/* A set of threads. 
 *
 * Creating and destroying threads can be expensive on some platforms, so we
 * try to only create once, then reuse.
 */

/*

    This file is part of VIPS.
    
    VIPS 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 2 of the License, or
    (at your option) any later version.

    This program 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, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    02110-1301  USA

 */

/*

    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk

 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <glib/gi18n-lib.h>

#include <stdio.h>
#include <stdlib.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif /*HAVE_UNISTD_H*/
#include <errno.h>

/*
#define VIPS_DEBUG
 */

#include <vips/vips.h>
#include <vips/internal.h>
#include <vips/thread.h>
#include <vips/debug.h>

typedef struct _VipsThreadsetMember {
	/* The set we are part of.
	 */
	VipsThreadset *set;

	/* The underlying glib thread object.
	 */
	GThread *thread;

	/* The task the thread should run next.
	 */
	const char *domain;
	GFunc func; 
	void *data;
	void *user_data;

	/* The thread waits on this when it's free.
	 */
	VipsSemaphore idle;

	/* Set by our controller to request exit.
	 */
	gboolean kill;
} VipsThreadsetMember;

struct _VipsThreadset {
	GMutex *lock;

	/* All the VipsThreadsetMember we have created.
	 */
	GSList *members;

	/* The set of currently idle threads.
	 */
	GSList *free;

	/* The current number of threads, the highwater mark, and 
	 * the max we allow before blocking thread creation.
	 */
	int n_threads;
	int n_threads_highwater;
	int max_threads;
};

/* The maximum relative time (in microseconds) that a thread waits
 * for work before being stopped.
 */
static const gint64 max_idle_time = 15 * G_TIME_SPAN_SECOND;

/* The thread work function.
 */
static void *
vips_threadset_work( void *pointer )
{
	VipsThreadsetMember *member = (VipsThreadsetMember *) pointer;
	VipsThreadset *set = member->set;

	VIPS_DEBUG_MSG( "vips_threadset_work: starting %p\n", member );

	for(;;) {
		/* Wait for at least 15 seconds to be given work.
		 */
		if( vips_semaphore_down_timeout( &member->idle, 
			max_idle_time ) == -1 )
			break;

		/* Killed or no task available? Leave this thread.
		 */
		if( member->kill ||
			!member->func ) 
			break;

		/* If we're profiling, attach a prof struct to this thread.
		 */
		if( vips__thread_profile ) 
			vips__thread_profile_attach( member->domain );

		/* Execute the task.
		 */
		member->func( member->data, member->user_data );

		/* Free any thread-private resources -- they will not be
		 * useful for the next task to use this thread.
		 */
		vips_thread_shutdown();

		member->domain = NULL;
		member->func = NULL;
		member->data = NULL;
		member->user_data = NULL;

		/* We are free ... back on the free list!
		 */
		g_mutex_lock( set->lock );
		set->free = g_slist_prepend( set->free, member );
		g_mutex_unlock( set->lock );
	}

	/* Timed-out or kill has been requested ... remove from both free
	 * and member list.
	 */
	g_mutex_lock( set->lock );
	set->free = g_slist_remove( set->free, member );
	set->members = g_slist_remove( set->members, member );
	set->n_threads -= 1;
	VIPS_DEBUG_MSG( "vips_threadset_work: stopping %p (%d remaining)\n", 
		member, set->n_threads );
	g_mutex_unlock( set->lock );

	vips_semaphore_destroy( &member->idle );

	VIPS_FREE( member );

	return( NULL );
}

/* Create a new idle member for the set.
 */
static VipsThreadsetMember *
vips_threadset_add( VipsThreadset *set )
{
	VipsThreadsetMember *member;

	if( set->max_threads &&
		set->n_threads >= set->max_threads ) {
		vips_error( "VipsThreadset", 
			"%s", _( "threadset is exhausted" ) );
		return( NULL );
	}

	member = g_new0( VipsThreadsetMember, 1 );
	member->set = set;

	vips_semaphore_init( &member->idle, 0, "idle" );

