximum If there are lock-waiting tasks in exclusive mode with the number of overtaking tasks N, and there are tasks waiting for exclusive mode locks with a number less than the maximum number of overtaking tasks N, then the maximum number of overtaking tasks is N.
The order in which the lock rights are granted is changed so that the lock rights are granted before the task that has been overtaken by the shared mode lock requesting task the most among the tasks with less than the maximum number of overtaken tasks, and the task that issued the request is placed in a lock wait state. If there are N tasks waiting for an exclusive mode lock, a shared request processing means makes the task that issued the request wait for the lock so that it will be granted the lock right last among the tasks currently waiting for the lock; and an unlock request. However, if the next lock-waiting task to which the lock right should be granted is making a request in shared mode, all tasks that have issued a shared-mode lock request to which the lock right should be granted before any exclusive mode lock-waiting task and unlock request processing means for granting lock rights to.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In this embodiment, the shared resource exclusive control function 9 is the lock request processing unit 6.
, an unlock request processing section 7 , and an exclusive control table 8 . The lock request processing unit 6 includes a shared request processing means 1 that processes lock requests in a shared mode, and an exclusive request processing means 2 that processes lock requests in an exclusive mode. Further, the unlock request processing unit 7 includes an unlocking means 3 that unlocks a task that has requested an unlock, a shared waiting locking means 4 that performs a locking process when the request mode of the next lock waiting task is a shared mode, and an exclusive wait lock means 5 that performs lock processing when the request mode of the next lock wait task is exclusive mode.

FIG. 2 is a configuration diagram of the exclusive control table 8 of FIG. 1.

The exclusive control table 8 uses resource names as keys to uniquely identify resources subject to exclusive control within the system. The entry for each resource consists of a resource name field 81, a lock mode field 82, a locked task list 83, and a lock waiting task queue 84. The lock mode section 82 records the lock mode when a resource is locked. The locked task list 83 records the task identifiers of tasks that have locked the resource. The lock waiting task queue 84 is a queue of lock requests in a waiting state,
For a task issuing a shared mode lock request, a pair of task identifier and lock mode is recorded, and for a task issuing an exclusive mode lock request, a pair of task identifier, lock mode, and number of overtaking tasks is recorded.

Next, the operation of each processing section shown in FIG. 1 will be explained.

The share request processing means 1 processes lock requests in the share mode. That is, (1) If the lock mode section 82 is empty, the shared mode is recorded in the lock mode section 82, the task identifier of the task that issued the request is added to the locked task list 83, and the locking right is given to this task. .

(2) If the lock mode section 82 is not empty, the lock requests in the lock waiting task queue 84 are scanned in order from the beginning, and if the number of overtaking tasks is less than the maximum number N of overtaking tasks, the scanning is ended. Furthermore, when all lock requests have been checked, the scan ends. As a result of this scanning, if an exclusive mode lock request for which the maximum number of overtaking tasks is less than N disappears, the task identifier of the task that issued this shared mode lock request and the lock Add a pair with mode, interrupt the processing of this task, and wait for a lock. If the scan ends with the request at the head of the lock waiting task queue 84 and the resource is locked in shared mode, the task identifier of the task that issued this request is added to the locked task list 83 and this task is locked. Lock waiting task queue 84
1 for the number of overtaking tasks for all exclusive mode lock requests.
Add. In other cases, insert the task identifier and lock mode pair of the task that issued this shared mode lock request immediately before the exclusive mode lock request that has finished scanning,
The processing of this task is interrupted, the task is made to wait for a lock, and 1 is added to the number of overtaking tasks for all subsequent exclusive mode lock requests, including the exclusive mode lock request that has finished scanning.

According to (2) above, if a resource is locked in shared mode and there is a task waiting for the lock in exclusive mode, the lock waiting task in exclusive mode that can be overtaken by a new shared mode lock request task is This means that the number of shared mode lock requesting tasks is less than the maximum overtaking task number N, and no permanent blockage occurs.

The shared waiting lock means 4 performs lock processing when the next lock waiting task requests in the shared mode in the unlotter request process. That is, (1) lock mode section 8
2, record the shared mode in the lock waiting task queue 84
The task identifiers of all consecutive shared mode lock requests are recorded in the locked task list 83 from the beginning.

Next, the recorded lock request is deleted from the lock waiting task queue 84, the processing of these tasks is restarted, and lock rights are granted.

