path: root/ace/Sched_Params.h

/* -*- C++ -*- */
// $Id$

// ============================================================================
//
// = LIBRARY
//    ACE
//
// = FILENAME
//    Sched_Params.h
//
// = CREATION DATE
//    28 January 1997
//
// = AUTHOR
//    David Levine and Carlos O'Ryan
//
// ============================================================================

#ifndef ACE_SCHED_PARAMS_H
#define ACE_SCHED_PARAMS_H

#include "ace/OS.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

class ACE_Export ACE_Sched_Params
{
  // = TITLE
  //    Container for scheduling-related parameters.
  //
  // = DESCRIPTION
  //    ACE_Sched_Params are passed via
  //    ACE_OS::sched_params () to the OS to specify scheduling
  //    parameters.  These parameters include scheduling policy,
  //    such as FIFO, round-robin, or an implementation-defined
  //    "OTHER" (to which many systems default); priority; and
  //    a time-slice quantum for round-robin scheduling.
  //    A "scope" parameter specifies whether the ACE_Sched_Params
  //    applies to the current process, current lightweight process
  //    (LWP) (on Solaris), or current thread.  Please see the "NOTE"
  //    below about not all combinations of parameters being legal
  //    on a particular platform.
  //
  //    For the case of thread priorities, it is intended that
  //    ACE_OS::sched_params () usually be called from main () before
  //    any threads have been spawned.
  //    If spawned threads inherit their parent's priority (I think
  //    that's the default behavior for all of our platforms), then
  //    this sets the default base priority.  Individual thread priorities
  //    can be adjusted as usual using ACE_OS::thr_prio () or via the
  //    ACE_Thread interface.  See the parameter descriptions in the
  //    private: section below.
  //
  //    NOTE:  this class does not do any checking of parameters.
  //    It is just a container class.  If it is constructed with values
  //    that are not supported on a platform, the call to
  //    ACE_OS::sched_params () will fail by returning -1 with EINVAL
  //    (available through ACE_OS::last_error ()).

  //    NOTE:  Solaris 2.5.x threads in the RT class must set the
  //    priority of their LWP.  The only way to do that through ACE is
  //    for the RT thread itself to call ACE_OS::thr_setprio () with
  //    it's own priority.

  //    OS Scheduling parameters are complicated and often confusing.  Many
  //    thanks to Thilo Kielmann <kielmann@informatik.uni-siegen.de> for his
  //    careful review of this class design, thoughtful comments, and
  //    assistance with implementation, especially for PTHREADS platforms.
  //    Please send any comments or corrections to the ACE developers.
public:
  typedef int Policy;

  // = Initialization and termination methods.
  ACE_Sched_Params (const Policy policy,
                    const ACE_Sched_Priority priority,
                    const int scope = ACE_SCOPE_THREAD,
                    const ACE_Time_Value &quantum = ACE_Time_Value::zero);
  // Constructor.

  ~ACE_Sched_Params (void);
  // Termination.

  // = Get/Set methods:

  // = Get/Set policy
  Policy policy (void) const;
  void policy (const Policy);

  // = Get/Set priority.
  ACE_Sched_Priority priority (void) const;
  void priority (const ACE_Sched_Priority);

  // = Get/Set scope.
  int scope (void) const;
  void scope(const int);

  // = Get/Set quantum.
  const ACE_Time_Value &quantum (void) const;
  void quantum (const ACE_Time_Value &);

  // = Accessors for OS-specific priorities.
  // These return priority values for ACE_SCHED_OTHER if the Policy value
  // is invalid.
  static int priority_min (const Policy,
                           const int scope = ACE_SCOPE_THREAD);
  static int priority_max (const Policy,
                           const int scope = ACE_SCOPE_THREAD);

  static int next_priority (const Policy,
                            const int priority,
                            const int scope = ACE_SCOPE_THREAD);
  // The next higher priority.  "Higher" refers to scheduling priority,
  // not to the priority value itself.  (On some platforms, higher scheduling
  // priority is indicated by a lower priority value.)  If "priority" is
  // already the highest priority (for the specified policy), then it is
  // returned.

  static int previous_priority (const Policy,
                                const int priority,
                                const int scope = ACE_SCOPE_THREAD);
  // The previous, lower priority.  "Lower" refers to scheduling priority,
  // not to the priority value itself.  (On some platforms, lower scheduling
  // priority is indicated by a higher priority value.)  If "priority" is
  // already the lowest priority (for the specified policy), then it is
  // returned.

private:
  Policy policy_;
  // Scheduling policy.

  ACE_Sched_Priority priority_;
  // Default <priority_>: for setting the priority for the process, LWP,
  // or thread, as indicated by the scope_ parameter.

  int scope_;
  // <scope_> must be one of the following:
  //   ACE_SCOPE_PROCESS:  sets the scheduling policy for the
  //     process, and the process priority.  On some platforms,
  //     such as Win32, the scheduling policy can _only_ be
  //     set at process scope.
  //   ACE_SCOPE_LWP: lightweight process scope, only used with
  //     Solaris threads.
  //   ACE_SCOPE_THREAD: sets the scheduling policy for the thread,
  //     if the OS supports it, such as with Posix threads, and the
  //     thread priority.
  // NOTE:  I don't think that these are the same as POSIX
  //        contention scope.  POSIX users who are interested in,
  //        and understand, contention scope will have to set it
  //        by using system calls outside of ACE.

  ACE_Time_Value quantum_;
  // The <quantum_> is for time slicing.  An ACE_Time_Value of 0 has
  // special significance: it means time-slicing is disabled; with
  // that, a thread that is running on a CPU will continue to run
  // until it blocks or is preempted.  Currently ignored if the OS
  // doesn't directly support time slicing, such as on VxWorks, or
  // setting the quantum (can that be done on Win32?).
};

class ACE_Export ACE_Sched_Priority_Iterator
  // = TITLE
  //   An iterator over the OS-defined scheduling priorities.
  //
  // = DESCRIPTION
  //   The order of priorities (numeric value vs. importance) is OS
  //   dependant, it can be the case that the priorities are not even
  //   contigous.  This class permits iteration over priorities using
  //   the iterator pattern.
{
public:
  ACE_Sched_Priority_Iterator (const ACE_Sched_Params::Policy &policy,
                               int scope = ACE_SCOPE_THREAD);
  // Initialize the iterator, the arguments define the scheduling
  // policy and scope for the priorities (see ACE_Sched_Param).

  ~ACE_Sched_Priority_Iterator (void);
  // Default dtor.

  int more (void) const;
  // Check if there are more priorities.

  int priority (void) const;
  // Return the current priority.

  void next (void);
  // Move to the next priority.
  // The iteration is from lowest to highest importance.

  const ACE_Sched_Params::Policy &policy (void) const;
  // Accessor for the scheduling policy over which we are iterating.

  int scope (void) const;
  // Accessor for the scheduling

private:
  ACE_Sched_Params::Policy policy_;
  int scope_;
  // The Scheduling policy (FIFO, RR, etc.) and scheduling scope
  // (PROCESS, SYSTEM) we are iterating on.

  int priority_;
  // The current priority.

  int done_;
  // This is set to 1 when there are no more priorities. Cannot easily
  // compare against the highest priority on platforms were priorities
  // are non-contigous or descending.
};

#if defined (__ACE_INLINE__)
#include "ace/Sched_Params.i"
#endif /* __ACE_INLINE__ */

#endif /* ACE_SCHED_PARAMS_H */