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.