JPH0330027A - Exclusive control system - Google Patents

Abstract

PURPOSE:To execute the exclusive control by the occupied time of information and to smoothly execute the processing by providing an occupied time designating means of information at the time of obtaining a lock, and a means for waiting if the occupancy is ended in a short time, and deciding the lock to be unsuccessful if the occupancy extends over many hours. CONSTITUTION:A process 10 requests to obtain a lock against shared informa tion 12 to an exclusive control system 14. The exclusive control system 14 decides whether it is successful to obtain the lock or not from exclusive manage ment information 18 on a main storage 16, and repeats success/failure. At the time of requesting to obtain the lock, one of four kinds of locks of classifications of a share lock which does not permit updating from other proc ess and an EXC lock which does not permit reference and updating of informa tion from other process, and whether the occupied time for obtaining to the lock is long or short is designated. At the time of requesting to obtain the lock, when the designated time of the process which is being obtained is short, waiting is executed, and when said time is long, it is decided to be unsuccessful to obtain the lock, and the process processing jam caused by waiting for a lock release for many hours can be prevented.

Description

[Detailed Description of the Invention] [Summary] Regarding an exclusive control method that acquires a lock when accessing information shared by multiple processes and prohibits access from other processes, information based on already acquired locks is provided. For the purpose of acquiring locks according to the occupation time of the process and maintaining multiple lock types in the lock acquisition state, the information occupation time is specified when requesting lock acquisition, and the specified occupation time of the process that has currently succeeded in acquiring the lock is specified. When is short, it enters a waiting state, and when it is long, the lock acquisition is considered unsuccessful and does not wait. Also, when requesting a lock, the name of the process that has currently successfully acquired the lock is checked, and if it is the same as the requesting process name, the lock is successfully acquired, making it possible to hold multiple lock types through continuous lock acquisition by the same process. do.

[Field of Industrial Application] The present invention relates to an exclusive control method that acquires a lock when accessing information shared by a plurality of processes and prohibits access from other processes.

For exclusive control of information shared by multiple processes running on a computer, locks are acquired according to the information's occupancy time, multiple lock types are held, and the lock type is changed when the lock is released. A means to return to the previous state is desired.

[Prior Art] On a computer that implements multiple processes, the problem of sharing/excluding information between processes occurs regarding the use of shared information. For this purpose, two exclusive control operations are required: ``acquiring a lock'' to prohibit access to information from other processes, and ``releasing a lock'' to allow access.

Conventionally, when acquiring a lock, a shared lock (shsxre) that does not allow information to be updated from other processes is used, as shown in Figure 21.
lock) and an exclusive block (rEXC, hereinafter referred to as rEXC) that does not allow either reference or update of information from other processes, as shown in Figure 22.
Exclusive control is performed using two types of locks (referred to as "locks").

[Problems to be Solved by the Invention] However, in the conventional exclusive control method, when lock acquisition from multiple processes collides, a later lock acquisition request is Regardless of how long the information is occupied by the acquired lock, a decision must be made whether to wait until the lock is acquired or to give up.

Additionally, while acquiring a lock, you may want to change the type of lock depending on the content of the information. In the conventional technology, it is possible to change the lock type, but there is no means for having multiple lock types and returning the lock to the acquired state when the lock is released.

First, we will explain the problem caused by not knowing how long information is occupied by an acquired lock, using two examples.

(2) An example of this is the case shown in FIG. 23.

In FIG. 23, process A attempts to reference information P and requests acquisition of a share lock, and process B attempts to update information P and requests acquisition of an EXC lock.

In this case, if neither process A nor process B is able to acquire a lock, they will wait until they are able to acquire a lock.

Assume that lock acquisition requests are made by process A and process B in this order. Process A puts information P in a state where access from other processes attempting to update information P is prohibited. In this state, even if process B requests acquisition of the EXC lock in order to update information P, process B cannot acquire the EXC lock because process A has already acquired the share lock. Therefore, process B waits for process A to release the lock.

