conky/src/update-cb.cc

/* -*- mode: c++; c-basic-offset: 4; tab-width: 4; indent-tabs-mode: t -*-
 * vim: ts=4 sw=4 noet ai cindent syntax=cpp
 *
 * Conky, a system monitor, based on torsmo
 *
 * Please see COPYING for details
 *
 * Copyright (C) 2010 Pavel Labath et al.
 *
 * 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 3 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, see <http://www.gnu.org/licenses/>.
 *
 */

#include "config.h"
#include "logging.h"

#include "update-cb.hh"

#include <unistd.h>
#include <typeinfo>

namespace conky {
	namespace {
		semaphore sem_wait;
		enum {UNUSED_MAX = 5};
	}

	namespace priv {
		callback_base::~callback_base()
		{
			stop();
		}

		void callback_base::stop()
		{
			if(thread) {
				done = true;
				sem_start.post();
				if(pipefd.second >= 0)
					if(write(pipefd.second, "X", 1) != 1)
						NORM_ERR("can't write 'X' to pipefd %d: %s", pipefd.second, strerror(errno));
				thread->join();
				delete thread;
				thread = NULL;
			}
			if(pipefd.first >= 0) {
				close(pipefd.first);
				pipefd.first = -1;
			}
			if(pipefd.second >= 0) {
				close(pipefd.second);
				pipefd.second = -1;
			}
		}

		inline size_t callback_base::get_hash(const handle &h)
		{ return h->hash; }

		inline bool callback_base::is_equal(const handle &a, const handle &b)
		{
			if(a->hash != b->hash)
				return false;

			if(typeid(*a) != typeid(*b))
				return false;

			return *a == *b;
		}

		/*
		 * If a callback is not successfully inserted into the set, it must have
		 * the same hash as an existing callback. If this is so, merge the incoming
		 * callback with the one that prevented insertion. Keep the smaller of the
		 * two periods.
		 */
		void callback_base::merge(callback_base &&other)
		{
			if(other.period < period) {
				period = other.period;
				remaining = 0;
			}
			assert(wait == other.wait);
			unused = 0;
		}

		/*
		 * Register a callback (i.e. insert it into the callbacks set)
		 */
		callback_base::handle callback_base::do_register_cb(const handle &h)
		{
			const auto &p = callbacks.insert(h);

			/* insertion failed; callback already exists */
			if(not p.second)
				(*p.first)->merge(std::move(*h));

			return *p.first;
		}

		void callback_base::run()
		{
			if(not thread)
				thread = new std::thread(&callback_base::start_routine, this);

			sem_start.post();
		}

		void callback_base::start_routine()
		{
			for(;;) {
				sem_start.wait();
				if(done)
					return;

				// clear any remaining posts in case the previous iteration was very slow
				// (this should only happen if wait == false)
				while(sem_start.trywait());

				work();
				if(wait)
					sem_wait.post();
			}
		}

		callback_base::Callbacks callback_base::callbacks(1, get_hash, is_equal);
	}


	void run_all_callbacks()
	{
		using priv::callback_base;

		size_t wait = 0;
		for(auto i = callback_base::callbacks.begin(); i != callback_base::callbacks.end(); ) {
			callback_base &cb = **i;

			/* check whether enough update intervals have elapsed (up to period) */
			if(cb.remaining-- == 0) {
				/* run the callback as long as someone holds a pointer to it;
				 * if no one owns the callback, run it at most UNUSED_MAX times */
				if(!i->unique() || ++cb.unused < UNUSED_MAX) {
					cb.remaining = cb.period-1;
					cb.run();
					if(cb.wait)
						++wait;
				}
			}
			if(cb.unused == UNUSED_MAX) {
				auto t = i;
				++i;
				callback_base::callbacks.erase(t);
			} else 
				++i;
		}

		while(wait-- > 0)
			sem_wait.wait();
	}
}