	if( !(member->thread = vips_g_thread_new( "libvips worker", 
		vips_threadset_work, member )) ) {
		vips_semaphore_destroy( &member->idle );
		VIPS_FREE( member );

		return( NULL );
	}

	/* Ensure idle threads are freed on exit, this
	 * ref is increased before the thread is joined.
	 */
	g_thread_unref( member->thread );

	g_mutex_lock( set->lock );
	set->members = g_slist_prepend( set->members, member );
	set->n_threads += 1;
	set->n_threads_highwater = 
		VIPS_MAX( set->n_threads_highwater, set->n_threads );
	g_mutex_unlock( set->lock );

	return( member );
}

/** 
 * vips_threadset_new:
 * @max_threads: maxium number of system threads
 *
 * Create a new threadset. 
 *
 * If @max_threads is 0, new threads will be created when necessary by
 * vips_threadset_run(), with no limit on the number of threads.
 *
 * If @max_threads is > 0, then that many threads will be created by
 * vips_threadset_new() during startup and vips_threadset_run() will fail if
 * no free threads are available.
 *
 * Returns: the new threadset.
 */
VipsThreadset *
vips_threadset_new( int max_threads )
{
	VipsThreadset *set;

	set = g_new0( VipsThreadset, 1 );
	set->lock = vips_g_mutex_new();
	set->max_threads = max_threads;

	if( set->max_threads > 0 )
		for( int i = 0; i < set->max_threads; i++ ) {
			VipsThreadsetMember *member;

			if( !(member = vips_threadset_add( set )) ) {
				vips_threadset_free( set );
				return( NULL );
			}

			set->free = g_slist_prepend( set->free, member );
		}

	return( set );
}

/**
 * vips_threadset_run: 
 * @set: the threadset to run the task in
 * @domain: the name of the task (useful for debugging)
 * @func: the task to execute
 * @data: the task's data
 *
 * Execute a task in a thread. If there are no idle threads, create a new one,
 * provided we are under @max_threads.
 *
 * See also: vips_threadset_new().
 *
 * Returns: 0 on success, or -1 on error.
 */
int
vips_threadset_run( VipsThreadset *set, 
	const char *domain, GFunc func, gpointer data )
{
	VipsThreadsetMember *member;

	member = NULL;

	/* Try to get an idle thread.
	 */
	g_mutex_lock( set->lock );
	if( set->free ) {
		member = (VipsThreadsetMember *) set->free->data;
		set->free = g_slist_remove( set->free, member );
	}
	g_mutex_unlock( set->lock );

	/* None? Make a new idle but not free member.
	 */
	if( !member )
		member = vips_threadset_add( set );

	/* Still nothing? Thread create has failed.
	 */
	if( !member )
		return( -1 );

	/* Allocate the task and set it going.
	 */
	member->domain = domain;
	member->func = func;
	member->data = data;
	member->user_data = NULL;
	vips_semaphore_up( &member->idle );

	return( 0 );
}

/* Kill a member.
 */
static void
vips_threadset_kill_member( VipsThreadsetMember *member )
{
	GThread *thread;

	thread = g_thread_ref( member->thread );
	member->kill = TRUE;

	vips_semaphore_up( &member->idle );

	(void) g_thread_join( thread );

	/* member is freed on thread exit.
	 */
}

/** 
 * vips_threadset_free:
 * @set: the threadset to free
 *
 * Free a threadset. This call will block until all pending tasks are
 * finished.
 */
void
vips_threadset_free( VipsThreadset *set )
{
	VIPS_DEBUG_MSG( "vips_threadset_free: %p\n", set );

	/* Try to get and finish a thread.
	 */
	for(;;) {
		VipsThreadsetMember *member;

		member = NULL;
		g_mutex_lock( set->lock );
		if( set->members )
			member = (VipsThreadsetMember *) set->members->data;
		g_mutex_unlock( set->lock );

		if( !member )
			break;

		vips_threadset_kill_member( member );
	}

	if( vips__leak )
		printf( "vips_threadset_free: peak of %d threads\n", 
			set->n_threads_highwater );

	VIPS_FREEF( vips_g_mutex_free, set->lock );
	VIPS_FREE( set );
}
