How to make a thread wait for another one in linux?

@benny_schoen 

In Linux, you can make a thread wait for another thread using synchronization mechanisms like condition variables or semaphores. The following steps outline how you can achieve this:

1. Include the necessary header files.

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#include <pthread.h>

1. Declare the necessary variables, such as a mutex and a condition variable.

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pthread_mutex_t mutex;
pthread_cond_t condition;

1. Initialize the mutex and condition variable before creating the threads.

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pthread_mutex_init(&mutex, NULL);
pthread_cond_init(&condition, NULL);

1. Create the threads, passing the necessary arguments.

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pthread_t thread1, thread2;
pthread_create(&thread1, NULL, function1, NULL);
pthread_create(&thread2, NULL, function2, NULL);

1. Implement the waiting logic in one of the threads. In this example, thread1 waits for thread2.

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void* function1(void* arg) {
  // Perform some work
  
  pthread_mutex_lock(&mutex);
  pthread_cond_wait(&condition, &mutex);
  pthread_mutex_unlock(&mutex);
  return NULL;
}

1. Implement the trigger logic in the other thread. In this example, thread2 signals thread1 to proceed.

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void* function2(void* arg) {
  // Perform some work
  
  pthread_mutex_lock(&mutex);
  pthread_cond_signal(&condition);
  pthread_mutex_unlock(&mutex);
  return NULL;
}

1. Wait for the threads to finish executing.

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pthread_join(thread1, NULL);
pthread_join(thread2, NULL);

1. Cleanup and destroy the mutex and condition variable.

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pthread_mutex_destroy(&mutex);
pthread_cond_destroy(&condition);

By using these synchronization mechanisms, you can ensure that one thread waits for another to reach a certain point before continuing execution.

@benny_schoen 

It's important to note that this example demonstrates how to make one thread wait for another using condition variables. You can also achieve thread synchronization using other mechanisms like semaphores or barriers, depending on your specific requirements.

Additionally, consider error handling and thread safety while implementing thread synchronization in your Linux application. Proper synchronization mechanisms help prevent race conditions and data inconsistencies between threads.