Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims priority from Japanese Patent Application No. 2008-086668 filed on Mar. 28, 2008, the entire disclosure of which is incorporated herein 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a technology of managing the number of socket descriptors (referred to as “sockets” in this specification) allocated to each of one or more network applications operating in a computer system. 
     2. Related Art 
     A socket interface is used for programming a general network application, and the application uses a socket descriptor (or socket) generated by the socket interface to identify a communication destination for communication. 
     In a computer system which has a relatively large amount of built-in memory, such as a personal computer, the network application can use sockets without considering the upper-limit number of sockets. In contrast, a computer system built in an apparatus such as a printer has a small amount of built-in memory, and only a small number of sockets corresponding to the amount of the memory can be used. Therefore, it is usual that the number of sockets which can be used are allocated in advance to each network application, and a program is created with the allocated sockets. 
     In the latter case (the computer system built in an apparatus such as a printer), since a certain number of sockets need to be allocated even to rarely used applications, the number of sockets to be allocated to an application for a main function (for example, a print function in the printer) which is most frequently used in the apparatus is reduced, thus reducing the number of client connections which can be established at the same time. A simple solution to such a problem of reduction in the network performance of a product is to increase the amount of built-in memory, which naturally causes an increase in cost. 
     As for socket allocation, JP-A-2000-148426 discloses a technology in which sockets to be used by an application that monitors a printer are reserved in advance in order to avoid a situation where communication cannot be performed because of socket shortage, and the reserved sockets are used in response to a request of the application. With this technology, the application can be always operated normally. However, since sockets that are not being used are also always reserved, the socket resources are not efficiently used in the entire product. 
     SUMMARY 
     An advantage of some aspects of the invention is to more properly allocate a limited number of sockets to applications in a computer system, so as to contribute to the improvement of the system network performance. 
     According to a first aspect of the invention, there is provided a socket management device that manages the number of sockets allocated to each of one or more applications operating in a computer system, the socket management device including: an application management module that stores a total socket count indicating the total number of sockets which can be allocated to all of the one or more applications, and a target socket count for each of the one or more applications indicating a target value for the number of sockets allocated to each of the one or more applications; a scheduling module that recalculates, when a socket-count change request indicating a socket acquisition request or a socket release request is received from any of the one or more applications, the target socket count of the request-source application which has issued the socket-count change request, based on the received socket-count change request and based on the total socket count and the target socket count for each of the one or more applications, which are stored in the application management module, and that updates the target socket count of the request-source application stored in the application management module so as to have the recalculated target socket count; and a response module that generates a response to the socket-count change request based on the target socket count recalculated by the scheduling module, and that notifies the response to the request-source application. 
     The socket management device stores the total socket count and the target socket count for each of the one or more applications, and recalculates, when a socket acquisition request or a socket release request (either is also called a socket-count change request) is received from any of the one or more applications, the target socket count of the request-source application which has issued the socket-count change request, based on the received socket-count change request and based on the stored total socket count and target socket count for each of the one or more applications. The socket management device generates a response to the socket-count change request based on the recalculated target socket count, and returns the response to the request-source application. 
     The response may indicate the recalculated target socket count of the request-source application, or may indicate whether the socket-count change request, particularly, the socket acquisition request, has been allowed (for example, indicate that all of the requested number of sockets can be obtained, that part of the requested number of sockets can be obtained, or that any socket cannot be obtained). 
     Therefore, the request-source application can check the target socket count of the request-source application, or check whether the socket-count change request, particularly, the socket acquisition request, can be allowed, from the response received from the socket management device. When the request-source application determines whether to actually obtain a socket from an operating system according to the checking result, the number of sockets actually allocated to the application meets the target socket count of the application calculated by the socket management device. As a result, it is possible to allocate a proper number of sockets to each application. 
