JPS59117649A - Reference counter system - Google Patents

Abstract

PURPOSE:To prevent the overflow of a counter, by extending or reducing the reference counter as required in garbage collection. CONSTITUTION:In garbage collection where unnecessary cells are recovered in a cell link structure where there is a probability that one cell is referred by plural cells, when a cell structure is constituted newly or a new cell is added to an already constituted cell structure, the value of bit 4 indicating a free cell is changed from (1) to (0) when the new cell is used, and the value of a counter 5 becomes (1). The value of the counter is updated in accordance with the increase or the reduction of pointers indicating busy cells. When the number of pointers indicating cells exceeds 6, the value of the counter becomes 7, and a cell only for counter is linked to the cell, thus preventing the overflow of the counter.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a reference counter method used for garbage collection.

(2) Comparison with the prior art In a cell-connected structure in which one cell may be referenced by multiple cells, some cells become unnecessary during the process of processing this structure, and are recycled and used. Collecting unnecessary cells when desired is called carpet collection.

Consider, for example, the case of diagram ff11 in which cells are connected by pointers and the pointers are stretched in only one direction. In Figure 1, each cell has a pointer pointing in only one direction, and each cell has two branches. Note that the shaded portion in the figure indicates the terminal node. In this case, one cell points to another cell (it may or may not point to it) and is also pointed to by the other cell (
In a connected structure of one cell, one or several of these cells are pointed to by the processing system. These cells and the cells that are directly or indirectly connected to them are considered to be in use.

In this connected structure, if the pointer of a cell is disconnected and that cell and some of the cells directly or indirectly connected to it become free and are not pointed to by other cells or the processing system, these cells are considered used. These are subject to garbage collection.

If you are looking at a certain cell in the memory cells and trying to determine whether it is a used cell (garbage), this cell is pointed to by a pointer from another cell (! or processing system). I wish I could find out if there is one.7Th
However, if the pointer is extended in only one direction, it is difficult to know how many cells are pointing to the cell of interest. Therefore, a counter is attached to each cell, and each time a new pointer 1 is placed between cells in the cell connection structure, the counter of the cell pointed to by that pointer is increased, and conversely, the pointer is deleted. One possible method is to decrement a counter each time the cell is accessed, thereby determining whether or not a given cell is being pointed to by another cell. This counter is called a reference counter, and a garbage collection method using this counter has already been proposed.

Is there any other processing for cell-connected structures in the Garpedge collection method? There is a method of stopping for a while, marking cells in use in memory during that time, and collecting all unmarked cells as garbage after the process is complete, but this method has the problem that the original processing must be temporarily interrupted. There is. On the other hand, the method using a reference counter has the advantage that garbage collection can be performed in parallel with processing by the processing system. However, even with this method in which all reference counters are used, the overflow of the reference counter has not yet been solved. Usually, the number of bits for the counter taken in each cell is fixed, and it is impossible to deal with this when it is necessary to directly represent more than the number of bits that can be expressed by this number of bits.

(3) Purpose of the Invention In view of the conventional drawbacks, the present invention aims to solve the problem of overflow of the reference counter provided in each cell in garbage collection, and to provide a reference counter method. be.

(4) Structure of the Invention According to the present invention, the object is to provide a cell connection structure in which one cell may be referenced by multiple cells, and in the process of processing the structure, some cells may become unnecessary. If you want to regenerate and use the unnecessary cells, attach a reference pointer to each cell during garbage collection to collect the unnecessary cells, and add a new pointer between a certain cell in the cell connection structure P1. In this method, the counter of the cell pointed to by the pointer is incremented each time the pointer is deleted, and the counter is fully decremented each time the pointer is deleted.Thereby, it is possible to know whether any cell is pointed to by another cell or not. This is achieved by providing a reference counter method characterized in that the reference counter is expanded or contracted as necessary.

(5) Embodiments of the Invention Below, a 1f) embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows the configuration of the system of the present invention, and the input/output relationships are omitted in the figure. The cell connection structure consists of two memory gates.
The normal central processing unit 1 existing in the area occupied by mk accesses two memories and processes the cell connection structure.

