/*
 * HttpAuth
 *
 * Copyright (C) 2008 Stefan Walter
 *
 * This program 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 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 General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the
 * Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * -------------------------------------------------------------------------
 * Ideas from tpool.c - htun thread pool functions
 * Copyright (C) 2002 Moshe Jacobson <moshe@runslinux.net>,
 *                    Ola Nordström <ola@triblock.com>
 * -------------------------------------------------------------------------
 */

/*
 * most of the theory and implementation of the thread pool was taken
 * from the o'reilly pthreads programming book.
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <err.h>
#include <string.h>
#include <assert.h>
#include <signal.h>

#define __USE_GNU
#include <pthread.h>

#include "tpool.h"

typedef struct _tpool_work {
	void (*handler_routine)(void*);
	void *arg;
	struct _tpool_work *next;
} tpool_work;

typedef struct _tpool_thread {
	pthread_t handle;
	int is_active;
	struct _tpool_thread *next;
} tpool_thread;

static int tpool_max_threads = 0;
static int tpool_min_threads = 0;
static int tpool_running_threads = 0;
static int tpool_idle_threads = 0;
static int tpool_zombie_threads = 0;
static tpool_thread *tpool_thread_list = NULL;

static int tpool_max_queue_size = 0;
static int tpool_cur_queue_size = 0;
static tpool_work *tpool_queue_head = NULL;
static tpool_work *tpool_queue_tail = NULL;
static pthread_mutex_t tpool_queue_lock;
static pthread_cond_t tpool_queue_not_full;
static pthread_cond_t tpool_queue_not_empty;
static pthread_cond_t tpool_queue_empty;

static int tpool_queue_closed = 0;
static int tpool_shutdown = 0;
static int tpool_initialized = 0;

#define PTHREQ(x) do { \
	int r = (x); \
	if (r != 0) { \
		fprintf (stderr, "fatal: '%s' failed: %s", #x, strerror (r)); \
		assert (0 && "" #x); \
	} } while (0)

static void*
tpool_thread_func (void *data)
{
	tpool_thread *thread = (tpool_thread*)data;
	tpool_work *work;
	int stop = 0;
	sigset_t set;

	/* We handle these signals on the main thread */
	sigemptyset (&set);
	sigaddset (&set, SIGINT);
	sigaddset (&set, SIGTERM);
	pthread_sigmask (SIG_BLOCK, &set, NULL);

	assert (thread);
	assert (tpool_initialized);

	PTHREQ (pthread_mutex_lock (&tpool_queue_lock));

	assert (thread->is_active);
	++tpool_running_threads;
	++tpool_idle_threads;

	while (!tpool_shutdown && !stop) {

		/* No work to do? */
		while (tpool_cur_queue_size == 0 && !tpool_shutdown && !stop) {

			/* Too many idle threads? */
			if (tpool_running_threads > tpool_min_threads) {
				stop = 1;
				break;
			}

			/*
			 * Sleep until there is work, while asleep the queue_lock
			 * is relinquished
			 */
			PTHREQ (pthread_cond_wait (&tpool_queue_not_empty, &tpool_queue_lock));
		}

		/* Are we shutting down? */
		if (stop || tpool_shutdown)
			break;

		/* Pop the work off the queue */
		work = tpool_queue_head;
		tpool_cur_queue_size--;
		if (tpool_cur_queue_size == 0)
			tpool_queue_head = tpool_queue_tail = NULL;
		else
			tpool_queue_head = work->next;

		/* Broadcast queue state to anyone who's waiting */
		if (tpool_cur_queue_size < tpool_max_queue_size)
			PTHREQ (pthread_cond_broadcast (&tpool_queue_not_full));
		if (tpool_cur_queue_size == 0)
			PTHREQ (pthread_cond_signal (&tpool_queue_empty));

		--tpool_idle_threads;
		assert (tpool_idle_threads >= 0);

		/* Unlock the queue lock while processing */
		PTHREQ (pthread_mutex_unlock (&tpool_queue_lock));

			/* Perform the work */
			(work->handler_routine) (work->arg);
			free (work);

		PTHREQ (pthread_mutex_lock (&tpool_queue_lock));

		++tpool_idle_threads;
	}

	--tpool_idle_threads;
	--tpool_running_threads;
	++tpool_zombie_threads;
	thread->is_active = 0;
	assert (tpool_running_threads >= 0);
	assert (tpool_idle_threads >= 0);

	PTHREQ (pthread_mutex_unlock (&tpool_queue_lock));

	/* So we can double check the result code */
	return thread;
}

static void
free_pool_stuff (void)
{
	tpool_work *work;

	if (!tpool_initialized)
		return;

	/* No threads should be running at this point */
	assert (!tpool_thread_list);

	/* Clean up memory */
	while (tpool_queue_head != NULL) {
		work = tpool_queue_head;
		tpool_queue_head = tpool_queue_head->next;
		free (work);
	}

	pthread_cond_destroy (&tpool_queue_not_full);
	pthread_cond_destroy (&tpool_queue_not_empty);
	pthread_cond_destroy (&tpool_queue_empty);
	pthread_mutex_destroy (&tpool_queue_lock);

	tpool_initialized = 0;
}

int
tpool_init (int max_threads, int min_threads, int max_queued)
{
	assert (!tpool_initialized);