     The reason why the socket management device does not manage the actual socket count held by each application but manages the target socket count of the application will be described below. Specifically, since the actual socket count is managed by the OS, even though a socket is released in the application, time lag occurs until the socket is actually released in the OS. Many usual OSs hold a socket to be released, for several tens of seconds to several minutes before actually releasing it. In other words, it is difficult to know the actual socket count from the outside of the OS. For this reason, the socket management device according to the first aspect of the invention does not manage the actual socket count but manages the target socket count. Accordingly, the actual socket count is not always equal to the target socket count. Therefore, the socket management device may take into account the difference between the actual socket count held by each application and the target socket count of the application, to schedule the target socket count. 
     It is preferable that the socket management device according to the first aspect of the invention be configured as follows. Specifically, the application management module further stores a priority level of each of the one or more applications; and the scheduling module recalculates the target socket count of the request-source application based on the received socket-count change request, based on the total socket count and the target socket count for each of the one or more applications, which are stored in the application management module, and based on the priority level of the request-source application, which is stored in the application management module. For example, the scheduling module determines a socket-allocation-count ratio among the one or more applications based on the priority level of each of the one or more applications, stored in the application management module, and calculates the target socket count of the request-source application according to the determined socket-allocation-count ratio. 
     In this case, it is possible to control socket allocation with the priority level of each application being taken into account, such that a socket is more preferentially allocated to an application having a higher priority level. 
     Further, it is preferable that the socket management device according to the first aspect of the invention be configured as follows. Specifically, the scheduling module controls a socket-allocation-count ratio among the one or more applications according to a remaining socket count which corresponds to the difference between the total socket count and the sum of the target socket counts of the one or more applications. 
     Therefore, it is possible to change the socket-allocation-count ratio among the one or more applications depending on the remaining socket count indicating the remaining number of sockets which have not yet been allocated to any application. For example, the smaller the remaining socket count is, the larger the socket-allocation-count ratio of an application that has a higher priority level can be made. As a result, even when the remaining socket count is reduced, the number of sockets allocated to an application that has a higher priority level is not changed much, thereby maintaining the network performance of the entire system at a high level. 
     Furthermore, it is preferable that the socket management device according to the first aspect of the invention be configured as follows. Specifically, the socket management device further includes a socket acquisition module that judges whether to allow the request-source application to obtain a socket, based on the target socket count of the request-source application recalculated by the scheduling module, and that obtains, when it is judged that the request-source application is allowed to obtain a socket, a new socket for the request-source application from an operating system of the computer system. 
     With this configuration, the socket management device can obtain a socket for each application from the operating system as a deputy of the application, instead of leaving this socket acquisition task to the application. Therefore, the actual socket allocation count of each application can be made to reliably meet the target socket count thereof. 
     According to a second aspect of the invention, there is provided a socket management system including: one or more applications; and the socket management device having the configuration described above. 
     In the socket management system according to the second aspect of the invention, each application can obtain a socket for the application from the operating system. Specifically, each application includes a socket acquisition module that judges whether socket acquisition has been allowed, based on the response notified from the socket management device, and that obtains a new socket from an operating system of the computer system when it is judged that socket acquisition has been allowed. 
     In the socket management system according to the second aspect of the invention, the socket management device can obtain a socket for each application from the operating system as a deputy of the application. In this case, each application uses the socket for the application, obtained by the socket management device, to establish a network connection. 
     According to a third aspect of the invention, there is provided a socket management method of managing the number of sockets allocated to each of one or more applications operating in a computer system, the socket management method including: an application management step of storing a total socket count indicating the total number of sockets which can be allocated to all of the one or more applications, and a target socket count for each of the one or more applications indicating a target value for the number of sockets allocated to each of the one or more applications; a scheduling step of recalculating, when a socket-count change request indicating a socket acquisition request or a socket release request is received from any of the one or more applications, the target socket count of the request-source application which has issued the socket-count change request, based on the received socket-count change request and based on the total socket count and the target socket count for each of the one or more applications, which are stored in the application management step, and of updating the target socket count of the request-source application stored in the application management step so as to have the recalculated target socket count; and a response step of notifying a response corresponding to the target socket count recalculated in the scheduling step to the request-source application which has issued the socket-count change request. 