On the other hand, Garb
In parallel with this, the processor 3 collects cellular style beggar beds in the cell area of the memory and adds them to the column of free cells, which are unused cells. It is controlled so that the central processing bag @l and the three GC processors do not access the same access unit of memory at the same time. The unit of access is page 1! f: 54F. Koreke Figure 3 Buddha)
Shown below. Figure 3 (In N, 4 indicates a free cell, pit 25 indicates a counter, and 6 indicates one entire cell. The general structure of this cell is shown in Figure 3 (Bl. That is, 1
One cell consists of two pointers 7a and 7b, a 3-bit counter 5, and a bit 4 indicating a free cell.

When configuring a new cell structure or adding all new cells to an existing cell structure, the processing system selects one unused cell from the free cell list and uses it. In each cell, bit 4 indicating a free cell is 1" at the free cell stage, and the color correction is %l". When a cell is newly used and pointed to by another pointer, bit 4 indicating 7th cell changes to 10" and the counter 5's value becomes %l". Thereafter, the first shift of the counter is updated in accordance with the increase/decrease in the pointer pointing to the cell in use.

The counter of each cell shows up to 6" lit. When the number of pointers pointing to the cell exceeds 6", the counter of that cell becomes 7", and immediately after that cell is a cell dedicated to the counter. This is shown in Figure 4 (4), ■). Figure 4) is the number of pointers pointing to cell 8.
The following cases are shown, and in Figure 4 (I3), the number of pointers is 1.
6"? is exceeded. In FIG. 4 (13), the structure of the counter-only cell 8 is the pointer J (7a) of the general cell.
The part is used as a counter. Therefore, it is possible to use free cells scattered from the free cell list (which is the same as the general cell) as a counter-only cell. By preferentially using cells within the same page in response to the overcrow of the general cell counter that occurred in , it is possible to prevent serious page faults. However, this method is not used in the embodiment of Suiden 1.

! 4 kl (In f31, cell A is pointed to by seven or more pointers, and is accompanied by a counter-only cell 8. In this state, the counter of cell A is marked @, which means cell Ai This indicates that the number of pointers pointing to cell A is displayed on the counter-only cell 8.The extended counter section on the counter-only cell following cell A displays the number of pointers pointing to cell A.Counter-only cell The above counter (the counter in the same bit position as the general cell counter) is "east", because this counter-only cell is never pointed to by anything other than cell A. 1. Logically speaking, cell AK and subsequent cell V are cell B.

In W441jA(B), when the number of pointers pointing to cell A decreases and becomes less than 6", the counter-only cell is separated and the counter that displays the number of pointers pointing to this cell itself becomes 0" and becomes a cigar bed collection. Therefore, we will have to wait for the eruption to be completed.Cell connection status id'gA4
It changes as shown in Figure (2). Each cell in use is considered to have become garbage at the point when the counter value becomes 0" and is collected by garbage collection. The processor 3, which performs garbage collection, examines the memory 21 in address order, When garbage is found, the counter @ of this cell is set to %0 “Free cell? -1" and connect it to the top of the list of free cells. Cells that are related to garbage cells found during garbage collection in the 7ζth address order are cells with a high probability of being garbage cells. In the concatenated structure, it is possible to temporarily suspend the investigation session in address order and read 11J cells to the Jl'l pointed by the pointer.If the above free cell management is performed on a page-by-page basis, processing efficiency will be further improved. There's a possibility.

The extension counter's fffi is generally sufficient, and if it is normal, it will overflow.Z) It is thought that it is unlikely that it will overflow, but if it does, the processing system will interrupt the entire process and notify the user. .

In order to deal with the case where the extended counter of the counter-dedicated cell overflows and reaches 7 in the first embodiment, it is conceivable to use one bit of the extended counter as a bit indicating the itk of the counter-dedicated cell. This will be referred to as a second embodiment. In this method, a plurality of counter cells can be concatenated, and the extended counter section of the counter-dedicated cell that is concatenated afterward displays the more significant bits.

Details #1 including memory 2 and processor 3 in Figure 2
A block diagram is shown in Figure 5. In Figure 5, Ml, M
2 is a memory. The memory M2 is a pointer section, and the memory M2 is a bit indicating a free cell and a counter section.

