C language multithreaded programming: a beginner's guide and troubleshooting

C Language Multithreading Programming Guide: Creating Threads: Use the pthread_create() function to specify thread ID, properties, and thread functions. Thread synchronization: Prevent data competition through mutexes, semaphores, and conditional variables. Practical case: Use multi-threading to calculate the Fibonacci number, assign tasks to multiple threads and synchronize the results. Troubleshooting: Solve problems such as program crashes, thread stop responses, and performance bottlenecks.

C Language Multithreaded Programming: A Newbie Guide and Troubleshooting

introduction

Multithreaded programming is a powerful technology that allows programs to perform multiple tasks in parallel. In C, multithreading is implemented using the POSIX threading library. This article will provide a guide to multithreaded programming for beginners in C languages ​​and answer some common difficult questions.

Create and run threads

To create a thread, you need to call pthread_create() function. It requires three parameters:

• Thread ID : A pointer to save the newly created thread ID
• Thread properties : Specify properties such as thread stack size and priority
• Thread function : a function to be executed by a thread

The following code creates a thread called my_thread() :

 #include <pthread.h>

void *my_thread(void *arg)
{
    // The code executed by the thread is returned NULL;
}

int main()
{
    pthread_t thread_id;

    pthread_create(&thread_id, NULL, my_thread, NULL);
    pthread_join(thread_id, NULL); // Wait for the thread to complete return 0;
}

Thread synchronization

When multiple threads access shared resources, synchronization is required to avoid data race. This can be achieved by:

• Mutex : Restricts only one thread to access shared resources at the same time.
• Semaphore : allows multiple threads to access shared resources at the same time, but limits the number of threads to access resources.
• Condition variable : allows threads to wait for a specific condition to be satisfied.

Practical cases

The following is a practical case of using multithreading to calculate Fibonacci sequences:

 #include <pthread.h>

#define NUM_THREADS 4
#define MAX_NUMBER 100

int fib_numbers[MAX_NUMBER];

void *calculate_fib_numbers(void *arg)
{
    int start = (int) arg;
    int end = start NUM_THREADS - 1;

    for (int i = start; i <= end; i )
        fib_numbers[i] = fib(i);

    return NULL;
}

int main()
{
    pthread_t threads[NUM_THREADS];

    for (int i = 0; i < NUM_THREADS; i )
        pthread_create(&threads[i], NULL, calculate_fib_numbers, (void *) (i * NUM_THREADS));

    for (int i = 0; i < NUM_THREADS; i )
        pthread_join(threads[i], NULL);

    // Print result for (int i = 0; i < MAX_NUMBER; i )
        printf("%d", fib_numbers[i]);

    return 0;
}

Troubleshooting

• The program crashes with the error "segment fault" : It may be that the memory area that the thread does not own. Make sure to use mutexes or other synchronization mechanisms to protect shared resources.
• Thread stops responding : It may be an infinite loop or other deadlock situation. Try to use a debugger or logging to find out the cause of the deadlock.
• Thread execution is too slow : it may be due to competition among threads or other performance bottlenecks. Try benchmarking the code and find out the slower points.

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