Abstract:
A job processing method is provided for use in an information processing system including three or more information processing devices connected to a common transmission line: 
     (a) first of all, in case the occurrence of a job is detected at one of the three or more processing devices, it is broadcast to the remaining plural processing device; 
     (b) next, that job execution for that job is started at a first processing device which is one of the plural processing devices receiving the job occurrence broadcast or the processing device having broadcast the job occurrence; 
     (c) then, the first processing device having started that job execution is monitored at the others of the plural processing devices which are not presently involved in that job execution but have been informed of that job occurrence; and 
     (d) the job is executed irrespective of the presence of an abnormal processing device in case a second processing device, which is one of the plural monitoring processing devices, detects an abnormality of the processing device executing that job.

Description:
This application is a continuation of Ser. No.  08 / 436 , 862 , filed on May  8 ,  1995 , now abandoned which is a continuation of Ser. No.  07 / 625 , 779  filed on Dec.  7 ,  1990 , now abandoned which is a Continuation of application Ser. No.  06 / 894 , 820 , filed Jul.  24 ,  1986  now abandoned which is a Reissue application of U.S. Pat. No.  4 , 462 , 075  issued Jul.  24 ,  1984 . 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a job processing method for an information processing system which includes a plurality of information processing devices connected to a common transmission line. More specifically, the present invention relates to a job processing method for executing a job in a reliable manner, even if an abnormality occurs in the processing device executing the job, by use of the remaining processing devices. 
     2. Description of the Prior Art 
     In the case where a job request has occurred in an information processing system including a plurality of information processing devices, that job has been executed according to the prior art in the following different ways: 
     (1) the job is executed by the processing device which has detected the job request occurrence; or 
     (2) that processing device which detects the job request demands that another processing device perform the execution of that job so that the job may be executed by the other processing device. 
     In the aforementioned case (1), there arises a disadvantage in that the job is not executed if the processing device having detected the job request becomes abnormal and is disabled. 
     In the aforementioned case (2), the first processing device having referred the job execution to a second processing device keeps monitoring the second processing device to which the job has been referred. Therefore, when the second processing device having the task of executing the job becomes disabled, the first processing device can detect that disorder so that the job can be assigned another processing device for execution. However, there arises a disadvantage in that the job cannot be executed when both the first and second processing devices becomes disabled at the same time. 
     SUMMARY OF THE INVENTION 
     The present invention has been conceived to eliminate the disadvantages concomitant with the prior art thus far described and has an object to provide a job processing device for an information processing system, in which, even if an abnormality occurs in either the processing device which has detected the occurrence of a job request or a processing device to which the job execution has been referred by the former device, that job can be executed by means of the remaining processing devices. 
     According to the present invention, there is provided a job processing method for use in an information processing system including three or more information processing devices connected with a common transmission line: 
     (a) First of all, in the case where the occurrence of a job request is detected at one of the three or more processing devices, this condition is broadcast on the transmission line to the remaining plural processing devices; 
     (b) Next, job execution is started at a first processing device which is any one of the plural processing devices informed of the job request occurrence or the processing device having broadcast the job request occurrence; 
     (c) Then, the first processing device having started that job execution is monitored by the others of the plural processing devices which are not presently involved in that job execution, but have been informed of that job request occurrence; and 
     (d) The job is executed irrespective of the presence of an abnormal processing device in case a second processing device, which is one of the plural monitoring processing devices, detects an abnormality of the processing device executing that job. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the overall construction of a loop transmission system to which the present invention is applied; 
     FIG. 2 is a block diagram showing one embodiment of an information processing device according to the present invention; 
     FIG. 3 is a schematic diagram showing the construction of one example of a storage unit in the transmission controller of FIG. 2; 
     FIG. 4 is a schematic diagram showing the construction of one example of a storage unit in the information processor of FIG. 2; 
     FIG. 5 is a schematic diagram showing the construction of one example of a job occurrence message according to the present invention; 
     FIG. 6 is a flow chart showing one example of the message receiving process of the transmission controller of FIG. 2; 
     FIGS.  7 (A) to (E) are flow charts showing one example of the processes of the processing units of the information processor of FIG. 2; and 
     FIGS. 8 to  12  are schematic diagrams showing respective examples of candidacy, job execution declaration, job executing, job completion and abnormal broadcast messages according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail by way of an example of an information processing system using a loop transmission. FIG. 1 shows the overall construction of that system. In FIG. 1, reference numeral  1  indicates a uni-directional loop transmission line acting as a common transmission line, in which three or more information processors having an identical construction are coupled. The construction of an ith information processor  1 i is shown in FIG. 2 by way of an example. Each information processor is composed of a transmission controller  20 , an information processor  30  and a plurality of I/O devices  40 . 
     Next, the operations will be described in the order of the following items: 
     (1) Detection of Job Occurrence Request and Transmission of Job Occurrence Message; 
     (2) Reception of Job Occurrence Message at other Processors; 
