C Program to Show Thread Interface and Memory Consistency Errors
Last Updated :
28 Apr, 2025
Thread interface and Memory consistency errors are demonstrated in this program. Threads are a way for a program to split itself into two or more concurrently running tasks. This means that a program can perform multiple operations at the same time, rather than having to execute them one after the other.
However, if the program uses multiple threads, it can split the tasks into two threads: one thread to download the file, and another thread to display the progress bar. This way, the download and save operations can run concurrently with the progress bar updates, resulting in a faster and more responsive program.
A thread is a separate flow of execution in a program. This means that a program with multiple threads can have multiple parts that are executed concurrently. In the context of a C program, a threaded interface is a set of functions and data structures that allow the creation and management of threads.
Example:
C
// C program which uses two threads to print "Hello" and
// "World" to the console simultaneously
#include <pthread.h>
#include <stdio.h>
// Function that will be executed by the first thread
void* hello_thread_function(void* arg)
{
// Print "Hello" to the console
printf("Hello\n");
// Return NULL to indicate successful execution of the
// thread
return NULL;
}
// Function that will be executed by the second thread
void* world_thread_function(void* arg)
{
// Print "World" to the console
printf("World\n");
// Return NULL to indicate successful execution of the
// thread
return NULL;
}
int main()
{
// Create the first thread
pthread_t hello_thread;
pthread_create(&hello_thread, NULL,
hello_thread_function, NULL);
// Create the second thread
pthread_t world_thread;
pthread_create(&world_thread, NULL,
world_thread_function, NULL);
// Wait for the first thread to finish execution
pthread_join(hello_thread, NULL);
// Wait for the second thread to finish execution
pthread_join(world_thread, NULL);
// Return success
return 0;
}
Output:
Hello
World
Explanation: In this program, we have used the pthread_create() function to create two threads that execute the hello_thread_function and world_thread_function functions, respectively. These functions simply print "Hello" and "World" to the console.
Since the two threads run concurrently, the output of this program may be either "Hello\nWorld\n" or "World\nHello\n", depending on which thread finishes first. This is because the two threads are independent and there is no guarantee about the order in which they will be executed.
One potential problem with using threads is that they can introduce memory consistency errors. This happens when multiple threads try to access and modify the same memory location simultaneously, without proper synchronization. For example, if two threads try to increment the same counter at the same time, one of the updates may be lost, resulting in an incorrect final value of the counter.
Memory Consistency Errors
Memory consistency errors are a type of runtime error that can occur in programs with multiple threads. These errors occur when different threads have inconsistent views of the program's memory, resulting in unexpected behavior or runtime errors.
Example:
C
// C program to demonstrates the
// use of threads and memory
// consistency errors
#include <pthread.h>
#include <stdio.h>
// Global variable shared by all threads
int shared_var = 0;
// Function executed by the first thread
void* thread_func1(void* arg)
{
// Increment the shared variable by 1
shared_var++;
// Print the value of the shared variable
printf("Thread 1: shared_var = %d\n", shared_var);
return NULL;
}
// Function executed by the second thread
void* thread_func2(void* arg)
{
// Increment the shared variable by 1
shared_var++;
// Print the value of the shared variable
printf("Thread 2: shared_var = %d\n", shared_var);
return NULL;
}
int main(int argc, char* argv[])
{
pthread_t thread1, thread2;
// Create the first thread
if (pthread_create(&thread1, NULL, thread_func1, NULL)
!= 0) {
fprintf(stderr, "Error creating thread 1\n");
return 1;
}
// Create the second thread
if (pthread_create(&thread2, NULL, thread_func2, NULL)
!= 0) {
fprintf(stderr, "Error creating thread 2\n");
return 1;
}
// Wait for the threads to finish
if (pthread_join(thread1, NULL) != 0) {
fprintf(stderr, "Error joining thread 1\n");
return 1;
}
if (pthread_join(thread2, NULL) != 0) {
fprintf(stderr, "Error joining thread 2\n");
return 1;
}
return 0;
}
Output:
Thread 1: shared_var = 1
Thread 2: shared_var = 2
Explanation: This program creates two threads, each of which increments a shared variable by 1, and then prints its value. Since the threads access and modify the shared variable simultaneously, there is a potential for memory consistency errors. Depending on the order in which the threads are executed, the final value of the shared variable may not be what we expect.
Example 2:
C
// C program to create a global variable shared_counter
// that will be shared among the threads. Each thread will
// increment this variable by 1, and then print its thread
// ID and the updated value of shared_counter.
