Standard practice for implementing threads in C++?

Question

Hello SO World,

I'm looking forward to an interview in C++ in the coming weeks. (yay) So I have been relearning C++ and studying up. Unfortunately I have realized that I've never implemented threads in C++, and am somewhat concerned about a quiz on concurrency.

As far as I can tell, C++ uses pthreads in Linux and some other device in Windows. Is this correct? Is there another industry standard, more OO way to handle threads in C++ that I should be expected to know? And are there any good web resources that you can point me to for practicing and learning threads in C++?

Thanks!

Answer 1

There is a boost threads library which is probably the closest to a standard.

Generally threads are supplied by the OS so you get whatever the OS supplied. Also peoples first exposure to threading is often in a GUI, to allow a background calculation to not block the GUI, and so people tend to use the thread functions supplied by the particular GUI framework (MFC/Qt etc)

Answer 2

In windows the only way to create threads is using the win32 API. Every library you may have that creates threads on windows eventually uses win32 CreateThread()

QT Contains a nice C++ wrapper around a thread that is cross platform. Usually a good practice is to have a MyThread class that contains all the nitty-gritty details of setting up a thread, checking for error codes, getting it's exit code and the like. The MyThread class would have a pure virtual function called run() which is intended to actually do whatever you'd want the thread to do. The user of the MyThread class is expected to inherit from it and implement run() this way you can isolate the user of the class from the details for actually creating the thread.

MyThead also needs to have a method start() which initiates the thread. The thread would start at some entry point inside the class (this usually needs to be a static method) and then this eventually leads to the user's run() method to be invoked.

Answer 3

Well, until C++0x gets here, there is no standard way to do threading in C++. You can use whatever facilities your operating system provides. So yes, if you are on a UNIX-like operating system, you can use pthreads. On Windows, you can use the Windows API.

There are 3rd party toolkits out there that attempt to provide a uniform and portable threading API, e.g. boost threads and QT.

It is also not difficult to write your own portable abstraction layer either. We did this because the boost API didn't have everything we needed several years ago (e.g. no way to set priority).

Answer 4

Currently C++ is entirely unaware that threads exist. Different OSes provide threading libraries to make them available. The next version of C++, so called C++0x, is going to make a thread library standard. If I were to start a multithreaded app today I would go with either boost threads or the threads that were a part of any package I might be using i.e. QT or WxWidgets.

Answer 5

Beyond Qt, wxWidgets, Boost and native, OS-provided threading facilities, you can just Google around for thread libraries for C++. They are probably more portable and lightweight as well (if all you are looking for is threading). However, if you have a need for more facilities and the aforementioned libraries provide them, then go ahead and use them. Boost is especially good, it has other facilities as well, but admittedly it's threading library, as Brian Neal said, is limited in some regards.

Answer 6

I've seen several 'real-world' implementations of threading using C++, and they have all been implemented by someone's writing a Thread class to wrap the underlying O/S API

For example, on Windows there's a CreateThread API: your Thread class would pass its this value to the void* lpParameter parameter of the CreateThread API; and your LPTHREAD_START_ROUTINE, which you implement as a private static method of the Thread class, then needs to cast void* back to Thread*' in order to get the Thread` instance.

Answer 7

For your interview, neither boost nor qt is helpful at all. you could just use them as the high level libs and interfaces, and no one would ask you how to use boost or qt in such an interview. For understanding threading and mutex etc, see a document from http://code.google.com/p/effoaddon/downloads/list, named EffoAddons.pdf.

Raw source 
http://effoaddon.googlecode.com/svn/trunk/devel/effo/codebase/addons/thrd/src/thrd/thrd.cpp,
 high level abstract interface 
http://effoaddon.googlecode.com/svn/trunk/devel/effo/codebase/addons/thrd/include/thrd_i.h,
 and code support wait and signal 
http://effoaddon.googlecode.com/svn/trunk/devel/effo/codebase/addons/queue/include/iqb_ops_i.h.

you'd better study something underlying, not just high level interfaces, though write C++.