Completed code for assignment 4 of Operating Systems.

os/ass4/main.c

-#include "stdio.h"
-#include "stdlib.h"
-#include "pthread.h"
+/*
+ * Assignment 4 of Operating Systems: PThread simulation.
+ * 
+ * Sander van Veen (6167969) and Taddeus Kroes (6054129).
+ * <sandervv@gmail.com>      and <taddeuskroes@hotmail.com>.
+ * 
+ * Submission date: 21 november 2010.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
 
 #include <unistd.h>
 #include <time.h>
 #include <sys/time.h>
 #include <sys/times.h>
 
+#include "main.h"
+
 int forks_len;
 pthread_mutex_t *forks;
 pthread_cond_t wait_threshold;
 pthread_barrier_t wait_barrier;
 
-typedef struct diner_stats {
-    unsigned int meals;
-    unsigned int forks;
-    unsigned int id;
-    unsigned int locked;
-} diner_stats;
-
 int diner_finished = 0;
 
-#define TIME_LIMIT 2.f
-
+/*
+ * Release fork taken by a philosopher.
+ */
 static inline void release_fork(diner_stats *stats, int f) {
     if(diner_finished)
         return;
+    
+    // Unlock left or right fork.
+    stats->locked ^= 1 << (f % 2);
+    pthread_mutex_unlock(forks+f);
+}
+
+/*
+ * Try to claim a fork, but do not wait if the fork cannot be claimed.
+ * This call is therefore non-blocking.
+ */
+static inline int try_take_fork(diner_stats *stats, int f) {
+    // Try to lock left or right fork.
+    if(diner_finished || !pthread_mutex_trylock(forks+f))
+        return 1;
 
-    stats->locked ^= 1 << f;
-    pthread_mutex_unlock(&forks[f]);
+    stats->locked |= 1 << (f % 2);
+    stats->forks++;
+    
+    return 0;
 }
 
+/*
+ * Claim a fork, and wait (blocking) if the fork is already taken.
+ */
 static inline void take_fork(diner_stats *stats, int f) {
     if(diner_finished)
         return;
 
+    // Lock left or right fork.
     pthread_mutex_lock(forks+f);
-    stats->locked |= 1 << f;
+    stats->locked |= 1 << (f % 2);
     stats->forks++;
 }
 
 #define PHILO_EATING \
     if(diner_finished) \
-        break; \
+        return 1; \
     \
     stats->meals++;
 
-void philo_left(diner_stats *stats, int id) {
-    while(!diner_finished) {
-        // Let the philosopher take two forks.
-        take_fork(stats, id);
-        take_fork(stats, (id+1) % forks_len);
+static const char *philo_type_names[] = {"left", "right", "optimistic", "shy",
+                                         "random"};
+static const philo_t philo_types[] = {&philo_left, &philo_right, &philo_shy, \
+                                      &philo_optimistic, &philo_random};
 
-        PHILO_EATING;
+static const int philo_type_count = sizeof(philo_types) / sizeof(philo_t);
 
-        release_fork(stats, (id+1) % forks_len);
-        release_fork(stats, id);
-    }
+/*
+ * Philosopher favoring the left fork above the right fork. He will wait for
+ * both forks, and wouldn't release the first while he is waiting on the second.
+ */ 
+int philo_left(diner_stats *stats, int id) {
+    // Let the philosopher take two forks (first left, then right).
+    take_fork(stats, id);
+    take_fork(stats, (id+1) % forks_len);
+
+    PHILO_EATING;
+
+    // Release both forks.
+    release_fork(stats, (id+1) % forks_len);
+    release_fork(stats, id);
+
+    return 0;
 }
 
-void philo_right(diner_stats *stats, int id) {
-    while(!diner_finished) {
-        // Let the philosopher take two forks.
-        take_fork(stats, (id+1) % forks_len);
-        take_fork(stats, id);
+/*
+ * Philosopher favoring the right fork above the left fork. He will wait for
+ * both forks, and wouldn't release the first while he is waiting on the second.
+ */ 
+int philo_right(diner_stats *stats, int id) {
+    // Let the philosopher take two forks (first right, then left).
+    take_fork(stats, (id+1) % forks_len);
+    take_fork(stats, id);
 
-        PHILO_EATING;
+    PHILO_EATING;
+    
+    // Release both forks.
+    release_fork(stats, id);
+    release_fork(stats, (id+1) % forks_len);
 
-        release_fork(stats, id);
-        release_fork(stats, (id+1) % forks_len);
-    }
+    return 0;
 }
 
