Control method for preventing incorrect reset of common resource and multicomputer system executing the method

Abstract: A control method for preventing the incorrect resetting of a common resource in a multicomputer system comprising a plurality of clusters each having a processor and a common memory which each cluster can access, comprises steps of storing in a common memory an IPL (initial Program Load) generation ID (Identifier) which is unique to an IPL number of each cluster, setting an acquisition ID and the IPL generation ID in the common resource, when the right to use the common resource in the common memory is acquired, and comparing the IPL generation ID when the faulty cluster stops, with the IPL generation ID set in the common resource, and only when the two IPL generation IDs are equal, resetting the right to use the common resource, when the right to use the common resource which the stopped faulty cluster acquires is reset. Thus, when resetting a common resource when a cluster included in a system stops operating due to a fault, incorrect resetting can be prevented so that the cluster does not reset the right to use the common resource acquired after restart of the IPL.

Description: BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates to a control method for preventing the incorrect resetting of a common resource in a multicomputer system comprising a plurality of clusters each including a processor, and further comprising a common memory which each cluster can access. Moreover the present invention relates to a multicomputer system for carrying through such control method. (2) Description of the Related Art In a multicomputer system including a plurality of clusters interconnected through a common memory, when one of the clusters is faulty and breaks down, it is necessary to reset the right to use a common resource which was acquired by the faulty cluster, so as not to effect the operation of other clusters. Previously the resetting of the right to use a common resource has been carried out by a cluster which detects that another cluster is faulty, and by referring to an identifier (ID) of a resource acquisition in the Common resource, which cluster is faulty. As mentioned above, in the prior art, there is a problem as follows. Namely, if the faulty cluster restarts an IPL (Initial Program Load) and acquires a right to use a common resource, before a cluster which detects the faulty cluster starts to reset the right to use the common resource, the cluster which resets the resource sometimes resets the right to use the common resource which was acquired after the restart of the IPL. The present invention is intended to solve the above problem. SUMMARY OF THE INVENTION An object of the present invention is to provide a control method for preventing the incorrect resetting of a common resource, and a multicomputer system executing the method, wherein when resetting a common resource when a cluster included in a system stops operating due to a fault, the incorrect resetting can be prevented so that the faulty cluster does not reset the right to use the common resource acquired after restart of the IPL. According to one aspect of the present invention, there is provided a control method for preventing the incorrect resetting of a common resource in a multicomputer system comprising the steps according to the characterizing part of the claim 1. According to another aspect of the present invention, there is provided a multicomputer system which executes a control method for preventing incorrect resetting of the right to use a common resource and comprising a plurality of clusters each including a processor and a common memory which each cluster can access. According to this aspect of the present invention, the above-mentioned object is solved by the features of the characterizing part of claim 2. An improved embodiment of the inventive multicomputer system results from the subclaim 3. Other features and advantages of the invention will be apparent from the following description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A, 1B, 1C, and 1D are block diagrams showing a problem in the related art of the present invention; Fig. 2 is a block diagram for explaining a summary of an embodiment of the invention; Figs. 3A, 3B, 3C, and 3D are block diagrams for explaining process of the embodiment of Fig. 2; Figs. 4A, 4B, and 4C are block diagrams for explaining an operational example of the embodiment of Fig. 2; Fig. 5 is a flowchart of a common resource resetting process in the embodiment of Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before explaining the embodiment, a problem in the related arts will be explained in detail with reference to Figs. 1A to 1D. The following explanation is based on an example where clusters 13a and 13b are connected to each other through a common memory 10 and the cluster 13a uses a common resource 12. To acquire a right to use a common resource, as shown in Fig. 1A, the cluster 13a sets an ID A indicating itself, as an acquisition ID, in the common resource 12 for which the right of use is requested. Then, as shown in Fig. 1B, the cluster 13a goes down due to a fault, and the system stops operating, and then after being repair, the IPL is carried out again. The cluster 13a then resets the right to use the common resource 12 which was acquired before the fault occurred as a part of the IPL process. In this reset process, the acquisition ID in the common resource 12 is set to a non-holding state. After the right to use the common resource 12 is reset as shown in Fig. 