Patent Abstract:
In a GC processing in which a memory area is managed by being divided, collection efficiency of an area is further optimized. In order to realize the technology, a calculator including an arithmetic unit and a memory includes a storage unit which stores reference source information of data which is stored in a plurality of storage areas which are allocated to the memory in each of the storage areas; and a control unit which determines a storage area in which updated reference source information is different from reference source information which is recorded in the storage unit to be an area as a release target.

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a calculator, a recording medium, and a memory managing method, and relates to a calculator which performs managing of a memory of a calculator, a recording medium, and a memory managing method. 
       BACKGROUND ART 
       [0002]    In a calculator system, as implicit collection means of an object in a memory which is used in a program, there is a garbage collection (hereinafter, referred to as GC) technology. A Java (registered trademark) virtual machine (hereinafter, referred to as JVM) is one of representative processing systems in which GC is adopted. 
         [0003]    In GC, an unnecessary object (hereinafter, referred to as dead object) is found by checking reference relations of objects in a memory, and an automatic collection is executed. Specifically, GC processing is performed by tracing reference relations of an object in a memory from a source (hereinafter, referred to as reference route) in which a program can trace a reference, and by determining an object of which tracing could not reach the end as a dead object, and collecting the dead objects. In GC in the related art, a method of checking the entire memory area which is used at one time is adopted, and in this method, a processing time which is proportional to a memory amount is necessary. 
         [0004]    In recent years, increase in capacity of a memory which is mounted on a calculator has progressed, and accordingly, there has also been a tendency for processing time of GC to increase. GC is roughly classified into a Stop the World method, and a Concurrent method. In the Stop the World method, processing of a program is stopped while the GC processing is performed. For this reason, an increase in GC time leads to stopping of the program for a long time which is not intended, and there is a concern that availability of a calculator system may remarkably deteriorate. On the other hand, in the Concurrent method, since the GC processing is performed in parallel to processing of the program, a stop time reduces; however, there is a problem in that an execution performance of the program deteriorates (NPL 1). 
         [0005]    A GC method in which the entire memory area is divided into a plurality of small areas instead of being processed at one time, and is processed in respective small areas in order to solve the above described problem which is associated with a large capacity of a memory has been proposed (NPL 2) (PTL 1). When adopting the method, since an amount of a memory area to be processed at one time is reduced, it is possible to prevent stopping of a program for a long time even when the Stop the World method is used. 
         [0006]    In addition, in the GC technology in which a memory area is processed by being divided into a plurality of small areas, it is known that efficient GC processing is performed by including an auxiliary structure which is referred to as a barrier set for indicating a portion of which a value is changed in the memory area (NPL 1). 
         [0007]    In addition, as a memory managing method in the related art, there also is a method of dividing a memory area into a plurality of small areas in order to explicitly manage the memory area from a program (PTL 2). In addition, there is a method in which an automatic collection process with respect to an unnecessary area which is present in respective small areas is performed in parallel with respect to the method (PTL 3). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1: U.S. Pat. No. 7,340,494 
         PTL 2: JP-A-2009-37547 
         PTL 3: JP-A-2011-53862 
       
     
       Non-Patent Literature 
       [0000]    
       
         NPL 1: “Garbage Collection: Algorithms for Automatic Dynamic Memory Management” (Richard Jones, Rafael Lins, 1996, John Wiley &amp; Sons Inc, ISBN: 978-0471941484) 
         NPL 2: I Richard L. Hudson, “Incremental collection of mature objects, In Proceedings of the International Workshop on Memory Management, pp. 388-403”, 1992 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0013]    When a memory area is divided into a plurality of small areas, which small area is to be selected as a processing target of GC is important in order to enhance a performance of a calculator system. 
         [0014]    In general, a distribution of unnecessary areas in the memory area is not uniform. For this reason, there is a possibility that only small areas with a small unnecessary area are selected depending on a selection method. In this case, since unnecessary areas which can be collected in one GC processing are small, it is necessary to perform the GC processing a plurality of times, and this leads to a deterioration in performance of the calculator system. In contrast, when it is possible to select only small areas with a plurality of unnecessary areas, unnecessary areas which can be collected in one GC processing increases. For this reason, the number of execution times of the GC processing is reduced, and it is possible to enhance the performance of the calculator system. 
