#include <rtl.h>

OS_RESULT os_mut_wait (
    OS_ID mutex,        /* The mutex to acquire */
    U16   timeout );    /* Length of time to wait */

The os_mut_wait function tries to acquire the mutex identified by the function argument. If the mutex has not been locked by another task, the calling task acquires and locks the mutex and might continue immediately. If the mutex has been locked by another task, then the RTX kernel puts the calling task to sleep until the mutex becomes unlocked or until the timeout expires.

The timeout argument can have any value between 0 and 0xFFFE. Set timeout to 0xFFFF for an indefinite timeout period. If a value of 0 has been specified, then the calling task continues immediately even if there is a higher priority task in the ready list.

This function also raises the priority of the owning task of the mutex, if it is lower than the priority of the calling task. This programming method is called priority inheritance and is used to eliminate priority inversion problems. When a mutex is released, the original priority of the owning task will be restored.

The os_mut_wait function is in the RL-RTX library. The prototype is defined in rtl.h.

Note

• Timeout is measured in number of system intervals.
• You must initialize the mutex object using the os_mut_init function before you can perform any operation on it.

The os_mut_wait function returns the completion value:

os_mut_init, os_mut_release

#include <rtl.h>

OS_MUT mutex1;

void f1 (void) {
  os_mut_wait (&mutex1, 0xffff);
   ..
  /* Critical region 1 */
   ..
  /* f2() will not block the task. */
  f2 ();
  os_mut_release (&mutex1);
}

void f2 (void) {
  os_mut_wait (&mutex1, 0xffff);
   ..
  /* Critical region 2 */
   ..
  os_mut_release (&mutex1);
}

__task void task1 (void) {
   ..
  os_mut_init (&mutex1);
  f1 ();
   ..
}

__task void task2 (void) {
   ..
  f2 ();
   ..
}