1B, the cluster 13a reacquires the right to use the common resource 12 as shown in Fig. 1C. On the other hand, when the cluster 13b detects that the cluster 13a has stopped, the right to use the common resource 12 is reset, as shown in Fig. 1D, to prevent the cluster 13a from holding the acquired right for the common resource 12. At that time, the cluster 13b resets the right to use the common resource 12 after confirming that the acquisition ID of the common resource 12 is the cluster ID of the cluster 13a, i.e., A. However, since the cluster 13b cannot distinguish whether the acquisition ID is in a failed state, or in the state following the reset of the right to use the common resource 12 by the cluster 13a which then acquires the right again, so the cluster 13b sometimes forces an incorrect resetting of the right to use the common resource 12 reacquired by the cluster 13a even if it is not necessary, particularly when the reset process is delayed. In addition, the reason the cluster 13a reset the right to use the common resource 12 by itself at the time of reestablishment of IPL is because it was able to reuse of the common resource 12 in the case where the system is constituted by only one cluster. Further, in the case where the IPL cannot be immediately restarted, cluster 13b resets the right to use the common resource 12 which was acquired by the faulty cluster 13a, so that the common resource 12 can be used by other clusters. An embodiment of the present invention is explained summarizedly with reference to Fig. 2. In Fig. 2, reference numeral 10 denotes a common memory, 11 is an IPL generation ID storage for storing IPL generation IDs corresponding to each cluster and each IPL, 12 is a common resource, 13a and 13b are clusters each provided with a processor that can operate independently, 14 is an IPL generation ID updating portion for updating the IPL generation ID in the IPL generation ID storage 11 at the time of IPL, 15 is a common resource acquisition portion for acquiring the right to use the common resource 12, 16 is a resource acquisition information setting portion for setting the IPL generation ID and the acquisition ID in the common resource 12, 17 is a common resource release portion for releasing the acquired right to use the common resource 12, 18 is a cluster self-resetting portion for resetting a common resource, and 19 is a common resource reset portion for resetting other clusters when a cluster is faulty. The clusters 13a and 13b are connected to the common memory 10 and constitute a multicomputer system. The IPL generation ID storage 11 is provided in the common memory 10, and when the IPL is executed in the cluster 13a or 13b, the updating of the IPL generation ID is carried out by using the IPL generation ID updating portion 14. The IPL generation ID has a unique value corresponding to each IPL. The unique value is a number that is incremented by one when an IPL process is executed. The common resource 12 functions as, for example, a lock word of a control table utilized commonly by clusters 13a and 13b. In this embodiment, besides the acquisition ID corresponding to the cluster holding the right to use a resource in the common resource 12, a field is provided for setting the IPL generation ID of a cluster which has acquired the right to use the common resource. When the right to use the common resource 12 is acquired by the common resource acquisition portion 15, the resource acquisition information setting portion 16 sets the IPL generation ID and the acquisition ID in the common resource 12. The common resource release portion 17 clears the IPL generation ID and the acquisition ID in the common resource 12, when the use of the common resource 12 ends. The cluster self-resetting portion 18 for resetting a common resource resets the right to use the common resource 12 which is acquired by that cluster and puts the IPL generation ID and the acquisition ID in a non-holding state when the cluster is faulty and executes IPL again. The common resource reset portion 19 for resetting other clusters resets the right to use the common resource 12 which is held by the faulty cluster, when a faulty cluster in another cluster is detected. Particularly in this embodiment, the IPL generation ID at the time when the faulty cluster stops is compared with the IPL generation ID set in the common resource 12. If only the two IPL generation IDs are equal, the right to use the common resource 12 is reset. In Fig. 2, to simplify the explanation, the processing structures of the clusters 13a and 13b are shown separately. However, the constitutions of the two clusters are actually symmetrical, and the clusters monitor each other mutually using the same processing structure. The same applies in the case of three or more clusters. In this embodiment, when the right to use the common resource 12 is acquired by a cluster, the IPL generation ID corresponding to that cluster is set in the common resource. If the cluster stops operating while it is holding the right to use the common resource 12, for all of the rights being held for the common resources 12, the acquisition ID and the IPL generation ID set in the common resource 12 are compared with a cluster ID and IPL generation ID corresponding to the faulty cluster. If these IDs coincide, it is determined that the faulty cluster is holding the right to use the common resource and the reestablishment of the IPL has not been executed, and the right to use the common source 12 is reset. Accordingly, when a cluster in the system stops operating while it is holding the right