         [0015]    As a method of selecting a small area, a method of selecting all of small areas in regular order is disclosed in NPL 2. In such a case, since all of small areas are selected at equal frequency, there is a concern that only small areas with small unnecessary area may be consecutively selected. However, there still is a problem when considering a load in the selection process, in order to equally select (check) all of small areas by also including a small area of which collection efficiency is not good, and the performance of the calculator system deteriorates to that extent. 
         [0016]    In addition, a technology in which it is possible to select small areas with a plurality of unnecessary areas by checking an amount of the unnecessary area in each small area using GC of the Concurrent method, as another selection method of a small area is disclosed in PTL 1. However, also in this case, since GC of the Concurrent method is used in parallel, there is a problem of deterioration in performance similarly to GC of a common Concurrent method. In GC processing in which a memory area is managed by being divided, further optimization of collection efficiency of an area is desired. 
       Solution to Problem 
       [0017]    In order to solve the above-described problem, for example, the invention described in claims is applied. That is, a calculator including an arithmetic unit and a memory which includes a storage unit which stores reference source information of data which is stored in a plurality of storage areas which are allocated to the memory in each of the storage areas; and a control unit which determines a storage area in which updated reference source information is different from reference source information which is recorded in the storage unit to be an area as a release target is applied. 
       Advantageous Effects of Invention 
       [0018]    According to one aspect of the present invention, it is possible to select an area of a release target more efficiently, using a change in a reference source in an area when selecting an area as a GC processing target. 
         [0019]    Other problems and effects of the present invention will become clear in the following descriptions. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a block diagram which illustrates a configuration example of the calculator in a first embodiment to which the present invention is applied. 
           [0021]      FIG. 2  is a schematic diagram which illustrates a configuration example of a heap area according to the embodiment. 
           [0022]      FIG. 3A  is a diagram which schematically illustrates an example of information for managing reference source information according to the embodiment. 
           [0023]      FIG. 3B  is a diagram which schematically illustrates a relationship between the information for managing reference source information and an object in a heap area according to the embodiment. 
           [0024]      FIG. 4  is a flowchart which illustrates a flow of a recording process of reference source information using a Java program execution unit according to the embodiment. 
           [0025]      FIG. 5  is a flowchart which illustrates a flow of a selection process of a GC target using reference source information using a GC processing unit according to the embodiment. 
           [0026]      FIG. 6  is a block diagram which illustrates a configuration example of a calculator according to a second embodiment. 
           [0027]      FIG. 7  is a schematic diagram which illustrates barrier set information according to the second embodiment. 
           [0028]      FIG. 8A  is a schematic diagram which illustrates an example of information for managing reference source information according to the second embodiment. 
           [0029]      FIG. 8B  is a diagram which schematically illustrates a relationship between the information for managing reference source information according to the second embodiment and an object on a heap area. 
           [0030]      FIG. 9  is a flowchart which illustrates a flow of a recording process of reference source information using a Java program execution unit according to the second embodiment. 
           [0031]      FIG. 10  is a flowchart which illustrates a flow of a selection process of a GC target using reference source information using a GC processing unit according to the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0032]      FIG. 1  illustrates a configuration of a calculator  1  according to a first embodiment to which the present invention is applied. According to the embodiment, an example in which a Java VM  10  functions in the calculator  1  is used. 
         [0033]    In the calculator  1 , a general-purpose server device in which a CPU  2 , a memory  3 , and a storage unit  4  are provided is used. The CPU  2  executes the Java VM  10  in the memory  3  in cooperation with a Java program  70  and an OS  80 . In addition, in the Java VM  10 , a GC processing unit  30 , and a Java program execution unit  60  are executed, and reference source managing information  40 A, and a reference route  50  are held. 
         [0034]    A heap area  20  is allocated to the memory  3  using the OS  8 . 
         [0035]      FIG. 2  schematically illustrates a configuration of the heap area  20 . In the heap area  20 , an arbitrary numbers of small heap areas  21   a  to  21   c  are provided. The number or size of small heap areas  21  included in the heap area  20  may be changed in a process of executing the Java VM  10  using the CPU  2 . In addition, the small heap areas  21  are managed by small area identifiers  22   a  to  22   c , respectively, and respectively different values are registered in small area identifiers  22 . 
