broken p/c solution plus README

threads-cv/Makefile

@@ -6,6 +6,7 @@ SRCS   := join.c \
 	join_no_lock.c \
 	join_no_state_var.c \
 	join_modular.c \
+	pc_single_cv.c \
 	pc.c
 
 OBJS   := ${SRCS:c=o}

threads-cv/README.md

@@ -0,0 +1,19 @@
+
+# Condition Variables
+
+Code examples from condition variables chapter. Build by typing `make`;
+run the resulting executable to see how it works. Insert `sleep()` calls
+of various lengths to control timing and force bad things to happen.
+
+## Fork/Join Problem
+
+- `join_spin.c`: Working solution but wastes CPU.
+- `join_no_lock.c`: What happens when you don't put a lock around the state change and signal
+- `join_no_state_var.c`: What happens if you don't have a state variable
+- `join.c`: A working solution
+- `join_modular.c`: A modularized version
+
+## Producer/Consumer Problem
+- `pc_single_cv.c`: What happens if you only use one condition variable
+- `pc.c`: A working solution
+

threads-cv/pc_single_cv.c

@@ -0,0 +1,108 @@
+#include <assert.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include "common.h"
+#include "common_threads.h"
+
+int max;
+int loops;
+int *buffer; 
+
+int use_ptr  = 0;
+int fill_ptr = 0;
+int num_full = 0;
+
+pthread_cond_t cv = PTHREAD_COND_INITIALIZER;
+pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
+
+int consumers = 1;
+int verbose = 1;
+
+
+void do_fill(int value) {
+    buffer[fill_ptr] = value;
+    fill_ptr = (fill_ptr + 1) % max;
+    num_full++;
+}
+
+int do_get() {
+    int tmp = buffer[use_ptr];
+    use_ptr = (use_ptr + 1) % max;
+    num_full--;
+    return tmp;
+}
+
+void *producer(void *arg) {
+    int i;
+    for (i = 0; i < loops; i++) {
+	Mutex_lock(&m);            // p1
+	while (num_full == max)    // p2
+	    Cond_wait(&cv, &m);    // p3
+	do_fill(i);                // p4
+	Cond_signal(&cv);          // p5
+	Mutex_unlock(&m);          // p6
+    }
+
+    // end case: put an end-of-production marker (-1) 
+    // into shared buffer, one per consumer
+    for (i = 0; i < consumers; i++) {
+	Mutex_lock(&m);
+	while (num_full == max) 
+	    Cond_wait(&cv, &m);
+	do_fill(-1);
+	Cond_signal(&cv);
+	Mutex_unlock(&m);
+    }
+
+    return NULL;
+}
+                                                                               
+void *consumer(void *arg) {
+    int tmp = 0;
+    // consumer: keep pulling data out of shared buffer
+    // until you receive a -1 (end-of-production marker)
+    while (tmp != -1) { 
+	Mutex_lock(&m);           // c1
+	while (num_full == 0)     // c2 
+	    Cond_wait(&cv, &m);   // c3
+	tmp = do_get();           // c4
+	Cond_signal(&cv);         // c5
+	Mutex_unlock(&m);         // c6
+    }
+    return NULL;
+}
+
+int
+main(int argc, char *argv[])
+{
+    if (argc != 4) {
+	fprintf(stderr, "usage: %s <buffersize> <loops> <consumers>\n", argv[0]);
+	exit(1);
+    }
+    max = atoi(argv[1]);
+    loops = atoi(argv[2]);
+    consumers = atoi(argv[3]);
+
+    buffer = (int *) malloc(max * sizeof(int));
+    assert(buffer != NULL);
+
+    int i;
+    for (i = 0; i < max; i++) {
+	buffer[i] = 0;
+    }
+
+    pthread_t pid, cid[consumers];
+    Pthread_create(&pid, NULL, producer, NULL); 
+    for (i = 0; i < consumers; i++) {
+	Pthread_create(&cid[i], NULL, consumer, (void *) (long long int) i); 
+    }
+    Pthread_join(pid, NULL); 
+    for (i = 0; i < consumers; i++) {
+	Pthread_join(cid[i], NULL); 
+    }
+    return 0;
+}
+