新手学C/C++：一篇代码学会使用std::future , std::promise std:

#include

#include

#include

#include

#include

using namespace std::chrono;

struct testDb

{

?? ?std::string operator()(std::string recvData){

?? ??? ?std::this_thread::sleep_for(seconds(5));

?? ??? ?return "Db_" + recvData;

?? ?}

};

struct testFile

{

?? ?std::string operator()(std::string recvData){

?? ??? ?std::this_thread::sleep_for(seconds(5));

?? ??? ?return "File_" + recvData;

?? ?}

};

std::string fetchDataFromDB(std::string recvData) {

?? ?//确保函数要5秒才能执行完成

?? ?std::this_thread::sleep_for(seconds(5));

?? ?//处理创建数据库连接、获取数据等事情

?? ?return "DB_" + recvData;

}

std::string fetchDataFromFile(std::string recvData) {

?? ?//确保函数要5秒才能执行完成

?? ?std::this_thread::sleep_for(seconds(5));

?? ?//处理获取文件数据

?? ?return "File_" + recvData;

}

void fetchDataFromDB1(std::promise* promiSEObj,std::string recvData) {

?? ?//确保函数要5秒才能执行完成

?? ?std::this_thread::sleep_for(seconds(5));

?? ?//处理创建数据库连接、获取数据等事情

?? ?promiSEObj->set_value("DB_" + recvData);

}

void fetchDataFromFile1(std::promise* promiSEObj,std::string recvData) {

?? ?//确保函数要5秒才能执行完成

?? ?std::this_thread::sleep_for(seconds(5));

?? ?

?? ?//处理获取文件数据

?? ?promiSEObj->set_value("File_" + recvData);;

}

int main() {

?? ?////获取开始时间

?? ?//system_clock::time_point start = system_clock::now();

?? ?////从数据库获取数据

?? ?//std::string dbData = fetchDataFromDB("Data");

?? ?////从文件获取数据

?? ?//std::string fileData = fetchDataFromFile("Data");

?? ?////获取结束时间

?? ?//auto end = system_clock::now();

?? ?//auto diff = duration_cast(end - start).count();

?? ?//std::cout << "Total Time taken= " << diff << "Seconds" << std::endl;

?? ?////组装数据

?? ?//std::string data = dbData + " :: " + fileData;

?? ?////输出组装的数据

?? ?//std::cout << "Data = " << data.c_str() << std::endl;

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?//c++11的方法：使用std::future 和 std::promise

?? ?//system_clock::time_point start1 = system_clock::now();

?? ?//std::promise promiSEObj;

?? ?//std::future futureDB = promiSEObj.get_future();

?? ?//std::thread th(fetchDataFromDB1,&promiSEObj,"Data");

?? ?//std::promise promiseFile;

?? ?//std::future futureFile = promiseFile.get_future();

?? ?//std::thread th1(fetchDataFromFile1,&promiseFile,"Data");

?? ?//th.join();

?? ?//th1.join();

?? ?//std::string dbData1 = futureDB.get();

?? ?//std::string fileData1 = futureFile.get();

?? ?//auto end1 = system_clock::now();

?? ?//auto diff1 = duration_cast(end1 - start1).count();

?? ?//std::cout << "Total Time taken= " << diff1 << "Seconds" << std::endl;

?? ?//std::string data1 = dbData1 + " :: " + fileData1;

?? ?//std::cout << "Data1 = " << data1.c_str() << std::endl;

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?//用lambda函数作为回调调用std::async

?? ?/*auto start2 = system_clock::now();

?? ?std::future futureDB2 = std::async([](std::string recvData){std::this_thread::sleep_for(seconds(5)); return "DB_" + recvData; },"Data");

?? ?std::future futureFile2 = std::async([](std::string recvData){?? ?std::this_thread::sleep_for(seconds(5)); return "File_" + recvData; },"Data");

?? ?std::string dbData2 = futureDB2.get();

?? ?std::string fileData2 = futureFile2.get();

?? ?auto end2 = system_clock::now();

?? ?auto diff2 = duration_cast(end2 - start2).count();

?? ?std::cout << "Total Time taken= " << diff2 << "Seconds" << std::endl;

?? ?std::string data2 = dbData2 + " :: " + fileData2;

?? ?std::cout << "Data2 = " << data2.c_str() << std::endl;*/

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?//用Function对象作为回调调用std::async

?? ?/*auto start3 = system_clock::now();

?? ?std::future futureDB3 = std::async(testDb(),"Data");

?? ?std::future futureFile3 = std::async(testFile(),"Data");

?? ?std::string dbData3 = futureDB3.get();