     (3) Execution of Job; 
     (4) Monitor of Job Execution; and 
     (5) Abnormal Detection and Processings therefor. 
     (1) Detection of Job Occurrence Request and Transmission of Job Occurrence Message 
     The following description is directed by way of an example to the case in which, when trouble occurs in a signal device for trains, its cause is automatically analyzed so that a maintenance man is informed of the problem of . Let it be assumed that the trouble in a certain signal device (although not shown) is detected by one of the plural I/O devices  40  of a processor  11 . Then, this I/O device sends code data SAB indicative of the trouble in the signal device, number data SNO identifying the signal device, and data SDA concerning the signal device to the information processor  30 . A processing unit  32  in that information processor  30  detects, when it receives the data SAB, SNO and SDA through an interface  33 , that a job to be processed has been requested. The processing unit  32  partly stores this data SAB, SNO and SDA in a job occurrence message storage area  342  of a storage unit  34  as is shown in FIG.  4  and partly sends this data to transmission controller  20 . 
     The construction of a storage unit  24  in the transmission controller  20  is shown in FIG. 3. A processing unit  22  in the transmission controller  20  reads out, when it receives the data SAB, SNO and SDA through an interface  23 , both the device address data “11”, which is stored in a device address storage area  241  of the storage unit  24 , and the message sequence number data “0” which is stored in a message sequence number storage area  242 , which is set at “0” at this point because it is assumed that no message M has been sent as yet from that information processor  11 . And, a sending buffer area  244  is set with a job occurrence message Jm, having a format as shown in FIG.  5 . Reference letters F appearing in areas  51  and  57  of the message Jm designate flags indicative of the leading and trailing portions of the message. An area  52  is set with code data CD 1  indicating that the message is a job occurrence message (other types of code data indicate other types of messages). An area  53  is one which is to be set with a sender address SA and is set in this case with the address “11” of the aforementioned processor  11  as the address SA. An area  54  is to be set with a message sequence number DN and is set in this case with the summed value “1” of the previous sequence number “0” and an incremented valve “1”. At this time, the value of the message sequence number storage area  242  is counted up only one for the subsequent message sent. An area  55  is to be set with a content code CC (which will be detailed later) and is set in this case with the code data SAB obtained from the I/O device  40  which has detected the trouble in the signal device and which identifies the aforementioned trouble of the signal device. An area  56  is one which is to be set with sub-data SD (which will be detailed later) and is set in this case with both the number SNO of the aforementioned troubled signal device and the data SDA concerning that signal device. 
     The processing unit  22  sends a copy of the job occurrence message Jm, which has been stored in the sending buffer area  244 , to the transmission loop  1  through an interface  21 . 
     Thus, the job occurrence message JM sent from the information processor  11  circulates once through information processors  12 ,  13 , - - - , and  1 n until it returns to the information processor  11 . FIG. 6 shows one example of the message receiving process at the processing unit  22  of the transmission controller  20 . On the other hand, FIGS.  7 (A) to (E) show a variety of processing examples at the processing unit  32  of the information processor  11 . The operations of the information processor according to the present invention will be described in the following with reference to those Figures. The processing unit  22  in the information processor  11  starts, when it receives that message JM through the interface  21  (at a process  701  of FIG. 4) and detects the sender address SA and the sequence number DN, which are in a predetermined positional relationship from the start flag F. The sender address SA and the address stored in the device address storage area  241  of the information processor  11  are compared (at a process  702  of FIG.  6 ). In this case, they are coincident. Therefore, it is possible to detect that the message JM is one which has been sent from the processor  11 . Since that message JM is a self-sent again  one, it need not be sent so that it is prevented from being sent from the processor  11  to the processor  12  (at a process  707  of FIG.  6 ). In other words, that message JM is taken out of the loop transmission line  1 . Next, it is determined whether a message having the same sequence number is stored in the sending buffer area  244 . In this case, the area  244  stores the same job occurrence message JM as that received so that the sequence numbers of the messages received and stored are coincident. Therefore, the coincident message stored in the area  244  is unnecessary and is deleted, because it is judged at this point that that message JM has been transmitted successfully to the respective devices in the system (at a process  708  of FIG.  6 ). 
     However, when a message which is stored in the sending buffer area  244  is not deleted from that area  244  after a predetermined period has elapsed after the message sending operation from that area  244 , the processing unit  22  judges that the message has been sent out once but has not returned, and therefore sends it again. 
     The sending process of the job occurrence message is completed in the manner thus far described. 
     Incidentally, the sequence number DN is used to discriminate the messages having a common information processor as their sender. More specifically, in case a plurality of messages having a common information processor as their sender are sent, the sequence number DN is used to judge which message circulates once but fails to return. 
     The aforementioned content code CC indicates the content of the general concept expressed by the data and is used to classify the data according to type, and therefore, it has a limited number of different combinations. 
     In contrast, the aforementioned sub-data SD concerns the content code and the so-called “variable parameter” or the like for specifically supplementing the concept of the content code with numerical values or the like thereby to provide control data associated with the content code so that the content to be designated thereby is substantially infinite. 
     In a system relating to trains, for example, the items of Table 1 are some examples of the content code and the subdata: 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Content of Control Data 
                 Content Code 
                 Sub-Data 
               