         [0036]    In addition, the heap area  20  may include an area other than the small heap area  21 . In addition, the small heap area  21   a , or the like, in the heap area  20  may be an area which can be explicitly managed from a program as disclosed in above described PTL 3. More specifically, the heap area  20  may be Java heap, and all or a part of the small heap areas  21  may be an external heap area. 
         [0037]    The Java program execution unit  60  secures an object which is necessary in the middle of executing the Java program  70  in the small heap area  21   a , or the like. In addition, the Java program execution unit  60  stores reference information with respect to an object in the small heap area  21  in the reference route  50 , and operates the object. 
         [0038]    In the reference source managing information  40 A, each of small heap areas  21   a  to  21   c , and an object name of a reference source thereof are managed by being correlated with each other. In the calculator  1 , when a reference source object name at a time of GC processing, and an object name of a reference source at a time of generating the object which is recorded in the reference source managing information  40 A are different from each other, the small heap area  21  is determined to be a release target. That is, there is a high possibility that an area in which a change occurs in reference relations of data is an unnecessary area, and in particular, it is possible to assume that an unnecessary object is stored in the small heap area  21  in which a reference source object name at a time of generating data is deleted, due to a change in reference relations of data. 
         [0039]      FIGS. 3A and 3B  schematically illustrate a configuration of the reference source managing information  40 A, and an example of data. The reference source managing information  40 A is, for example, information in a form of a table, and includes an identifier field  41 , and a reference source object field  42 . The same number of rows as those of the small heap area  21  are included in the reference source managing information  40 A, and each row corresponds to one small heap area  21 . In the identifier field  41 , a value of the small area identifier  22  of a corresponding small heap area  21  is maintained. In the reference source object field  42 , identification information of an object (object ID, or the like) which refers to the inside of a corresponding small heap area  22  is maintained. 
         [0040]    For example, as illustrated in  FIG. 3B , a small heap area  21   b  of which a value of a small area identifier  22   b  is “2” stores an object B and an object C, and when the objects B and C are referred to from an object A, the objects are included in a row of which the small area identifier field  41  is “2”, and the reference source object field is “A” in the reference source managing information  40 A. In addition, when objects D and E are stored in the small heap area  21   c  of which a value of the small area identifier  22   c  is “3”, and the objects D and E are referred to from the object A or the object B, respectively, the objects D and E are included in a row of which the small area identifier field  41  is “3”, and the reference source object field  42  is A and B, in the reference source managing information  40 A. 
         [0041]    In the GC processing unit  30 , an object which is not used in the heap area  20  is specified by tracing reference relations of an object which is stored in the reference route  50 , and a corresponding memory area is released. In addition, the GC processing unit  30  is invoked when the Java program execution unit  60  fails in securing of an object in the small heap area  21   a , or the like, (for example, memory leaking), and starts the GC processing. In addition, a trigger for invoking the GC processing unit  30  using the Java program execution unit  60  is not limited to this. 
         [0042]    Hitherto, the configuration of the calculator  1  according to the embodiment has been described. Subsequently, a “recording process of reference source information”, and a “selection process of GC target using reference source information” which are one of characteristics of the calculator  1  will be described. 
         [0043]    The Java program execution unit  60  changes the reference source managing information  40 A when a reference between objects which are stored in the small heap area  21   a , or the like, is changed. In addition, the GC processing unit  30  selects the small heap area  21   a , or the like, which is a processing target based on the reference source managing information  40 A when receiving a notification from the Java program execution unit  60 . An unused object which is collected in the GC processing using the GC processing unit  30  is limited to an object in the selected small heap area  21   a , or the like, and an object in a small heap area other than that is not collected even when the object is not used. 
         [0044]      FIG. 4  illustrates a flow of the “recording process of reference source information” in which the reference source managing information  40 A is changed by the Java program execution unit  60 . 
         [0045]    First, the Java program execution unit  60  starts the process at a predetermined timing such as a point in time at which a reference in an object which is stored in each small heap area  21 , or the like, is changed in the middle of executing the Java program  70 . 
         [0046]    In S 101 , the Java program execution unit  60  substitutes an object of which a reference stored inside is changed for a variable S. 
         [0047]    In S 102 , the Java program execution unit  60  substitutes the small area identifier  22  corresponding to the small heap area  21  including a heap position which is indicated by a new reference after change for a variable D. 
         [0048]    In S 103 , the Java program execution unit  60  adds “S” to the reference source object field  42  with respect to a row of which the small area identifier field  41  is “D” in the reference source managing information  40 A. The Java program execution unit  60  ends the flow of the process thereafter. 
