C++ Event Manager Multi-Thread Reliable? - c++

Question

i making class event manager like below
EventManager.h
#ifndef EVENTMANAGER_H
#define EVENTMANAGER_H
#include <thread>
#include <mutex>
#include <chrono>
#include <atomic>
#include <condition_variable>
#include <vector>
#include "../../object/EObject.h"
class EventManager : public EObject {
public:
EventManager();
virtual ~EventManager();
int start_event();
void stop_event();
void add(const char* name, int interval, EObject * instance);
private:
static const int MAX_EVENT = 10;
std::atomic<int> event_total;
struct {
int event_id;
std::string event_name;
int interval;
std::atomic<bool> next_execute;
EObject * instance;
std::unique_ptr<std::condition_variable> cv;
std::unique_ptr<std::mutex> mtx;
} my_event[MAX_EVENT];
std::thread * event_thread;
std::atomic<bool> shall_stop;
std::atomic<bool> has_stopped;
std::atomic<int> worker_delay;
void worker();
//timing
std::vector<std::unique_ptr<std::thread>> timing_work;
void timing(int id);
};
#endif /* EVENTMANAGER_H */
EventManager.cpp
#include <iostream>
#include "EventManager.h"
#include "../../object/EVariant.h"
using namespace std;
EventManager::EventManager() {
event_thread = nullptr;
has_stopped = true;
shall_stop = false;
worker_delay = 5; //milli second
event_total = 0;
}
EventManager::~EventManager() {
}
int EventManager::start_event() {
if (event_thread) {
cout << "Event thread can not create\n" << flush;
return -1;
} else {
event_thread = new std::thread([this] {
this->worker();
});
cout << "Event thread created\n" << flush;
}
return 0;
}
void EventManager::stop_event() {
shall_stop = true;
for (int i = 0; i < 5; i++) {
this_thread::sleep_for(chrono::microseconds(10));
if (has_stopped) break;
}
delete event_thread;
event_thread = nullptr;
}
void EventManager::worker() {
has_stopped = false;
while (1) {
if (shall_stop) break;
for (int i = 0; i < event_total; i++) {
// cout << "Event Manager: " << my_event[i].event_name << " - checking \n" << flush;
if (my_event[i].next_execute) {
EVariant var = EVariant();
var.push("event_name", my_event[i].event_name);
my_event[i].instance->update(var);
my_event[i].next_execute = false;
{
condition_variable * cv = my_event[i].cv.get();
mutex * mtx = my_event[i].mtx.get();
unique_lock<mutex> lock(*mtx);
cv->notify_one();
// cout << "Event Manager: " << my_event[i].event_name << " - hey wakeup \n" << flush;
}
}
}
this_thread::sleep_for(chrono::milliseconds(worker_delay));
}
shall_stop = false;
has_stopped = true;
}
void EventManager::timing(int id) {
int _id = id;
cout << "Timing thread: " << my_event[_id].event_name << " - " << this_thread::get_id() << " - i was born\n" << flush;
while (1) {
int delay = my_event[_id].interval;
// cout << "Event Manager: " << my_event[_id].event_name << " - i delay \n" << flush;
this_thread::sleep_for(chrono::milliseconds(delay));
my_event[_id].next_execute = true;
{
// cout << "Event Manager: " << my_event[_id].event_name << " - i sleep \n" << flush;
condition_variable * cv = my_event[_id].cv.get();
mutex * mtx = my_event[_id].mtx.get();
unique_lock<mutex> lock(*mtx);
cv->wait(lock);
// cout << "Event Manager: " << my_event[_id].event_name << " - OK wakeup \n" << flush;
}
}
cout << "Timing thread: " << id << " - i'm quit\n" << flush;
}
void EventManager::add(const char* name, int interval, EObject* instance) {
cout << "Event adding : " << name << "\n" << flush;
event_total += 1;
int id = event_total - 1;
my_event[id].event_id = id;
my_event[id].event_name = name;
my_event[id].interval = interval;
my_event[id].instance = instance;
my_event[id].next_execute = false;
unique_ptr<mutex> mtx(new mutex());
my_event[id].mtx = std::move(mtx);
unique_ptr<condition_variable> cov(new condition_variable());
my_event[id].cv = std::move(cov);
//create thread delay
// std::thread th([this] {
// this->timing(event_total - 1);
// });
unique_ptr<thread> thd(new thread([this] {
this->timing(event_total - 1);
}));
// timing_collection.push_back(std::move(th));
timing_work.push_back(std::move(thd));
}
Calling
//event i2c communication
p_event_manager.emplace("I2C", new EventManager());
p_event_manager.at("I2C")->add("i2c_buffer", 10, pI2c.at("i2c-1"));
p_event_manager.at("I2C")->add("i2c_poll_tb", 30, p_touch_button.at("TouchButton1"));
p_event_manager.at("I2C")->add("i2c_micro_poll", 50, bsc_app);
p_event_manager.at("I2C")->start_event();
Algorithm:
When add function called, the function will add the struct and create new thread for delay cycle, the thread will move to vector, the thread will change flag of event for next execute on event main thread.
The problem:
The problem is often that the thread for delay is not successful created, so the event is not called. How to fix it?

Answer 1

Using this_thread::sleep_for() inside a timer function is not advisable, and you are likely to miss a trigger point during the sleep cycle. Excessive polling for the trigger point will also result in unnecessary wasted of CPU cycles. So you should rely mainly on condition_variables that trigger at the exact time without polling.
For example you can push a std::pair<time_point,thread_id> in an ordered container sorted in chronological order. Also see if priority queue could suit your needs. Your routine is overly complicated, simplicity has its own quality.