               
                   
               
             
             
               
                 The work begins at 4:30. 
                 Beginning Code 
                 Data of 4:30 
               
               
                 The work ends at 23:50. 
                 Ending Code 
                 Data of 23:50 
               
               
                 The train M5 was troubled at the 
                 Trouble Code 
                 Data of Station 
               
               
                 station F at 12:00. 
                   
                 F, Train M5 
               
               
                   
                   
                 &amp; 12:00 
               
               
                 The train M10 left the station G 
                 Pursuit Code 
                 Data of Station 
               
               
                 at 12:30. 
                   
                 G, Train M10 
               
               
                   
                   
                 &amp; 12:30 
               
               
                 The signal device 90 is abnormal, 
                 Signal Device 
                 Signal Device 
               
               
                 and the data for its analysis are SDA. 
                 Abnormal Code 
                 90 (SNO) &amp; 
               
               
                   
                 (SDA) 
                 Data (SDA) 
               
               
                 — 
                 — 
                 — 
               
               
                 — 
                 — 
                 — 
               
               
                 — 
                 — 
                 — 
               
               
                 — 
                 — 
                 — 
               
               
                   
               
             
          
         
       
     
     (2) Reception of Job Occurrence Message at Other Processors 
     Next, the reception at the other processors of the job occurrence message sent from the processor  11  in the aforementioned manner will be described in the following. The transmission controller  20  of each of the processors  12 ,  13 ,  14 , - - - , and  1 n, which are not the senders of that message, first judges, when it receives that job occurrence message JM (at the process  701  of FIG.  6 ), whether or not it is a self-sent message (at the process  702  of FIG.  6 ). More specifically, the processing unit  22  in the transmission controller  20  receives that message JM (which has a construction such as shown in FIG. 5) through the interface  21 . The sender address SA of the area  53 , which is arranged at a predetermined position with respect to the position of the flag F of the start area  51  of that message, is detected and compared with the device address which is stored in the area  241  of the storage unit  24 . In this case, no coincidence takes place, so that the message JM is transferred to the transmission loop  1 . It is judged (simultaneously with a process  703  of FIG. 6) whether or not there is coincidence in a receiving buffer area  243  between that message JM and the sender address SA and sequence number DN of the transmission loop  1  (at a process  704  of FIG.  6 ). In this case, there is no storage of this message in the area  243 , and it is judged that no coincidence takes place. In other words, it is found that the message JM represents the first reception of that message at this processor. Next, in accordance with whether or not the content code of that message JM is registered in a content code table storage area  245 , it is judged whether or not that message JM is to be processed somehow by the processor itself (at a process  705  of FIG.  6 ). The area  245  of each of the processors stores in advance a plurality of content codes identifying those jobs to be processed by the respective processors. Now, let it be assumed that the same content code as the code data SAD indicative of the abnormality in the signal device, i.e., the content code of that message JM, is registered in the areas  245  of those processors  12 ,  13  and  14  of the processors  12 ,  13 , - - - , and  1 n, but not in the areas of the remaining processors. 
     In this case, the execution of the job is limited to the processors  12 ,  13  and  14  in which the results of the judging process  705  is YES. Therefore, that message JM is stored only in the receiving buffer areas  243  of the processors  12 ,  13  and  14  (at a process  706  of FIG.  6 ). The result is that the remaining processors do not store that message JM. 
     In the manners thus far described, the job occurrence message JM is received by the plural information processors. 
     Next, at each of the information processors which have received and stored that message JM, a judging process is performed for judging whether or not the job relating to the message JM is to be executed by the processor itself or whether or not the execution of that job simply is to be monitored by that processor. That judging process is performed in the following way. 
