Add exercise code for Dobby

Author: Margo

synch1x/GNUmakefile

@@ -0,0 +1,17 @@
+PROGRAMS = dobby dobby-soln
+all: $(PROGRAMS)
+
+O ?= 2
+include ../common/rules.mk
+
+%.o: %.c $(BUILDSTAMP)
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(DEPCFLAGS) $(O) -o $@ -c $<
+
+$(PROGRAMS): %: %.o
+	$(CC) $(CFLAGS) -pthread $(O) -o $@ $^
+
+clean:
+	rm -f *.o *.core $(PROGRAMS)
+	rm -rf $(DEPSDIR) *.dSYM
+
+.PHONY: all clean

synch1x/dobby.c

@@ -0,0 +1,68 @@
+// Solves the dobby-the-elf and the house elf problem
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define NELVES 25
+#define RANDOM_INT(lo, hi) ((int)(lo + ((double)random() / RAND_MAX) * (hi - lo + 1)))
+
+
+// The argument is simply the elf's ID number
+void *
+elf_thread(void *arg)
+{
+    long long id;
+
+    id = (long long)arg;
+
+    // Prepare sumptious feast
+    usleep(RANDOM_INT(1,1000));
+    printf("Elf %lld prepared sumptious feast!\n", id);
+  
+    // Clean up after messy Hogwarts students
+    usleep(RANDOM_INT(1,1000));
+    printf("Elf %lld cleaned up after messy students!\n", id);
+   
+    // Say, "Harry Potter is the greatest Wizard Ever."
+    usleep(RANDOM_INT(1,1000));
+    printf("Elf %lld: Harry Potter is the greatest Wizard Ever!\n", id);
+
+    return (NULL);
+}
+
+int
+main(void)
+{
+    pthread_t *thread_ids;
+
+    // Create the elf threads -- malloc space to capture their IDs because
+    // we'll check that they all exited at the end.
+    thread_ids = malloc(sizeof(pthread_t) * NELVES);
+    if (thread_ids == NULL) {
+        fprintf(stderr, "Dobby: Malloc of elf thread ids failed %s\n",
+	    strerror(errno));
+        exit (1);
+    }
+
+    for (long long i = 0; i < NELVES; i++) {
+        if (pthread_create(thread_ids + i, NULL, &elf_thread, (void *)i) != 0) {
+            fprintf(stderr, "Dobby: pthread_create %lld failed %s\n",
+	        i, strerror(errno));
+            exit(1);
+        }
+    }
+
+    // TODO: Figure out how to wait on elves and when to print out Dobby's
+    // message. (You'll have to figure out how to get the thing to place here
+    // for the elf's ID number, then you can uncomment this.)
+    // printf("Thanks for your work, Elf %d!\n", IDNUM);
+
+    free(thread_ids);
+
+    printf("Dobby is done\n");
+}
+