         [0049]    In addition, when “S” is included in the reference source object field  42  of the row in advance, there is no operation to be performed. Also in a case in which “S” is included in the small heap area  21  of which small area identifier  22  corresponds to “D”, there is no operation to be performed. 
         [0050]    Subsequently,  FIG. 5  illustrates a flow of a “selection process of GC target using reference source information”. The process is a process for selecting the small heap area  21   a , or the like, which is a processing target based on the reference source managing information  40 A using the GC processing unit  30 . The GC processing unit  30  starts the flow of the process at a predetermined timing such as a point in time of receiving a notification from the Java program execution unit  60 . 
         [0051]    In S 200 , the GC processing unit  30  initializes a variable R to a null set. 
         [0052]    In S 201 , the GC processing unit  30  checks whether or not there is an unprocessed small heap area in all of the small heap areas in the reference source managing information  40 A. When there is an unprocessed small heap area (Yes in S 201 ), the process proceeds to S 202 , and when there is no unprocessed small heap area (No in S 201 ), the process proceeds to S 209 . 
         [0053]    In S 202 , the GC processing unit  30  sets the subsequent row in the reference source managing information  40 A to a variable C. 
         [0054]    In S 203 , the GC processing unit  30  sets a value of the small area identifier field  41  in the variable C to a variable T. 
         [0055]    In S 204 , the GC processing unit  30  sets a value of the reference source object field  42  in the variable C to a variable I. 
         [0056]    In S 205 , the GC processing unit  30  checks whether or not a reference included in all of objects in the variable I indicates the inside of T with respect to the objects. When there is an object which does not include such a reference (No in S 205 ), the GC processing unit  30  adds “T” to the variable R in S 206 , and the process returns to S 201 . When there is not the above-described object (Yes in S 205 ), the process returns to S 201 . 
         [0057]    In S 207 , the GC processing unit  30  selects a small heap area which is included in R as a GC target area. 
         [0058]    In addition, a condition of determining whether or not to add “T” to the variable R by the GC processing unit  30  in S 205  is not limited to the above-described condition. For example, “T” may be added to the variable R when the number of objects which do not include such a reference exceeds a threshold value which is designated by an API for a Java program, an option when starting the Java VM  10 , an external file, or the like, by checking whether or not a reference included in all of objects in the variable I indicates the inside of “T” with respect to the objects. Alternatively, the GC processing unit  30  may perform the addition only when the number of elements of the variable R does not reach the maximum number of elements, by maintaining the maximum number of elements which is designated by the API for a Java program, an option when starting the Java VM  10 , an external file, or the like. 
         [0059]    As described above, according to the calculator  1  in the first embodiment, it is possible to select the small heap area  21  which is a release target more efficiently using a change in reference source object name. That is, since it is not necessary to check reference relations by setting all of small heap areas  21   a  to  21   c  as candidates of the release target to specify an unnecessary area, it is possible to expect high speed processing to that extent, and there is an effect of reducing a processing load. 
         [0060]    In particular, since the calculator  1  selects a small heap area which is assumed to be an unnecessary area (area storing only an unnecessary object or a plurality of unnecessary objects) due to changing of a reference source to another small heap area  21 , or deleting as a release target area, there also is an effect of improving efficiency of area collecting in the release processing. 
       Second Embodiment 
       [0061]    In the “selection process of GC target using reference source information” according to the first embodiment, checking of a reference in all of objects stored in the reference source object field  42  in the reference source managing information  40 A is performed. 
         [0062]    When there are a plurality of reference source objects with respect to each small heap area  21 , it is also assumed that the number of objects which are stored in the reference source object field  42  increases. In a calculator system  200  according to a second embodiment, one of characteristics is that a processing time is shortened due to a more efficient selection process, and an execution performance of a program is improved. More specifically, the selection process is efficiently performed using a barrier set. 
         [0063]      FIG. 6  illustrates a configuration example of the calculator system  200 . A main difference from the first embodiment is that barrier set information  90  is maintained in a Java VM  142 , and reference source managing information  40 B in which an existing reference source barrier set, or a newly added reference source barrier set is managed is maintained instead of the reference source managing information  40 A. Since other configurations are the same as those of the first embodiment, detailed descriptions will be omitted. 
