C++ Actor Framework  0.18
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 <chrono>
#include <iostream>
#include <map>
#include <sstream>
#include <thread>
#include <utility>
#include <vector>
#include "caf/all.hpp"
CAF_BEGIN_TYPE_ID_BLOCK(dining_philosophers, first_custom_type_id)
CAF_ADD_ATOM(dining_philosophers, take_atom)
CAF_ADD_ATOM(dining_philosophers, taken_atom)
CAF_ADD_ATOM(dining_philosophers, eat_atom)
CAF_ADD_ATOM(dining_philosophers, think_atom)
CAF_END_TYPE_ID_BLOCK(dining_philosophers)
using std::cerr;
using std::cout;
using std::endl;
using std::chrono::seconds;
using namespace caf;
namespace {
// atoms for chopstick and philosopher interfaces
// a chopstick
using chopstick
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) -> result<taken_atom, bool> {
self->become(taken_chopstick(self, self->current_sender()));
return {taken_atom_v, 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) -> result<taken_atom, bool> {
return {taken_atom_v, 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_v);
send(right_, take_atom_v);
});
// 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_v);
become(eating_);
} else {
send(current_sender() == left_ ? right_ : left_, put_atom_v);
send(this, eat_atom_v);
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_v);
send(this, eat_atom_v);
become(thinking_);
});
// philosopher obtained both chopstick and eats (for five seconds)
eating_.assign([=](think_atom) {
send(left_, put_atom_v);
send(right_, put_atom_v);
delayed_send(this, seconds(5), eat_atom_v);
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_v);
// philosophers start to think after receiving {think}
return {
[=](think_atom) {
aout(this) << name_ << " starts to think\n";
delayed_send(this, seconds(5), eat_atom_v);
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
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(id_block::dining_philosophers)