C1, cl is the address register of memory 841. The memory Mi is divided into two areas (area-〇", area type]"), and the multiple address registers C1 and Gl can address different areas simultaneously. If attempts are made to address the same area at the same time, register C1 has priority.

The value addressed in register C1 is read out to register C2, the value addressed in register Gl is read out to register G2, and register C5 is the central processing bag! C3 and G3, which are write registers for writing from irl to memory M1, are address registers of memory M2. Memory M2 is divided into two areas (corresponding to Ml), and register C
3 and G3h can address different areas 1 at the same time. If attempts are made to address the same area at the same time, C3 has priority. The address basket in register C3 is read out to register C4, and the value addressed in register G3 is read out to shifter G4. Register C6ti is a write register for writing from the central processing device to memory Mθ, and register G5. G5 is a register that points to the head of the free cell list of areas %0#9%l#, respectively.

Register G7. C9. Gio'd is the next stack after the backup of registers GJ-G4 by accessing 10II and z1, respectively.The connections are not shown.

The central processing unit 7 and the GC processor 3, the operations of which will be described below, operate with synchronized clocks and can independently access the memories IJ Ml and M2. Memo IJ Ml, M2 are each 2
It is divided into two areas, and the central processing unit and processor can simultaneously access two different areas in each of the memo IJM) and M2. , when attempting to access the A1-area, the central processing unit has priority, and the memories M1 and M2 can be accessed independently. That is, for example, from the central processing unit to the memory M
While accessing one address in memory M2, the GC processor (or central processing unit) can access another address in memory M2.

Explanation of Access to Memory from the Central Processing Unit 6 When accessing the memory from the central processing unit, the main contents are stored in the memory λ41. Memory M
Since Fir information indicating whether the cell is a free cell or not and a counter indicating how many pointers point to the cell are stored in memory M2, access from the central processing unit to memory M2 is performed between cells. This is only performed when resetting the pointer and performing related processing.

Therefore, the central processing unit usually has registers C1゜C2,C
5i is used to access memory MJ. When performing pointer resetting and related processing, C3, C
4, access memory M2 using C6. Access to normal cells is not essential to the invention.
Also, since various cases can be considered, I will not discuss them here.
The problem is the memo IJM when the pointer is changed,
This is an access to M2. The process associated with pointer resetting can be considered in the following two cases.

(il If there is an increase or decrease in the number of counter-only cells (lfl
(For cases other than il, the above fil, (ul is unable to decide which processing bay to use as a central processing unit from the beginning, so it checks the fiir of the related counter to decide the processing.It takes one free cell and When adding to the connected structure, the central processing unit performs the processing on the memory Ml and accordingly the memory M2.
Change the contents of the corresponding address above. Regardless of the process of extracting free cells, when the pointer is rewired, the counter position of the cell whose counter pupil is changed accordingly is first referenced. That is, the corresponding address 'y)l[ on the memory M2 is transferred to the register C71 and read out from the central processing unit.

FIG. 6 shows an example in which the pointer pointing Hi from cell A is changed from cell A to cell c2. To explain this example, first the counter of cell B is learned. If the counter of cell B is 6" or less, this value is decremented. If the counter of cell B is 7", the value of the extended counter section of the counter-only cell following cell B is checked. (In this case, the memory Ml is accessed.) If the extended counter part l!75 is 8# or more, the value is 1.
is decremented and stored again. Expanded counter section @ Myoi 7
In the case of ", the counter-only cell is separated from cell B, and cell B points to the cell that the counter-only cell was pointing to.
Then, the pointer from cell A to cell B is transferred from cell A to cell C, and the counter of cell C is updated. Check n1tt of the counter of cell C. If this is less than 5", this [t-%
If lN is increased and re-stored by 1%6, then the counter of cell C is [
tt7" After closing, a counter-only cell is inserted and connected next to cell C, and its expanded counter is set to 1. If the counter value of cell C is %7, the already connected counter-only cell is expanded. The value of the counter section is incremented by "1".