If process A continues to acquire the share lock for a long time, process B will not be able to proceed with its processing during that time, resulting in unnecessary delays.

Another example is the case shown in FIG.

In FIG. 24, process C attempts to update information Q and requests acquisition of an EXC lock, and process D attempts to reference information Q and requests acquisition of a share lock.

At this time, if neither process C nor process D is able to acquire the lock, it is assumed that they return immediately without waiting for the lock to be acquired.

Now, assume that process C and process D acquire locks in this order. When process C acquires the EXC lock, information Q becomes in a state where access from all other processes attempting to manipulate information Q is prohibited. In this state, even if process D tries to refer to information Q and requests to acquire a share lock, process D will not be able to access information Q. I can get Tsuku, and I'll be back soon. In this case, the process D stops operating the information Q and returns 1-. However, if the EXC lock was acquired for a short period of time as in process C in FIG. 24, process D could have continued processing if it had been in the waiting state during that time.

Next, an example will be given of a problem that occurs when a plurality of lock types are held and when the locks are released, it is not possible to release only some of the locks.

First, acquire a share lock to view information. Change the lock type from shared lock to EX based on the information content
Change to C lock. In the conventional technology, this change would result in changing the lock type from a shared lock to an EXC lock. In other words, only the EXC lock exists. If the lock is released in such a state, all locks on the information R will be released. However, after the lock is released, there are cases where it is desired to manipulate information while acquiring a share lock that only prohibits changes to the information from other programs.

In the case of the conventional technology, (1) the release of the lock is delayed, as in process XX1 in FIG. ■Process X in Figure 26
Like X2, the lock is first released and a shared lock is acquired. However, in the case of ■, the process ZZ1 that attempts to refer to the information YY1 is delayed. ■In the case of process
After X2 releases the lock and acquires a new lock, there is a possibility that the information ZZ2 is manipulated like the process YY2, and the consistency of the information ZZ2 is no longer guaranteed.

As is clear from the above, exclusive control over information shared by multiple processes involves acquiring locks according to the information's occupancy time, maintaining multiple lock types, and releasing some of the lock types when the lock is released. A method for returning to the previous state and a method for canceling it all at once are required.

The present invention has been made in view of these conventional problems, and provides an exclusive control method that makes it possible to acquire a lock and change the type of lock in accordance with the time that information is occupied by the already acquired lock. Realize.

[Means to solve the problem] FIG. 1 is a diagram explaining the principle of the present invention.

First, the present invention has shared information that is shared by multiple processes executed on a computer, and when this shared information is accessed (referenced or updated), it is locked to prevent other processes from accessing it. The target is an exclusive control method that obtains

Regarding such an exclusive control method, the present invention includes an occupancy time specifying means for specifying whether the occupancy time of information upon successful lock acquisition is a long occupancy time or a short occupancy time; Check the specified occupation time of a process that has successfully acquired the lock, and if the specified occupation time is short, it will go into a waiting state, and if the specified occupation time is too long, the lock acquisition will be unsuccessful; Performs exclusive control.

Also, when a lock acquisition request is made, there is a check means for determining the name of the process currently successful in acquiring the lock; if the process name determined by the check means is the same as the process name that made the lock acquisition request; provides a method for successfully acquiring a new lock; a method for successively acquiring locks in the same process, holding multiple lock types, and releasing the locks at once when the lock is released; A method for canceling is realized at the same time.

Here, the types of locks acquired when accessing shared information include the first lock (shared lock) acquired when accessing information that only allows access without allowing other processes to update the information, and There are two types of locks: a second lock (EXC lock) acquired when updating information that does not permit either reference or update of information from a process.

[Operations] According to the exclusive control method of the present invention having such a configuration, when a lock acquisition is requested, the occupation time of the process that currently occupies the information due to the successful lock acquisition is extended, and the occupancy time is reduced. If the occupied time is short, the lock can be successfully acquired after waiting for the lock to be released. On the other hand, if the occupied time is long, the lock can be unsuccessfully acquired, thereby preventing processing stagnation caused by waiting for the lock to be released for a long time.