         [0064]    The barrier set information  90  is information which manages whether or not there is a change in each barrier set area when the heap area  20  is divided into areas with a fixed length (hereinafter, referred to as “barrier set area”). An area length of the barrier set area may be set to an appropriate fixed value, or a value which is designated by the API for a Java program, an option when starting the Java VM  10 , an external file, or the like. 
         [0065]      FIG. 7  schematically illustrates a configuration of the barrier set information  90  and an example of data. The barrier set information  20  includes a barrier set identifier field  91 , and a barrier set value field  92 . The barrier set information  90  includes the same number of rows as those of the barrier set area in the heap area  20 , and each row corresponds to one barrier set area. The barrier set identifier field  91  maintains a value which uniquely identifies a corresponding barrier set area (hereinafter, referred to as “barrier set identifier”). The barrier set value field  92  maintains a value indicating whether or not there is a change in a corresponding barrier set area. 
         [0066]    When a length of the small heap area  21  is an integer multiple (including one time) of a length of a barrier set area, it is possible to select an area more efficient in the selection process, since information stored in the barrier set information  90  becomes more accurate. For this reason, it is desirable to set the length of the barrier set area to 1/integer of the length of the small heap area  21   a , or the like. 
         [0067]      FIG. 8A  schematically illustrates a configuration of the reference source managing information  40 B according to the second embodiment and a data example. The reference source managing information  40 B includes a field  45  for registering a reference source barrier set which is added in advance (hereinafter, referred to as “added field  45 ”), and a field  47  for registering a reference source barrier set which is newly added (hereinafter, referred to as “new addition field  47 ”). 
         [0068]    Both the fields are formed of barrier set identifiers of 0 or more. 
         [0069]    A barrier set identifier which is included in the added field  45  is an identifier including an object which refers to the inside of the small heap area  21   a , or the like, corresponding to the row in a corresponding barrier set area, at a point in time at which a selection process of the GC target area is finally performed. 
         [0070]    The barrier set identifier which is included in the new addition field  47  is an identifier in which a reference to the corresponding small heap area  21   a , or the like, corresponding to the row is written in a corresponding barrier set area, after a point in time at which a selection process of the GC target area is finally performed. 
         [0071]    For example, as illustrated in  FIG. 8B , objects B and C are stored in the small heap area  21   b  of which a value of the small area identifier  22   b  is “2” at a point in time at which a selection process of a GC target is finally performed. Since the objects B and C are referred to from an object A in the barrier set area of which the barrier set identifier is “2”, the reference source managing information  40 B includes a row in which the small area identifier field  41  is “2”, and the added field  45  is “2”. 
         [0072]    In addition, objects D and E are stored in the small heap area  21   c  in which a value of the small area identifier  22   c  is “3” at a point in time at which a selection process of a GC target is finally performed. Since the respective objects D and E are referred to from an object A in the barrier set area in which the barrier set identifier is “2”, and an object B in the barrier set area in which the barrier set identifier is “4”, the reference source managing information  43 B includes a row in which the small area identifier field  41  is “3”, and the added field  45  is “2” and “4”. 
         [0073]    In addition, when a reference with respect to the object D from the object B is changed to a reference from the object B to the object A after a point in time at which a selection process of a GC target is finally performed, the reference source managing information  40 B includes a row in which the small area identifier field  41  is “1”, and the new addition field  47  is “4”. 
         [0074]    In addition, the added field  45  and the new addition field  47  of the reference source managing information  40 B may be set to one field in a lump; however, a method of managing the fields separately is efficient, and is preferable. That is, the reason for this is that, it is possible to more efficiently use the value in the barrier set information  90  when being managed in a dividing manner, since it is clear that a value of the barrier set value field  92  in the barrier set information  90  is normally “changed” in the barrier set area which is changed after a point in time at which the selection process of the GC target is finally performed. 
         [0075]      FIG. 9  illustrates a flow of the “recording process of reference source information” when the Java program execution unit  50  of the calculator  200  changes the reference source managing information  40 B. 
         [0076]    First, the Java program execution unit  50  starts the process at a predetermined timing such as a point in time at which a reference in an object stored in each small heap area  21  is changed in the middle of executing the Java program  70 . 
         [0077]    In S 300 , the Java program execution unit  60  substitutes a barrier set identifier in a barrier set area including an object of which a reference which is stored inside is changed for a variable S. 
