POSIX create terminate thread

In this paper, the reference 《 The embedded Linux Development tutorial 》 and 《Linux/UNIX System programming manual 》.

Create thread

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

thread Used to point to the newly created thread ID;
attr Used to represent a property object that encapsulates various properties of a thread , If attr by NULL, New threads use the default properties ;
start_routine Is the name of the function called when the thread starts executing ;
arg Is the parameter start_routine Specify the parameters of the function .

Thread termination

The process can be terminated by directly calling exit()、 perform main() Medium return、 Or through some other thread of the process exit() To achieve . In any of the above cases , All threads will be terminated . If the main thread has no tasks to process after creating other threads , Then it should block the wait until all threads are finished , Or you should call pthread_exit(NULL).
call exit() The function terminates the entire process , And call pthread_exit() It will only cause the calling thread to terminate , At the same time, it executes at the top level of the created thread return The thread implicitly calls pthread_exit().

void pthread_exit(void *retval);

retval It's a void Pointer to type , You can treat the return value of a thread as pthread_exit() Parameters passed in , This value is also pthread_join() Treat as exit status . If the last thread of the process calls pthread_exit(), The process will return the value with the status 0 sign out .

Thread example

The main thread created 5 Threads , this 5 Threads execute concurrently with the main thread , After the main thread creates the thread, it calls pthread_exit() Function exit thread , Other threads are
Print the serial number of the current thread . When the main thread executes before other processes pthread_exit() when , The process will not exit , Only the last thread is completed , The process will exit .

[email protected]-virtual-machine:~/workspace/test$ cat sample.c 
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NUM_THREADS 5

void *PrintHello(void *threadid){
    	// Thread functions 
   long tid;
   tid = (long)threadid;
   printf("Hello World! It's me, thread #%ld!\n", tid);	// Print the parameters corresponding to the thread 
   pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
    
   pthread_t threads[NUM_THREADS];
   int rc;
   long t;
   for(t=0; t<NUM_THREADS; t++){
    	// Loop creation 5 Threads 
      printf("In main: creating thread %ld\n", t);
      rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);	// Create thread 
      if (rc){
    
         printf("ERROR; return code from pthread_create() is %d\n", rc);
         exit(-1);
      }
   }
   printf("In main: exit!\n");
   pthread_exit(NULL);	// Main thread exit 
}

Here are the results , The main thread in the program calls pthread_exit() Function does not terminate the entire process , But when the last thread calls pthread_exit() When the program finishes running .

[email protected]-virtual-machine:~/workspace/test$ gcc sample.c -o sample -[email protected]-virtual-machine:~/workspace/test$ ./sample
In main: creating thread 0
In main: creating thread 1
Hello World! It's me, thread #0!
Hello World! It's me, thread #1!
In main: creating thread 2
In main: creating thread 3
Hello World! It's me, thread #2!
In main: creating thread 4
Hello World! It's me, thread #3!
In main: exit!
Hello World! It's me, thread #4!
[email protected]-virtual-machine:~/workspace/test$