to use the common resource 12, another cluster immediately resets the right to use the common resource 12. Thus, a wait state for other clusters to acquire the right to use the common resource 12 is avoided by eliminating the need for the faulty cluster to reset the right to use the common resource 12. Further, in a case where a faulty cluster reestablishes the IPL and the right to use the common resource 12 is reset and then acquired, since the IPL generation ID set in the common resource 12 is updated, an incorrect resetting of the right to use the common resource 12 by another cluster can be avoided. The embodiment of this invention will now be explained in detail. Figures 3A to 3D show processes according this embodiment, Figs. 4A to 4C show an example of the operation of this embodiment, and Fig. 5 shows a flowchart of the resetting process of the common resource by another cluster. First, the cluster IPL, common resource acquisition, release, and common resource reset processes are explained. As shown in Fig. 3A, in the IPL (Initial Program Load) process of the cluster 13a, the right to use the common resource which was acquired before the cluster itself stopped, is reset, and the IPL generation ID for that cluster in the IPL generation ID storage 11 is increased by one. In the case when the cluster 13a acquires the right to use the common resource 12, as shown in Fig. 3B, an ID A for that cluster is set to in the acquisition field in the common resource 12, and simultaneously an IPL generation ID n stored in the IPL generation ID storage 11 is set in the IPL generation ID field in the common resource 12. In releasing the right to use the common resource 12, as shown in Fig. 3C, the IPL generation ID field and the acquisition ID field in the common resource 12 are initialized and put in a non-holding state. When the cluster 13a stops the system while holding the right to use the common resource 12, as shown in Fig. 3D, another cluster 13b resets the right to use the common resource 12, and the fields of the IPL generation ID and the acquisition ID in the common resource 12 are initialized to the non-holding state. This invention particularly relates to the resetting of the right to use the common resource 12. Namely, when the cluster 13a reestablishes the IPL and resets the right to use the common resource by itself, and further reacquires the right of use, the reset of the right to use the common resource 12 by the cluster 13b is suppressed. The above operating example is explained with reference to Figs. 4A to 4C. When the cluster 13a obtains the right to use the common resource 12, as shown in Fig. 4A, the current IPL generation ID n and the acquisition ID A for that cluster are set in the common resource 12 by the resource acquisition information setting portion 16. It is assumed that in this state the cluster 13a is faulty. When the cluster 13b detects the system being stopped by the cluster 13a, as shown in Fig. 4B, the cluster 13b reads the IPL generation ID n corresponding to the cluster 13a at that time from the IPL generation ID storage 11. After that, all the common resource 12 are searched to find the common resource wherein the acquisition ID is A corresponding to the cluster 13a, and the IPL generation ID is n, and the right to use the common resource 12 is reset. If the acquisition ID A and the IPL generation ID n in the common resource 12 coincide to the above read IDs, as shown in Fig. 4C, the cluster 13b resets the right to use the common resource 12, and the fields of the IPL generation ID and the acquisition ID in the common resource are put in a non-holding state. If the acquisition IDs coincide and the IPL generation IDs do not coincide, the corresponding common resource 12 is determined to be the common resource that was reacquired by that cluster and the right to use the common resource 12 is not reset. Accordingly, the reset operation can be surely executed and an incorrect resetting of resources is prevented. Figure 5 shows a process flowchart of the common resource reset portion 19 for resetting another cluster shown in Fig. 2. The process flow is explained with reference to steps S1 to S6 shown in Fig. 5. S1: When a fault in another cluster is detected by a fault detection portion (not shown in the figure), the IPL generation ID at the time the cluster becomes faulty and the cluster ID for the faulty cluster are acquired. S2: The information in each common resource 12 is compared with the information acquired in the step S1. S3: If the cluster ID of the faulty cluster coincides with the acquisition ID in the common resource 12, the process proceeds to the next step S4. If the cluster ID does not coincide with the acquisition ID, the process proceeds to the step S6, since the right to use the common resource 12 has not been acquired by the faulty cluster. S4: When the IPL generation ID at the time the cluster becomes faulty is equal to the IPL generation ID in the common resource 12, the process proceeds to the next step S5, and if not equal, the process proceeds to the step S6. S5: In order to reset the right to use the common resource 12, a resource holding information in the common resource 12 is put in a non-holding state. Namely, the IPL generation ID and the acquisition ID in the common resource 12 are initialized to zero. S6: It is determined whether the above process has ended for all the common resources 12, and if ended, the process of resetting the resource ends. If an unprocessed common resource exists, the process returns to the step S2 and the subsequent steps are repeated.

