Makefile

@@ -3,10 +3,30 @@
 # Makefile
 
 TARGETS: runsim testsim
-binaries=runsim testsim
+binaries=runsim testsim runsim.o testsim.o liblicense.o liblicense.a
 
-%: %.c
-	gcc -o $@ $<
+all: runsim testsim liblicense.a testsim.o runsim.o
+
+#%: %.c
+#	gcc -o $@ $<
+
+runsim: testsim runsim.o liblicense.a
+	gcc -o runsim -pthread runsim.o -L. -llicense
+
+testsim: testsim.o liblicense.a
+	gcc -o testsim testsim.o -L. -llicense
+
+testsim.o: testsim.c
+	gcc -c testsim.c -o testsim.o
+
+runsim.o: runsim.c
+	gcc -c runsim.c -pthread -o runsim.o
+
+liblicense.a: liblicense.o
+	ar rcs liblicense.a liblicense.o
+
+liblicense.o: liblicense.c
+	gcc -c liblicense.c -pthread -o liblicense.o
 
 .PHONY: clean
 

config.h

@@ -11,4 +11,6 @@
 // program expires after this amount of seconds
 #define TIME_LIMIT 100
 
+#define SEM_NAME "urschler"
+
 #endif

liblicense.c

+// Tony Urschler
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <semaphore.h>
+#include <sys/stat.h>
+#include "config.h"
+#include "license.h"
+
+#define FLAGS (O_CREAT | O_EXCL)
+#define PERMS (mode_t)(S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
+
+
+// waits for a license to become available
+int getlicense(sem_t* sem, int* nlicenses) {
+    sem_wait(sem);
+    if (errno != EINTR) {
+        perror("License: failed to lock sem\n");
+        return -1;
+    }
+    *nlicenses -= 1;
+    return 0;
+}
+
+// returns a license
+int returnlicense(sem_t* sem, int* nlicenses) {
+    if (sem_post(sem) == -1) {
+        perror("License: Failed to unlock sem\n");
+        return -1;
+    }
+    *nlicenses += 1;
+    return 0;
+}
+
+// initializes semaphore with appropriate value
+// if semaphore already exists, gives access
+int initlicense(sem_t **sem, int val) {
+    while (((*sem = sem_open(SEM_NAME, FLAGS, PERMS, val)) == SEM_FAILED) &&
+            (errno == EINTR));
+    if (*sem != SEM_FAILED)
+        return 0;
+    if (errno != EEXIST)
+        return -1;
+    while (((*sem = sem_open(SEM_NAME, 0)) == SEM_FAILED) && (errno == EINTR));
+    if (*sem != SEM_FAILED)
+        return 0;
+    return -1;
+}
+
+// adds n amount of licenses
+int addtolicenses(int n, sem_t* sem, int* nlicenses) {
+    for (int i = 0; i < n; i++) {
+        if (sem_post(sem) == -1) {
+            perror("License: Failed to unlock sem\n");
+            return -1;
+        }
+        *nlicenses += 1;
+    }    
+    return 0;
+}
+
+// removes n amount of licenses
+int removelicenses(int n, sem_t* sem, int* nlicenses) {
+    for (int i = 0; i < n; i++) {
+        sem_wait(sem);
+        if (errno != EINTR) {
+            perror("License: failed to lock sem\n");
+            return -1;
+        }
+        *nlicenses -= 1;
+    }
+    return 0;
+}
+
+// logs msg to file
+int logmsg(const char* msg) {
+    return 0;
+}
+
+
+
+
+
+
+
+

liblicense.h

+// Tony Urschler
+
+#ifndef LICENSE_H
+#define LICENSE_H
+
+int getlicense(sem_t* sem, int* nlicenses);
+int returnlicense(sem_t* sem, int* nlicenses);
+int initlicense(sem_t **sem, int val);
+int addtolicenses(int n, sem_t* sem, int* nlicenses);
+int removelicenses(int n, sem_t* sem, int* nlicenses);
+int logmsg(const char* msg);
+
+#endif

license.c

-// Tony Urschler
-
-#include <stdio.h>
-
-int getlicense(void) {
-    return 0;
-}
-
-int returnlicense(void) {
-    return 0;
-}
-
-int initlicense(void) {
-    return 0;
-}
-
-int addtolicenses(int n) {
-    return 0;
-}
-
-int removelicenses(int n) {
-    return 0;
-}
-
-int logmsg(const char* msg) {
-    return 0;
-}

license.h

@@ -3,11 +3,11 @@
 #ifndef LICENSE_H
 #define LICENSE_H
 
-int getlicense(void);
-int returnlicense(void);
-int initlicense(void);
-int addtolicenses(int n);
-int removelicenses(int n);
+int getlicense(sem_t* sem, int* nlicenses);
+int returnlicense(sem_t* sem, int* nlicenses);
+int initlicense(sem_t **sem, int val);
+int addtolicenses(int n, sem_t* sem, int* nlicenses);
+int removelicenses(int n, sem_t* sem, int* nlicenses);
 int logmsg(const char* msg);
 
 #endif

runsim.c

 // Tony Urschler
 
 #include <errno.h>
+#include <fcntl.h>
 #include <limits.h>
+#include <semaphore.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/shm.h>
@@ -11,6 +13,7 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include "config.h"
+#include "liblicense.h"
 
 int segment_id;
 int* nlicenses;
@@ -74,6 +77,48 @@ int main(int argc, char* argv[]) {
     *nlicenses = n;
     printf("Value of memory: %d\n", *nlicenses);
 
+    // forking child
+    pid_t pid;
+    pid = fork();
+    
+    // setup semaphore
+    sem_t* sem;
+    if (initlicense(&sem, n) == -1) {
+        perror("License initiation failed.");
+        exit(EXIT_FAILURE);
+    }
+
+    for (int i = 0; i < 5; i++) {
+        while(sem_wait(sem) == -1)
+            if (errno != EINTR) {
+                perror("Failed to lock semlock");
+                exit(EXIT_FAILURE);
+            }
+        if (pid == 0) {
+            sleep(.5);
+            printf("c\n");
+        }
+            else {
+            sleep(1);
+            printf("p\n");
+        }
+        if (sem_post(sem) == -1) {
+            perror("Failed to unlock semlock");
+            exit(EXIT_FAILURE);
+        }
+        if (pid == 0)
+            sleep(.5);
+        else
+            sleep(.5);
+    }
+    
+    // close and unlink semaphore
+    int error;
+    if (sem_close(sem) == -1)
+        error = errno;
+    if ((sem_unlink(SEM_NAME) != -1) && !error);
+    if (error)
+        errno = error;
 
     // deallocating shared memory
     shmdt(nlicenses);

testsim.c

 // Tony Urschler
 // September 26, 2021
 
-
+#include <semaphore.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>