Week 6 workshop - forking

Week 6-workshop/README.md

@@ -0,0 +1,6 @@
+## Workshop 6 content
+
+Workshop content: https://web.archive.org/web/20210904135855/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/workshop6.php \
+`plotchess.sh`: https://web.archive.org/web/20210904140621/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/plotchess.sh\
+`goodchessmove.c`: https://web.archive.org/web/20210904140051/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/goodchessmove.c \
+`manychessmoves.c` solution: https://web.archive.org/web/20210904140231/https://teaching.csse.uwa.edu.au/units/CITS2002/workshops/manychessmoves.c\

Week 6-workshop/goodchessmove.c

@@ -0,0 +1,23 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char const *argv[])
+{
+    if (argc != 3)
+    {
+        printf("Usage: goodchessmove [GAMESTATE] [OUTPUT]\n");
+        exit(EXIT_FAILURE);
+    }
+    
+    // placeholder for a real chess program
+    printf("Executing chess move. GAMESTATE: %s, OUTPUT: %s\n",
+           argv[1], argv[2]);
+
+    // do chess
+    sleep(5);
+
+    fflush(stdout);
+    printf("Finished executing chess move. Wrote %s\n", argv[2]);
+    exit(EXIT_SUCCESS);
+}

Week 6-workshop/manychessmoves.c

@@ -0,0 +1,111 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/wait.h>
+
+struct current_instance {
+    char *gamestate;
+    char *output;
+    int instance_no;
+};
+
+struct fork_list {
+    pid_t *fork_list;
+    int concurrent_forks;
+};
+
+int execute_chessmove(struct current_instance *instance)
+{
+    // concatenate original filename and the instance number
+    int len = snprintf(NULL, 0, "%s-%d ", instance->output, instance->instance_no);
+    char output_filename[len];
+    snprintf(output_filename, len, "%s-%d ", instance->output, instance->instance_no);
+    char *arguments[] = {
+        "./goodchessmove",
+        instance->gamestate, 
+        output_filename,
+        NULL
+    };
+    return execvp(arguments[0], arguments);
+}
+
+pid_t new_fork(struct current_instance *instance)
+{
+    pid_t pid;
+    switch (pid = fork()) 
+    {
+    case -1:
+        printf("fork() failed\n");
+        exit(EXIT_FAILURE);
+    case 0:
+        exit( execute_chessmove(instance) );
+    }
+    return pid;
+}
+
+void populate_forks(int fork_count, struct fork_list *forks, struct current_instance *instance)
+{
+    if (fork_count > forks->concurrent_forks) {
+        fork_count = forks->concurrent_forks;
+    }
+    
+    for (size_t i = 0; i < fork_count; i++) {
+        forks->fork_list[i] = new_fork(instance);
+        instance->instance_no++;
+    }
+}
+
+void replace_fork(pid_t old_pid, struct fork_list *forks, struct current_instance *instance)
+{
+    for (size_t i = 0; i < forks->concurrent_forks; i++) {
+        if (forks->fork_list[i] == old_pid) {
+            forks->fork_list[i] = new_fork(instance);
+            instance->instance_no++;
+            return;
+        }
+    }
+}
+
+int numberOfCores(void) // From worshop spec.
+{
+    return sysconf(_SC_NPROCESSORS_ONLN);
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc != 4)
+    {
+        printf("Usage: manychessmoves [N PROCESSES] [GAMESTATE] [OUTPUT]\n");
+        exit(EXIT_FAILURE);
+    }
+
+    int n_forks = atoi(argv[1]);
+    int concurrent_forks = numberOfCores();
+    pid_t fork_pids[concurrent_forks];
+
+    struct fork_list fork_list = { fork_pids, concurrent_forks };
+    struct current_instance instance = { argv[2], argv[3], 0 };
+
+    populate_forks(n_forks, &fork_list, &instance);
+
+    pid_t child;
+    int status;
+    while (concurrent_forks > 0)
+    {
+        child = wait( &status );
+        if (status != 0) {
+            printf("chess instance failed.\n");
+            exit(EXIT_FAILURE);
+        }
+
+        if (instance.instance_no < n_forks) {
+            replace_fork(child, &fork_list, &instance);
+        } else {
+            concurrent_forks--;
+        }
+    }
+    exit(EXIT_SUCCESS);    
+}