Claims: A control method for preventing the incorrect resetting of the right to use a common resource in a multicomputer system comprising a plurality of clusters (13a, 13b) each including a processor, and said system further comprising a common memory (10) which each cluster can access, characterised in that the method comprises steps of storing in an initial program load, "IPL", generation identifier, "ID", storage (11) in said common memory (10) an IPL generation ID for each cluster which is unique to an IPL of that cluster; setting an identifier of an acquiring cluster and the corresponding IPL generation ID in a common resource (12) in said common memory (10), when the right to use said common resource is acquired; and when a first cluster (13b) detects that a second cluster (13a) is faulty, said first cluster (13b) reading the IPL generation ID for said second cluster (13a) from said IPL generation ID storage (11), and when determining whether to reset the right to use a common resource acquired by said second, faulty, cluster (13a), said first cluster (13b) comparing said IPL generation ID read from the IPL generation ID storage (11) with the IPL generation ID stored in said common resource (12), and only resetting said right to use said common resource if they are equal. A multicomputer system for executing a method for preventing incorrect resetting of the right to use a common resource, said system comprising a plurality of clusters (13a, 13b) each including a processor, and said system further comprising a common memory (10) which each cluster can access, characterised by an initial program load, "IPL", generation identifier, "ID", storage (11) in said common memory for storing an IPL generation ID for each cluster which is unique to an IPL of that cluster; a resource acquisition information setting portion (16) provided in each cluster for setting an identifier of an acquiring cluster and the corresponding IPL generation ID in a common resource (12) in said common memory (10), when the right to use said common resource is acquired; and a common resource reset portion (19) provided in each of the plurality of clusters comprising means for, when a first cluster (13b) detects that a second cluster (13a) is faulty, reading the IPL generation ID for said second cluster (13a) from said IPL generation ID storage (11), and means for determining whether to reset the right to use a common resource acquired by said second, faulty, cluster (13a), by comparing said IPL generation ID read from the IPL generation ID storage (11) with the IPL generation ID stored in said common resource (12), and means for resetting said right to use said common resource only if they are equal. A multicomputer system as set forth in claim 2, wherein each cluster further comprises an initial program load generation identifier updating portion (14) for updating the initial program load generation identifier in the initial program load generation identifier storage (11) at initial program load time; a common resource acquisition portion (15) for acquiring the right to use the common resource (12), and a resource acquisition information setting portion (16) for setting the common resource acquisition identifier and the initial program load generation identifier in the common resource (12); a common resource release portion (17) for releasing the acquired right to use the common resource (12); and a cluster self-resetting portion (18) for resetting the right to use the common resource (12) which is acquired at the initial program load time.

Inventors: FUSHIMI MASATO, HIRAISHI TOSHINORI, FUSHIMI, MASATO, HIRAISHI, TOSHINORI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1991
Main classification: G06F9
IPC codes: G06F9, G06F15