	/* set the desired thread pool values */
	tpool_max_threads = max_threads;
	tpool_running_threads = 0;
	tpool_idle_threads = 0;
	tpool_zombie_threads = 0;
	tpool_min_threads = min_threads;

	/* initialize the work queue */
	tpool_max_queue_size = max_queued;
	tpool_cur_queue_size = 0;
	tpool_queue_head = NULL;
	tpool_queue_tail = NULL;
	tpool_queue_closed = 0;
	tpool_shutdown = 0;

	/* create the mutexs and cond vars */
	PTHREQ (pthread_mutex_init (&tpool_queue_lock, NULL));
	PTHREQ (pthread_cond_init (&tpool_queue_not_empty, NULL));
	PTHREQ (pthread_cond_init (&tpool_queue_not_full, NULL));
	PTHREQ (pthread_cond_init (&tpool_queue_empty, NULL));

	tpool_initialized = 1;
	return 0;
}

static void
join_pool_threads (int all)
{
	tpool_thread *thread, **spot;
	void *exit_code;

	/* Should be called from within the lock */

	for (spot = &tpool_thread_list, thread = *spot;
	     thread && (all || tpool_zombie_threads > 0); ) {

		assert (thread->handle);

		if (all || !thread->is_active) {
			if (!thread->is_active)
				--tpool_zombie_threads;

			/* Join the thread */
			PTHREQ (pthread_join (thread->handle, &exit_code));
			assert (exit_code == thread);

			/* Remove and get the next in list */
			*spot = thread->next;
			free (thread);

		} else {
			/* Just get the next in list */
			spot = &thread->next;
		}

		thread = *spot;
	}
}

int
tpool_add_work (void (*routine)(void*), void *arg)
{
	tpool_work *work;
	tpool_thread *thread;
	int r, ret = -1;

	assert (tpool_initialized);

	PTHREQ (pthread_mutex_lock (&tpool_queue_lock));

	/* Join any old threads */
	join_pool_threads (0);

	/* Should have found all of these above */
	assert (tpool_zombie_threads == 0);

	/* Are we closed for business? */
	if (tpool_shutdown || tpool_queue_closed) {
		errno = ECANCELED;
		goto done;
	}

	/* No idle threads to run this work? */
	if (!tpool_idle_threads) {

		/* See if we can start another thread */
		if (tpool_max_threads <= 0 ||
		    tpool_running_threads < tpool_max_threads) {

			/* The thread context */
			thread = calloc (1, sizeof (tpool_thread));
			if (thread == NULL) {
				errno = ENOMEM;
				goto done;
			}

			/* Start the thread */
			thread->is_active = 1;
			r = pthread_create (&thread->handle, NULL, tpool_thread_func, (void*)thread);
			if (r != 0) {
				errno = r;
				free (thread);
				goto done;
			}

			/* Add the new thread to the list */
			thread->next = tpool_thread_list;
			tpool_thread_list = thread;
		}
	}

	/*
	 * If the queue is full, yield this thread, and see if
	 * another processes something out of the queue.
	 */
	if (tpool_max_queue_size > 0 && tpool_cur_queue_size >= tpool_max_queue_size) {
		PTHREQ (pthread_mutex_unlock (&tpool_queue_lock));
		pthread_yield();
		PTHREQ (pthread_mutex_lock (&tpool_queue_lock));
	}

	/* Are we closed for business? */
	if (tpool_shutdown || tpool_queue_closed) {
		errno = ECANCELED;
		goto done;
	}

	/* Is the queue still full? */
	if (tpool_max_queue_size > 0 && tpool_cur_queue_size >= tpool_max_queue_size) {
		errno = EAGAIN;
		goto done;
	}

	/* Allocate the work structure */
	work = calloc (1, sizeof (tpool_work));
	if (work == NULL) {
		errno = ENOMEM;
		goto done;
	}

	work->handler_routine = routine;
	work->arg = arg;
	work->next = NULL;

	if (tpool_cur_queue_size == 0) {
		tpool_queue_tail = tpool_queue_head = work;
	} else {
		tpool_queue_tail->next = work;
		tpool_queue_tail = work;
	}

	PTHREQ (pthread_cond_broadcast (&tpool_queue_not_empty));
	tpool_cur_queue_size++;
	ret = 0;

done:
	PTHREQ (pthread_mutex_unlock (&tpool_queue_lock));
	return ret;
}

int
tpool_destroy (int finish)
{
	assert (tpool_initialized);

	PTHREQ (pthread_mutex_lock (&tpool_queue_lock));

	/* Can't have two places calling shutdown */
	assert (!tpool_queue_closed && !tpool_shutdown);

	/* close the queue to any new work */
	tpool_queue_closed = 1;

	/* if the finish flag is set, drain the queue */
	if (finish) {
		while (tpool_cur_queue_size != 0)
			PTHREQ (pthread_cond_wait (&tpool_queue_empty, &tpool_queue_lock));
	}

	/* Set the shutdown flag */
	tpool_shutdown = 1;

	PTHREQ (pthread_mutex_unlock (&tpool_queue_lock));

	/* wake up all workers to rechedk the shutdown flag */
	PTHREQ (pthread_cond_broadcast (&tpool_queue_not_empty));
	PTHREQ (pthread_cond_broadcast (&tpool_queue_not_full));

	join_pool_threads (1);
	free_pool_stuff ();

	return 0;
}