Furthermore, if the process name that requested the lock acquisition is the same as the name of the process that has currently successfully acquired the lock, the lock acquisition is successful and multiple lock types are held, so the lock type can be changed and the lock can be released. You can unlock multiple locks at once or only some of them.

[Example] In FIG. 1, 10 is a process, and in addition to this process 10, there are a plurality of other processes. 12 is information shared by multiple processes including process 10; 14
is an exclusive control system that executes exclusive control of the present invention, 16
is the main memory, and 18 is exclusive control management information formed on the main memory 16.

In the embodiment of FIG. 2, the process 10 handles an excessive lock acquisition request as follows.

(2) The process 10 requests the exclusive control system 14 to acquire a lock on the shared information 12.

(2) The exclusive control system 14 determines the success or failure of lock acquisition from the exclusive control management information 18 on the main memory 16.

(2) The exclusive control system 14 returns success/failure of lock acquisition to the process 10.

Here, when the process 10 requests acquisition of a lock, it specifies the lock type shown in FIG. 3 and the occupation time type shown in FIG. 4 for each of the shared lock and EXC lock.

As a result, the lock types according to the present invention are: (A) EXCong (exclusive &lo
ng) (B) EXC sheet (exclusive)
e & short) (C) share long (sbxr
e & lonK (D) share short (share
There are four types of locks (short), and the process 10 specifies one of the four locks.

FIG. 5 is an explanatory diagram showing an example of the format of the exclusive control management information 18 shown in FIG.

In FIG. 5, the exclusive control management information includes an information name 20 indicating information on the object of exclusive control, and a lock specification status 22 of this information.
, 24.26.28, a pointer 30 to the process management list 34, a pointer 32 to the waiting state process management list 40, and a pointer 32 to the process management list 34.

Lock specification status 22 to 28 are EXC long, EXC
Number of processes that requested lock acquisition by short, shared long, and shared short and succeeded in acquiring the lock, or processes that are in a waiting state A, B, C,
Indicates D. This number of processes A-D is reduced by 1 when a lock release is requested. If the number of processes for a lock specification is 0, it means that there are no processes requesting to acquire the lock with that specification, and if the number of processes is not 0, it means that there are no processes requesting to acquire the lock with that specification. Indicates how many there are.

The lock specification status in the exclusive control management information with information name a in Figure 6 is the number of processes (A, B,
Since C, D) are (0. 1, 0. 0), B = 1 indicates that there is one process that specified EXC short and requested to acquire the lock, and other specifications are This indicates that no process has acquired the lock.

Referring again to FIG. 5, the process management list 34 includes a process name 36 indicating the process that has acquired the lock.
are kept in list format.

In addition, there is a partial lock acquisition process management list 38 before the process management list 34, in which process names 36 that have already successfully acquired locks are listed, followed by process names 36 that are in a waiting state. A waiting state process management list 40 is provided. Looking at this point with respect to FIG. 6, the process management list 34 of the exclusive control management information indicates that the process p1 has successfully acquired the lock and that there is no process in the waiting state.

FIG. 7 shows that in the embodiment shown in FIG. 2, when an attempt is made to acquire a lock for certain information, exclusive control is determined based on the lock specification status of the exclusive control management information of the information and the lock specification of this acquisition request. The system judgment, that is, the judgment processing by the exclusive control system 14 as to whether lock acquisition should be successful or unsuccessful, or whether the process should be placed in a waiting state, is summarized in a table.

Using an example, we will explain what kind of processing the exclusive control system 14 performs based on the exclusive control management information 18 of that information when attempting to acquire a lock on certain information according to the table in FIG. .

[Processing 1] At first, when no process has acquired a lock, the exclusive control management information 18 of information b is as shown in FIG. In this state, if there is a lock acquisition request specifying EXC short for information b, the lock acquisition is successful based on ■ in FIG. 7, and the process name pi is registered in the process management list 34. .

