stuff

Examples/concurrency/sem_list2.c

@@ -0,0 +1,99 @@
+/*
+ * sem_list2.c - Uses a semaphore as a way to control access
+ *               to a critical section for a singly linked list
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <semaphore.h>
+
+typedef struct node {
+	int val;
+	struct node* next;
+} node;
+
+typedef struct list {
+	node* head;
+} list;
+
+// shared global
+static list mylist;
+
+// start flag
+volatile int start = 0;
+
+// flag semaphore
+sem_t flag;
+
+// The thread process
+void* thread_routine()
+{
+	printf("Worker thread: %lu ready\n", pthread_self());
+	
+	// wait for start from master thread
+	while(start == 0);
+
+	for (int j = 0; j < 1000000; j++)
+	{
+		sem_wait(&flag);
+		node* new_node = malloc(sizeof(node));
+		new_node->val = j;
+		new_node->next = mylist.head;
+		mylist.head = new_node;
+		sem_post(&flag);
+	}
+
+	printf("Worker thread: %lu done\n", pthread_self());
+
+	return NULL;
+}
+
+// Main process
+int main()
+{
+	sem_init(&flag, 0, 1);
+
+	#define THREAD_COUNT 10
+	pthread_t thr_ids[THREAD_COUNT];
+
+	mylist.head = NULL;
+	
+    // Create the threads
+	for(int i = 0; i < THREAD_COUNT; i++) {
+		if(pthread_create(&thr_ids[i], NULL, thread_routine, NULL) == -1) {
+			printf("COULD NOT CREATE A THREAD\n");
+			exit(EXIT_FAILURE);
+		}
+	}
+
+    // Signal threads to start
+	start = 1;
+
+    // Wait for all threads to finish
+	for(int i = 0; i < THREAD_COUNT; i++) {
+		pthread_join(thr_ids[i],NULL);
+	}
+
+    // Count the elements in the list
+	int length = 0;
+	node* itr = mylist.head;
+	while(itr != NULL) {
+		length++;
+		itr = itr->next;
+	}
+	printf("List contains %d elements\n", length);
+
+    // Free the list
+	while(mylist.head != NULL) {
+		node* to_delete = mylist.head;
+        mylist.head = mylist.head->next;
+        free(to_delete);
+	}
+	
+    sem_destroy(&flag);
+
+	return EXIT_SUCCESS;
+}