C language multi-threaded programming: core knowledge analysis and practical questions answering

C language multi-threaded programming is implemented through the POSIX thread library, and its core includes thread creation, thread synchronization and thread termination. Thread creation uses the pthread_create() function. The thread synchronization mechanism includes mutexes, conditional variables and semaphores. The thread can be terminated through pthread_exit(), pthread_cancel() and pthread_join(). In practical examples, create and run multi-threaded programs, use mutexes to protect shared data, and ensure thread-safe access.

C language multi-threaded programming: core knowledge analysis and practical questions answering

introduction

Multithreaded programming is a concurrent programming technology that allows multiple tasks to be performed simultaneously within one application. In C, multithreading programming can be performed using the POSIX threads library.

Core knowledge analysis

Thread creation

To create a thread, you can use pthread_create() function:

 int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void *), void *arg);

• thread : used to store the ID of the newly created thread.
• attr : thread attribute, which can be initialized through pthread_attr_init() function.
• start_routine : The thread starts the function, specifying the code that the thread runs.
• arg : The argument passed to the startup function.

Thread synchronization

The thread synchronization mechanism is used to coordinate access and operations between multiple threads. Common methods include:

• Mutex : Ensure that only one thread accesses shared data at the same time.
• Condition variable : allows threads to pause execution until a specific condition is met.
• Semaphore : limits the number of threads that can access shared resources at the same time.

Thread termination

Threads can be terminated in a number of ways:

• pthread_exit() : terminated by the thread itself.
• pthread_cancel() : Cancel thread from outside.
• pthread_join() : Wait for thread to terminate.

Practical questions answer

How to create and run a multi-threaded program

 #include <stdio.h>
#include <pthread.h>

void *print_hello(void *arg) {
  printf("Hello from thread %d!\n", (int)arg);
  return NULL;
}

int main() {
  pthread_t tid;

  // Create a new thread pthread_create(&tid, NULL, print_hello, 0);

  // The main thread waits for the new thread to terminate pthread_join(tid, NULL);

  return 0;
}

How to use mutex to protect shared data

 #include <stdio.h>
#include <pthread.h>

// Global shared variable int shared_variable = 0;

// mutex pthread_mutex_t mutex;

void *increment_shared_variable(void *arg) {
  for (int i = 0; i < 100000; i ) {
    // Lock pthread_mutex_lock(&mutex);

    // Modify the shared_variable variable;

    // Unlock pthread_mutex_unlock(&mutex);
  }

  return NULL;
}

int main() {
  // Initialize the mutex pthread_mutex_init(&mutex, NULL);

  pthread_t tid1, tid2;

  // Create two threads pthread_create(&tid1, NULL, increment_shared_variable, NULL);
  pthread_create(&tid2, NULL, increment_shared_variable, NULL);

  // Wait for the thread to terminate pthread_join(tid1, NULL);
  pthread_join(tid2, NULL);

  printf("Shared variable: %d\n", shared_variable);

  // Destroy the mutex pthread_mutex_destroy(&mutex);

  return 0;
}

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