/*
      This file is part of GNUnet
      (C) 2009 Christian Grothoff (and other contributing authors)

      GNUnet is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published
      by the Free Software Foundation; either version 2, or (at your
      option) any later version.

      GNUnet is distributed in the hope that it will be useful, but
      WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      General Public License for more details.

      You should have received a copy of the GNU General Public License
      along with GNUnet; see the file COPYING.  If not, write to the
      Free Software Foundation, Inc., 59 Temple Place - Suite 330,
      Boston, MA 02111-1307, USA.
 */

/**
 * @file include/gnunet_scheduler_lib.h
 * @brief API to schedule computations using continuation passing style
 * @author Christian Grothoff
 */

#ifndef GNUNET_SCHEDULER_LIB_H
#define GNUNET_SCHEDULER_LIB_H

#ifdef __cplusplus
extern "C"
{
#if 0                           /* keep Emacsens' auto-indent happy */
}
#endif
#endif

/**
 * Opaque reference to a task.
 */
typedef unsigned long long GNUNET_SCHEDULER_TaskIdentifier;


/**
 * Constant used to indicate that the scheduled
 * task has no others as prerequisites.
 */
#define GNUNET_SCHEDULER_NO_TASK ((GNUNET_SCHEDULER_TaskIdentifier) 0)

/**
 * Reasons why the schedule may have triggered
 * the task now.
 */
enum GNUNET_SCHEDULER_Reason
{
  /**
   * This is the very first task run during startup.
   */
  GNUNET_SCHEDULER_REASON_STARTUP = 0,

  /**
   * We are shutting down and are running all shutdown-related tasks
   * (regardless of timeout, etc.).
   */
  GNUNET_SCHEDULER_REASON_SHUTDOWN = 1,

  /**
   * The specified timeout has expired.
   * (also set if the delay given was 0).
   */
  GNUNET_SCHEDULER_REASON_TIMEOUT = 2,

  /**
   * The reading socket is ready.
   */
  GNUNET_SCHEDULER_REASON_READ_READY = 4,

  /**
   * The writing socket is ready.
   */
  GNUNET_SCHEDULER_REASON_WRITE_READY = 8,

  /**
   * The prerequisite task is done.
   */
  GNUNET_SCHEDULER_REASON_PREREQ_DONE = 16
};


/**
 * Valid task priorities.  Use these, do not
 * pass random integers!
 */
enum GNUNET_SCHEDULER_Priority
{
  /**
   * Run with the same priority as the current job.
   */
  GNUNET_SCHEDULER_PRIORITY_KEEP = 0,

  /**
   * Run when otherwise idle.
   */
  GNUNET_SCHEDULER_PRIORITY_IDLE = 1,

  /**
   * Run as background job (higher than idle,
   * lower than default).
   */
  GNUNET_SCHEDULER_PRIORITY_BACKGROUND = 2,

  /**
   * Run with the default priority (normal
   * P2P operations).  Higher than BACKGROUND.
   */
  GNUNET_SCHEDULER_PRIORITY_DEFAULT = 3,

  /**
   * Run with high priority (important requests).
   * Higher than DEFAULT.
   */
  GNUNET_SCHEDULER_PRIORITY_HIGH = 4,

  /**
   * Run with priority for interactive tasks.
   * Higher than "HIGH".
   */
  GNUNET_SCHEDULER_PRIORITY_UI = 5,

  /**
   * Run with priority for urgent tasks.  Use
   * for things like aborts and shutdowns that
   * need to preempt "UI"-level tasks.
   * Higher than "UI".
   */
  GNUNET_SCHEDULER_PRIORITY_URGENT = 6,

  /**
   * This is an internal priority level that is only used for tasks
   * that are being triggered due to shutdown (they have automatically
   * highest priority).  User code must not use this priority level
   * directly.  Tasks run with this priority level that internally
   * schedule other tasks will see their original priority level
   * be inherited (unless otherwise specified).
   */
  GNUNET_SCHEDULER_PRIORITY_SHUTDOWN = 7,

  /**
   * Number of priorities (must be the last priority).
   * This priority must not be used by clients.
   */
  GNUNET_SCHEDULER_PRIORITY_COUNT = 8
};

#include "gnunet_time_lib.h"
#include "gnunet_network_lib.h"


/**
 * Context information passed to each scheduler task.
 */
struct GNUNET_SCHEDULER_TaskContext
{
  /**
   * Reason why the task is run now
   */
  enum GNUNET_SCHEDULER_Reason reason;