     The processing units  22  in each of the processors  12 ,  13  and  14  inform the processing unit  32  therein of the fact that there is in the receiving buffer area  243  a message which has not been read yet. The processing unit  32 , when it receives that information, sets an interrupt flag ORF to “1”, if it is involved in a job execution, thereby to interrupt the job being executed. If it is not involved in job execution, the processing unit  32  leaves the interrupt flag ORF at “0”. The processing unit  32  first commands the processing unit  22  to read that message JM out of the receiving buffer area  243  (at a process  801  of FIG.  7 (A)). Then, the processing unit  22  reads that message JM out of the area  243 , transfers the same to the processing unit  32  and deletes part of the message JM from the area  243 . In this regard, the sender address SA and the sequence number DN of that message JM are held in the area  243  for a predetermined time so that they may be used to prevent the same message JM from being received twice or more, after which this data is also deleted. 
     The processing unit  32  detects that the code data of that message JM is CD and judges that the message JM is a job occurrence message (at a process  803 ). Next, the job occurrence message is stored into the job occurrence message storage area  342  (at a process  807 ). 
     Here, it is desirable that the newly occurring job be executed by the information processor having the least load. In the embodiment being described by way of example, a relative time RT from the instant when the job occurrence message is received at each processor to the instant when the processor is available for executing that job is used as an index for indicating the load condition of the processor. When the information processor receives the job occurrence message during the execution of another job, it becomes available for executing the job of that message after it has executed that other job. When the information processor receives that message while it is doing no job, on the other hand, it instantly becomes available. Therefore, the processor has less load if it has a shorter relative time RT before it becomes available. The processes of calculating that relative time RT are performed at steps  807  to  813  in the following manner. 
     It is judged whether or not the aforementioned interrupt flag ORF is “1” (at the process  807 ). When the flag ORF is “0”, there is no job being executed so that the newly occurring job of the received message can be instantly executed, and a buffer area  345  is partially set to be “0” as the relative time RT in such a processor (at the process  808 ). When the flag ORF is “1”, there is a job to be interrupted, and the start is effected, after a set timer  104  for setting the relative time RT, as shown in FIG. 2, has been set to be “0”, so that the time RT before the job is completed may be measured (at the process  809 ). Next, the interrupt flag ORF is reset to be “0” (at the process  810 ), and the execution of the interrupted job is restarted (at the process  811 ). After the execution of the interrupted job has been completed (at the process  812 ), the value of the timer  104  at that time is set as the relative time RT in a portion of the buffer area  345  (at the process  813 ). 
     Next, the generation of a random variable is executed to generate a random variable RV, which is set in a portion of the buffer area  345 . Then, this buffer area  345  is set with a candidacy code CD 2  (which identifies a message as a candidacy message), the content code CC (which is the code SAB indicating the abnormality of the signal device) of the job occurrence message stored in the area  342 , and a code PSDA (which is the number SNO of the abnormal signal device, in this case) forming a part of the sub-data SD. Incidentally, combination of the content code CC and the code PSDA will be referred to as a “job code”. The processing unit  32  sends the candidacy code CD 2 , the job code TN, the relative time RT and the random variable RV, that have been set in the buffer area  345  in the manner described, to the transmission controller  20  (at a process  814 ). 
     The processing unit  22  of the transmission controller  20  thus having received that data sets a candidacy message CM shown in FIG. 8 in the sending buffer area  244  similarly to the aforementioned case in which the job occurrence message JM is formed. The areas  51  and  57  of that message CM are set with the flags indicating the starting and ending portions of the message. The area  52  is set with the received code data CD 2  indicative of the candidacy message CM. The area  53  is set with the sender address SA. The area  54  is set with the sequence number DN. The area  55  is set with the content code CC. An area  561  is set with the code PSDA. An area  58  is set with the relative time RT. An area  59  is set with the random variable RV. 
     The processing unit  22  sends a copy of the candidacy message CM stored in the sending buffer area  244  to the transmission line  1  and takes that copy out of the transmission line  1  similarly to the case of the job occurrence message JM if the copy circulates once and returns. Incidentally, in the case of the job occurrence message JM, the same job occurrence message JM as the copy having once circulated and returned is merely erased from the sending buffer area  244 . In the case of the candidacy message CM, however, the same message CM as the copy having once circulated and returned is additionally transferred to the receiving buffer area  243  immediately before it is deleted from the area  244 . 