-void philo_optimistic(diner_stats *stats, int id) {
-    while(!diner_finished) {
-        // Let the philosopher take one of the two forks.
-        if(!pthread_mutex_trylock(&forks[id])) {
+/*
+ * Philosopher with optimistic behaviour: try to take the left or right fork, 
+ * and if one fork is taken succesfully, wait till the second fork is released.
+ */
+int philo_optimistic(diner_stats *stats, int id) {
+    // Let the philosopher take the left fork of the two forks.
+    if(!try_take_fork(stats, id)) {
+        if(diner_finished)
+            return 1;
+
+        // Left fork is already taken, so try to take the right fork.
+        if(!try_take_fork(stats, (id+1) % forks_len)) {
             if(diner_finished)
-                break;
-
-            if(!pthread_mutex_trylock(&forks[(id+1) % forks_len])) {
-                if(diner_finished)
-                    break;
-                // No fork available, be faster next time!
-                sched_yield();
-            }
-            else {
-                stats->locked |= 1 << ((id+1) % forks_len);
-                stats->forks++;
-                
-                if(diner_finished)
-                    break;
-
-                take_fork(stats, id);
-
-                PHILO_EATING;
-
-                release_fork(stats, id);
-                release_fork(stats, (id+1) % forks_len);
-            }
+                return 1;
+            // No forks available, be faster next time!
+            sched_yield();
         }
         else {
-            stats->locked |= 1 << id;
-            stats->forks++;
-            take_fork(stats, (id+1) % forks_len);
+            // Grabbed the right fork successfully.
+            if(diner_finished)
+                return 1;
+
+            take_fork(stats, id);
 
             PHILO_EATING;
 
+            // Release both forks.
             release_fork(stats, id);
             release_fork(stats, (id+1) % forks_len);
         }
     }
-}
+    else {
+        // Grabbed the left fork successfully.
+        take_fork(stats, (id+1) % forks_len);
 
-void philo_shy(diner_stats *stats, int id) {
+        PHILO_EATING;
 
+        // Release both forks.
+        release_fork(stats, id);
+        release_fork(stats, (id+1) % forks_len);
+    }
+
+    return 0;
 }
 
-typedef void(*philo_t)(diner_stats *, int);
+/*
+ * Philosopher with shy behaviour: try again next time, when taking one of the
+ * forks fails.
+ */
+int philo_shy(diner_stats *stats, int id) {
+    // Try to take the right fork.
+    if(!try_take_fork(stats, (id+1) % forks_len)) {
+        if(diner_finished)
+            return 1;
+        
+        // Failed to take fork, so try again next time.
+        sched_yield();
+    }
+    // Let the philosopher try to take the left fork.
+    else if(!try_take_fork(stats, id)) {
+        if(diner_finished)
+            return 1;
+
+        // Release the right fork and try again next time.
+        release_fork(stats, (id+1) % forks_len);
+        sched_yield();
+    }
+    else {
+        // Grabbed the left and right fork successfully.
+        PHILO_EATING;
+
+        // Release both forks.
+        release_fork(stats, id);
+        release_fork(stats, (id+1) % forks_len);
+    }
+
+    return 0;
+}
 
-static const char *philo_type_names[] = {"left", "right", "optimistic"};//, "shy"};
-static const philo_t philo_types[] = {&philo_left, &philo_right, \
-                                      &philo_optimistic};//, &philo_shy};
+/*
+ * Philosopher with random behaviour: change each iteration to one of the other
+ * philosopher behaviours.
+ */
+int philo_random(diner_stats *stats, int id) {
+    // Pick a behaviour randomly (except for the "random" behaviour, since that
+    // would be recursive and thus useless to simulate).
+    return (*philo_types[rand() % (philo_type_count - 1)])(stats, id);
+}
 
 void *philo_start(void *raw_stats) {
     diner_stats *stats = (diner_stats *) raw_stats;
     int id = stats->id,
-        type = rand() % (sizeof(philo_types) / sizeof(philo_t));
+        type = rand() % philo_type_count;
     
     printf("P #%u: hello everybody, i'm %s!\n", id, philo_type_names[type]);
 
     // Philosophers wait for each other, before they can start eating diner.
     pthread_barrier_wait(&wait_barrier);
+    
+    while(!diner_finished && !(*philo_types[type])(stats, id));
 
