95 lines
3.7 KiB
C
95 lines
3.7 KiB
C
#include <stdio.h>
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// C program for Banker's Algorithm (Safety & Resource Request)
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// Optimized for minimal code size (e.g., for writing on paper)
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int main() {
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int p, r, i, j, k, pid, req_pid = -1; // p=procs, r=res; req_pid: -1=initial, >=0 processing req
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printf("P R:"); scanf("%d%d", &p, &r); // Input num processes and resources
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int av[r], max[p][r], al[p][r], nd[p][r], req[r]; // av=avail, al=alloc, nd=need
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int w[r], fin[p], seq[p]; // w=work, fin=finish, seq=safe sequence
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// Input available, max, allocation matrices
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printf("Av:"); for(j=0; j<r; j++) scanf("%d", &av[j]);
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printf("Max:\n"); for(i=0; i<p; i++) for(j=0; j<r; j++) scanf("%d", &max[i][j]);
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printf("Alloc:\n"); for(i=0; i<p; i++) for(j=0; j<r; j++) scanf("%d", &al[i][j]);
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// Calculate need matrix: need = max - alloc
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for(i=0; i<p; i++) for(j=0; j<r; j++) nd[i][j] = max[i][j] - al[i][j];
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S:; // Safety Check Algorithm Label
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int s_idx = 0, c = 0, safe = 0; // s_idx=seq index, c=count finished, safe=flag
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for(j=0; j<r; j++) w[j] = av[j]; // work = avail
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for(i=0; i<p; i++) fin[i] = 0; // finish[p] = {false}
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// Find sequence using safety algorithm logic
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while(c < p) { // Loop until all processes are finished or deadlock
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int found = 0; // Flag to check if a process was found in this pass
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for(i=0; i<p; i++) { // Iterate through processes
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if(!fin[i]) { // If process i not finished
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int possible = 1; // Check if need <= work
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for(j=0; j<r; j++) if(nd[i][j] > w[j]) { possible = 0; break; }
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if(possible) { // If need <= work
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for(k=0; k<r; k++) w[k] += al[i][k]; // work = work + alloc
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fin[i] = 1; seq[s_idx++] = i; c++; found = 1; // Mark finished, add to seq
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}
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}
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}
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if(!found) break; // If no process found in a full pass, break (unsafe state)
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}
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if(c == p) safe = 1; // If all processes finished, state is safe
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// --- End Safety Check ---
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// Handle result based on phase (initial check or request check)
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if(req_pid == -1) { // Phase 1: Initial State Check
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if(safe) {
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printf("SAFE. Seq:"); for(i=0; i<p; i++) printf(" P%d", seq[i]); puts("");
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} else { puts("UNSAFE"); goto end; } // If unsafe initially, exit
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// Phase 2: Resource Request
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printf("PID Req:"); scanf("%d", &pid); req_pid = pid; // Get requesting proc ID
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printf("Req:"); for(j=0; j<r; j++) scanf("%d", &req[j]); // Get request vector
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// Check 1: Request <= Need
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for(j=0; j<r; j++) if(req[j] > nd[pid][j]) { puts("Err:Req>Need"); goto end; }
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// Check 2: Request <= Available
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for(j=0; j<r; j++) if(req[j] > av[j]) { puts("Wait:Req>Avail"); goto end; }
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// Tentatively allocate resources
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for(j=0; j<r; j++) { av[j]-=req[j]; al[pid][j]+=req[j]; nd[pid][j]-=req[j]; }
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puts("Checking req safety...");
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goto S; // Re-run safety check on the new state
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} else { // Phase 3: Post-Request Safety Check Result
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if(safe) { // Request is granted if new state is safe
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printf("Req OK. Seq:"); for(i=0; i<p; i++) printf(" P%d", seq[i]); puts("");
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} else { // Request denied if new state is unsafe
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puts("Req DENIED (unsafe)");
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// Rollback state to before tentative allocation
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pid = req_pid; // Restore pid for rollback
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for(j=0; j<r; j++) { av[j]+=req[j]; al[pid][j]-=req[j]; nd[pid][j]+=req[j]; }
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}
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// No further action needed after handling the single request
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}
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end: return 0; // End of program
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}
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/*
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```
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P R: 5 3
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Av: 3 3 2
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Max:
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7 5 3
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3 2 2
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9 0 2
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2 2 2
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4 3 3
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Alloc:
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0 1 0
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2 0 0
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3 0 2
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2 1 1
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0 0 2
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```
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*/
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