  /**
   * Set of file descriptors ready for reading;
   * note that additional bits may be set
   * that were not in the original request
   */
  const struct GNUNET_NETWORK_FDSet *read_ready;

  /**
   * Set of file descriptors ready for writing;
   * note that additional bits may be set
   * that were not in the original request.
   */
  const struct GNUNET_NETWORK_FDSet *write_ready;

};


/**
 * Signature of the main function of a task.
 *
 * @param cls closure
 * @param tc context information (why was this task triggered now)
 */
typedef void (*GNUNET_SCHEDULER_Task) (void *cls,
                                       const struct
                                       GNUNET_SCHEDULER_TaskContext * tc);


/**
 * Initialize and run scheduler.  This function will return when all
 * tasks have completed.  On systems with signals, receiving a SIGTERM
 * (and other similar signals) will cause "GNUNET_SCHEDULER_shutdown"
 * to be run after the active task is complete.  As a result, SIGTERM
 * causes all active tasks to be scheduled with reason
 * "GNUNET_SCHEDULER_REASON_SHUTDOWN".  (However, tasks added
 * afterwards will execute normally!).  Note that any particular
 * signal will only shut down one scheduler; applications should
 * always only create a single scheduler.
 *
 * @param task task to run first (and immediately)
 * @param task_cls closure of task
 */
void GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_Task task, void *task_cls);


/**
 * Request the shutdown of a scheduler.  Marks all currently
 * pending tasks as ready because of shutdown.  This will
 * cause all tasks to run (as soon as possible, respecting
 * priorities and prerequisite tasks).  Note that tasks
 * scheduled AFTER this call may still be delayed arbitrarily.
 */
void GNUNET_SCHEDULER_shutdown ();


/**
 * Get information about the current load of this scheduler.  Use this
 * function to determine if an elective task should be added or simply
 * dropped (if the decision should be made based on the number of
 * tasks ready to run).
 *
 * * @param p priority-level to query, use KEEP to query the level
 *          of the current task, use COUNT to get the sum over
 *          all priority levels
 * @return number of tasks pending right now
 */
unsigned int GNUNET_SCHEDULER_get_load (enum GNUNET_SCHEDULER_Priority p);


/**
 * Obtain the reason code for why the current task was
 * started.  Will return the same value as 
 * the GNUNET_SCHEDULER_TaskContext's reason field.
 *
 * * @return reason(s) why the current task is run
 */
enum GNUNET_SCHEDULER_Reason
GNUNET_SCHEDULER_get_reason ();


/**
 * Cancel the task with the specified identifier.
 * The task must not yet have run.
 *
 * * @param task id of the task to cancel
 * @return the closure of the callback of the cancelled task
 */
void *GNUNET_SCHEDULER_cancel (GNUNET_SCHEDULER_TaskIdentifier task);


/**
 * Continue the current execution with the given function.  This is
 * similar to the other "add" functions except that there is no delay
 * and the reason code can be specified.
 *
 * * @param task main function of the task
 * @param task_cls closure of task
 * @param reason reason for task invocation
 */
void
GNUNET_SCHEDULER_add_continuation (GNUNET_SCHEDULER_Task task,
                                   void *task_cls,
                                   enum GNUNET_SCHEDULER_Reason reason);


/**
 * Schedule a new task to be run after the specified prerequisite task
 * has completed. It will be run with the priority of the calling
 * task.
 *
 * * @param prerequisite_task run this task after the task with the given
 *        task identifier completes (and any of our other
 *        conditions, such as delay, read or write-readiness
 *        are satisfied).  Use  GNUNET_SCHEDULER_NO_TASK to not have any dependency
 *        on completion of other tasks (this will cause the task to run as
 *        soon as possible).
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_after (GNUNET_SCHEDULER_TaskIdentifier prerequisite_task,
                            GNUNET_SCHEDULER_Task task,
			    void *task_cls);


/**
 * Schedule a new task to be run with a specified priority.
 *
 * * @param prio how important is the new task?
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_with_priority (enum GNUNET_SCHEDULER_Priority prio,
				    GNUNET_SCHEDULER_Task task,
				    void *task_cls);


/**
 * Schedule a new task to be run as soon as possible. The task
 * will be run with the priority of the calling task.
 *
 * * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_now (GNUNET_SCHEDULER_Task task,
			  void *task_cls);


/**
 * Schedule a new task to be run with a specified delay.  The task
 * will be scheduled for execution once the delay has expired. It
 * will be run with the priority of the calling task.
 *
 * * @param delay when should this operation time out? Use
 *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_delayed (struct GNUNET_TIME_Relative delay,
                              GNUNET_SCHEDULER_Task task,
			      void *task_cls);