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
// Global variable that will be shared among threads
int shared_counter = 0;
// Function that will be executed by each thread
void* thread_function(void* thread_id)
{
// Get the thread ID
pthread_t tid = (pthread_t)thread_id;
// Increment the shared counter
shared_counter++;
// Print the thread ID and the updated value of the
// shared counter
printf("Thread %ld: shared_counter = %d\n", (long)tid,
shared_counter);
// Return NULL to indicate successful execution of the
// thread
return NULL;
}
int main(int argc, char* argv[])
{
// Check if the number of arguments is correct
if (argc != 2) {
printf("Usage: %s <number_of_threads>\n", argv[0]);
exit(EXIT_FAILURE);
}
// Get the number of threads to create from the command
// line arguments
int num_threads = atoi(argv[1]);
// Create an array of pthread_t structures to store the
// thread IDs
pthread_t* threads = (pthread_t*)malloc(
num_threads * sizeof(pthread_t));
// Create the specified number of threads
for (int i = 0; i < num_threads; i++) {
int status = pthread_create(&threads[i], NULL,
thread_function,
(void*)threads[i]);
if (status != 0) {
printf("Error: pthread_create() returned error "
"code %d\n",
status);
exit(EXIT_FAILURE);
}
}
// Wait for all threads to finish execution
for (int i = 0; i < num_threads; i++) {
int status = pthread_join(threads[i], NULL);
if (status != 0) {
printf("Error: pthread_join() returned error "
"code %d\n",
status);
exit(EXIT_FAILURE);
}
}
// Free the memory allocated for the thread IDs
free(threads);
// Print the final value of the shared counter
printf("Final value of shared_counter: %d\n",
shared_counter);
// Return success
return 0;
}
Output:
Thread 0: shared_counter = 1
Thread 1: shared_counter = 2
Thread 2: shared_counter = 3
Thread 3: shared_counter = 4
Final value of shared_counter: 4
Explanation: When multiple threads try to access and modify the same variable simultaneously, there is a potential for memory consistency errors to occur. For example, if two threads try to increment shared_counter at the same time, one of the updates may be lost.
The output of the code will depend on the value of num_threads passed as a command line argument. The code will create num_threads threads and each thread will increment the shared variable shared_counter by 1. At the end, the final value of shared_counter will be printed.For example, if num_threads is 4, the output may look like this:
To avoid memory consistency errors, we need to use synchronization mechanisms such as mutexes or semaphores to ensure that only one thread can access and modify the shared memory at a time. There are several approaches that can be used to detect thread interface and memory consistency errors in a program. Some of these approaches include:
- Using a thread-safe programming language or libraries: One way to avoid thread interface and memory consistency errors is to use a programming language or libraries that are specifically designed to be thread-safe. This means that the language or libraries provide built-in mechanisms to ensure that threads do not interfere with each other's data and that memory is consistently accessed by all threads.
- Using synchronization mechanisms: Another approach to avoid thread interface and memory consistency errors is to use synchronization mechanisms such as mutexes, semaphores, and monitors. These mechanisms allow threads to coordinate their access to shared data and ensure that only one thread is able to access the data at a given time. This can prevent race conditions and other types of thread interface and memory consistency errors.
- Using transactions: In some cases, it may be possible to use transactions to ensure that memory accesses by multiple threads are atomic and consistent. Transactions allow multiple memory accesses to be treated as a single, indivisible operation, which can help prevent thread interface and memory consistency errors.
- Using static analysis tools: There are also a number of static analysis tools that can be used to automatically detect thread interface and memory consistency errors in a program. These tools use a variety of techniques, such as symbolic execution and data flow analysis, to identify potential issues in a program and provide suggestions for how to fix them.
Overall, the key to avoiding thread interface and memory consistency errors is to carefully design and implement your program to ensure that threads do not interfere with each other's data and that memory is consistently accessed by all threads. This may involve using a thread-safe programming language or libraries, synchronization mechanisms, transactions, or static analysis tools, depending on the specific needs of your program.