     According to a fourth aspect of the invention, there is provided a computer-readable computer program causing a computer to execute the method described above. 
     According to the aspects of the invention, sockets can be properly allocated to applications, thereby improving the connection performance for network communications. Since it is unnecessary to reserve in advance a socket that is not being actually used, waste of memory is reduced, thus allowing the corresponding memory resource to be allocated to another function. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of main parts in a computer system which includes a socket management system according to an embodiment of the invention. 
         FIG. 2  is a diagram showing an example of a pattern calculation table which is one component of a schedule algorithm. 
         FIG. 3  is a diagram showing an example of a socket-allocation-count ratio table which is another component of the schedule algorithm. 
         FIG. 4  is a diagram showing a sequence in which a socket management section is activated and then a certain application is activated. 
         FIG. 5  is a diagram showing a sequence in which the application issues a socket acquisition request. 
         FIG. 6  is a diagram showing a sequence in which the application issues a socket release request. 
         FIG. 7  is a diagram-showing a sequence in which the application is shut down and then a socket management section is shut down. 
         FIG. 8  is a block diagram showing a configuration of main parts in a computer system which includes a socket management system according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a block diagram showing a configuration of main parts in a computer system  10  which includes a socket management system according to an embodiment of the invention. 
     The computer system  10  shown in  FIG. 1  may have a relatively-large amount of memory like a personal computer or may have a relatively-small amount of memory like a computer system built in an apparatus such as a printer. In the latter case, advantages according to the principle of the invention are clearly provided. 
     As shown in  FIG. 1 , the computer system  10  includes an operating system (hereinafter referred to as “OS”)  100 , an application section  200 , and a socket management section  300 . The OS  100 , the application section  200 , and the socket management section  300  are typically realized when a computer machine executes corresponding computer programs. 
     The socket management section  300  corresponds to a socket management device according to an embodiment of the invention. The combination of the application section  200  and the socket management section  300  corresponds to a socket management system according to an embodiment of the invention. 
     The application section  200  is a group of one or more applications  202  each of which realizes a specific network service. Each of the applications  202  includes three modules, specifically, a service module  204 , a socket acquisition module  206 , and a socket control module  208 . 
     The service module  204  is programmed by using a socket interface function, and realizes a network-service function. 
     The socket acquisition module  206  has a function of obtaining the number of sockets required by the application  202  from the OS  100  and of returning a socket no longer required by the application  202  to the OS  100 , under the control of the socket control module  208 . 
     The socket control module  208  has a function of adjusting, while managing the number of sockets actually used (actually held) (that is, a holding socket count  210 ) for the network service of the application  202 , the holding socket count  210  of the application  202  to be equal to or lower than a target socket count notified by the socket management section  300 . 
     The socket management section  300  has a function of managing the upper-limit number of sockets (that is, a target socket count) which can be used by each application  202  in the application section  200 , operating under the control of the socket management section  300 , (but not managing the holding socket count  210  itself); of scheduling (recalculating), every time a socket acquisition request or a socket release request is received from an application  202 , the target socket count of the application  202  which has issued the request, according to the socket allocation state at that time point; and of notifying the target socket count to the application  202 . Note that a modification may be configured such that, instead of notifying the target socket count, the socket management section  300  notifies information indicating whether the application  202  can obtain a new socket, to the application  202  in the application section  200  based on the target socket count. 
