pthread_join - join with a terminated thread

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ pthread_join()                                                              │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       The  pthread_join()  function  waits for the thread specified by thread to terminate.  If that thread has
       already terminated, then pthread_join() returns immediately.  The thread  specified  by  thread  must  be
       joinable.

       If  retval  is not NULL, then pthread_join() copies the exit status of the target thread (i.e., the value
       that the target thread supplied to pthread_exit(3)) into the location  pointed  to  by  retval.   If  the
       target thread was canceled, then PTHREAD_CANCELED is placed in the location pointed to by retval.

       If  multiple  threads simultaneously try to join with the same thread, the results are undefined.  If the
       thread calling pthread_join() is canceled, then the target thread will remain joinable (i.e., it will not
       be detached).

EDEADLK
              A deadlock was detected (e.g., two threads tried to join with each other); or thread specifies the
              calling thread.

       EINVALthread is not a joinable thread.

       EINVAL Another thread is already waiting to join with this thread.

       ESRCH  No thread with the ID thread could be found.

       See pthread_create(3).

       POSIX.1-2001.

       POSIX threads library (libpthread, -lpthread)

       pthread_join - join with a terminated thread

       After a successful call  to  pthread_join(),  the  caller  is  guaranteed  that  the  target  thread  has
       terminated.   The  caller  may  then  choose to do any clean-up that is required after termination of the
       thread (e.g., freeing memory or other resources that were allocated to the target thread).

       Joining with a thread that has previously been joined results in undefined behavior.

       Failure to join with a thread that is joinable (i.e., one that  is  not  detached),  produces  a  "zombie
       thread".   Avoid  doing  this,  since  each zombie thread consumes some system resources, and when enough
       zombie threads have accumulated, it will no longer be possible to create new threads (or processes).

       There is no pthreads analog of waitpid(-1,&status,0), that is, "join with any terminated  thread".   If
       you believe you need this functionality, you probably need to rethink your application design.

       All of the threads in a process are peers: any thread can join with any other thread in the process.

       On success, pthread_join() returns 0; on error, it returns an error number.

pthread_cancel(3),    pthread_create(3),   pthread_detach(3),   pthread_exit(3),   pthread_tryjoin_np(3),
       pthreads(7)

Linux man-pages 6.9.1                              2024-05-02                                    pthread_join(3)

       POSIX.1-2008.

#include<pthread.h>intpthread_join(pthread_tthread,void**retval);