[Original] Teach you how to design multiple threads in Linux-multi-thread programming in Linux (2)

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[Original] Teach you how to design multiple threads in Linux (1)
-- Multi-thread programming in Linux Original Author: frozen_socker (popsicle) E_mail: dlskyfly@163.com

Next, let's look at the other two important functions pthread_exit and pthread_join.

The function prototype is as follows:

Void pthread_exit (void * value_ptr );

 

 

The termination of a thread can be a call to pthread_exit or the end of the thread's routine. That is to say, a thread can exit implicitly or explicitly call the pthread_exit function.

 

 

The unique parameter value_ptr of the pthread_exit function is the return code of the function. As long as the second parameter value_ptr in pthread_join is not null, this value is passed to value_ptr.

The function prototype is as follows:

Int pthread_join (pthread_t thread, void ** value_ptr );

 

The function pthread_join is used to wait for a thread to terminate.

 

 

The thread that calls pthread_join will be suspended until the end of the thread represented by the parameter thread. Pthread_join is a thread blocking function. The function called by pthread_join will wait until the end of the waiting thread.

If value_ptr is not null, the return value of the thread is stored at the position pointed to by the pointer. The returned value can be the value given by pthread_exit, or pthread_canceled is returned if the thread is canceled.

 

 
When a non-detached thread is terminated, its memory resources (thread Descriptor and stack) will not be released until a thread uses pthread_join for it. Therefore, a pthread_join call must be called for each non-detached thread created to avoid Memory leakage. Otherwise, when the thread is detachable, calling pthread_exit will terminate the call thread and release all resources without waiting for it to terminate.

 

 

At most one thread can wait for the specified thread to terminate. If a thread is already waiting for the thread to terminate, calling pthread_join again to wait for the same thread will return an error.

// Example_2.c
# Include <stdio. h>
# Include <pthread. h>

Void * pthread_func_test (void * Arg );

Int main ()
...{
Pthread_t pt1, pt2;
Pthread_create (& pt1, null, pthread_func_test, "this is the thread_one ");
Pthread_create (& pt2, null, pthread_func_test, "this is the thread_two ");
Pthread_join (pt1, null );
Pthread_join (pt2, null); // What happens if this row is not written? Or write pthread_join (pt1, null); what will happen?
}

Void * pthread_func_test (void * Arg)
...{
Printf ("% s", ARG );
Pthread_exit (null); // explicit declaration
}

 

So far, we have learned three important functions: Create, exit, and join. Next, we will continue to explain the thread mutex problem in multi-thread programming.