Editing RTLinux (section)

== Threads ==
RT-Linux implements a POSIX API for a thread's manipulation. A thread is created by calling the <code>pthread_create</code> function. The third parameter of <code>pthread_create</code> is a function which contains the code executed by the thread.

It is necessary to set thread priorities in RTLinux. Threads with higher priorities can preempt threads with lower priorities. For example, we can have a thread controlling a stepper motor. In order to move the motor fluently, it is necessary to start this thread in strictly regular intervals. This can be guaranteed by assigning a high priority to this thread. The example threads2.c sets different thread priorities. Setting of thread priority is done by code shown below:

<syntaxhighlight lang="C">
int init_module(void)
{
    pthread_attr_t attr;
    struct sched_param param;
    pthread_attr_init(&attr);
    param.sched_priority = 1;
    pthread_attr_setschedparam(&attr, &param);
    pthread_create(&t1, &attr, &thread_code, "this is thread 1");
    rtl_printf("Thread 1 started\n");
    /* ... */
}
</syntaxhighlight>

The output the program is as follows.

<pre>
Thread 1 started
Thread 2 started
Thread 3 started
Message: this is thread 1
Message: this is thread 2
Message: this is thread 2
Message: this is thread 2
Message: this is thread 1
Message: this is thread 1
Message: this is thread 3
Message: this is thread 3
Message: this is thread 3
</pre>

The thread 2 has the highest priority and the thread 3 has the lowest priority. The first message is printed by the middle priority thread 1 because it is started a short time before the thread 2.