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/* Copyright (c) 2010-2025. The SimGrid Team. All rights reserved. */
/* This program is free software; you can redistribute it and/or modify it
* under the terms of the license (GNU LGPL) which comes with this package. */
/***************** Centralized Mutual Exclusion Algorithm *********************/
/* This example implements a centralized mutual exclusion algorithm. */
/* There is no bug on it, it is just provided to test the state space */
/* reduction of DPOR. */
/******************************************************************************/
#include "simgrid/s4u.hpp"
constexpr int AMOUNT_OF_CLIENTS = 4;
constexpr int CS_PER_PROCESS = 2;
XBT_LOG_NEW_DEFAULT_CATEGORY(centralized, "my log messages");
namespace sg4 = simgrid::s4u;
class Message {
public:
enum class Kind { GRANT, REQUEST, RELEASE };
Kind kind = Kind::GRANT;
sg4::Mailbox* return_mailbox = nullptr;
explicit Message(Message::Kind kind, sg4::Mailbox* mbox) : kind(kind), return_mailbox(mbox) {}
};
static void coordinator()
{
std::queue<sg4::Mailbox*> requests;
sg4::Mailbox* mbox = sg4::Mailbox::by_name("coordinator");
bool CS_used = false; // initially the CS is idle
int todo = AMOUNT_OF_CLIENTS * CS_PER_PROCESS; // amount of releases we are expecting
while (todo > 0) {
auto m = mbox->get_unique<Message>();
if (m->kind == Message::Kind::REQUEST) {
if (CS_used) { // need to push the request in the vector
XBT_INFO("CS already used. Queue the request");
requests.push(m->return_mailbox);
} else { // can serve it immediately
XBT_INFO("CS idle. Grant immediately");
m->return_mailbox->put(new Message(Message::Kind::GRANT, mbox), 1000);
CS_used = true;
}
} else { // that's a release. Check if someone was waiting for the lock
if (not requests.empty()) {
XBT_INFO("CS release. Grant to queued requests (queue size: %zu)", requests.size());
sg4::Mailbox* req = requests.front();
requests.pop();
req->put(new Message(Message::Kind::GRANT, mbox), 1000);
todo--;
} else { // nobody wants it
XBT_INFO("CS release. resource now idle");
CS_used = false;
todo--;
}
}
}
XBT_INFO("Received all releases, quit now");
}
static void client()
{
aid_t my_pid = sg4::this_actor::get_pid();
sg4::Mailbox* my_mailbox = sg4::Mailbox::by_name(std::to_string(my_pid));
// request the CS 3 times, sleeping a bit in between
for (int i = 0; i < CS_PER_PROCESS; i++) {
XBT_INFO("Ask the request");
sg4::Mailbox::by_name("coordinator")->put(new Message(Message::Kind::REQUEST, my_mailbox), 1000);
// wait for the answer
auto grant = my_mailbox->get_unique<Message>();
XBT_INFO("got the answer. Sleep a bit and release it");
sg4::this_actor::sleep_for(1);
sg4::Mailbox::by_name("coordinator")->put(new Message(Message::Kind::RELEASE, my_mailbox), 1000);
sg4::this_actor::sleep_for(static_cast<double>(my_pid));
}
XBT_INFO("Got all the CS I wanted, quit now");
}
int main(int argc, char* argv[])
{
sg4::Engine e(&argc, argv);
e.load_platform(argv[1]);
e.add_actor("coordinator", e.host_by_name("Tremblay"), coordinator);
e.add_actor("client", e.host_by_name("Fafard"), client);
e.add_actor("client", e.host_by_name("Boivin"), client);
e.add_actor("client", e.host_by_name("Jacquelin"), client);
e.add_actor("client", e.host_by_name("Ginette"), client);
e.run();
return 0;
}
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