From 8044ba68e3dbb754e4d58a30519bcdcabe745b25 Mon Sep 17 00:00:00 2001
From: John Breaux <JohnBreaux@my.unt.edu>
Date: Sat, 23 Apr 2022 04:48:47 -0500
Subject: [PATCH] Implement graph reduction algorithm

---
 src/reducible.cpp | 65 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 57 insertions(+), 8 deletions(-)

diff --git a/src/reducible.cpp b/src/reducible.cpp
index 6503613..af23576 100644
--- a/src/reducible.cpp
+++ b/src/reducible.cpp
@@ -5,22 +5,71 @@
    +-----------------------------------------------+  */
 #include "graph.hpp"
 
+using std::vector;
+
+bool blocked(const int num_processes, const int num_resources, const vector<int> resource_counts, const graph::matrix &matrix, int process_id);
+
 /* reducible:
       Perform the graph reduction algorithm on the adjacency matrix to detect deadlocks
       This algorithm is described in section 5.2 of the Zybook
+
+      The graph reduction algorithm is implemented here with a few obvious optimizations:
+         The algorithm should clear at least one blocked process per iteration;
+         This leads to an easy failure condition, since fewer processes should be blocked than there are remaining iterations.
+         By extension,
    @params: none, uses class-internal data
    @returns:
       bool:
-         true if graph is not reducible (deadlock)
-         false if graph is reducible (no deadlock)
+         true if graph is deadlocked (not reducible)
+         false if graph is not deadlocked (reducible)
 */
 bool graph::reducible() {
-   // TODO: Implement a function which checks if a process is blocked
-   // TODO: Use that function to implement the graph reduction algorithm
-   //? Make sure when reducing the graph, you don't try to delete the
-   return false;
+   // Make a copy of the matrix, so we don't overwrite it
+   matrix m_copy = m;
+   // run for num_processes iterations; there's no point to doing more, since at least one process should clear each time
+   for (int num_iterations = 0; num_iterations < num_processes; num_iterations++) {
+      int num_blocked = 0;
+      // calculate whether every process is blocked or not
+      for(int p = 0; p < num_processes; p++) {
+         // check if process is blocked
+         if (blocked(num_processes,num_resources,resource_counts,m_copy, p)) {
+            //indicate process is blocked
+            num_blocked++;
+         } else {
+            // erase unblocked process from the graph
+            m_copy[p][p] = 0;
+            for (int r = num_processes; r < num_processes + num_resources; r++) {
+               m_copy[r][p] = 0; m_copy[p][r] = 0;
+            }
+         }
+      }
+      // print the number of blocked processes
+      printf("\nIteration %d:\nnum_blocked: %d\n", num_iterations+1, num_blocked);
+      // If more processes are blocked than can be cleared before the algorithm finishes, give up
+      if (num_blocked == num_processes - num_iterations) return true;
+      // Print the new matrix
+      printf("| ");for(auto x:m_copy){for(auto y:x)printf("%d, ",y);printf("\b\b |\n| ");}printf("\b\b  \b\b");
+      // If no processes are blocked, we won!
+      if (num_blocked == 0) return false;
+   }
+   return true;
 }
 
-bool graph::is_blocked(int process_id) {
-   return true;
+bool blocked(const int np, const int nr, const vector<int> rc, const graph::matrix &m, int process_id) {
+   //* Calculate free resources, and compare free units to requests
+   vector<int> resources = rc;
+   for (int r = 0; r < nr; r++) {
+      // Calculate the number of units available
+      for (int p = 0; p < np; p++) {
+         // subtract units currently in use
+         // a resource is in use when >0 in the allocation quadrant of the table, i.e. [(np,0), (nr+np, np))
+         resources[r] -= m[r+np][p];
+      }
+      // If the program requests more resources than are available, it's blocked
+      if (m[process_id][r+np] > resources[r]) {
+         return true;
+      }
+   }
+   // else process is not blocked
+   return false;
 }
\ No newline at end of file