         [0078]    In S 301 , the Java program execution unit  60  substitutes the small area identifier  22  corresponding to the small heap area  21  including a heap position which is indicated by a new reference after change for a variable D. 
         [0079]    In S 302 , the Java program execution unit  60  adds “S” to the new addition field  47  with respect to a row in which the small area identifier field  41  is “D” in the reference source managing information  40 B. 
         [0080]    In addition, when “S” is included in the new addition field  47  of the row in advance, there is no operation to be performed. In addition, also in a case in which “S” is included in the small heap area  21  in which the small area identifier  41  corresponds to “D”, there is no operation to be performed. 
         [0081]    In S 303 , the Java program execution unit  60  sets a value of the barrier set value field  92  to “changed” in a row of which the barrier set identifier field  91  is “D” in the barrier set information  90 . Thereafter, the Java program execution unit  60  ends the flow of the process. 
         [0082]    In the second embodiment,  FIG. 10  illustrates a flow of the “selection process of GC target using reference source information” when the GC processing unit  30  selects the small heap area  21   a , or the like, as a processing target based on the reference source managing information  40 B. In the process, processes of S 404 , S 405 , S 406 , and S 409  are different from the “selection process (FIG.  5 )” in the first embodiment, and steps other than those are the same. 
         [0083]    In S 400 , the GC processing unit  30  initializes the variable R to a null set. 
         [0084]    In S 401 , the GC processing unit  30  checks whether or not there is an unprocessed area in all of small heap areas in the reference source managing information  40 B. When there is an unprocessed area (Yes in S 401 ), the process proceeds to S 402 , and when there is no unprocessed area (No in S 401 ), the process proceeds to S 408 . 
         [0085]    In S 402 , the GC processing unit  30  sets the subsequent row in the reference source managing information  40 B to a variable C. 
         [0086]    In S 403 , the GC processing unit  30  sets a value of the small area identifier field  41  in the variable C to a variable T. 
         [0087]    In S 404 , the GC processing unit  30  sets a value of the added field  45  in the variable C to a variable I. 
         [0088]    In S 405 , the GC processing unit  30  adds an element of the new addition field  47  in C to the added field  45  in C, and sets a value of the new addition field  47  to an empty value. In addition, an addition to an element included in the added field  45  may not be performed. 
         [0089]    In S 406 , the GC processing unit  30  checks a row to which the barrier set information  90  corresponds with respect to all of barrier set identifiers in the variable I, and checks whether or not there is a barrier set identifier in which a value of the barrier set value field  92  of the corresponding row is “changed”. When there is an object of which the value of the barrier set value field  92  is “changed” (Yes in S 406 ), the GC processing unit  30  proceeds to S 407 , and returns to S 401  by adding “T” to the variable R. When there is no such object (No in S 406 ), the process returns to S 201 . In addition, similarly to the step S 205  in  FIG. 5 , a condition of determining whether or not “T” is to be added to the variable R by the GC processing unit  30  is not limited to the above-described condition. 
         [0090]    In S 407 , the GC processing unit  30  selects a small heap area which is included in “R” as a GC target area. 
         [0091]    Thereafter, in S 408 , the GC processing unit  30  sets a value of the barrier set value field  91  to “not changed” with respect to all of rows in the barrier set information  90 , and ends the process. 
         [0092]    In this manner, according to the calculator  200  according to the second embodiment, it is possible to efficiently select a release target area, when there are a plurality of reference source objects with respect to each small heap area  14211 . 
         [0093]    Hitherto, embodiments of the present invention have been described; however, the invention is not limited to the above-described various examples, and it is possible to apply various configurations, or the like, without departing from the scope of the invention. For example, in the above-described example, each function unit is exemplified as a function unit which functions due to cooperation between the CPU and the program; however, it is also possible to configure a part thereof as hardware. It is also possible to switch a sequential order of various processes. 
         [0094]    In addition, various programs in the embodiments can be stored in a portable non-transitory electronic, electrical, and/or magnetic recording medium, or can be downloaded and installed through a network such as the Internet. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1 ,  200 : calculator 
           70 : Java program 
           10 : Java VM 
           20 : heap area 
           30 : GC processing unit 
           40 A,  40 B: reference source managing information 
           50 : reference route 
           60 : Java program execution unit 
           90 : barrier set information

Technology Classification (CPC): 6