Example:
C
// C program to use a mutex to avoid memory consistency
// errors
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
// Global variable that will be shared among threads
int shared_counter = 0;
// Mutex to protect the shared counter
pthread_mutex_t shared_counter_mutex
= PTHREAD_MUTEX_INITIALIZER;
// Function that will be executed by each thread
void* thread_function(void* thread_id)
{
// Get the thread ID
long tid = (long)thread_id;
// Lock the mutex to protect the shared counter
pthread_mutex_lock(&shared_counter_mutex);
// Increment the shared counter
shared_counter++;
// Print the thread ID and the updated value of the
// shared counter
printf("Thread %ld: shared_counter = %d\n", tid,
shared_counter);
// Unlock the mutex
pthread_mutex_unlock(&shared_counter_mutex);
// Return NULL to indicate successful execution of the
// thread
return NULL;
}
int main(int argc, char* argv[])
{
// Check if the number of arguments is correct
if (argc != 2) {
printf("Usage: %s <number_of_threads>\n", argv[0]);
exit(EXIT_FAILURE);
}
// Get the number of threads to create from the command
// line arguments
int num_threads = atoi(argv[1]);
// Create an array of pthread_t structures to store the
// thread IDs
pthread_t* threads = (pthread_t*)malloc(
num_threads * sizeof(pthread_t));
// Create the specified number of threads
for (int i = 0; i < num_threads; i++) {
int status = pthread_create(
&threads[i], NULL, thread_function, (void*)i);
if (status != 0) {
printf("Error: pthread_create() returned error "
"code %d\n",
status);
exit(EXIT_FAILURE);
}
}
// Wait for all threads to finish execution
for (int i = 0; i < num_threads; i++) {
int status = pthread_join(threads[i], NULL);
if (status != 0) {
printf("Error: pthread_join() returned error "
"code %d\n",
status);
exit(EXIT_FAILURE);
}
}
// Free the memory allocated for the thread IDs
free(threads);
// Print the final value of the shared counter
printf("Final value of shared_counter: %d\n",
shared_counter);
// Return success
return 0;
}
Output:
Explanation: In this program, we use the pthread_mutex_lock() and pthread_mutex_unlock() functions to protect the shared counter. When a thread wants to access the shared counter, it first locks the mutex, performs the necessary operations on the counter, and then unlocks the mutex. This ensures that only one thread can access the shared counter at a time, preventing memory consistency errors. In the example program, each thread first locks the mutex before incrementing the shared counter. This ensures that only one thread can increment the counter at a time and that the updates are not lost. When the thread is finished with the shared counter, it unlocks the mutex, allowing other threads to access and modify the counter. This ensures that the program maintains a consistent view of the shared memory and that all threads can work together to produce the correct final result.
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Implicit Return Type int in CIn C, every function has a return type that indicates the type of value it will return, and it is defined at the time of function declaration or definition. But in C language, it is possible to define functions without mentioning the return type and by default, int is implicitly assumed that the ret
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Callbacks in CIn C language, a callback is a function that is passed as an argument to another code, which is expected to call back (execute) the argument at a given time. In simple terms, a callback is the process of passing a function (executable code) to another function as an argument, which is then called by
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Nested Functions in CNesting of functions refers to placing the definition of the function inside another functions. In C programming, nested functions are not allowed. We can only define a function globally.Example:C#include <stdio.h> int main() { void fun(){ printf("GeeksForGeeks"); } fun(); return 0; }Outputmai
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Variadic Functions in CIn C, variadic functions are functions that can take a variable number of arguments. This feature is useful when the number of arguments for a function is unknown. It takes one fixed argument and then any number of arguments can be passed.Let's take a look at an example:C#include <stdio.h> #in
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_Noreturn function specifier in CIn C, the _Noreturn specifier is used to indicate that a function does not return a value. It tells the compiler that the function will either exit the program or enter an infinite loop, so it will never return control to the calling function. This helps the compiler to optimize code and issue warni
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Predefined Identifier __func__ in CBefore we start discussing __func__, let us write some code snippets and anticipate the output: C // C program to demonstrate working of a // Predefined Identifier __func__ #include <stdio.h> int main() { // %s indicates that the program will read strings printf("%s", __func__); return 0; } Ou
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C Library math.h FunctionsThe math.h header defines various C mathematical functions and one macro. All the functions available in this library take double as an argument and return double as the result. Let us discuss some important C math functions one by one. C Math Functions1. double ceil (double x) The C library functio
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C Arrays & Strings
C ArraysAn array in C is a fixed-size collection of similar data items.Items are stored in contiguous memory locations. Can be used to store the collection of primitive data types such as int, char, float, etc., as well as derived and user-defined data types such as pointers, structures, etc.C// A simple C
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Properties of Array in CThe properties of the arrays vary in different programming languages. In this article, we will study the different properties of Array in the C programming language.1. Fixed Size of an ArrayIn C, the size of an array is fixed after its declaration. It should be known at the compile time and it canno
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Multidimensional Arrays in C - 2D and 3D ArraysA multi-dimensional array in C can be defined as an array that has more than one dimension. Having more than one dimension means that it can grow in multiple directions. Some popular multidimensional arrays include 2D arrays which grows in two dimensions, and 3D arrays which grows in three dimension
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Initialization of Multidimensional Array in CIn C, multidimensional arrays are the arrays that contain more than one dimensions. These arrays are useful when we need to store data in a table or matrix-like structure. In this article, we will learn the different methods to initialize a multidimensional array in C. The easiest method for initial
