JP2867441B2 - List processing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a list structure in which data as storage units are linked by pointers, and particularly to a list processing system having the list structure.

(Prior Art) Conventionally, in this type of list processing method, each data is allocated to a list area in a storage area, and the data holds a pointer to another data to form a list structure. To process this list structure, the following method was used to identify the form of each data.

One is a well-known tagged pointer method in which a tag indicating the form of the data is combined in one word of a computer expression together with an address in a list area where the data exists.

FIG. 6 is an explanatory diagram showing an example of a tagged pointer. The tagged pointer 201 includes a pointer 203 indicating the address to which the data 202 is allocated, and a tag 204 indicating the form of the data 202. With this tag, the data type to which the pointer points can be identified.

In addition, an object tag method in which a tag indicating a data type is added to the head of each data is known.

FIG. 7 is an explanatory diagram showing an example of data according to the object tag method. Instead of using one word as a pointer in the pointer 301, a tag indicating the data type is provided at the head of the data 302.

In both methods, each data holds a pointer to other data or an immediate value to form a list structure. The list processing system is a system that creates and changes these list structures. Therefore, during execution of the system, data that may not be referenced from anywhere may appear. Such data is called garbage data. In the list processing system, when data is sequentially allocated to the list area, the list area eventually runs out, and garbage collection is performed to reuse the list area in which the garbage data is placed.

There are several types of garbage collection, but basically data that can be traced from a pointer that is a certain route is used data, and in any method, only the used data is packed at one end of the list area. It is approaching. Each method is consistent in that this makes the remaining area reusable. For example, the copy method is
When the list area is divided into two and one of the list areas is used up, the garbage area is collected by packing the data in use from the head of the other list area. At the place where the moved data was originally located, a pointer to the destination is written, and if other data refers to it, it is directed to the destination.

Also, in the mark sweep method, in order to know from where the used data is being referenced, a reverse pointer is created from the referenced data to the referenced data, and the used data is placed at the top of the list area. Squeeze into
At this time, since the data pointed to by the reverse pointer is referred to by the pointer, the pointer is directed to the movement destination.

(Problem to be Solved by the Invention) In the above-described conventional list processing method, since a tag is added to the pointer data in the tagged pointer,
The list area to which data is assigned can be restricted. For example,
If one word is 32 bits and the pointer part is 24 bits, 4 gigabytes can be used logically. However, there is a drawback that only 16 megabytes can be used.

The object tag method has a drawback that the efficiency of determining the shape of the data is low because the shape of the data cannot be known without referring to the data.

In the garbage collection, the mark sweep method complicates the processing because all pointers to data are reversed and recovered. As a result, there is a drawback that the interruption time of the list processing system is lengthened, or the list area is divided into two parts by the copy method, and the available storage area is substantially reduced by half.

An object of the present invention is to provide an instruction via an indirect pointer from a certain data to another data without directly setting a pointer, and to include, in reference information to other data in each data, an address of the indirect pointer indicating the data. In addition, by using a tagged pointer to which a tag indicating the type of the data is attached, and connecting and managing the unused indirect pointers with the pointer, the above-described drawbacks can be eliminated, and the shape of the data can be determined efficiently.
An object of the present invention is to provide a list processing method configured so that an effective storage area can be increased.

(Means for Solving the Problems) According to a list processing method of the present invention, there is provided an indirect pointer reference means for instructing, via an indirect pointer, from a certain data to another data without directly setting a pointer, Data identification means for identifying data by using a tagged pointer in which a tag indicating the type of the data is added to the address of the indirect pointer pointing to the data as reference information to other data; And a free chain management means for connecting and managing the pointers with a pointer.

(Example) Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a list processing method according to the present invention.

In FIG. 1, 1 is an input / output control unit, 2 is a list processing control unit, 3 is a storage area management unit, 4 is a storage area, 5 is an indirect pointer area, 6 is a list area, 7 is an indirect reference means, and 8 is an indirect reference means. Data identification means, 9 is free chain management means, 10, 11
Is data, 12 to 14 are variables, and 15 and 16 are indirect pointers.

Upon receiving a user request from the input / output control unit 1, the list processing control unit 2 performs a syntax analysis, and requests the storage area management unit 3 to create / update data as necessary. The result is returned to the list processing control unit 2 and transmitted from the input / output control unit 1 to the user. The storage area management unit 3 manages the storage area 4. By providing an indirect pointer area 5 and a list area 6 in the storage area 4, an indirect reference means 7 is realized. Further, the storage area 4 is further composed of some variables. The variable FT14 points to unused data in the indirect pointer area, and the unused data describes addresses of other unused data.

In this way, a NULL pointer is recorded in the last unused data, and the unused data in the indirect pointer area forms a chain structure linked by the pointer. As described above, the unused indirect pointer is stored in the free chain management unit 9.
Is managed by

The variable LT13 holds the start address of the list area 6 as an initial value. Each time data is allocated to the list area 6, the value of the variable LT13 increases, and always indicates the position of the data to be allocated next. The variable ROOT12 is a root pointer for extracting data currently in use at the time of garbage collection.

Now, the variable ROOT12 points to the indirect pointer 15, and the indirect pointer 15 points to the data 10. The first element of the data 10 is a pointer to the data 11, but does not directly point to the data 11 but holds the address of the indirect pointer 16 together with the data type t of the data 11.
Point. As described above, the data identification unit 8 is realized by integrating the tag and the address.