     The reason why the socket management section  300  does not manage the actual socket count held by each application  202  but manages the target socket count of the application  202  will be described below. Specifically, since the actual socket count is managed by the OS, even though a socket is released in the application  202 , time lag occurs until the socket is actually released in the OS  100 . Many usual OSs hold a socket to be released, for several tens of seconds to several minutes before actually releasing it. In other words, it is difficult to know the actual socket count from the outside of the OS. For this reason, the socket management section  300  does not-manage the actual socket count held by each application  202  but manages the target socket count of the application  202 . Accordingly, the target socket count is not always equal to the actual socket count. Therefore, the socket management section  300  may take into account the difference between the actual socket count held by each application  202  and the target socket count of the application  202 , to schedule the target socket count. 
     The socket management section  300  includes three modules, specifically, an application interface module  302 , an application management module  304 , and a scheduling module  306 . 
     The application interface module  302  is used to perform communications with the respective applications  202  included in the application section  200 . The application interface module  302  has a function of mediating communication performed between each application  202  and the application management module  304  to register the application  202  in the application management module  304  when the application  202  is activated; a function of mediating communication performed between each application  202  and the application management module  304  to delete the registration of the application  202  when the application  202  is shut down; a function of mediating communication performed between each application  202  and the scheduling module  306  to schedule (recalculate) the target socket count when a socket acquisition request or a socket release request (hereinafter referred to as “socket-count change request”) is issued by the application  202 ; and a function of mediating communication performed between each application  202  and the application management module  304  to notify the scheduled (recalculated) target socket count to the application  202 . 
     The application management module  304  stores and manages application information  310  related to the identifier (ID), the priority level, and the target socket count of each application  202  that is currently operating (currently registered) in the application section  200 , and stores and manages the total socket count (the maximum number of sockets which can be provided by the OS  100 )  308  which can be used by the entire application section  200 . The identifier (ID) of each application  202  is code the application management module  304  assigns to the application  202  when the application management module  304  registers the application  202 . The priority level of each application  202  is specified in advance in the application  202 . When an application  202  is activated, its priority level is notified by the application  202 . 
     The application management module  304  has a function of registering an application  202  when the application  202  is activated (specifically, of generating and registering the application information  310 ); a function of deleting the registration of an application  202  when the application  202  is shut down (of deleting the application information  310 ); a function of calling the scheduling module  306  when a socket-count change request (a socket acquisition request or a socket release request) is issued by an application  202 , and of notifying the pieces of application information  310  of all registered applications  202  and the total socket count  308  to the scheduling module  306 ; a function of updating the application information  310  of an application  202  so as to have a target socket count scheduled (recalculated) by the scheduling module  306 ; and a function of notifying the scheduled (recalculated) target socket count of an application  202  to the application  202 . 
     The scheduling module  306  has a function of scheduling (recalculating), when a socket-count change request is issued by an application  202 , the target socket count, which indicates the upper-limit number of sockets the application  202  can use, by using a schedule algorithm  312  set in advance, and of writing the calculation result to the application management module  304 . 
     The optimum specific contents of the schedule algorithm  312  differ for each product category or for each product in which the computer system  10  is included. Thus, it is preferable that the schedule algorithm  312  be configured in the form of a program or data which can be separated from a program of the socket management section  300 . Of course, the schedule algorithm  312  may be included in the program of the socket management section  300 . 
     The schedule algorithm  312  is called from the application management module  304  when a socket-count change request is issued by an application  202 . Then, the schedule algorithm  312  reads the pieces of application information (the ID, the priority level, and the target socket count)  310  of all registered (currently operating) applications  202  from the application management module  304 , and schedules (recalculates) only the target socket count of the application  202  (for example, Application #1) which has issued the socket-count change request. 
     It is important that the schedule algorithm  312  does not schedule the target socket counts of all currently operating (registered) applications  202  but schedules only the target socket count of one application  202  which has issued the socket-count change request. This is because the client generally should have the initiative in determining when to end the network service provided to the client by each application  202 . Therefore, the computer system  10 , which provides the network service, should not forcibly close the socket used for the network service (if the socket is forcibly closed by the computer system  10 , an error occurs in the client). 