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Pass Array to Functions in CPassing an array to a function allows the function to directly access and modify the original array. In this article, we will learn how to pass arrays to functions in C.In C, arrays are always passed to function as pointers. They cannot be passed by value because of the array decay due to which, whe
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How to pass a 2D array as a parameter in C?A 2D array is essentially an array of arrays, where each element of the main array holds another array. In this article, we will see how to pass a 2D array to a function.The simplest and most common method to pass 2D array to a function is by specifying the parameter as 2D array with row size and co
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What are the data types for which it is not possible to create an array?In C, an array is a collection of variables of the same data type, stored in contiguous memory locations. Arrays can store data of primitive types like integers, characters, and floats, as well as user-defined types like structures.However, there are certain data types for which arrays cannot be dir
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How to pass an array by value in C ?In C programming, arrays are always passed as pointers to the function. There are no direct ways to pass the array by value. However, there is trick that allows you to simulate the passing of array by value by enclosing it inside a structure and then passing that structure by value. This will also p
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Strings in CA string is an array of characters terminated by a special character '\0' (null character). This null character marks the end of the string and is essential for proper string manipulation.Unlike many modern languages, C does not have a built-in string data type. Instead, strings are implemented as a
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Array of Strings in CIn C, an array of strings is a 2D array where each row contains a sequence of characters terminated by a '\0' NULL character (strings). It is used to store multiple strings in a single array.Let's take a look at an example:C#include <stdio.h> int main() { // Creating array of strings for 3 str
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What is the difference between single quoted and double quoted declaration of char array?In C programming, the way we declare and initialize a char array can differ based on whether we want to use a sequence of characters and strings. They are basically same with difference only of a '\0' NULL character.Double quotes automatically include the null terminator, making the array a string l
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C String FunctionsC language provides various built-in functions that can be used for various operations and manipulations on strings. These string functions make it easier to perform tasks such as string copy, concatenation, comparison, length, etc. The <string.h> header file contains these string functions.st
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C Pointers
C PointersA pointer is a variable that stores the memory address of another variable. Instead of holding a direct value, it holds the address where the value is stored in memory. It is the backbone of low-level memory manipulation in C. Accessing the pointer directly will just give us the address that is stor
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Pointer Arithmetics in C with ExamplesPointer Arithmetic is the set of valid arithmetic operations that can be performed on pointers. The pointer variables store the memory address of another variable. It doesn't store any value. Hence, there are only a few operations that are allowed to perform on Pointers in C language. The C pointer
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C - Pointer to Pointer (Double Pointer)In C, double pointers are those pointers which stores the address of another pointer. The first pointer is used to store the address of the variable, and the second pointer is used to store the address of the first pointer. That is why they are also known as a pointer to pointer.Let's take a look at
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Function Pointer in CIn C, a function pointer is a type of pointer that stores the address of a function, allowing functions to be passed as arguments and invoked dynamically. It is useful in techniques such as callback functions, event-driven programs, and polymorphism (a concept where a function or operator behaves di
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How to Declare a Pointer to a Function?A pointer to a function is similar to a pointer to a variable. However, instead of pointing to a variable, it points to the address of a function. This allows the function to be called indirectly, which is useful in situations like callback functions or event-driven programming.In this article, we w
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Pointer to an Array | Array PointerA pointer to an array is a pointer that points to the whole array instead of the first element of the array. It considers the whole array as a single unit instead of it being a collection of given elements.Example:C #include<stdio.h> int main() { int arr[5] = { 1, 2, 3, 4, 5 }; int *ptr = arr;
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Difference between constant pointer, pointers to constant, and constant pointers to constantsIn this article, we will discuss the differences between constant pointer, pointers to constant & constant pointers to constants. Pointers are the variables that hold the address of some other variables, constants, or functions. There are several ways to qualify pointers using const. Pointers to
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Pointer vs Array in CMost of the time, pointer and array accesses can be treated as acting the same, the major exceptions being:  1. the sizeof operator sizeof(array) returns the amount of memory used by all elements in the array sizeof(pointer) only returns the amount of memory used by the pointer variable itself 2.
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Dangling, Void , Null and Wild Pointers in CIn C programming pointers are used to manipulate memory addresses, to store the address of some variable or memory location. But certain situations and characteristics related to pointers become challenging in terms of memory safety and program behavior these include Dangling (when pointing to deall
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Near, Far and Huge Pointers in CIn older times, the intel processors had 16-bit registers, but the address bus was 20-bits wide. Due to this, CPU registers were not able to hold the entire address at once. As a solution, the memory was divided into segments of 64 kB size, and the near pointers, far pointers, and huge pointers were
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restrict Keyword in CThe restrict keyword is a type qualifier that was introduced in the C99 standard. It is used to tell the compiler that a pointer is the only reference or access point to the memory it points to, allowing the compiler to make optimizations based on that information.Let's take a look at an example:C#i
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