[Processing 2] When the exclusive control management information 18 of information C is as shown in FIG. 10, that is,
When process p2 has successfully acquired a lock with a shared long specification for information C, if process p3 requests a lock acquisition with the lock specification set to EXC short,
Based on ■ in FIG. 7, the exclusive control system fails to acquire the lock.

[Process 3] When the exclusive control management information 18 of information d is as shown in Fig. 1, that is,
When process p4 has successfully acquired a lock with the EXC short designation on information d, and process p5 requests a lock acquisition with the lock designation as share short, based on ■ in Figure 7, the exclusive control system
to wait state.

The process p5 wakes up from this waiting state and becomes able to acquire the lock when the process p4 releases the lock. Exclusive control management information l8 when process p5 wakes up from a wait state and successfully acquires a lock
is as shown in Figure 12.

[Process 4] When the exclusive control management information 18 of information e is as shown in FIG. 13, that is, when process p6 successfully acquires a lock with share long designation and a lock with share short designation for information e, process p7 If a request is made to acquire a lock by setting the lock specification to EXC short, the exclusive control system 14 either causes the lock acquisition to fail from ■ in FIG. 7, or places process p7 in a waiting state from ■ in FIG. 7. Make it one way or the other.

At this time, the exclusive control system 14 makes a determination in the following order: (failure) = (waiting state) -> (success), and the process p7 fails to acquire the lock.

[Processing 5] Figure 14 shows that when no process has made a request to acquire a lock for information f, process p8 requests acquisition of a lock with share long specified for information f. , and represents the exclusive control management information 18 when the request is successful.

Furthermore, if the process p8 specifies EXC short and requests acquisition of a lock for the same information f, the acquisition of the lock will fail at point 2 in FIG. 7 under current circumstances. However, looking at the process management list 34 in the exclusive control management information 18 in FIG. 14, the only process that has successfully acquired a lock in the past is its own process p8.

In such a case, the exclusive control system 14 of the present invention searches the process management list 34, and if the self-process is the only process that has already successfully acquired a lock,
Successfully acquire a lock later. This allows the type of lock to be changed. In the process shown in FIG. 14, the process name p8 is further added to the process management list 34, and the EXC short lock acquisition request of the process p8 is successful. That is, the lock type of the same process p8 is changed from share short to ECX short. This ECX
The state of the exclusive control management information 18 after acquiring a new lock due to the short designation is as shown in FIG.

The process shown in FIG. 15 for changing the lock type by successively acquiring locks by the same process will be described in more detail.

First, in order to acquire consecutive locks in the same process, the process management list 3 of the exclusive management information 18 is shown in FIG.
4 is provided with an ID field 42 in addition to the process name 36, and an identifier indicating the order of lock acquisition can be arbitrarily set in the ID field 42.

Therefore, when the same process p8 acquires a lock twice for the information f shown in FIG. 14.15, the process management list 34 acquires a lock in the ID section as shown in FIGS. 17(a) and (b). No. indicating the order. 1, No. 2 is set. That is, a new process management list is created redundantly every time a lock is acquired.

FIGS. 17(c) and 17(d) show unlocking. That is, if the lock acquisition state shown in FIG. 17(b) is unlocked using the process management list obtained in the second lock acquisition, the state shown in FIG. When unlocking is performed using the process management list obtained in the first lock acquisition, the lock is released.

The advantage of the method of creating and controlling a process management list redundantly each time a lock is acquired according to the present invention, as shown in FIG. 17, is that, as shown in FIG.
When the lock is acquired for the second time, the same ID part value No. If you use 1, you only need to unlock once using the process management list obtained from the first lock acquisition.
The key point is that lock acquisition that has been set twice can be canceled in one go, and the lock can be released quickly.

