Add initial lab 4

Lab4/.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

Lab4/.idea/Lab4.iml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module classpath="CMake" type="CPP_MODULE" version="4" />

Lab4/.idea/codeStyles/codeStyleConfig.xml

@@ -0,0 +1,5 @@
+<component name="ProjectCodeStyleConfiguration">
+  <state>
+    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default" />
+  </state>
+</component>

Lab4/.idea/misc.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CMakeWorkspace" PROJECT_DIR="$PROJECT_DIR$" />
+</project>

Lab4/.idea/modules.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/Lab4.iml" filepath="$PROJECT_DIR$/.idea/Lab4.iml" />
+    </modules>
+  </component>
+</project>

Lab4/.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$/.." vcs="Git" />
+  </component>
+</project>

Lab4/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.22)
+project(Lab4 C)
+
+set(CMAKE_C_STANDARD 99)
+
+add_executable(Lab4 Lab4.c)

Lab4/Lab4.c

@@ -0,0 +1,100 @@
+/*
+ * Question 2: You see the number 1 most of the time. It is sometimes different because there are periods of time when the threads are reading/writing to the same place, but with the number of increments being 100, it is not likely that the threads will be reading/writing at the same time. In the CPU what happens is that a value is loaded into a register, while another thread completes a task, and then the value is written back to the memory. This leads to missing increments/decrements.
+ *
+ * Question 4: You see the number 1 often. Since the number of increments is 1000, the chance has increased for threads to be reading/writing at the same time. This leads to more missing increments/decrements.
+ *
+ * Question 6: You see the number 1 almost never. The number of loops at this point almost guarantees that the threads will be reading/writing at the same time, and the counter missing increments/decrements.
+ *
+ * Question 8: The number 1 is the only thing displayed. This is because the mutex lock ensures that the threads will not be reading/writing at the same time, and the counter will not miss increments/decrements. When another thread tried to lock the mutex, it waits for it to first become unlocked, ensuring proper thread synchronization.
+ */
+
+
+#include<pthread.h>
+#include<stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <semaphore.h>
+
+#define RANDOM_WITHIN_RANGE(a, b, seed) (rand_r(&seed)%b+a)
+
+int gv = 1;
+pthread_mutex_t mutex;
+sem_t sem;
+
+#define loop 10000
+
+void *inc() {
+	for (int i = 0; i < loop; i++) {
+		pthread_mutex_lock(&mutex);
+		gv++;
+		pthread_mutex_unlock(&mutex);
+	}
+}
+
+void *dec() {
+	for (int i = 0; i < loop; i++) {
+		pthread_mutex_lock(&mutex);
+		gv--;
+		pthread_mutex_unlock(&mutex);
+	}
+}
+
+void *minus() {
+	int i = 0;
+	for (i = 0; i < 10; i++) {
+		printf("-");
+		sem_wait(&sem);
+	}
+	return NULL;
+}
+
+void *plus(void *argg) {
+	unsigned int seed = *((unsigned int *) argg);
+	int interval = RANDOM_WITHIN_RANGE(100000, 500000, seed);
+	int i = 0;
+
+	for (i = 0; i < 10; i++) {
+		printf("+");
+		//usleep(interval);
+		sem_post(&sem);
+	}
+	return NULL;
+}
+
+int main(int argc, char **argv) {
+	setvbuf(stdout, NULL, _IONBF, 0);
+	int i = 0;
+
+	// Init Mutex
+	pthread_mutex_init(&mutex, NULL);
+	// Create thread pool and run threads
+	pthread_t thread[2];
+	pthread_create(&thread[i], NULL, &inc, NULL);
+	pthread_create(&thread[i + 1], NULL, &dec, NULL);
+	// Wait for threads to finish
+	pthread_join(thread[i], NULL);
+	pthread_join(thread[i + 1], NULL);
+	// Destroy Mutex
+	pthread_mutex_destroy(&mutex);
+	// Print final value
+	printf("%d\n", gv);
+
+	// Init Semaphore
+	sem_init(&sem, 0, 0);
+	for (i = 0; i < 1; i++) {
+		unsigned int *t = (unsigned int *) malloc(sizeof(unsigned int));
+		*t = rand();
+
+		pthread_create(&(thread[i]), NULL, &plus, (void *) t);
+		pthread_create(&(thread[i + 1]), NULL, &minus, NULL);
+
+		pthread_join(thread[i], NULL);
+		pthread_join(thread[i + 1], NULL);
+	}
+	sem_destroy(&sem);
+
+	return 0;
+}
+//TODO: Delete this comment
+//Semaphore doesn't work because it increments the semaphore all at once before the other thread even gets the chance to print
+//Just as an example to fix it you would need two semaphores so you can signal back and forth between the two threads

Lab4/run.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+while :
+  do
+  output=$(./build/Lab4)
+  if [ "$output" != "1" ]; then
+    echo "$output"
+  fi
+  done