     Thus, the candidacy message CM is sent to the transmission line  1  from the plural processors  12 ,  13  and  14  which have received the job occurrence message JM. 
     In the manner thus far described, the candidacy message CM having been sent to the transmission line  1  is stored, irrespective of whether or not it is a self-transmitted message, in the receiving buffer areas  243  of the processors  11 ,  12 ,  13  and  14  in which the same content code as the content code CC of that message CM is in the content code table storage area  245 . 
     The following processes are performed in the processors  11 ,  12 ,  13  and  14 , respectively. Specifically, the processing unit  32  is informed similarly to the foregoing description by the processing unit  22  of the fact that the message has arrived at the receiving buffer area  243 . If the processing unit  32  is executing another job when it receives that information, it sets the interrupt flag ORF to be “1”. Otherwise, the processing unit  32  leaves the interrupt flag ORF at “0” (which will be merely called an “interrupting process”). The processing unit  32  reads that message out of the receiving buffer area  243  (at the process  801 ). Next, it is judged whether or not that message is a job occurrence message (at the process  803 ). The code of the area  52  of that message is CD 2  and is different from the code CD 1  indicative of a job occurrence message JM so that the process is advanced to step  821  of FIG.  7 (B). Here, it is judged that the code of the area  52  of that message is CD 2  indicative of the candidacy message CM (at the process  821  of FIG.  7 (B)), and this message CM is stored into a candidacy message storage area  343  (at a process  823 ). 
     When the candidacy message CM is the first such message received, a checking timer  105  for closing the candidacy, as shown in FIG. 2, is set to the initial state “0”. Therefore, whether or not the candidacy message CM is the first such message received is judged in accordance with whether or not the timer  105  is “0” (at a process  825 ). In this regard, it will be recalled that each processor cable of candidacy will transmit a candidacy message. In case it is the first reception of such message, the candidacy closing timer  105  is started (at a process  827 ). In case it is not the first reception of such message, the start of the timer  105  is unnecessary so that the process is shifted without any execution of the process  827  to the interrupt releasing process composed of processes  829  and  831 . If the interrupt flag ORF is “0” (at the process  829 ), more specifically, there is no job to be executed, the process ends. If the flag ORF is “1”, the interrupt flag is reset to be “0” to execute the interrupted job, and the process ends after the completion of that job (at the process  831 ). 
     If the timer value of the candidacy checking timer  105  reaches a predetermined time T 1  which is slightly longer than that for the candidacy message CM to once circulate the loop, the time-up signal is fed to the processing unit  32  and is left at the value T 1 . The processing unit  32  is informed by the time-up signal of the fact that the candidacy is closed, and performs the aforementioned interrupting process. Next, the candidacy message of the area  343  is examined to select the processor to execute the job (at a process  833  of FIG. (C)). In case there is only one message CM in the area  343 , the processor which is indicated by the address SA of that message CM is selected. In case there are a plurality of messages CM in the area  343 , the message having the shortest relative time RT is selected from the respective messages CM. If there is one message CM having the shortest time, the processor indicated by the address SA of that message CM is selected. If there are two or more messages CM having the same shortest time, the random variables RV of that message are compared to select the message CM having the smallest random variable RV. If two or more messages CM having the same shortest time and random variable are found, their addresses SA are compared to select the message CM having the smallest address SA and to select the processor indicated by the address SA of that message. 
     At these processes, incidentally, in case where two or more messages CM are found in which both the relative times RT and the random variables RV are the same minimum values, that selecting process  833  may be executed again after new random variables RV are generated at the respective processors indicated by the addresses SA of those messages CM and after the candidacy messages having their random variables RV renewed are newly sent from the respective processors. Thus, the address SA of the single processor selected is stored as the address JA in the area  344 . 
     It is judged whether or not the single processor thus selected is the processor itself (at a process  835 ). More specifically, it is judged whether or not the sender address SA of the single message selected at the process  833  coincides with the address of the area  241  itself. The result is that the job of the message CM is executed by the processor itself, if the coincidence takes place, and is monitored unless otherwise controlled. 