     A specific example of the schedule algorithm  312  will be described below. In the example, the schedule algorithm  312  includes a pattern calculation table  312 A shown in  FIG. 2  and a socket-allocation-count ratio table  312 B shown in  FIG. 3 . 
     The pattern calculation table  312 A shown in  FIG. 2  indicates the types of socket allocation patterns to be selected according to the ratio (%) of a remaining socket count with respect to the total socket count (the specific content of each pattern is defined in the socket-allocation-count ratio table  312 B of  FIG. 3 ). The remaining socket count is a value obtained by subtracting the sum of the target socket counts of the applications  202  from the total socket count, in other words, is the number of sockets which have not yet been obtained by any application. Note that the target socket count of each application  202  is set to “1” as an initial value when the application  202  is activated (registered), and the target socket count is updated thereafter every time it is scheduled. 
     Which socket allocation pattern is to be used is determined from the pattern calculation table  312 A of  FIG. 2 . 
     For example, when the ratio of the remaining socket count with respect to the total socket count is equal to or higher than 50% (in other words, when the remaining socket count is relatively high), “Pattern 1” is selected. When the ratio of the remaining socket count with respect to the total socket count is equal to or higher than 20% and is lower than 50% (in other words, when the remaining socket count is intermediate), “Pattern 2” is selected. When the ratio of the remaining socket count with respect to the total socket count is lower than 20% (in other words, when the remaining socket count is relatively low), “Pattern 3” is selected. 
     The socket-allocation-count ratio table  312 B shown in  FIG. 3  defines, for each of the socket allocation patterns selected in  FIG. 2 , the socket-allocation-count ratio (the ratio of a socket count allocatable to each application with respect to the remaining socket count) (%) according to the priority level of the application. For example, in “Pattern 1”, which is selected when the remaining socket count is relatively high, the socket-allocation-count ratio is 50% for an application  202  whose priority level is “Level 1” (high) and the socket-allocation-count ratio is 20% for an application  202  whose priority level is “Level 3T” (low). In this way, the difference in socket-allocation-count ratio between the higher priority level and the lower priority level is relatively small. 
     In “Pattern 2T”, which is selected when the remaining socket count is intermediate, the socket-allocation-count ratio is 60% for an application  202  whose priority level is “Level 1” (high) and the socket-allocation-count ratio is 10% for an application  202  whose priority level is “Level 3” (low). In this way, the difference in socket-allocation-count ratio between the higher priority level and the lower priority level is intermediate. 
     Further, in “Pattern 3”, which is selected when the remaining socket count is relatively low, the socket-allocation-count ratio is 80% for an application  202  whose priority level is “Level 1” (high) and the socket-allocation-count ratio is 5% for an application  202  whose priority level is “Level 3” (low). In this way, the difference in socket-allocation-count ratio between the higher priority level and the lower priority level is significantly large. 
     The priority level of each application  202  is determined such that a higher priority level is given to an application whose level of importance is higher. For example, in the case of a printer, it is possible to give a high priority level, for example, “Level it”, to the printing protocol related to the most important printing function, and to give a low priority level, for example, “Level 3T”, to applications, such as Web and Telnet, whose levels of importance are low. 
     According to the socket-allocation-count ratio table  312 B shown in  FIG. 3 , an application having a higher priority level is given a higher socket-allocation-count ratio than that given to an application having a lower priority level; and the smaller the remaining socket count is, the larger the difference in socket-allocation-count ratio between a higher priority level and a lower priority level becomes. As a result, even when the remaining socket count is changed, an application that has a higher priority level (in other words, has a higher importance level) can stably hold a certain number of sockets. 
     An operation of the computer system  10 , having the above-described configuration, will be described below with reference to sequence diagrams shown in  FIGS. 4 to 7 . 
