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| 1 | +packageOthers; |
| 2 | + |
| 3 | +/** |
| 4 | + * This file contains an implementation of BANKER'S ALGORITM |
| 5 | + * Wikipedia: https://en.wikipedia.org/wiki/Banker%27s_algorithm |
| 6 | + * |
| 7 | + * The algorithm for finding out whether or not a system is in a safe state can be described as follows: |
| 8 | + * 1. Let Work and Finish be vectors of length ‘m’ and ‘n’ respectively. |
| 9 | + * Initialize: Work= Available |
| 10 | + * Finish [i]=false; for i=1,2,……,n |
| 11 | + * 2. Find an i such that both |
| 12 | + * a) Finish [i]=false |
| 13 | + * b) Need_i<=work |
| 14 | + * |
| 15 | + * if no such i exists goto step (4) |
| 16 | + * 3. Work=Work + Allocation_i |
| 17 | + * Finish[i]= true |
| 18 | + * goto step(2) |
| 19 | + * 4. If Finish[i]=true for all i, |
| 20 | + * then the system is in safe state. |
| 21 | + * |
| 22 | + * Time Complexity: O(n*n*m) |
| 23 | + * Space Complexity: O(n*m) |
| 24 | + * where n = number of processes and m = number of resources. |
| 25 | + * |
| 26 | + * @author AMRITESH ANAND (https://github.com/amritesh19) |
| 27 | + */ |
| 28 | + |
| 29 | +importjava.util.Scanner; |
| 30 | + |
| 31 | +publicclassBankersAlgorithm { |
| 32 | + |
| 33 | +/** |
| 34 | + * This method finds the need of each process |
| 35 | + */ |
| 36 | +staticvoidcalculateNeed(intneedArray[][],intmaxArray[][],intallocationArray[][],inttotalProcess,inttotalResources) |
| 37 | + { |
| 38 | +for (inti =0 ;i <totalProcess ;i++){ |
| 39 | +for (intj =0 ;j <totalResources ;j++){ |
| 40 | +needArray[i][j] =maxArray[i][j] -allocationArray[i][j]; |
| 41 | + } |
| 42 | + } |
| 43 | + } |
| 44 | + |
| 45 | +/** |
| 46 | + * This method find the system is in safe state or not |
| 47 | + * @param processes[] int array of processes (0...n-1), size = n |
| 48 | + * @param availableArray[] int array of number of instances of each resource, size = m |
| 49 | + * @param maxArray[][] int matrix(2-D array) of maximum demand of each process in a system, size = n*m |
| 50 | + * @param allocationArray[][] int matrix(2-D array) of the number of resources of each type currently allocated to each process, size = n*m |
| 51 | + * @param totalProcess number of total processes, n |
| 52 | + * @param totalResources number of total resources, m |
| 53 | + * |
| 54 | + * @return boolean if the system is in safe state or not |
| 55 | + */ |
| 56 | +staticbooleancheckSafeSystem(intprocesses[],intavailableArray[],intmaxArray[][],intallocationArray[][],inttotalProcess,inttotalResources) |
| 57 | + { |
| 58 | +int [][]needArray =newint[totalProcess][totalResources]; |
| 59 | + |
| 60 | +calculateNeed(needArray,maxArray,allocationArray,totalProcess,totalResources); |
| 61 | + |
| 62 | +boolean []finishProcesses =newboolean[totalProcess]; |
| 63 | + |
| 64 | +int []safeSequenceArray =newint[totalProcess]; |
| 65 | + |
| 66 | +int []workArray =newint[totalResources]; |
| 67 | + |
| 68 | +for (inti =0;i <totalResources ;i++) |
| 69 | +workArray[i] =availableArray[i]; |
| 70 | + |
| 71 | +intcount =0; |
| 72 | + |
| 73 | +// While all processes are not finished or system is not in safe state. |
| 74 | +while (count <totalProcess) |
| 75 | + { |
| 76 | +booleanfoundSafeSystem =false; |
| 77 | +for (intm =0;m <totalProcess;m++) |
| 78 | + { |
| 79 | +if (finishProcesses[m] ==false) |
| 80 | + { |
| 81 | +intj; |
| 82 | + |
| 83 | +for (j =0;j <totalResources;j++) |