     Now, let it be assumed that the job identified in the candidacy message CM is executed by the processor  12  so that the job execution is monitored by the processors  11 ,  13  and  14 . 
     (3) Execution of Job 
     At the processor  12 , the process is shifted from  835  to  837 . The processing unit  32  of the processor  12  sends both a job execution declaration code CD 3  and a job code TN to be executed to the transmission controller  20 . The latter job code TN is a copy of the job code of the message CM in the area  343 , which is solely selected at the process  833 . 
     The transmission controller  20  thus having received the codes CD 3  and TN executes the processings similar to the aforementioned ones to set into the sending buffer area  244  a job execution declaration message DCM which is shown in FIG.  9 . The transmission controller  20  then sends the copy of that message DCM to the loop transmission line  1  and deletes the message DCM from the sending buffer area  244  after the message DCM has once circulated through that transmission line  1  and returned. Thus, the sending operation of the job execution declaration message DCM ends. 
     The processing unit  32  reads the content code CC of the job occurrence message JM out of the area  342 . In accordance with the content code CC thus read out, one program is selected from those which are stored in plural in advance in an area  341 . In case a signal device becomes abnormal, a signal device abnormality analyzing program is selected because the content code is the signal device abnormality code SAB. Then, the execution of the job for analyzing the data SDA of that message JM with that selected analyzing program is started. The processing unit  32 , while executing that job, sends a job executing message BM, as shown in FIG. 10, through the transmission controller  20  for a predetermined period T 0  similarly to the aforementioned process. That message BM has its code CD 4  indicating the job executing message. 
     After completion of the execution of that job, the processing unit  32  stores a code CD 5  indicative of the job completion, the code TN of that job and data D indicative of the result of the job execution into the buffer area  345 . Then, those job codes and the data D indicating the result of the job execution are transmitted to the I/O device  40  via interface  33  so that they are displayed (at a process  839 ). In the case of the abnormal signal device, the I/O device  40  for informing the signal maintenance man responds to the job code TN to display the number of the signal devices which is abnormal together with the state thereof, the cause for the abnormality and so on in response to the result data D. 
     Then, the codes CD 5  and TN and the result data D of the buffer area  345  are sent to the transmission controller  20 . This transmission controller  20  sets a job completion message EM, as shown in FIG. 11, in the sending buffer area  244  and sends the copy of that message EM to the loop transmission line  1 , both similarly to the aforementioned process, until it deletes that message EM from the sending buffer area if that copy once circulates and returns. The processing unit  32  clears the areas  341  to  345  to zero and resets the timers  104  to  107  to be “0”, thus leading to the end state (at the process  841 ). 
     Incidentally, since the interrupt flag ORF for the job execution is “0”, there is no necessity for the resetting operation after the end of a process  841 . 
     (4) Monitor of Job Execution 
     At the processors  11 ,  13  and  14 , the process is shifted from  835  to  836 . In the step  835 , the processors  11 ,  13  and  14  have determined that they are not selected to execute the job, and in this case, the timer  106  therein is reset and started for monitoring whether or not the job execution declaration message DCM is normally sent by the selected processor  12 . After that, the interrupt releasing processes (i.e., the processes  829  and  831  of FIG.  7 (B)) are executed. 
     The processor (e.g., the processor  12  in this case) for the job execution is monitored in accordance with whether or not the timer  106  is timed out (which will be described in detail hereinafter). In other words, whether or not the job execution declaration was normally effected. 
     In case the processor  12  is normal, the job execution declaration message DCM of FIG. 9 is sent from the processor  12  and is received by the processors  11 ,  13  and  14  similarly to the foregoing description. At each of the processors  11 ,  13  and  14 , the processing unit  32  executes the aforementioned interrupting process and then the processes  801  and  803  of FIG.  7 (A) and the process  821  of FIG.  7 (B) are performed, after which the operation is shifted to a process  851  of FIG.  7 (D). In accordance with the fact that the code of the area  52  of that message DCM is CD 3 , it is judged that the message DCM is the job execution declaration message, and the process is advanced to  852 . At the time when the process is advanced to  852 , the timer  106  has not timed out yet. The timer  106  is stopped, and then the timer  107  for monitoring whether or not the job is being normally executed at the processor  12  is set to be “0”. After that, the aforementioned interrupt releasing process is executed. 
