Using pthread_self to find the thread id

Every thread created using pthread_create gets assigned a uniue thread id, with which it is recognized.

Note: Refer to creation of threads using pthreads in the post " "

The parent gets to know the thread id after the pthread_create is executed sucessfully, but while executing the thread if we want to access the thread id we have to use the function pthread_self.

The function pthread_self does not take any arguments, and returns the thread id, which is of kind pthread_t.

In the following program we are creating a thread which executes the function "hello". In the function "hello" we have used pthread_self to find out the thread id and then printed the same. Note that pthread_t is an unsigned long data type and hence we have to use %u while printing using printf.

#include <stdio.h> #include <pthread.h> #include <stdlib.h> void * hello(void *temp) { char *ret; ret="Finished"; pthread_t self_id; self_id=pthread_self(); printf("\nHello from thread %u\n",self_id); return ret; } main() { pthread_t thread_id,thread_id1; pthread_attr_t attr; int ret; void *res; ret=pthread_create(&thread_id,NULL,&hello,NULL); printf("\nCreated thread %u", thread_id); pthread_join(thread_id,&res); printf("Thread returned: %s \n",(char *)res); }

Save the file as self_pthread.c

Compile it using gcc by passing the "-lpthread" flag.

cc -lpthread self_pthread.c -o self_pthread ./self_ptherad Created thread 3076365168 Hello from thread 3076365168 Thread returned: Finished

We can see that the thread_id printed by the main function, parent, and the thread are the same, indicating that the value returned by pthread_self is the correct value.