?? ?std::string fileData3 = futureFile3.get();

?? ?auto end3 = system_clock::now();

?? ?auto diff3 = duration_cast(end3 - start3).count();

?? ?std::cout << "Total Time taken= " << diff3 << "Seconds" << std::endl;

?? ?std::string data3 = dbData3 + " :: " + fileData3;

?? ?std::cout << "Data3 = " << data3.c_str() << std::endl;*/

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?//使用函数指针调用std::async作为回调

?? ?//auto start4 = system_clock::now();

?? ?//std::future futureDB4 = std::async(std::launch::async | std::launch::deferred,fetchDataFromDB,"Data");

?? ?//std::future futureFile4 = std::async(std::launch::async | std::launch::deferred,fetchDataFromFile,"Data");

?? ?//std::string dbData4 = futureDB4.get();

?? ?//std::string fileData4 = futureFile4.get();

?? ?//auto end4 = system_clock::now();

?? ?//auto diff4 = duration_cast(end4 - start4).count();

?? ?//std::cout << "Total Time taken= " << diff4 << "Seconds" << std::endl;

?? ?//std::string data4 = dbData4 + " :: " + fileData4;

?? ?//std::cout << "Data4 = " << data4.c_str() << std::endl;

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?////使用函数指针创建packaged_task来完成回调需求

?? ?//auto start5 = system_clock::now();

?? ?//std::packaged_task taskDB(fetchDataFromDB);

?? ?//std::packaged_task taskFile(fetchDataFromFile);

?? ?//std::future futureDB5 = taskDB.get_future();

?? ?//std::future futureFile5 = taskFile.get_future();

?? ?//std::thread th5DB(std::move(taskDB),"Data");

?? ?//std::thread th5File(std::move(taskFile),"Data");

?? ?//th5DB.join();

?? ?//th5File.join();

?? ?//std::string dbData5 = futureDB5.get();

?? ?//std::string fileData5 = futureFile5.get();

?? ?//auto end5 = system_clock::now();

?? ?//auto diff5 = duration_cast(end5 - start5).count();

?? ?//std::cout << "Total Time taken= " << diff5 << "Seconds" << std::endl;

?? ?//std::string data5 = dbData5 + " :: " + fileData5;

?? ?//std::cout << "Data5 = " << data5.c_str() << std::endl;

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?

?? ?////使用函数对象创建packaged_task来完成回调需求

?? ?/*auto start6 = system_clock::now();

?? ?std::packaged_task taskDB(std::move(testDb()));

?? ?std::packaged_task taskFile(std::move(testFile()));

?? ?std::future futureDB6 = taskDB.get_future();

?? ?std::future futureFile6 = taskFile.get_future();

?? ?std::thread th6DB(std::move(taskDB),"Data");

?? ?std::thread th6File(std::move(taskFile),"Data");

?? ?th6DB.join();

?? ?th6File.join();

?? ?std::string dbData6 = futureDB6.get();

?? ?std::string fileData6 = futureFile6.get();

?? ?auto end6 = system_clock::now();

?? ?auto diff6 = duration_cast(end6 - start6).count();

?? ?std::cout << "Total Time taken= " << diff6 << "Seconds" << std::endl;

?? ?std::string data6 = dbData6 + " :: " + fileData6;

?? ?std::cout << "Data6 = " << data6.c_str() << std::endl;*/

?? ?std::cout << "--------------------------------------------------------------------------" << std::endl;

?? ?

?? ?/*auto start7 = system_clock::now();

?? ?std::packaged_task taskDB([](std::string recvData){std::this_thread::sleep_for(seconds(5)); return "DB_" + recvData; });

?? ?std::packaged_task taskFile([](std::string recvData) {std::this_thread::sleep_for(seconds(5)); return "File_" + recvData;});

?? ?std::future futureDB7 = taskDB.get_future();

?? ?std::future futureFile7 = taskFile.get_future();

?? ?std::thread th7DB(std::move(taskDB),"Data");

?? ?std::thread th7File(std::move(taskFile),"Data");

?? ?th7DB.join();

?? ?th7File.join();

?? ?std::string dbData7 = futureDB7.get();

?? ?std::string fileData7 = futureFile7.get();

?? ?auto end7 = system_clock::now();

?? ?auto diff7 = duration_cast(end7 - start7).count();

?? ?std::cout << "Total Time taken= " << diff7 << "Seconds" << std::endl;

?? ?std::string data7 = dbData7 + " :: " + fileData7;

?? ?std::cout << "Data7 = " << data7.c_str() << std::endl;*/

?? ?system("pause");

?? ?return 0;

}

（编辑：李大同）

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