     The job executing processor  12  is monitored in accordance with whether or not the timer  107  is timed out (which will be described in detail hereinafter). Specifically, whether or not the job is being normally executed. 
     In case the processor  12  is normal, the message BM of the job execution shown in FIG. 10 is sent and received by the processors  11 ,  13  and  14 , as has been described hereinbefore. At each of the processors  11 ,  13  and  14 , the processing unit  32  executes the aforementioned interrupting process and then the processes  801  and  803  of FIG.  7 (A), the process  821  of FIG.  7 (B) and the process  851  of FIG.  7 (D) are performed, after which the operation is shifted to a process  853 . In accordance with the fact that the code of the area  52  of that message BM is CD 4 , it is judged that the message BM is the job executing message, and the process is advanced to  854 . At the time when the process is advanced to  854 , the timer  107  has not timed out yet. The timer  107  is reset to be “0”. After that, the aforementioned interrupt releasing process is executed. Thus, while the job is being executed at the processor  12 , the timer  107  is repeatedly rest to be “0” and started. 
     In case the processor  12  is normal, as has been described hereinbefore, the job completion message EM of FIG. 11 is sent and received by the processors  11 ,  13  and  14 . At each of the processors  11 ,  13  and  14 , the processing unit  32  consecutively executes the processes  801  and  803  of FIG.  7 (A), the process  821  of FIG.  7 (B) and the processes  851  and  853  of FIG.  7 (D)), after the aforementioned interrupt releasing process has been executed, until it is shifted to a process  856 . In accordance with the fact that the code of the area  52  of that message EM is CD 5 , it is judged that the message EM is the job completion message, and the process is advanced to  857 . At the time when the process is advanced to  857 , the timer  107  is not timed out yet. This timer  107  is stopped and that message EM is stored in the buffer area  345 . The job code TN of that message EM and the result data D are read out of the area  345  and are sent to the I/O device  40 . In case the signal device is abnormal, the I/O device  40  for informing the signal maintenance man displays the number of the signal device which is abnormal in response to the job code TN together with the state of and cause for the abnormality and so on in response to the result data D. The processing unit  34  clears the area  341  to  345  to zero and resets the timers  104  to  107  to be “0”, thus effecting the stop state (at the process  857 ). 
     Thus, the monitoring of the job execution is completed. 
     (5) Abnormal Detection and Processings therefor 
     The timer  106  of FIG. 2 is, as has been described hereinbefore, a timer for monitoring whether or not the job execution declaration was normally performed. The timer  106  is so constructed that it is timed out at a time T 2 , which is slightly longer than the time for the job execution declaration message DCM to be sent from the job executing processor and to circulate once through the loop transmission line  1  and return, thereby to generate a time-up signal until it is stopped. 
     The timer  107  of FIG. 2 is, as has been described hereinbefore, a timer for monitoring whether or not the job is being normally executed. The timer  107  is so constructed that it is timed out at a time T 3 , which is the summation of the sending period T 0  of the aforementioned job executing message BM and the time T 3 ′ for the message BM to circulate once through the loop and return, thereby to generate a time-up signal until it is stopped. 
     Therefore, the processing unit  32  judges, when it receives the time-up signal from the timer  106  or  107 , that the job executing processor has become abnormal either during the time period from the candidacy to the declaration of the job execution or during the job execution. The processing unit  32  sends, after the execution of the aforementioned interrupting process, the address JA (which stored in the area  344 ) of the processor selected at the aforementioned process  833  of FIG.  7 (C), the code CD 6  indicative of the abnormal broadcasting message and the job code TN to the transmission controller  20 . This transmission controller  20  sets an abnormal broadcasting message AM of FIG. 12 in the sending buffer area  243  and sends a copy of that message AM to the loop transmission line  1  both similarly to the foregoing description so that it deletes that message AM from the sending buffer area if the copy thereof once circulates and returns. It is judged whether or not there is in the area  343  the candidacy message CM which has the same sender address SA as the address JA of the area  344  (at a process  861  of FIG.  7 (E)). If there is no message, the process to be taken because the processor of the address JA is abnormal (which process will be called a “countermeasure process”, as will be detailed hereinafter) has been already completed. Therefore, not the countermeasure process but the aforementioned