       FIG. 4  shows a sequence in which, after the computer system  10  is activated, the socket management section  300  is first activated and then a certain application  202  is activated. 
     As shown in  FIG. 4 , first, a main task  400  of the computer system  10  generates and initializes the application interface module  302  of the socket management section  300  (Step S 1 ). Next, the application interface module  302  generates and initializes the application management module  304  (Step S 2 ). The application management module  304  specifies the total socket count  308  (Step S 3 ). The total socket count  308  may be a fixed value programmed in advance by the application management module  304 , or may be specified based on total socket count data which is externally read. Next, the application management module  304  returns a response indicating that the application management module  304  has been normally generated, to the application interface module  302  (Step S 4 ). 
     The application interface module  302  generates the scheduling module  306  (Step S 5 ). The scheduling module  306  returns a response indicating that the scheduling module  306  has been normally generated, to the application interface module  302  (Step S 6 ). The application interface module  302  returns a response indicating that the application interface module  302  has been normally generated, to the main task  400  (Step S 7 ). As described above, the socket management section  300  is generated. 
     When activation of a certain application  202  is requested thereafter, the main task  400  generates the service module  204  of the application  202  (Step S 8 ). The service module  204  generates the socket control module  208  (Step S 9 ). The socket control module  208  notifies the priority level of the application  202  to the application interface module  302  of the socket management section  300 , to make a request for registration of the application  202  (Step S 10 ). The application interface module  302  of the socket management section  300  notifies the priority level of the application  202  to the application management module  304 , to make a request for registration of the application  202  (Step S 1 ). 
     The application management module  304  generates and stores application information (the ID, the priority level, and the target socket count (initial value is “1”))  310  of the application  202 , thereby registering the application  202 . Then, the application management module  304  returns a response that includes the ID of the registered application  202  to the application interface module  302  (Step S 12 ). This response information is sequentially returned from the application interface module  302  to the socket control module  208  (Step S 13 ), from the socket control module  208  to the service module  204  (Step S 14 ), and from the service module  204  to the main task  400  (Step S 15 ). As described above, the application  202  is activated. 
       FIG. 5  is a sequence following the sequence shown in  FIG. 4 . In the sequence of  FIG. 5 , the application  202  issues a socket acquisition request. 
     First, the service module  204  of the application  202  sends a socket acquisition request (one of socket-count change requests) that includes a desired acquisition socket count (which is usually one but may be two or more), to the socket control module  208  (Step S 21 ). The socket control module  208  sends a schedule request that includes the desired acquisition socket count and the ID of the application  202 , to the application interface module  302  of the socket management section  300  (Step S 22 ). The application interface module  302  sends the schedule request to the scheduling module  306  (Step S 23 ). 
     The scheduling module  306  sends an application information acquisition request to the application management module  304  (Step S 24 ). The application management module  304  returns the total socket count and the pieces of application information  310  of all applications  202  that are currently registered, to the scheduling module  306  (Step S 25 ). 
     The scheduling module  306  uses the schedule algorithm  312  to perform scheduling (recalculation) of the target socket count of the request-source application  202 , which has issued the socket acquisition request, based on the returned total socket count and pieces of application information  310 , the acquisition socket count desired by the request-source application  202 , and the priority level of the request-source application  202  (Step S 26 ). 
     For example, the remaining socket count is calculated by subtracting, from the total socket count, the sum of the current target socket counts of all applications  202  currently operating, the current target socket counts being obtained from the pieces of application information  310 . With the use of  FIG. 2 , one socket allocation pattern is selected according to the ratio of the remaining socket count with respect to the total socket count. According to the selected socket allocation pattern shown in  FIG. 3 , a socket-allocation-count ratio for the priority level of the request-source application  202  is determined. By multiplying the socket-allocation-count ratio by the remaining socket count, a socket count newly allocatable to the request-source application  202  is calculated. Then, the calculated allocatable socket count is compared with the above-mentioned desired acquisition socket count. 
