Let's take a look at some examples. We'll assume that the proper include files (<pthread.h> and <sched.h>) have been included, and that the thread to be created is called new_thread() and is correctly prototyped and defined.
The most common way of creating a thread is to simply let the values default:
pthread_create (NULL, NULL, new_thread, NULL);
In the above example, we've created our new thread with the defaults, and passed it a NULL as its one and only parameter (that's the third NULL in the pthread_create() call above).
Generally, you can pass anything you want (via the arg field) to your new thread. Here we're passing the number 123:
pthread_create (NULL, NULL, new_thread, (void *) 123);
A more complicated example is to create a non-joinable thread with round-robin scheduling at priority 15:
pthread_attr_t attr; // initialize the attribute structure pthread_attr_init (&attr); // set the detach state to "detached" pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED); // override the default of INHERIT_SCHED pthread_attr_setinheritsched (&attr, PTHREAD_EXPLICIT_SCHED); pthread_attr_setschedpolicy (&attr, SCHED_RR); attr.param.sched_priority = 15; // finally, create the thread pthread_create (NULL, &attr, new_thread, NULL);
To see what a multithreaded program “looks like,” you could run the pidin command from the shell. Say our program was called spud. If we run pidin once before spud created a thread and once after spud created two more threads (for three total), here's what the output would look like (I've shortened the pidin output to show only spud):
# pidin pid tid name prio STATE Blocked 12301 1 spud 10r READY # pidin pid tid name prio STATE Blocked 12301 1 spud 10r READY 12301 2 spud 10r READY 12301 3 spud 10r READY
As you can see, the process spud (process ID 12301) has three threads (under the “tid” column). The three threads are running at priority 10 with a scheduling algorithm of round robin (indicated by the “r” after the 10). All three threads are READY, meaning that they're able to use CPU but aren't currently running on the CPU (another, higher-priority thread, is currently running).
Now that we know all about creating threads, let's take a look at how and where we'd use them.