{"id":6092,"date":"2021-02-18T06:14:03","date_gmt":"2021-02-18T06:14:03","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/synchronized-outputstreams\/"},"modified":"2023-06-26T09:32:22","modified_gmt":"2023-06-26T09:32:22","slug":"synchronized-outputstreams","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/synchronized-outputstreams\/","title":{"rendered":"Synchronized Output Streams with C++20"},"content":{"rendered":"

What happens when you write without synchronization to std::cout<\/code>? You get a mess. With C++20, this should not be anymore.<\/p>\n

<\/p>\n

\"TimelineCpp20\"<\/p>\n

Before I present synchronized output streams with C++20, I want to show non-synchronized output in C++11.<\/p>\n

 <\/p>\n

<\/p>\n

\n
\/\/ coutUnsynchronized.cpp<\/span>\r\n\r\n#include <chrono><\/span>\r\n#include <iostream><\/span>\r\n#include <thread><\/span>\r\n\r\nclass<\/span> Worker<\/span>{\r\npublic:<\/span>\r\n  Worker(std::<\/span>string n):<\/span>name(n) {};\r\n    void<\/span> operator<\/span>() (){\r\n      for<\/span> (int<\/span> i =<\/span> 1<\/span>; i <=<\/span> 3<\/span>; ++<\/span>i) {\r\n        \/\/ begin work<\/span>\r\n        std::<\/span>this_thread::<\/span>sleep_for(std::<\/span>chrono::<\/span>milliseconds(200<\/span>));      \/\/ (3)<\/span>\r\n        \/\/ end work<\/span>\r\n        std::<\/span>cout <<<\/span> name <<<\/span> \": \"<\/span> <<<\/span> \"Work \"<\/span> <<<\/span> i <<<\/span> \" done !!!\"<\/span> <<<\/span> '\\n'<\/span>; \/\/ (4)<\/span>\r\n      }\r\n    }\r\nprivate:<\/span>\r\n  std::<\/span>string name;\r\n};\r\n\r\n\r\nint<\/span> main<\/span>() {\r\n\r\n  std::<\/span>cout <<<\/span> '\\n'<\/span>;\r\n  \r\n  std::<\/span>cout <<<\/span> \"Boss: Let's start working.<\/span>\\n\\n<\/span>\"<\/span>;\r\n \r\n  std::<\/span>thread<\/span> herb=<\/span> std::<\/span>thread<\/span>(Worker(\"Herb\"<\/span>));                        \/\/ (1)<\/span>\r\n  std::<\/span>thread<\/span> andrei=<\/span> std::<\/span>thread<\/span>(Worker(\"  Andrei\"<\/span>));\r\n  std::<\/span>thread<\/span> scott=<\/span> std::<\/span>thread<\/span>(Worker(\"    Scott\"<\/span>));\r\n  std::<\/span>thread<\/span> bjarne=<\/span> std::<\/span>thread<\/span>(Worker(\"      Bjarne\"<\/span>));\r\n  std::<\/span>thread<\/span> bart=<\/span> std::<\/span>thread<\/span>(Worker(\"        Bart\"<\/span>));\r\n  std::<\/span>thread<\/span> jenne=<\/span> std::<\/span>thread<\/span>(Worker(\"          Jenne\"<\/span>));            \/\/ (2)<\/span>\r\n  \r\n  \r\n  herb.join();\r\n  andrei.join();\r\n  scott.join();\r\n  bjarne.join();\r\n  bart.join();\r\n  jenne.join();\r\n  \r\n  std::<\/span>cout <<<\/span> \"<\/span>\\n<\/span>\"<\/span> <<<\/span> \"Boss: Let's go home.\"<\/span> <<<\/span> '\\n'<\/span>;                   \/\/ (5)<\/span>\r\n  \r\n  std::<\/span>cout <<<\/span> '\\n'<\/span>;\r\n  \r\n}\r\n<\/pre>\n<\/div>\n
 <\/p>\n
The boss has six workers (lines 1 – 2). Each worker has to take care of three work packages that take 1\/5 second each (line 3). After the worker is done with his work package, he screams out loudly to the boss (line 4). Once the boss receives notifications from all workers, he sends them home (line 5).
What a mess for such a simple workflow! Each worker screams out his message ignoring his coworkers!<\/p>\n
\"coutUnsynchronized\"<\/p>\n