With the above, you can access the pointer part of each cell using Memo 17 M
], and access to the "bit indicating free cell" and the counter is performed to memory M2.

ff [Access from the GC processor to memory will be explained.

The GC processor normally checks the counter section of the memory M2, and when it finds an address where the counter number is 10'', it accesses the memories M1 and M2 in order to connect the cell corresponding to that address to the free cell.

Access to memory is for each area (area %Q#.

%l''), the central processing unit has priority over the process 1 For example, when the central processing unit is accessing only area qI of memory Ml, the Gc processor accesses area -1' of memory M1 and area qI of memory M2 separately. /l, %3", but not the area o# of memory M1 at the same time. Therefore, if the processor tries to access the same area of the same memory (Ml and M2) as the central processing unit, it will not be accessed in that cycle. After two or several cycles of that month, the central processing unit accesses the unaccessed area.

Garbage collection of memory by the processor is performed in areas 11# and 11#, which are managed separately.If access to one area is blocked (at the same time as an access from the central processing unit), that access will be canceled. is suspended (suspended until the next restart) and processing for other areas is started (or what was suspended is resumed).In other words, the GC processor tries to access memory areas that are not accessed by the central processing unit as much as possible. For example, if the GC processor is microprogram controlled, access to the access area %l for area 0" is controlled by a control system consisting of separate control storage devices, and is controlled by the central processing unit. Control is performed so that the access that does not overlap with the access is performed.

The operation of the GC processor will be described in more detail.

Assume that the GC processor first accesses area l. The start address of area l is set in register G8, and this f
[tl is set in the register G3 while incrementing each cell, and the counter li[ of each cell is checked. When a cell whose counter strength is 0 is found, the counter value of the cell connected to that cell is decremented (as in the case of access from the central processing unit), and the counter value % Q # is %I', set the bit indicating the free cell to 1, and connect this cell to the free cell in area -1. Since the beginning of the free cell is pointed to by the register G6 (in area 1'), after the new cell is connected to the beginning of the new cell, the register G6 is controlled to point to the beginning of the new free cell.

In FIG. 5, Ql is a circuit that inputs and updates the value of register G4 (in some cases, it is incorrect), and G2. G3 is a circuit that adds the contents of registers C4 and G4, and G4
．． This is a circuit that updates the value of Qbfq register shift and G8. G6 is register G2. This is a circuit that inputs the outputs of G5 and G6, updates them (sometimes not), and outputs them. In FIG. 5, the control circuit is omitted.

When the process of connecting the garbage cell to the free cell is completed, the processor starts accessing the memory M2 again, and the counter value becomes qQI. Search for the cell that is.

(61 Effects of the Invention According to the present invention, the area occupied by the realness counter in the entire memory cell area can be kept small, and garbage collection can be performed in parallel with the processing of the cell connection structure by the central processing unit. 7. As a result, the entire process can be prevented from being interrupted for a long time due to garbage collection.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the serial storage structure of cells, Fig. 2 is a block diagram showing the system configuration according to the present invention, Fig. 3 is a diagram showing the structure of the memory access unit, and Fig. 4 is a diagram showing the structure of the unit of memory access. Figure 5 is a partial detailed diagram of the block diagram in Figure 2, and Figure 6 is a diagram showing the relationship between the counters of each cell and the connections between cells. An example is shown. In the figure, l is a central processing unit, 2 is a memory, 3 is a GC processor, and 4 is a bit indicating a 7-receive cell. 5 is a counter, 6 is a page, 7a and 7b are pointers,
8 indicates a counter-dedicated cell, respectively.

Claims (1)

[Claims] In a cell-linked structure where one cell may be referenced by multiple cells, if some cells become unnecessary in the process of processing the structure and you want to regenerate and use them, collect the unnecessary cells. In the garbage collection to be performed, a reference counter is attached to each cell, and a new pointer i is added between a certain cell in the connected structure of the cells.
Each time a pointer is added, the counter of the cell pointed to by the pointer is incremented, and each time the pointer is deleted, the counter is decremented, thereby determining whether any cell is being pointed to by another cell. . A reference counter method, characterized in that the reference counter is expanded or contracted as necessary.