Add initial fb_arc_set modules

README.md

@@ -1,8 +1,9 @@
 This project contains some basic UNIX command line tools I had to do for TU.
 
 Currently the toolset is ther following:
-* mygrep - a simplified version of grep
-* http - an implementation of HTTP 1.1 client and server
-* cpair - a program that searches for the closest pair of points in a set of 2D-points
+* (mygrep)[mygrep] - a simplified version of grep
+* (http)[http] - an implementation of HTTP 1.1 client and server
+* (cpair)[cpair] - a program that searches for the closest pair of points in a set of 2D-points
+* (fb_arc_set)[fb_arc_set] - a set of programs that removes cycles in a directed graph
 
 Feel free to read the descriptions for each tool.

fb_arc_set/Makefile

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+CC = gcc
+CFLAGS = -std=c99 -pedantic -Wall -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_SVID_SOURCE -D_POSIX_C_SOURCE=200809L -g -c
+TARGET_1 = generator
+TARGET_2 = supervisor
+
+all: $(TARGET_1).c $(TARGET_2).c
+	$(CC) $(CFLAGS) $(TARGET_1).c $(TARGET_2).c
+	$(CC) $(TARGET_1).o -o $(TARGET_1)
+	$(CC) $(TARGET_2).o -o $(TARGET_2)
+
+generator: $(TARGET_1).c
+	$(CC) $(CFLAGS) $(TARGET_1).c
+	$(CC) $(TARGET_1).o -o $(TARGET_1)
+
+supervisor: $(TARGET_2).c
+	$(CC) $(CFLAGS) $(TARGET_2).c
+	$(CC) $(TARGET_2).o -o $(TARGET_2)
+
+install:
+	cp $(TARGET_1) /usr/local/bin/graph-$(TARGET_1)
+	cp $(TARGET_2) /usr/local/bin/graph-$(TARGET_2)
+
+clean:
+	$(RM) $(TARGET_1)
+	$(RM) $(TARGET_2)
+	$(RM) *.o
+	$(RM) *.tgz
+
+package:
+	tar -cvzf fb_arc_set.tgz $(TARGET_1).c $(TARGET_2).c Makefile

fb_arc_set/README.md

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+# fb_arc_set
+The aim of these 2 modules is to implement an algorithm which removes cycles in a directed graph by removing the least edges possible.
+A set of edges which must be removed to make a graph acyclic is also called a feedback arc set; and the
+set with the least edges is a minimal feedback arc set.
+
+## Algorithm
+
+A simple randomized algorithm for this problem generates a feedback arc set by executing following steps:
+* Order the vertices of the graph randomly, i.e. generate a random permutation of the set of vertices.
+* Select all edges ( u, v ) for which u > v in the ordering. These edges form a feedback arc set.
+
+## generator
+
+The generator program takes a graph as input. The program repeatedly generates a random solution
+to the problem as described above and writes its result to a circular buffer. It repeats this procedure until it is notified by the supervisor to terminate.
+
+    SYNOPSIS
+    generator EDGE1...
+    EXAMPLE
+    generator 0-1 1-2 1-3 1-4 2-4 3-6 4-3 4-5 6-0
+
+## supervisor
+
+The supervisor sets up the shared memory and the semaphores and initializes the circular buffer required
+for the communication with the generators. It then waits for the generators to write solutions to the
+circular buffer.
+The supervisor program takes no arguments.
+Once initialization is complete, the supervisor reads the solutions from the circular buffer and remem-
+bers the best solution so far, i.e. the solution with the least edges. Every time a better solution than the previous best solution is found, the supervisor writes the new solution to standard output. If a generator writes a solution with 0 edges to the circular buffer, then the graph is acyclic and the supervisor terminates. Otherwise the supervisor keeps reading results from the circular buffer until it receives a `SIGINT` or a `SIGTERM` signal.
+Before terminating, the supervisor notifies all generators that they should terminate as well. This can
+be done by setting a variable in the shared memory, which is checked by the generator processes before
+writing to the buffer. The supervisor then unlinks all shared resources and exits
+
+**Note: The description is from the task I got from TU.**