     As a result of the comparison, when the calculated allocatable socket count is equal to or larger than the desired acquisition socket count, it means that the request-source application  202  can newly obtain all of the desired acquisition socket count. In this case, the desired acquisition socket count is added to the current target socket count of the request-source application  202  to obtain a new target socket count (recalculated target socket count). 
     On the other hand, as a result of the comparison, when the calculated allocatable socket count is one or more but is lower than the desired acquisition socket count, it means that the number of sockets that can be obtained by the request-source application  202  equals to the calculated allocatable socket count. In this case, the calculated allocatable socket count is added to the current target socket count of the request-source application  202  to obtain a new target socket count (recalculated target socket count). 
     Further, when the calculated allocatable socket count is lower than 1, it means that the request-source application  202  cannot obtain a new socket. In this case, a value identical to the current target socket count of the request-source application  202  is obtained as a new target socket count (recalculated target socket count). 
     As described above, the scheduling module  306  schedules (recalculates) the target socket count of the request-source application  202 . The scheduling module  306  updates the target socket count in the application information  310  of the request-source application  202 , stored in the application management module  304 , so as to have the scheduled (recalculated) target socket count (Steps S 27  to S 28 ). 
     Then, the scheduling module  306  returns a response indicating that scheduling of the target socket count has been completed, to the application interface module  302  (Step S 29 ). The response is further returned from the application interface module  302  to the socket control module  208  (Step S 30 ). 
     The socket control module  208  sends a request to obtain the updated target socket count to the application interface module  302  (Step S 31 ). The application interface module  302  thus sends the request to obtain the updated target socket count to the application management module  304  (Step S 32 ). 
     The application management module  304  returns a notification of the updated target socket count of the request-source application  202 , stored in the application management module  304 , to the application interface module  302  (Step S 33 ). The notification of the updated target socket count is returned from the application interface module  302  to the socket control module  208  (Step S 34 ), and is further returned from the socket control module  208  to the service module  204  (Step S 35 ). 
     Note that a modification may be configured such that, instead of the notification of the updated target socket count, a notification of the number of sockets that can be newly obtained is returned from the application management module  304  to the service module  204 . 
     As described above, the request-source application  202 , which has issued the socket acquisition request, can understand the number of sockets that can be newly obtained (for example, equal to the above-mentioned desired acquisition socket count; equal to 1 or more but lower than the desired acquisition socket count; or equal to 0) based on the notification returned from the application management module  304 . For example, when the notification of the updated target socket count is returned, the number of sockets that can be newly obtained is calculated by subtracting the number of obtained sockets from the notified target socket count. Then, the socket acquisition module  206  (not shown in the sequence) of the request-source application section  200  actually obtains the same number of sockets as the number of sockets that can be obtained, from the OS  100 . 
     As described above, the socket management section  300  does not perform anything about the operation in which each application  202  actually obtains a socket from the OS  100 , but just plays a role of providing the target socket count (in other words, an advice as to whether a new socket can be obtained) to each application  202 . 
       FIG. 6  shows a sequence in which the application  202  issues an obtained-socket release request. 
     First, the service module  204  of the application  202  sends a socket release request (one of socket-count change requests) for a socket no longer required, to the socket control module  208  (Step S 41 ). The socket control module  208  sends a schedule request which includes a desired release socket count to the application interface module  302  of the socket management section  300  (Step S 42 ). Further, the application interface module  302  sends the schedule request to the scheduling module  306  (Step S 43 ). 
     The scheduling module  306  thus obtains, from the application management module  304 , the application information  310  of the request-source application  202 , which has sent the socket release request (Steps S 44  and S 45 ). The scheduling module  306  subtracts the desired release socket count from the target socket count in the application information  310  of the request-source application  202 , thereby obtaining a new target socket count of the request-source application  202  (Step S 46 ). 
