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pthread_attr_setschedparam(3)


NAME

  pthread_attr_setschedparam - Changes the values of the parameters
  associated with a scheduling policy of the specified thread attributes
  object


SYNOPSIS

  #include <pthread.h>

  int pthread_attr_setschedparam(
	  pthread_attr_t *attr,
	  const struct sched_param *param );


LIBRARY

  DECthreads POSIX 1003.1c Library (libpthread.so)


STANDARDS

  Interfaces documented on this reference page conform to industry standards
  as follows:

  IEEE Std 1003.1c-1995, POSIX System Application Program Interface


PARAMETERS

  attr
      Thread attributes object for the scheduling policy whose parameters are
      to be set.

  param
      A structure containing new values for scheduling parameters associated
      with the scheduling policy attribute of the specified thread attributes
      object. Note that DECthreads provides only the sched_priority
      scheduling parameter.  See the Description section for information
      about this scheduling parameter.


DESCRIPTION

  This routine sets the scheduling parameters associated with the scheduling
  policy attribute of the thread attributes object specified by the attr
  argument.

  Use the sched_priority field of a sched_param structure to set a thread's
  execution priority. The effect of the scheduling priority you assign
  depends on the scheduling policy specified for the attributes object
  specified by the attr argument.

  By default, a created thread inherits the priority of the thread calling
  pthread_create(3). To specify a priority using this routine, scheduling
  inheritance must be disabled at the time the thread is created. Before
  calling pthread_create(3), call pthread_attr_setinheritsched(3) and specify
  the value PTHREAD_EXPLICIT_SCHED for the inherit argument.

  An application specifies priority only to express the urgency of executing
  the thread relative to other threads. DO NOT USE PRIORITY TO CONTROL MUTUAL
  EXCLUSION WHEN ACCESSING SHARED DATA. With a sufficient number of
  processors present, all ready threads, regardless of priority, execute
  simultaneously.

  Valid values of the sched_priority scheduling parameter depend on the
  chosen scheduling policy. Use the POSIX routines sched_get_priority_min(3)
  or sched_get_priority_max(3) to determine the low and high limits of each
  policy.

  Additionally, DECthreads provides nonportable priority range constants, as
  follows:

  SCHED_FIFO:
      PRI_FIFO_MIN to PRI_FIFO_MAX

  SCHED_RR:
      PRI_RR_MIN to PRI_RR_MAX

  SCHED_OTHER:
      PRI_OTHER_MIN to PRI_OTHER_MAX

  SCHED_FG_NP:
      PRI_FG_MIN_NP to PRI_FG_MAX_NP

  SCHED_BG_NP:
      PRI_BG_MIN_NP to PRI_BG_MAX_NP

  The default priority varies by DECthreads platform. On Tru64 UNIX, the
  default is 19 (that is, the POSIX priority of a normal timeshare process).
  On other platforms, the default priority is the midpoint between
  PRI_FG_MIN_NP and PRI_FG_MAX_NP.


RETURN VALUES

  If an error condition occurs, this routine returns an integer value
  indicating the type of error. Possible return values are as follows:

  0   Successful completion.

  [EINVAL]
      The value specified by param is not a valid thread attributes object,
      or the value specified by param is invalid.

  [ENOTSUP]
      An attempt was made to set the attribute to an unsupported value.


ERRORS

  None


SEE ALSO

  Functions: pthread_attr_init(3), pthread_attr_getschedparam(3),
  pthread_attr_setinheritsched(3), pthread_attr_setschedpolicy(3),
  pthread_create(3), sched_yield(3)

  Manuals: Guide to DECthreads and Programmer's Guide

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