The exclusive request processing means 2 processes exclusive mode lock requests. That is, (1) If the lock mode section 82 is empty, the lock mode of the request is recorded in the lock mode section 82, the task identifier of the task that issued this request is recorded in the locked task list 83, and locking rights are granted. .

(2) If the lock mode field 82 is not empty, add the task identifier of the task that issued the request, the lock mode of this request, and the number of overtaking tasks O to the end of the lock waiting task queue 84, and issue this request. interrupts the processing of the task and waits for the lock.

The lock release means 3 performs a lock release process when an unloading request is made, and if there is a task waiting for a lock,
The shared waiting locking means 4 or the exclusive waiting locking means 5 is called to perform lock processing for the next lock waiting task.

That is, (1) The task identifier of the task that requested unlotta is deleted from the locked task list 83, and when the locked task list 83 becomes empty, the contents of the lock mode section 82 are deleted.

(2) Subsequently, when the locked task list 82 becomes empty, if the lock request at the head of the lock waiting task queue 84 is in the shared mode, the shared waiting locking means 4 is called, and if the locking request is in the exclusive mode, the exclusive waiting locking means 5 is called.

The exclusive wait locking means 5 is called by the lock release means 3 and performs lock processing for lock waiting tasks in exclusive mode.

That is, (1) Record the lock mode of the request at the head of the lock waiting task queue 84 in the lock mode section 82 and the task identifier in the locked task list 83, and delete this lock request from the lock waiting task queue 84. , restarts processing of the task that issued the lock request, and grants lock rights.

Next, the specific operation of this embodiment will be explained with reference to an example of the contents of the exclusive control table 8 in FIG. 3. In this embodiment, it is assumed that the maximum number of overtaking tasks N is a fixed value of two.

3(a) to 3(f) each show the state of the exclusive control table 8 at a certain point in time.

In FIG. 3(a), task T1 has locked resource R in mutual mode, and task T2 is waiting to lock it in exclusive mode with the number of overtaking tasks being O. At this time, when task T3 makes a lock request in the shared mode, the sharing request processing means 1 is called. Since the resource R is locked in shared mode, the lock waiting task queue 84 is scanned from the beginning to find the exclusive mode lock request of task T2. The number of overtaking tasks in this request is 0, which is smaller than the maximum number of overtaking tasks, 2, so scanning is terminated. Since the scan ends at the head of the lock waiting task queue 84 and the resource R is locked in shared mode, the task identifier T3 of the requested task is added to the locked task list 83, and the requested task is given the locking right. Given. Further, 1 is added to the number of overtaking tasks of task T2. As a result, the exclusive control table 8 is in the state shown in FIG. 3(b).

Next, when task T4 makes a lock request in exclusive mode, exclusive request processing means 2 is called. Since the resource R is already locked, a set of the task identifier T4, request mode E, and number of overtaking tasks O for this task is recorded in the lock waiting task queue 84, and the processing of this task is interrupted and the task becomes locked. .

As a result, the exclusive control table 8 is in the state shown in FIG. 3(C).

Next, when task T5 makes a request in the sharing mode, the sharing request processing means 1 is called. Since the resource R is already locked in the coexistence mode, the task queue 84 waiting for a lock is sequentially scanned from the top to find the exclusive mode lock request of the task T2.

The number of overtaking tasks is 1, which is smaller than the maximum number of overtaking tasks 2, so scanning is ended. Since the request ends with the first request in the lock waiting task queue 84 and the resource R is locked in the shared mode, the task identifier T5 is added to the mouth/vine task list 83 and the locking right is given to the task T5. Further, 1 is added to the number of overtaking tasks for all exclusive mode lock requests after the lock request for which scanning has been completed. As a result, the exclusive control table 8 is
).

Next, when task T6 requests a lock in the shared mode, the sharing request processing means 1 is called. Since resource R is already locked in shared mode, the lock waiting task queue 84
is sequentially scanned from the beginning to find the exclusive mode lock request of task T2. The number of overtaking tasks is 2, which is equal to the maximum number of overtaking tasks 2, so scanning is continued. Next, find the exclusive mode lock request of task T4. The number of overtaking tasks is 1, which is smaller than the maximum number of overtaking tasks 2, so scanning is ended. Since the end is not at the head of the lock waiting task queue 84, the pair of task identifier T6 and request mode S of the task newly requesting the lock is inserted immediately before the request that has finished scanning, and the processing of task T6 is interrupted. , it will be waiting for a lock. Also, task T4 that has finished scanning
1 is added to the number of overtaking tasks for the exclusive mode lock request.

