deadlock avoidance

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I am 006!

最新推荐文章于 2024-01-10 22:20:01 发布

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分类专栏： Linux C++算法系列

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本文介绍了一个使用C++标准库中的线程和互斥锁来避免死锁的示例程序。该程序演示了如何为员工分配午餐伙伴，并通过发送电子邮件通知他们。通过使用std::lock确保了在更新员工的午餐伙伴列表时不会发生竞态条件。

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/****************************************************************************
@File Name: test.cpp
@Author: wangzhicheng
@mail: 2363702560@qq.com
@Created Time: Fri 17 Mar 2017 07:21:52 PM CST
****************************************************************************/
#include <iostream>
#include <string>
#include <vector>
#include <thread>
#include <mutex>
#include <chrono>
using namespace std;
static const string BLANK = " ";
struct Employee
{
	string m_id;
	vector<string>lunch_partners;
	mutex m_lock;
	Employee(const string &id):m_id(id)
	{
	}
	void Output(string &strOut)
	{
		strOut = m_id;
		strOut += " lunch parntners = ";
		for(const auto &str:lunch_partners)
		{
			strOut += str;
			strOut += BLANK;
		}
	}
};
void SendMail(const Employee &e0, const Employee &e1)
{
	// e0 send mail to e1
	this_thread::sleep_for(chrono::seconds(1));
}
void assign_lunch_partner(Employee &e0, Employee &e1)
{
	if(&e0 == &e1) return;
	// Locks the given Lockable objects lock1, lock2, ..., lockn using a deadlock avoidance algorithm to avoid deadlock
	lock(e0.m_lock, e1.m_lock);
	lock_guard<mutex>lk0(e0.m_lock, adopt_lock);
	lock_guard<mutex>lk1(e1.m_lock, adopt_lock);
	e0.lunch_partners.emplace_back(e1.m_id);
	e1.lunch_partners.emplace_back(e0.m_id);
	SendMail(e0, e1);
	SendMail(e1, e0);
};
int main()
{
	Employee e0("e0");
	Employee e1("e1");
	Employee e2("e2");
	Employee e3("e3");
	string str;
	vector<thread>threads;
	threads.emplace_back(assign_lunch_partner, ref(e0), ref(e1));
	threads.emplace_back(assign_lunch_partner, ref(e0), ref(e2));
	threads.emplace_back(assign_lunch_partner, ref(e0), ref(e3));
	threads.emplace_back(assign_lunch_partner, ref(e1), ref(e2));
	for(auto &th:threads)
	{
		th.join();
	}
	e0.Output(str);
	cout << str << endl;
	e1.Output(str);
	cout << str << endl;
	e2.Output(str);
	cout << str << endl;
	e3.Output(str);
	cout << str << endl;

	return 0;
}