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Simple Multithreading Example in C

This is a simple C program that demonstrates multithreading using POSIX threads (pthreads).

Overview

The program creates 5 threads that run concurrently. Each thread:

  1. Receives a unique ID and message
  2. Prints a starting message
  3. Simulates work by sleeping for 1 second
  4. Prints a completion message
  5. Exits gracefully

The main thread waits for all threads to complete using pthread_join().

Files

  • multithreading_example.c - The main C source file

Prerequisites

  • GCC compiler (or another C compiler that supports pthreads)
  • POSIX threads library (usually included with most Linux/Unix systems)

On Debian/Ubuntu systems, install the required packages with:

sudo apt-get update
sudo apt-get install build-essential

Compilation

Compile the program using GCC with the -pthread flag:

gcc -pthread multithreading_example.c -o multithreading_example

The -pthread flag:

  • Links the pthread library
  • Defines necessary preprocessor macros
  • Ensures proper thread support

Execution

Run the compiled program:

./multithreading_example

Expected Output

The output will show threads executing concurrently. You'll see messages like:

Main: Starting multithreading example...

Main: Creating thread 1
Main: Creating thread 2
Main: Creating thread 3
Main: Creating thread 4
Main: Creating thread 5

Main: All threads created, waiting for them to complete...

Thread 1: Starting - Hello from thread
Thread 2: Starting - Hello from thread
Thread 3: Starting - Hello from thread
Thread 4: Starting - Hello from thread
Thread 5: Starting - Hello from thread
Thread 1: Finished work
Thread 2: Finished work
Thread 3: Finished work
Thread 4: Finished work
Thread 5: Finished work
Main: Thread 1 joined successfully
Main: Thread 2 joined successfully
Main: Thread 3 joined successfully
Main: Thread 4 joined successfully
Main: Thread 5 joined successfully

Main: All threads completed. Exiting program.

Note: The exact order of thread execution may vary between runs due to the nature of concurrent execution.

Key Concepts Demonstrated

  1. Thread Creation: Using pthread_create() to spawn new threads
  2. Thread Function: Each thread executes the thread_function
  3. Data Passing: Passing data to threads via structures
  4. Thread Synchronization: Using pthread_join() to wait for threads
  5. Concurrent Execution: Multiple threads running simultaneously

Thread Safety Notes

This example is designed to be simple and educational. In real-world applications, you would need to consider:

  • Race Conditions: Multiple threads accessing shared data
  • Mutexes: Using pthread_mutex_t to protect shared resources
  • Condition Variables: Using pthread_cond_t for thread communication
  • Thread-local Storage: Data that's local to each thread

Extending the Example

To modify the number of threads, change the NUM_THREADS macro at the top of the file:

#define NUM_THREADS 10  // Create 10 threads instead of 5

License

This is an educational example and is free to use.