     After the scheduling module  306  performs scheduling (recalculation) of the target socket count of the request-source application  202  in this manner, the scheduling module  306  specifies the scheduled (recalculated) target socket count in the application management module  304  (Steps S 47  and S 48 ). 
     A response indicating that scheduling has been completed is returned from the scheduling module  306  to the application interface module  302  (Step S 49 ), from the application interface module  302  to the socket control module  208  (Step S 50 ), and further from the socket control module  208  to the service module  204  (Step S 51 ). 
     Then, the socket acquisition module  206  (not shown in the sequence) of the request-source application  202  requests the OS  100  to release the socket no longer required. 
       FIG. 7  shows a sequence in which the application  202  is shut down and then the socket management section  300  is shut down. When shutdown of the application  202  is requested, the main task  400  sends a shutdown request to the service module  204  of the application  202  (Step S 61 ), and the service module  204  sends a shutdown request to the socket control module  208  (Step S 62 ). The socket control module  208  sends a request to delete the registration of the application  202  to the application interface module  302  of the socket management section  300  (Step S 63 ). Further, the application interface module  302  sends the request to delete the registration of the application  202  to the application management module  304  (Step S 64 ). 
     The application management module  304  deletes the application information  310  of the application  202 , thereby deleting the registration of the application  202 . The application management module  304  returns a response indicating that the registration of the application  202  has been deleted, to the application interface module  302  (Step S 66 ). The application interface module  302  returns the response to the socket control module  208  (Step S 67 ). 
     The socket control module  208  returns a response indicating that the socket control module  208  will be shut down to the service module  204  (Step S 68 ), and is shut down. The service module  204  returns a response indicating that the service module  204  will be shut down to the main task  400  (Step S 69 ), and is shut down. 
     Thereafter, when the computer system  10  is about to end the operation, the main task  400  sends a shutdown request to the application interface module  302  (Step S 70 ). The application interface module  302  sends a shutdown request to the scheduling module  306  (Step S 71 ). The scheduling module  306  returns a response indicating that the scheduling module  306  will be shut down to the application interface module  302  (Step S 72 ), and is shut down. 
     The application interface module  302  sends a shutdown request to the application management module  304  (Step S 73 ). The application management module  304  returns a response indicating that the application management module  304  will be shut down to the application interface module  302  (Step S 74 ), and is shut down. 
     Then, the application interface module  302  returns a response indicating that the application interface module  302  will be shut down to the main task  400  (Step S 75 ), and is shut down. Then, the main task  400  is shut down, thereby ending the operation of the computer system  10 . 
       FIG. 8  is a block diagram showing a configuration of main parts in a computer system  20  which includes a socket management system according to another embodiment of the invention. 
     In the computer system  10  shown in  FIG. 1 , each application  202  has the socket acquisition module  206 . In contrast, in the computer system  20  shown in  FIG. 8 , a socket management section  320  has socket acquisition modules  314  which obtain sockets for the corresponding applications  222 , from the OS  100 . In the computer system  20 , when a certain application  222  issues a socket-count change request (a socket acquisition request or a socket release request), the socket acquisition module  314  allocated to the request-source application  222  obtains a new socket from the OS  100  or releases an obtained socket, based on the target socket count of the request-source application  222 , scheduled by the scheduling module  306 . The request-source application  222  performs the network service using the socket obtained by the socket acquisition module  314 . 
     As described above, since the socket management section  320  not only calculates the target socket count of each application  222  but also actually obtains or releases a socket for the application  222  based on the target socket count, it is possible to reliably make the actual holding socket count of each application  222  equal to the target socket count thereof (except for a period of time lag from when the OS  100  is requested to release a socket to when the socket is actually released). 
     The preferred embodiments of the invention have been described above. The embodiments are merely examples used to explain the invention, and do not limit the scope of the invention. The invention can be applied to various aspects different from the above-described embodiments without departing from the gist thereof.

Technology Category: g