Here, the indirect pointer area 5 is allocated from the lower address of the storage area 4. In general, data is considered to be multiple words in size, much larger than a single word indirect pointer. Therefore, the boundary between the indirect pointer area 5 and the list area 6 can be provided at a lower address in the address space.

For example, in a computer in which one word is composed of 32 bits, the boundary address between the indirect pointer area 5 and the list area 6 is defined as
It is assumed to be less than or equal to 1,000,000 in hexadecimal. Then, the rule that the upper one byte is always 0 is satisfied for the address to the indirect pointer. Therefore, the upper one byte is tagged and used. By doing so, the shape of the data can be identified without referring to the destination pointed by the pointer, and the size of the list area is not limited.

Next, a procedure for assigning new data will be described. For data allocation, a data allocation area is secured between the indirect pointer and the list area 6.

FIG. 2 is a flowchart showing the data allocation process. Here, ← indicates substitution, and () indicates the contents of the storage area pointed to by the pointer. First, an indirect pointer is allocated. If FT14 is a NULL pointer, perform garbage collection and still have FT14 NULL
If so, the list processing system ends because the indirect pointer area is insufficient. At this time, if FT14 is not NULL, the value of FT14 is assigned to the register P, the address of the next indirect pointer pointed to by P is assigned to FT14, and the data is simply allocated from the point indicated by LT13. It is checked whether the area 6 can be secured. If the list area 6 cannot be secured even when the garbage collection is performed, the list processing system ends because the list area is insufficient. If secured, the value of LT13 is assigned to the indirect pointer pointed to by register P, and the data size assigned to LT13 is added. The tag indicating the form of the data allocated to the first byte of the register P is substituted, and P is returned as a result.

 Next, garbage collection will be described.

FIG. 3 is a flowchart showing the garbage collection process. First, mark all indirect pointers that can be traced from ROOT12. The method of marking is not particularly limited, but the lower two bits of the address value can always be set to 0 by making all data a multiple of 4 bytes, and this can be done by setting these bits to 1.

Next, a free chain of indirect pointers is created. FT
Substitute the start address of the NULL pointer into 14 and register P
To the start address of the indirect pointer area. if,
If the mark of the indirect pointer pointed to by P is off, the value of FT14 is substituted into the indirect pointer pointed to by P, and the value of P is substituted into FT14. If the mark of the indirect pointer pointed to by P is on, the contents of the first four bytes of the data ahead of the indirect pointer pointed to by P are saved to the indirect pointer pointed to by P. The value of P (address of indirect pointer) in the first 4 bytes of data
Is assigned. This is shown in FIG. Here, it is assumed that the tag value 0 is undefined.

Next, the register P is pointed to the next indirect pointer, the above operation is repeated until the end of the indirect pointer area 5, and finally the list area is collected. The contents of the registers P and Q are initialized with the head address of the list area 6, and the following processing is repeated until the contents of the register P become equal to LT13.

If the tag of the first 4 bytes of the data pointed to by the register P is 0, the first 4 bytes point to the indirect pointer, so the value saved in the indirect pointer is returned to the data, and the value of the register Q is returned. Assign to an indirect pointer.
Then, the data is transferred to the destination indicated by the register Q.
This is shown in FIG. The data size is added to the contents of the registers P and Q, respectively. If the tag pointed to by the register P is not 0, the data is garbage data, so only the contents of the register P are added to the data size.

When the content of the register P becomes equal to LT13, the content of the register Q is assigned to LT13, and the garbage collection ends.

(Effects of the Invention) As described above, according to the present invention, in addition to directing pointers from certain data to other data via indirect pointers, reference information to other data in each data includes: The address of the indirect pointer that points to the data uses a tagged pointer that has a tag indicating the type of the data, and the unused indirect pointers are linked and managed by the pointer, thereby limiting the size of the list area. The effect is that the tagged pointer is realized without giving it, and the form of the data can be identified without referring to the data. In the garbage collection, it is possible to deal with the movement of data only by correcting the indirect pointer without rewriting the contents of each data, so that the processing can be performed efficiently and the list area does not need to be divided into two equal parts. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a list processing method according to the present invention. FIG. 2 is a flowchart showing the data allocation processing of the present invention. FIG. 3 is a flowchart showing the garbage collection process of the present invention. 4 and 5 are explanatory diagrams showing an indirect pointer and a change in data in the garbage collection process of the present invention, respectively. FIG. 6 is an explanatory diagram showing a tagged pointer according to the prior art. FIG. 7 is an explanatory diagram showing an object tag according to the prior art. DESCRIPTION OF SYMBOLS 1 ... I / O control part, 2 ... List processing control part 3 ... Storage area management part, 4 ... Storage area 5 ... Indirect pointer area 6 ... List area, 7 ... Indirect reference means 8 ... Data Identification means 9 Free chain management means 10, 11, 202, 302 Data 12-14 Variable 15, 16 Indirect pointer 201 Tagged pointer 203, 301 Pointer 204 Tag

Claims (1)

(57) [Claims] 1. An indirect pointer reference means for instructing from a certain data to another data via an indirect pointer without directly setting a pointer, the reference information to other data in each of the data includes the data. Data identification means for identifying data by using a tagged pointer in which a tag indicating the type of the data is added to the address of the indirect pointer to be pointed; and a free chain for linking and managing unused indirect pointers with a pointer A list processing method comprising a management means.