/**
 * Schedule a new task to be run with a specified delay or when the
 * specified file descriptor is ready for reading.  The delay can be
 * used as a timeout on the socket being ready.  The task will be
 * scheduled for execution once either the delay has expired or the
 * socket operation is ready.  It will be run with the priority of
 * the calling task.
 *
 * * @param delay when should this operation time out? Use
 *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
 * @param rfd read file-descriptor
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_read_net (struct GNUNET_TIME_Relative delay,
			       struct GNUNET_NETWORK_Handle *rfd,
			       GNUNET_SCHEDULER_Task task,
			       void *task_cls);


/**
 * Schedule a new task to be run with a specified delay or when the
 * specified file descriptor is ready for writing.  The delay can be
 * used as a timeout on the socket being ready.  The task will be
 * scheduled for execution once either the delay has expired or the
 * socket operation is ready.  It will be run with the priority of
 * the calling task.
 *
 * * @param delay when should this operation time out? Use
 *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
 * @param wfd write file-descriptor
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_write_net (struct GNUNET_TIME_Relative delay,
				struct GNUNET_NETWORK_Handle *wfd, 
				GNUNET_SCHEDULER_Task task, 
				void *task_cls);


/**
 * Schedule a new task to be run with a specified delay or when the
 * specified file descriptor is ready for reading.  The delay can be
 * used as a timeout on the socket being ready.  The task will be
 * scheduled for execution once either the delay has expired or the
 * socket operation is ready. It will be run with the priority of
 * the calling task.
 *
 * * @param delay when should this operation time out? Use
 *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
 * @param rfd read file-descriptor
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_read_file (struct GNUNET_TIME_Relative delay,
				const struct GNUNET_DISK_FileHandle *rfd, 
				GNUNET_SCHEDULER_Task task,
				void *task_cls);


/**
 * Schedule a new task to be run with a specified delay or when the
 * specified file descriptor is ready for writing.  The delay can be
 * used as a timeout on the socket being ready.  The task will be
 * scheduled for execution once either the delay has expired or the
 * socket operation is ready. It will be run with the priority of
 * the calling task.
 *
 * * @param delay when should this operation time out? Use
 *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
 * @param wfd write file-descriptor
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_write_file (struct GNUNET_TIME_Relative delay,
				 const struct GNUNET_DISK_FileHandle *wfd,
				 GNUNET_SCHEDULER_Task task, 
				 void *task_cls);


/**
 * Schedule a new task to be run with a specified delay or when any of
 * the specified file descriptor sets is ready.  The delay can be used
 * as a timeout on the socket(s) being ready.  The task will be
 * scheduled for execution once either the delay has expired or any of
 * the socket operations is ready.  This is the most general
 * function of the "add" family.  Note that the "prerequisite_task"
 * must be satisfied in addition to any of the other conditions.  In
 * other words, the task will be started when
 * <code>
 * (prerequisite-run)
 * && (delay-ready
 *     || any-rs-ready
 *     || any-ws-ready
 *     || shutdown-active)
 * </code>
 *
 * * @param prio how important is this task?
 * @param prerequisite_task run this task after the task with the given
 *        task identifier completes (and any of our other
 *        conditions, such as delay, read or write-readiness
 *        are satisfied).  Use GNUNET_SCHEDULER_NO_TASK to not have any dependency
 *        on completion of other tasks.
 * @param delay how long should we wait? Use GNUNET_TIME_UNIT_FOREVER_REL for "forever",
 *        which means that the task will only be run after we receive SIGTERM
 * @param rs set of file descriptors we want to read (can be NULL)
 * @param ws set of file descriptors we want to write (can be NULL)
 * @param task main function of the task
 * @param task_cls closure of task
 * @return unique task identifier for the job
 *         only valid until "task" is started!
 */
GNUNET_SCHEDULER_TaskIdentifier
GNUNET_SCHEDULER_add_select (enum GNUNET_SCHEDULER_Priority prio,
                             GNUNET_SCHEDULER_TaskIdentifier
                             prerequisite_task,
                             struct GNUNET_TIME_Relative delay,
                             const struct GNUNET_NETWORK_FDSet * rs,
			     const struct GNUNET_NETWORK_FDSet * ws,
                             GNUNET_SCHEDULER_Task task, 
			     void *task_cls);

#if 0                           /* keep Emacsens' auto-indent happy */
{
#endif
#ifdef __cplusplus
}
#endif

#endif