That is, the ID of the process management list 34 shown in FIG.
The value in section 42 is an identifier that indicates the order of lock acquisition, but since the value of the identifier can be freely set regardless of the order of lock acquisition, two consecutive lock acquisitions are released by two unlocks. You can choose whether to unlock it once, or to unlock it once, depending on how the ID section is determined.

FIG. 20 shows a processing flow of exclusive control according to the embodiment of FIG. 2.

In steps 85, 86, 87 and s8 of FIG. 20, the exclusive control system 14 determines whether the lock acquisition is successful/failure or whether to place the lock in a waiting state based on the lock specification status in the exclusive control management information 18 as shown in FIG. It is done as shown in the list. Similarly, in step S9, search the process management list 34 in the exclusive control management information 18,
Whether or not to change the lock is determined depending on whether the process is an own process or not.

[Effects of the Invention] As explained above, according to the present invention, an exclusive control system is provided that is capable of acquiring locks and changing lock types in accordance with the information occupancy time on a computer that implements multiple processes. is realized, and the process can smoothly perform processing according to the exclusive status of shared information.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the present invention; Fig. 2 is an exemplary configuration diagram of the present invention; Fig. 3 is an explanatory diagram of the lock types of the present invention; Fig. 4 is an explanatory diagram of the types of occupied time of the present invention; FIG. 5 is an explanatory diagram of exclusive control management information of the present invention; FIG. 6 is an explanatory diagram of exclusive control management information of information a; FIG. 7 is an explanatory diagram of a judgment table for lock acquisition success, failure, and waiting state of the present invention; 8th. 9, 1.0, 11. 12. 13. 1
4. Figure 15 is an explanatory diagram of exclusive management information of information b-f; 1st
Figure 6 is an explanatory diagram of the process management list for continuous lock acquisition; Figure 17 is an explanatory diagram of the list when locking is acquired twice and unlocked; {Figure 8 is an explanatory diagram of the list when unlocking; Processing flow diagram; Fig. 20 is an explanatory diagram of the conventional shaIe lock acquisition state; Fig. 21 is an explanatory diagram of the conventional exclusive lock acquisition state; Fig. 22 is a delay state diagram of a process that subsequently requests lock acquisition; The figure shows a state in which a process that later requests to acquire a lock fails to acquire the lock and aborts the process; Figure 24 is an explanatory diagram of the conventional method that delays releasing the lock; Figure 25 shows the conventional method that releases the lock once. FIG. 14: Exclusive control system 16: Main memory 18: Exclusive control management information 20: Information name 22, 24, 26. , 28: Number of lock acquisition and waiting processes 30. 32: Pointer 34: Process management list 36: Process name 38: Lock acquisition waiting process management list 40: Waiting state process management list 42: ID section

Claims (3)

[Claims] (1) In an exclusive control method that has information shared by multiple processes executed on a computer and acquires a lock to prohibit access from other processes when accessing the information, an occupation time specifying means for specifying whether the information is occupied for a long time or a short time when the lock is successfully acquired when the lock is requested; a process that is currently successfully acquiring the lock when the lock is requested; An exclusive method is characterized in that exclusive control is performed according to the information occupancy time by providing a means for making lock acquisition unsuccessful when the specified occupancy time is short, and not entering the wait state when the specified occupancy time is long; control method. (2) In an exclusive control method in which information is shared by multiple processes running on a computer, and when accessing the information, a lock is acquired to prohibit access from other processes. , a check means for determining the name of the process that has currently succeeded in acquiring the lock when a lock acquisition is requested; if the process name determined by the check means is the same as the process name that requested the lock acquisition, a new process name is determined; means for successfully acquiring locks in the same process;
An exclusive control method that is characterized by being able to hold multiple lock types at the same time. (3) The types of locks acquired when accessing the information are the first lock, which is acquired when referencing information that only allows access to the information without allowing updates from other processes, and the first lock acquired when accessing information from other processes. 3. The exclusive control method according to claim 1, further comprising a second lock acquired when updating information that does not permit either reference or update.