interrupt releasing process is executed, thus ending the processings. If that candidacy message CM is in the area  343 , there is a necessity for that countermeasure process, and the process is advanced to  862 . The processing unit  32  deletes the candidacy message CM, which has the same sender address SA as the address JA, from the area  342 . After that, it is judged whether or not the candidacy message CM is in the area  343  (at a process  863 ). If there is no message having the same address, it is necessary to advance the process from the reception of the candidacy CM. Therefore, the candidacy closing timer  105  is reset and left to be “0” (at a process  864 ). After that, the aforementioned interrupt releasing process is performed. If there is a message CM having the same address, the timer  105  is reset to be “0” and is started (at a process  865 ), thus effecting the aforementioned interrupt releasing process. 
     Thus, the processes of the processors having detected the abnormality in the job executing processor are completed. 
     At the processor having received the abnormal broadcasting message AM from the transmission line  1 , on the other hand, the processing unit  32  consecutively executes the processes  801  and  803  of FIG.  7 (A), the process  821  of FIG.  7 (B) and the processes  851 ,  853  and  856  of FIG.  7 (D), after the aforementioned interrupting process, and detects that the code of the area of that message AM is CD 6 , after which it is shifted to a process  860 . The address JA of the area  61  of that abnormal broadcasting message AM is stored in the area  344 . After that, the process is advanced to the aforementioned one  361 , at which the same processing as the foregoing description is executed, so that the candidacy message CM (i.e., the candidacy message MC of the processor at an abnormal state) of the address JA is brought into a state at which it is deleted from the area  343 . 
     As the time elapses, moreover, the respective timers  105  of the plural processors at the monitored state are timed out. The respective processors at the monitored state are shifted to the aforementioned process  833  of FIG.  7 (C) in response to the time-up signals of their own timers  105  thereby to select the processor to execute the job in response to the candidacy message of the processor at the abnormal state. Therefore, the processor to execute the job is elected from the processors at the monitored state thereby to effect the job execution. 
     The processes thus far described are repeated on and on. 
     In case the processor  12  becomes abnormal, one processor  13  of the plural processors  11 ,  13  and  14  monitoring that processor  12  becomes the processor to execute the job, whereas the processors  11  and  14  monitor the processor  13 . If the processor  13  becomes abnormal, too, one processor  11  of those monitoring processors  11  and  14  becomes the processor to execute the job, whereas the remaining processor  14  monitors the processor  11 . 
     In the embodiment thus far described, incidentally, the relative time RT has been used to elect the processor to execute the job. Nevertheless, that relative time RT may be replaced by an accumulated load ratio P. 
     Here, this load ratio P is expressed by the following Equation:        P   =         Accumulated Executing Time       Accumulated Running Time       .                            
     In an alternative, a value PRT to be determined from the load ratio P and the relative time RT may also be used in place of the load ratio P. 
     Here, the value PRT is expressed by the following Equation: 
     
       
         PRT=ƒ(P,RT),  
       
     
     (wherein f for a function). 
     On the other hand, the time-up periods of the timers  104  to  107  of the embodiment thus far described are naturally determined on the basis of both the transmission time (which contains the resending time of the message in case it is necessary due to noises or the like for the message to be sent again), which is either actually measured or calculated between the information processor and the transmission control, and the transmission time (which contains the resending time of the message in case it is necessary due to noises or the like for the message to be sent again or which is determined by considering a bypass passage when there is a possibility of forming the bypass passage) between the respective two of the information processors. 
     As has been described hereinbefore, according to the present invention, there can be attained the following advantages: 
     (1) The job can be executed without fail. Specifically, no matter what processor gets out of order and no matter when the disorder takes place, that job never fails to be backed up by another processor. 
     (2) The loads upon the respective processors can be averaged. Specifically, it is possible to execute the job by such a processor of the plural processors as is judged to have the lightest load. 
     (3) Sufficient expandability can be enjoyed. Specifically, the processors can be increased or decreased without any difficulty partly because the functions of the respective processors are identical and partly because the process neither depends upon the number of the processors of the system nor requires the address of the receiver.