Banker's algorithm

The Banker's algorithm is a resource allocation and deadlock avoidance algorithm developed by Edsger Dijkstra that tests for safety by simulating the allocation of predetermined maximum possible amounts of all resources, and then makes a "s-state" check to test for possible deadlock conditions for all other pending activities, before deciding whether allocation should be allowed to continue.

Banker's algorithm is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

This page uses content from Wikipedia. The original article was at Banker's algorithm. The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)

Example input

Assuming that the system distinguishes between four types of resources, (A, B, C and D), the following is an example of how those resources could be distributed. Note that this example shows the system at an instant before a new request for resources arrives. Also, the types and number of resources are abstracted. Real systems, for example, would deal with much larger quantities of each resource.

Total resources in system:
A B C D
6 5 7 6

Available system resources are:
A B C D
3 1 1 2

Processes (currently allocated resources):
   A B C D
P1 1 2 2 1
P2 1 0 3 3
P3 1 2 1 0

Processes (maximum resources):
   A B C D
P1 3 3 2 2
P2 1 2 3 4
P3 1 3 5 0

Need= maximum resources - currently allocated resources
Processes (need resources):
   A B C D
P1 2 1 0 1
P2 0 2 0 1
P3 0 1 4 0

C

Standard binary heap-as-priority queue affair. Only that each node links back to its heap position for easier update.

There are two main() functions to choose from (look for #define BIG_EXAMPLE), one is for task example, the other is a much heavier duty test case. <lang c>/*PROGRAM TO IMPLEMENT BANKER'S ALGORITHM

 *   --------------------------------------------*/

1. include <stdio.h>

int curr[5][5],maxclaim[5][5],avl[5]; int alloc[5]={0,0,0,0,0}; int maxres[5],running[5],safe=0; int count=0,i,j,exec,r,p; main(){

 printf("\nEnter the number of resources:");
 scanf("%d",&r);
 printf("\nEnter the number of processes:");
 scanf("%d",&p);
 for(i=0;i<p;i++){
   running[i]=1;
   count++;
 }
 printf("\nEnter  Claim Vector:");
 for(i=0;i<r;i++) scanf("%d",&maxres[i]);

 printf("\nEnter Allocated Resource Table:");
 for(i=0;i<p;i++){
   for(j=0;j<r;j++) scanf("%d",&curr[i][j]);
 }

 printf("\nEnter Maximum Claim table:");
 for(i=0;i<p;i++){
   for(j=0;j<r;j++) scanf("%d",&maxclaim[i][j]);
 }

 printf("\nThe Claim Vector is:");
 for(i=0;i<r;i++) printf("\t%d",maxres[i]);
 printf("\nThe Allocated Resource Table:\n");
 for(i=0;i<p;i++){
   for(j=0;j<r;j++)
     printf("\t%d",curr[i][j]);
   printf("\n");
 }
 printf("\nThe  Maximum Claim Table:\n");
 for(i=0;i<p;i++){
   for(j=0;j<r;j++) printf("\t%d",maxclaim[i][j]);
   printf("\n");
 }
 for(i=0;i<p;i++)
   for(j=0;j<r;j++) alloc[j]+=curr[i][j];
 printf("\n Allocated resources:");
 for(i=0;i<r;i++) printf("\t%d",alloc[i]);
 for(i=0;i<r;i++) avl[i]=maxres[i]-alloc[i];
 printf("\n Available resources:");
 for(i=0;i<r;i++) printf("\t%d",avl[i]);
 printf("\n");
 while(count!=0){
   safe=0;
   for(i=0;i<p;i++){
     if(running[i]){
       exec=1;
       for(j=0;j<r;j++){
        if(maxclaim[i][j]-curr[i][j]>avl[j]){
           exec=0;
           break;
         }
       }
       if(exec){
         printf("\nProcess%d is executing\n",i+1);
         running[i]=0;
         count--;
         safe=1;
         for(j=0;j<r;j++) avl[j]+=curr[i][j];
         break;
       }
     }
   }
   if(!safe){
     printf("\nThe processes are in unsafe state");
     break;
   }
   if(safe) printf("\n The process is in safe state");
   printf("\n Available vector:");
   for(i=0;i<r;i++) printf("\t%d",avl[i]);
 }

}</lang>

Output:

Enter the number of resources:4

Enter the number of processes:5

Enter Claim Vector:8 5 9 7

Enter Allocated Resource Table: 2 0 1 1 0 1 2 1 4 0 0 3 0 2 1 0 1 0 3 0

Enter Maximum Claim table: 3 2 1 4 0 2 5 2 5 1 0 5 1 5 3 0 3 0 3 3

The Claim Vector is: 8 5 9 7 The Allocated Resource Table: 2 0 1 1 0 1 2 1 4 0 0 3 0 2 1 0 1 0 3 0

The Maximum Claim Table: 3 2 1 4 0 2 5 2 5 1 0 5 1 5 3 0 3 0 3 3

Allocated resources:	7	3	7	5
Available resources:	1	2	2	2

Process3 is executing

The process is in safe state
Available vector:	5	2	2	5

Process1 is executing

The process is in safe state
Available vector:	7	2	3	6

Process2 is executing

The process is in safe state
Available vector:	7	3	5	7

Process4 is executing

The process is in safe state
Available vector:	7	5	6	7

Process5 is executing

The process is in safe state
Available vector:	8	5	9	7