/*************************************************************************
 * Copyright (C) 2009-2013 Tavian Barnes <tavianator@tavianator.com>     *
 *                                                                       *
 * This file is part of The Dimension Library.                           *
 *                                                                       *
 * The Dimension Library is free software; you can redistribute it and/  *
 * or modify it under the terms of the GNU Lesser General Public License *
 * as published by the Free Software Foundation; either version 3 of the *
 * License, or (at your option) any later version.                       *
 *                                                                       *
 * The Dimension Library 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  *
 * Lesser General Public License for more details.                       *
 *                                                                       *
 * You should have received a copy of the GNU Lesser General Public      *
 * License along with this program.  If not, see                         *
 * <http://www.gnu.org/licenses/>.                                       *
 *************************************************************************/

/**
 * @file
 * Future objects.
 */

#include "dimension-internal.h"
#include <pthread.h>

/**
 * Since C doesn't support anything like C++'s mutable, we fake it by casting
 * away the constness.  This is okay since all valid dmnsn_futures live on the
 * heap, so cannot be const.
 */
#define MUTATE(future) ((dmnsn_future *)future)

/* Allocate a new dmnsn_future* */
dmnsn_future *
dmnsn_new_future(void)
{
  dmnsn_future *future = dmnsn_malloc(sizeof(dmnsn_future));
  future->progress = 0;
  future->total    = 1;

#if DMNSN_SPINLOCK
  dmnsn_initialize_spinlock(&future->spinlock, PTHREAD_PROCESS_PRIVATE);
#endif
  dmnsn_initialize_mutex(&future->mutex);
  dmnsn_initialize_cond(&future->cond);

  future->min_wait = 1.0;

  return future;
}

/* Join the worker thread and delete `future'. */
int
dmnsn_future_join(dmnsn_future *future)
{
  void *ptr;
  int retval = -1;

  if (future) {
    /* Get the thread's return value */
    dmnsn_join_thread(future->thread, &ptr);
    if (ptr && ptr != PTHREAD_CANCELED) {
      retval = *(int *)ptr;
      dmnsn_free(ptr);
    }

    /* Free the future object */
    dmnsn_destroy_cond(&future->cond);
    dmnsn_destroy_mutex(&future->mutex);
#if DMNSN_SPINLOCK
    dmnsn_destroy_spinlock(&future->spinlock);
#endif
    dmnsn_free(future);
  }

  return retval;
}

/* Cancel a background thread */
void
dmnsn_future_cancel(dmnsn_future *future)
{
  pthread_cancel(future->thread);
}

/** Lock the appropriate lock for a future. */
static inline void
dmnsn_lock_future(const dmnsn_future *future)
{
#if DMNSN_SPINLOCK
  dmnsn_lock_spinlock(&MUTATE(future)->spinlock);
#else
  dmnsn_lock_mutex(&MUTATE(future)->mutex);
#endif
}

/** Unlock the appropriate lock for a future. */
static inline void
dmnsn_unlock_future(const dmnsn_future *future)
{
#if DMNSN_SPINLOCK
  dmnsn_unlock_spinlock(&MUTATE(future)->spinlock);
#else
  dmnsn_unlock_mutex(&MUTATE(future)->mutex);
#endif
}

/** Lock the future's mutex specifically, if we have the spinlock already. */
static inline void
dmnsn_future_exchange_lock(const dmnsn_future *future)
{
#if DMNSN_SPINLOCK
  dmnsn_unlock_spinlock(&MUTATE(future)->spinlock);
  dmnsn_lock_mutex(&MUTATE(future)->mutex);
#endif
}

/** Unlock the future's mutex specifically, if we have the spinlock already. */
static inline void
dmnsn_future_exchange_unlock(const dmnsn_future *future)
{
#if DMNSN_SPINLOCK
  dmnsn_unlock_mutex(&MUTATE(future)->mutex);
  dmnsn_lock_spinlock(&MUTATE(future)->spinlock);
#endif
}

/** Get the current progress, without locking anything. */
static inline double
dmnsn_future_progress_unlocked(const dmnsn_future *future)
{
  return (double)future->progress/future->total;
}

/* Get the current progress of the worker thread, in [0.0, 1.0] */
double
dmnsn_future_progress(const dmnsn_future *future)
{
  double progress;

  dmnsn_lock_future(future);
    progress = dmnsn_future_progress_unlocked(future);
  dmnsn_unlock_future(future);

  return progress;
}

/* Wait until dmnsn_future_progress(future) >= progress */
void
dmnsn_future_wait(const dmnsn_future *future, double progress)
{
  dmnsn_future *mfuture = MUTATE(future);

  dmnsn_lock_future(mfuture);
    while (dmnsn_future_progress_unlocked(mfuture) < progress) {
      /* Set the minimum waited-on value */
      if (progress < mfuture->min_wait)
        mfuture->min_wait = progress;

      dmnsn_future_exchange_lock(mfuture);
        dmnsn_cond_wait(&mfuture->cond, &mfuture->mutex);
      dmnsn_future_exchange_unlock(mfuture);
    }
  dmnsn_unlock_future(mfuture);
}

/* Set the total number of loop iterations */
void
dmnsn_future_set_total(dmnsn_future *future, size_t total)
{
  dmnsn_lock_future(future);
    future->total = total;
  dmnsn_unlock_future(future);
}

/* Increment the number of completed loop iterations */
void
dmnsn_future_increment(dmnsn_future *future)
{
  /* Allow a thread to be canceled whenever it increments a future object --
     this is close to PTHREAD_CANCEL_ASYNCHRONOUS but allows consistent state
     on cancellation */
  pthread_testcancel();

  dmnsn_lock_future(future);
    ++future->progress;

    if (dmnsn_future_progress_unlocked(future) >= future->min_wait) {
      future->min_wait = 1.0;
      dmnsn_future_exchange_lock(future);
        dmnsn_cond_broadcast(&future->cond);
      dmnsn_future_exchange_unlock(future);
    }
  dmnsn_unlock_future(future);
}

/* Immediately set to 100% completion */
void
dmnsn_future_done(dmnsn_future *future)
{
  dmnsn_lock_future(future);
    future->progress = future->total;
    dmnsn_future_exchange_lock(future);
      dmnsn_cond_broadcast(&future->cond);
    dmnsn_future_exchange_unlock(future);
  dmnsn_unlock_future(future);
}