2.2.3.3 Scheduling Parameters Attribute

The scheduling parameters attribute specifies the execution priority of a thread. (Although the terminology and format are designed to allow adding more scheduling parameters in the future, only priority is currently defined.) The priority is expressed relative to other threads in the same policy on a continuum of minimum to maximum for each scheduling policy. A thread's priority falls within one of the following ranges, depending on its scheduling policy.

Low                 High

PRI_FIFO_MIN        PRI_FIFO_MAX

PRI_RR_MIN          PRI_RR_MAX

PRI_OTHER_MIN       PRI_OTHER_MAX

PRI_FG_MIN_NP       PRI_FG_MAX_NP

PRI_BG_MIN_NP       PRI_BG_MAX_NP

Section 2.7 describes how to specify priorities between the minimum and maximum values, and it also discusses how priority affects thread scheduling.

You can use either of the following methods to set the scheduling parameters attribute:

• Set the scheduling parameters attribute in the attributes object, which establishes the execution priority of a new thread when it is created. To do this, call the pthread_attr_ setschedparam routine. This allows the creator of a thread to establish the created thread's initial execution priority. Note that this value is used only if the attributes object is set so that the created thread does not inherit its priority from the creating thread. Inheriting priority is the default behavior.

• Change the scheduling policy and parameters of an existing thread by calling the pthread_setschedparam routine. This allows a thread to change its own execution policy and/or priority.