-    (*philo_types[type])(stats, id);
+    printf("P #%u: i'm leaving, after paying the bill.\n", id);
 
     pthread_exit(NULL);
 }
@@ -189,25 +271,26 @@ void host_start(int philos) {
     gettimeofday(&wct, NULL);
     double start_time = wct.tv_sec + wct.tv_usec / 1e6;
 	
-    // Duration of the diner party is 10 seconds. This loop will prevent the
-    // philosphers from exceeding this time limit.
+    // Duration of the diner party is 10 seconds (see main.h). This loop will
+    // prevent the philosphers from exceeding this time limit.
     do {
-        usleep(10);
+        // Check each 10 ms for deadlock.
+        usleep(10000);
         
-        // Check if deadlock occured. If an deadlock occured (all philosophers
-        // are waiting on their second fork), finish the diner immidiately.
+        // If an deadlock occured (all philosophers are waiting on their left or
+        // right fork), finish the diner party immidiately. It is unclear in the
+        // assignment, if the philosophers should leave the diner party, or if
+        // they only had to release their claimed forks. I choose the first
+        // assumption: leave the party. If they start arguing which fork is
+        // theirs, there's no party anymore.
         int p;
-        for(p = 0; p < philos && stats[p].locked & (1 << p); p++);
+        for(p = 0; p < philos && (stats[p].locked & 1 
+                                  || stats[p].locked & 2); p++);
 
         if( p == philos ) {
             puts("Host: deadlock occured.");
             diner_finished = 1;
 
-            for(p = 0; p < philos; p++) {
-                pthread_mutex_unlock(&forks[p]);
-                stats[p].locked = 0;
-            }
-
             break;
         }
 
@@ -218,28 +301,22 @@ void host_start(int philos) {
 
     puts("Host: diner is finished.");
     
-    // Wait on the other philosophers.
     for(int i = 0; i < philos; i++) {
-        // Reclaim all cutlery (mutexes). This is done twice, because some
-        // philosophers can continue take an fork while the host is still
-        // reclaiming the other forks.
-        for(int p = 0; p < philos; p++)
-            pthread_mutex_unlock(&forks[p]);
-
-        for(int p = 0; p < philos; p++)
+        // Reclaim all cutlery (mutexes) in reverse order.
+        for(int p = philos; p >= i; p--)
             pthread_mutex_unlock(&forks[p]);
         
+        // Wait on the other philosophers.
         if( (rc = pthread_join(threads[i], &status)) ) {
             fprintf(stderr, "return code from pthread_join() is %d\n", rc);
             exit(EXIT_FAILURE);
         }
 
-        printf("Philo #%d ate %d meal(s) and grabbed %d forks.\n",
+        printf("Philo #%d ate %d meal(s) and grabbed %d fork(s).\n",
                i, stats[i].meals, stats[i].forks);
-    }
-    
-    for(int i = 0; i < philos; i++)
+        
         pthread_mutex_destroy(&forks[i]);
+    }
 
     puts("Host: philosophers are done.");
     
@@ -249,7 +326,15 @@ void host_start(int philos) {
     pthread_exit(NULL);
 }
 
+/*
+ * Start the philosopher diner problem simulation. By default two philosophers
+ * are simulated. The first commandline argument changes the total philosophers
+ * being simulated. If the argument is less than two, the philosopher count is
+ * set to the default count of two.
+ */
 int main(int argc, const char **argv) {
+    // Get system clock's milliseconds and set it as seed to ensure a
+    // more "pseudo-random" simulation.
     struct timeval wtc;
     gettimeofday(&wtc, NULL);
     srand(wtc.tv_usec);

os/ass4/main.h

+/*
+ * Assignment 4 of Operating Systems: PThread simulation.
+ * 
+ * Sander van Veen (6167969) and Taddeus Kroes (6054129).
+ * <sandervv@gmail.com>      and <taddeuskroes@hotmail.com>.
+ * 
+ * Submission date: 21 november 2010.
+ */
+
+typedef struct diner_stats {
+    unsigned int meals;
+    unsigned int forks;
+    unsigned int id;
+    unsigned int locked;
+} diner_stats;
+
+/*
+ * Duration of the diner party (in seconds). When this time limit is reached,
+ * all philosophers are requested to pay their bill and leave the party.
+ */
+#define TIME_LIMIT 10.f
+
+int philo_left(diner_stats *stats, int id);
+int philo_right(diner_stats *stats, int id);
+int philo_optimistic(diner_stats *stats, int id);
+int philo_shy(diner_stats *stats, int id);
+int philo_random(diner_stats *stats, int id);
+
+typedef int(*philo_t)(diner_stats *, int);