stuff

Examples/conditions/prod_con5.c

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+/*
+ * prod_con5.c - Producer and consumer with unlimited sized buffer
+ *               An attempt to fix the problem of a consumer removing
+ *               from an empty shared space when more than one item
+ *               is to be consumed by waiting in a while loop until
+ *               enough elements are in the space
+ *               Unfortunately causes deadlock since the consumer is 
+ *               holding the the mutex lock while waiting for more items
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <string.h>
+#include <pthread.h>
+#include <semaphore.h>
+
+#define ELEMENTS 100
+#define PRODUCER_COUNT 10
+#define CONSUMER_COUNT 5
+#define ORDER_COUNT 2
+
+int count = 0;
+
+// Semaphores for controlling access
+sem_t fullCount;
+
+pthread_mutex_t element_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+// Start flag
+volatile int start = 0;
+
+// Producer Routine
+void* producer()
+{
+    // wait for start from master thread
+    while(!start);
+
+    for(int i = 0; i < ELEMENTS; i++) {
+
+        pthread_mutex_lock(&element_mutex);
+
+        // Add an element
+        count++;
+        printf("Producer %lu added, count: %d\n", pthread_self(), count);
+
+        // Signal the consumer that there something to consume
+        sem_post(&fullCount);
+        pthread_mutex_unlock(&element_mutex);
+        usleep(200);
+    }
+
+    return NULL;
+}
+
+// Consumer Routine
+void* consumer()
+{
+    // wait for start from master thread
+    while(!start);
+
+    for(int i = 0; i < ELEMENTS; i++) {
+        // Wait for element to consume
+        sem_wait(&fullCount);
+
+        pthread_mutex_lock(&element_mutex);
+        while(count < ORDER_COUNT);
+
+        for(int j = 0; j < ORDER_COUNT; j++) {
+            // Remove an element from the buffer
+            if(count == 0) {
+                printf("ERROR: Customer %lu removed with no elements\n", pthread_self());
+                exit(EXIT_FAILURE);
+            }
+            count--;
+        }
+        pthread_mutex_unlock(&element_mutex);
+        usleep(50);
+    }
+
+    return NULL;
+}
+
+
+// Main thread
+int main()
+{
+    sem_init(&fullCount, 0, 0);
+
+    pthread_t prod[PRODUCER_COUNT];
+    pthread_t cons[CONSUMER_COUNT];
+    for(int i = 0; i < PRODUCER_COUNT; i++) {
+        if(pthread_create(&prod[i], NULL, producer, NULL) == -1) {
+            printf("COULD NOT CREATE PRODUCER\n");
+            exit(EXIT_FAILURE);
+        }
+    }
+    for(int i = 0; i < CONSUMER_COUNT; i++) {
+        if(pthread_create(&cons[i], NULL, consumer, NULL) == -1) {
+            printf("COULD NOT CREATE CONSUMER\n");
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    start = 1;
+
+    for(int i = 0; i < PRODUCER_COUNT; i++) {
+        pthread_join(prod[i], NULL);
+    }
+    for(int i = 0; i < CONSUMER_COUNT; i++) {
+        pthread_join(cons[i], NULL);
+    }
+
+    int expected_final_count = PRODUCER_COUNT*ELEMENTS - CONSUMER_COUNT*ELEMENTS;
+
+    printf("Final count is: %d, expected %d\n", count, expected_final_count);
+
+    sem_destroy(&fullCount);
+    pthread_mutex_destroy(&element_mutex);
+
+    return EXIT_SUCCESS;
+}