Comtrol eCos - Manual (Page 51)

Thread priorities
Name
cyg_thread_get_priority, cyg_thread_get_current_priority,
cyg_thread_set_priority — Examine and manipulate thread priorities
Synopsis
#include < cyg/kernel/kapi.h >
cyg_priority_t cyg_thread_get_priority(cyg_handle_t thread);
cyg_priority_t cyg_thread_get_current_priority(cyg_handle_t thread);
void cyg_thread_set_priority(cyg_handle_t thread, cyg_priority_t priority );
Description
Typical schedulers use the concept of a thread priority to determine which thread should run next. Exactly
what this priority consists of will depend on the scheduler, but a typical implementation would be a small
integer in the range 0 to 31, with 0 being the highest priority. Usually only the idle thread will run at the
lowest priority. The exact number of priority levels available depends on the configuration, typically the option
CYGNUM_KERNEL_SCHED_PRIORITIES .
cyg_thread_get_priority can be used to determine the priority of a thread, or more correctly the value last used
in a cyg_thread_set_priority call or when the thread was first created. In some circumstances it is possible
that the thread is actually running at a higher priority. For example, if it owns a mutex and priority ceilings or
inheritance is being used to prevent priority inversion problems, then the thread’s priority may have been boosted
temporarily.
cyg_thread_get_current_priority returns the real current priority.
In many applications appropriate thread priorities can be determined and allocated statically. However, if it is
necessary for a thread’s priority to change at run-time then the
cyg_thread_set_priority function provides
this functionality.
Valid contexts
cyg_thread_get_priority and cyg_thread_get_current_priority can be called from thread or DSR con-
text, although the latter is rarely useful. cyg_thread_set_priority should also only be called from thread
context.
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