| 84 | +if (needArray[m][j] >workArray[j]) |
| 85 | +break; |
| 86 | + |
| 87 | +if (j ==totalResources) |
| 88 | + { |
| 89 | +for (intk =0 ;k <totalResources ;k++) |
| 90 | +workArray[k] +=allocationArray[m][k]; |
| 91 | + |
| 92 | +safeSequenceArray[count++] =m; |
| 93 | + |
| 94 | +finishProcesses[m] =true; |
| 95 | + |
| 96 | +foundSafeSystem =true; |
| 97 | + } |
| 98 | + } |
| 99 | + } |
| 100 | + |
| 101 | +// If we could not find a next process in safe sequence. |
| 102 | +if (foundSafeSystem ==false) |
| 103 | + { |
| 104 | +System.out.print("The system is not in the safe state because lack of resources"); |
| 105 | +returnfalse; |
| 106 | + } |
| 107 | + } |
| 108 | + |
| 109 | +System.out.print("The system is in safe sequence and the sequence is as follows: "); |
| 110 | +for (inti =0;i <totalProcess ;i++) |
| 111 | +System.out.print("P"+safeSequenceArray[i] +" "); |
| 112 | + |
| 113 | +returntrue; |
| 114 | + } |
| 115 | + |
| 116 | +/** |
| 117 | + * This is main method of Banker's Algorithm |
| 118 | + */ |
| 119 | +publicstaticvoidmain(String[]args){ |
| 120 | +intnumberOfProcesses,numberOfResources; |
| 121 | + |
| 122 | +Scannersc =newScanner(System.in); |
| 123 | + |
| 124 | +System.out.println("Enter total number of processes"); |
| 125 | +numberOfProcesses =sc.nextInt(); |
| 126 | + |
| 127 | +System.out.println("Enter total number of resources"); |
| 128 | +numberOfResources =sc.nextInt(); |
| 129 | + |
| 130 | +intprocesses[] =newint[numberOfProcesses]; |
| 131 | +for(inti =0;i <numberOfProcesses;i++){ |
| 132 | +processes[i] =i; |
| 133 | + } |
| 134 | + |
| 135 | +System.out.println("--Enter the availability of--"); |
| 136 | + |
| 137 | +intavailableArray[] =newint[numberOfResources]; |
| 138 | +for(inti =0;i <numberOfResources;i++){ |
| 139 | +System.out.println("resource "+i +": "); |
| 140 | +availableArray[i] =sc.nextInt(); |
| 141 | + } |
| 142 | + |
| 143 | +System.out.println("--Enter the maximum matrix--"); |
| 144 | + |
| 145 | +intmaxArray[][] =newint[numberOfProcesses][numberOfResources]; |
| 146 | +for(inti =0;i <numberOfProcesses;i++){ |
| 147 | +System.out.println("For process "+i +": "); |
| 148 | +for(intj =0;j <numberOfResources;j++){ |
| 149 | +System.out.println("Enter the maximum instances of resource "+j); |
| 150 | +maxArray[i][j] =sc.nextInt(); |
| 151 | + } |
| 152 | + } |
| 153 | + |
| 154 | +System.out.println("--Enter the allocation matrix--"); |
| 155 | + |
| 156 | +intallocationArray[][] =newint[numberOfProcesses][numberOfResources]; |
| 157 | +for(inti =0;i <numberOfProcesses;i++){ |
| 158 | +System.out.println("For process "+i +": "); |
| 159 | +for(intj =0;j <numberOfResources;j++){ |
| 160 | +System.out.println("Allocated instances of resource "+j ); |
| 161 | +allocationArray[i][j] =sc.nextInt(); |
| 162 | + } |
| 163 | + } |
| 164 | + |
| 165 | +checkSafeSystem(processes,availableArray,maxArray,allocationArray,numberOfProcesses,numberOfResources); |
| 166 | + |
| 167 | +sc.close(); |
| 168 | + } |
| 169 | +} |
| 170 | + |
| 171 | +/* |
| 172 | + Example: |
| 173 | + n = 5 |
| 174 | + m = 3 |
| 175 | +
|
| 176 | + Process Allocation Max Available |
| 177 | + 0 1 2 0 1 2 0 1 2 |
| 178 | +
|
| 179 | + 0 0 1 0 7 5 3 3 3 2 |
| 180 | + 1 2 0 0 3 2 2 |
| 181 | + 2 3 0 2 9 0 2 |
| 182 | + 3 2 1 1 2 2 2 |
| 183 | + 4 0 0 2 4 3 3 |
| 184 | +
|
| 185 | + Result: The system is in safe sequence and the sequence is as follows: P1, P3, P4, P0, P2 |
| 186 | + */ |