libcaf  0.15.3
dining_philosophers.cpp

An event-based "Dining Philosophers" implementation.

/******************************************************************************\
* This example is an implementation of the classical Dining Philosophers *
* exercise using only libcaf's event-based actor implementation. *
\ ******************************************************************************/
#include <map>
#include <thread>
#include <utility>
#include <vector>
#include <chrono>
#include <sstream>
#include <iostream>
#include "caf/all.hpp"
using std::cout;
using std::cerr;
using std::endl;
using std::chrono::seconds;
using namespace caf;
namespace {
// atoms for chopstick interface
using put_atom = atom_constant<atom("put")>;
using take_atom = atom_constant<atom("take")>;
using taken_atom = atom_constant<atom("taken")>;
// atoms for philosopher interface
using eat_atom = atom_constant<atom("eat")>;
using think_atom = atom_constant<atom("think")>;
// a chopstick
using chopstick = typed_actor<replies_to<take_atom>::with<taken_atom, bool>,
reacts_to<put_atom>>;
chopstick::behavior_type taken_chopstick(chopstick::pointer,
// either taken by a philosopher or available
chopstick::behavior_type available_chopstick(chopstick::pointer self) {
return {
[=](take_atom) -> std::tuple<taken_atom, bool> {
self->become(taken_chopstick(self, self->current_sender()));
return std::make_tuple(taken_atom::value, true);
},
[](put_atom) {
cerr << "chopstick received unexpected 'put'" << endl;
}
};
}
chopstick::behavior_type taken_chopstick(chopstick::pointer self,
const strong_actor_ptr& user) {
return {
[](take_atom) -> std::tuple<taken_atom, bool> {
return std::make_tuple(taken_atom::value, false);
},
[=](put_atom) {
if (self->current_sender() == user)
self->become(available_chopstick(self));
}
};
}
/* Based on: http://www.dalnefre.com/wp/2010/08/dining-philosophers-in-humus/
*
*
* +-------------+ {busy|taken}
* /-------->| thinking |<------------------\
* | +-------------+ |
* | | |
* | | {eat} |
* | | |
* | V |
* | +-------------+ {busy} +-------------+
* | | hungry |----------->| denied |
* | +-------------+ +-------------+
* | |
* | | {taken}
* | |
* | V
* | +-------------+
* | | granted |
* | +-------------+
* | | |
* | {busy} | | {taken}
* \-----------/ |
* | V
* | {think} +-------------+
* \---------| eating |
* +-------------+
*/
class philosopher : public event_based_actor {
public:
philosopher(actor_config& cfg,
std::string n,
chopstick l,
chopstick r)
name_(std::move(n)),
left_(std::move(l)),
right_(std::move(r)) {
// we only accept one message per state and skip others in the meantime
set_default_handler(skip);
// a philosopher that receives {eat} stops thinking and becomes hungry
thinking_.assign(
[=](eat_atom) {
become(hungry_);
send(left_, take_atom::value);
send(right_, take_atom::value);
}
);
// wait for the first answer of a chopstick
hungry_.assign(
[=](taken_atom, bool result) {
if (result)
become(granted_);
else
become(denied_);
}
);
// philosopher was able to obtain the first chopstick
granted_.assign(
[=](taken_atom, bool result) {
if (result) {
aout(this) << name_
<< " has picked up chopsticks with IDs "
<< left_->id() << " and " << right_->id()
<< " and starts to eat\n";
// eat some time
delayed_send(this, seconds(5), think_atom::value);
become(eating_);
} else {
send(current_sender() == left_ ? right_ : left_, put_atom::value);
send(this, eat_atom::value);
become(thinking_);
}
}
);
// philosopher was *not* able to obtain the first chopstick
denied_.assign(
[=](taken_atom, bool result) {
if (result)
send(current_sender() == left_ ? left_ : right_, put_atom::value);
send(this, eat_atom::value);
become(thinking_);
}
);
// philosopher obtained both chopstick and eats (for five seconds)
eating_.assign(
[=](think_atom) {
send(left_, put_atom::value);
send(right_, put_atom::value);
delayed_send(this, seconds(5), eat_atom::value);
aout(this) << name_
<< " puts down his chopsticks and starts to think\n";
become(thinking_);
}
);
}
const char* name() const override {
return name_.c_str();
}
protected:
behavior make_behavior() override {
// start thinking
send(this, think_atom::value);
// philosophers start to think after receiving {think}
return (
[=](think_atom) {
aout(this) << name_ << " starts to think\n";
delayed_send(this, seconds(5), eat_atom::value);
become(thinking_);
}
);
}
private:
std::string name_; // the name of this philosopher
chopstick left_; // left chopstick
chopstick right_; // right chopstick
behavior thinking_; // initial behavior
behavior hungry_; // tries to take chopsticks
behavior granted_; // has one chopstick and waits for the second one
behavior denied_; // could not get first chopsticks
behavior eating_; // wait for some time, then go thinking again
};
} // namespace <anonymous>
void caf_main(actor_system& system) {
scoped_actor self{system};
// create five chopsticks
aout(self) << "chopstick ids are:";
std::vector<chopstick> chopsticks;
for (size_t i = 0; i < 5; ++i) {
chopsticks.push_back(self->spawn(available_chopstick));
aout(self) << " " << chopsticks.back()->id();
}
aout(self) << endl;
// spawn five philosophers
std::vector<std::string> names {"Plato", "Hume", "Kant",
"Nietzsche", "Descartes"};
for (size_t i = 0; i < 5; ++i)
self->spawn<philosopher>(names[i], chopsticks[i], chopsticks[(i + 1) % 5]);
}
CAF_MAIN()