Next, when task T7 requests a lock in shared mode,
The sharing request processing means 1 is called. Since resource R is already locked in shared mode, the lock waiting task queue 84 is scanned in order from the beginning. Since there is no exclusive mode lock request for which the number of overtaking tasks is less than the maximum number of overtaking tasks, 2, the task identifier T is placed at the end of the lock waiting task queue 84.
A pair of task T7 and request mode S is added, and the processing of task T7 is interrupted to wait for a lock. As a result, the exclusive control table 8 is in the state shown in FIG. 3(e).

Next, when tasks T1, T3, and T5 make unlock requests in this order, the unlocking means 3
is called. For tasks T1 and T3, the task identifiers Tl and T3 are deleted from the locked task list 83, and since the locked task list is not empty in either case, the process ends here. Regarding the unlock request for task T5, if the task identifier T5 is deleted from the locked task list 83, the locked task list 83 becomes empty, so the request at the head of the lock waiting task queue 84 is checked. Since the first request is for the exclusive mode, the exclusive waiting lock means 5 is called and the exclusive mode E is set to the lock mode section 82.
Then, the task identifier T2 is recorded in the locked task list 83, this exclusive mode lock request is deleted from the lock waiting task queue 84, and the task that issued the lock request is restarted and given the lock right. As a result, the exclusive control table 8 is in the state shown in FIG. 3(f).

Next, when the task T2 makes an unlock request, the lock release means 3 is called and the task identifier T2 is deleted from the locked task list 83. Locked task list 83
Since it is now empty, the lock mode section 82 is deleted. Since the request at the head of the lock-waiting task queue 84 is in the shared mode, the share-waiting lock means 4 is called, and the locking mode section 82 has the shared mode S, and the locking task list 83 has the shared mode continuously from the head of the lock-waiting task queue 84. T6 is recorded as the task identifier for all shared mode lock requests, respectively. The request for task T6 is deleted from the lock waiting task queue 84, the processing of task T6 is restarted, and the lock right is granted. As a result, the exclusive control table 8 is in the state shown in FIG. 3(g).

In this embodiment, the maximum number of overtaking tasks is set to a fixed value N regardless of the type of resource, but a column for the maximum number of overtaking tasks is provided in the exclusive control table 8 to set a different maximum number of overtaking tasks N for each resource. It is also possible to record and use this to control.

〔Effect of the invention〕

As explained above, in the present invention, only when the number of shared mode lock requesting tasks that have overtaken a task waiting for a lock in exclusive mode is less than the maximum number of overtaking tasks N,
By allowing a task that requests a lock to overtake in shared mode, it is possible to improve the efficiency of using shared resources while avoiding the problem of permanent blockage.

It is a figure of the example of the content of a control table.

DESCRIPTION OF SYMBOLS 1...Sharing request processing means, 2...Exclusion request processing means, 3...Lock release means, 4...Sharing waiting locking means, 5...Exclusion waiting locking means, 6...Lock request Processing unit, 7... Unlock request processing unit, 8... Exclusive control table, 9... Shared resource exclusive control function, 10.
...Coexisting resource usage tasks.

Claims (1)

[Claims] In a shared resource exclusive control method for a computer system, in response to a shared mode lock request, if the resource is not locked, a locking right is granted to the task that issued the request, and the resource is in the shared mode. If the lock is locked, if there is no task waiting for a lock in exclusive mode, the lock right is given to the task that issued the request; If the number of shared mode lock requesting tasks that have overtaken the request order (hereinafter referred to as the "number of overtaking tasks") is less than the maximum number of overtaking tasks N, the task that issued the request is given locking rights, and the maximum number of overtaking tasks N If there are exclusive mode lock waiting tasks, and there are exclusive mode lock waiting tasks less than the maximum number of overtaking tasks N, then the maximum number of overtaking tasks N
The order in which the lock rights are granted is changed so that the lock rights are granted before the task that has been overtaken by the shared mode lock requesting task the most among the tasks with less than the maximum number of overtaken tasks, and the task that issued the request is placed in a lock wait state. If there are N tasks waiting for an exclusive mode lock, a shared request processing means makes the task that issued the request wait for the lock so that it will be granted the lock right last among the tasks currently waiting for the lock; and an unlock request. However, if the next lock-waiting task to which the lock right should be granted is making a request in shared mode, all tasks that have issued a shared-mode lock request to which the lock right should be granted before any exclusive mode lock-waiting task 1. A shared resource exclusive control system comprising: unlock request processing means for granting lock rights to a shared resource.