I heard about Reentrantlock recently which are available in Java. But I was trying to implement parallel data structures like priority queues using openmp and C++.
I was curious to know whether a similar equivalent exists in openmp and C++ or whether it can be implemented using pthreads? If there exists such an equivalent, please tell how to use it.
See the description of omp_nest_lock on page 270 (PDF page 279) in the OpenMP 4.5 standard.
A meta-question is "Why are you doing this?"
Why aren't you simply using something like TBB's Concurrent Priority Queue?
Do you need to be using OpenMP for other reasons?
Is this is for your own education?
If not, then TBB might be a simpler approach (it is now Apache Licensed).
(FWIW I work for Intel, who wrote TBB, but I work on OpenMP, not TBB :-))
Related
Basically I need to build an app where the main process does some operation based on the values of some global variables, and the secondary thread update this global variables (say each 100ms)
What library do you suggest to work with opencv, c++ and multithreading? (windows)
I have heard there are
OpenMP
Boost
Intel TBB
Which one do you suggest for this simple multi thread application?
C++ supports threads since its newest standard. I would consider using std::thread from the standard library, if C++11 is an option for you. You can find the documentation for example here.
The syntax is in my opinion very simple and easy to read (check out a few examples: mutex, future, etc).
OpenMP you can use for threads. You have OpenCV for computer vision.
Go with OpenMP. Here's the documentation.
Hope it helps.:)
I would suggest boost libraries since it has large community and you will find all possible solutions and examples codes. Variable passing is easier than ever in Boost Threads. However, c++11 has similar thread functionality as boost but you need to check availability of c++ 11. So if you have already installed boost for other functionality, go with boost. Else c++ thread is your way out.
I want to learn multi-threading in C++ but I'm not sure what type would be most useful. The ones I've seen tutorials on are:
Windows native calls
OpenMP
Boost
(I'm sure that there are probably more.)
What is each one's key features and what are they best used for?
Note: I've already done some multi-threading in C# by manually creating the threads, and more complexity of the threading will just make it more fun. :)
I'd start with pthreads if you have more of a C background, or Boost Thread if you are accustomed to more idiomatic C++. Either is reasonably portable and widely used.
How about TBB? It is portable and has easy to use parallel template patterns, concurrent containers, task scheduler and scalable memory allocaturs. TBB will let you manage threads directly, but that is not necessary in most of the cases.
Personally I would stay away from platform specific threads, unless there an urgent need to do something, well, platform specific.
Boost threads is portable and easy to use, but does have neither parallel patterns nor concurrent containers. You would need to manager threads manually, which can get ugly pretty quickly.
PThreads isn't available on Windows and its C. You really want to do multi-threading in C++, not C. RAII mixes well with mutexes and scoped locks.
Another option is PPL in Visual C++ 2010. It is similar to TBB, but as you may guess available for Windows only.
OpenMP is easy to use, but not very flexible. Since you already learned C++, you should use something more serious, such as TBB or PPL. For some strange reason Visual C++ 2010 doesn't support OpenMP 3. Too bad.
If you want to be portable, learn Posix threads. You know, all thread libraries provide more or less the same set of features, so it's up to you, but Posix will give you the basis.
openMP isn't exactly "multi-threading" as you mean it.
WinThreads (Windows) and pthreads (Linux) are POSIX threads and represent probably your best choice to get started. It is important to learn the distinction between processes and threads, then learn about the various memory access models that are associated with them. Next, try concurrency approaches like OpenMP and MPI "threads".
There are some basic concepts that will get repeated. Learn them well.
Basically, the title explains it all; I'm looking to make a game in C++ and I want to use multithreading for stuff like the physics engine and keeping the animation smooth on the loading screen. I've seen a few multithreading libraries, but I'm wondering which is best for my application, which will work well on Windows Mac and Linux. Does such a library exist?
You probably want boost::thread or Intels' Thread Building Blocks. I'd recommend TBB but it's not free, I think, so boost::thread for the free option.
If you can use c++0x threads, then use that.
If not, boost::thread is the best free multi-platform library.
My favourite is QThread. Part of Qt library.
Currently my recommendation would be OpenMP (libgomp on g++, IBM XlC++, MSVC++ all support it)
OpenMP offers a simple way of exploiting parallelism without interfering with algorithm design; an OpenMP program compiles and operates correctly in both parallel and serial execution environments. Using OpenMP's directive-based parallelism also simplifies the act of converting existing serial code to efficient parallel code.
See msdn
And GOMP
for starting points
Random quote:
To remain relevant, free software development tools must support emerging technologies. By implementing OpenMP, GOMP provides a simplified syntax tools for creating software targeted at parallel architectures. OpenMP's platform-neutral syntax meshes well with the portability goals of GCC and other GNU projects
Another nice library that includes cross platform threads is poco
I have a C# prototype that is heavily data parallel, and I've had extremely successful order of magnitude speed ups using the Parallel.For construct in .NETv4. Now I need to write the program in native code, and I'm wondering what my options are. I would prefer something somewhat portable across various operating systems and compilers, but if push comes to shove, I can go with something Windows/VC++.
I've looked at OpenMP, which looks interesting, but I have no idea whether this is looked upon as a good solution by other programmers. I'd also love suggestions for other portable libraries I can look at.
If you're happy with the level of parallelism you're getting from Parallel.For, OpenMP is probably a pretty good solution for you -- it does roughly the same kinds of things. There's also work and research being done on parallelized implementations of the algorithms in the standard library. Code that uses the standard algorithms heavily can gain from this with even less work.
Some of this is done using OpenMP, while other is using hand-written code to (attempt to) provide greater benefits. In the long term, we'll probably see more of the latter, but for now, the OpenMP route is probably a bit more practical.
If you're using Parallel.For in .Net 4.0, you should also look at the Parallel Pattern Library in VS2010 for C++; many things are similar and it is library based.
If you need to run on another platform besides Windows the PPL is also implemented in Intel's Thread Building Blocks which has an open source version.
Regarding the other comment on similarities / differences vs. .Net 4.0, the parallel loops in the PPL (parallel_for, parallel_for_each, parallel_invoke) are virtually identical to the .Net 4.0 loops. The task model is slightly different, but should be straightforward.
You should check out Intel's Thread Building Blocks. Visual Studio 2010 also offers a Concurrency Runtime native. The .NET 4.0 libraries and the ConcRT are designed very similarly, if not identically.
if you want something that is versatile, as in portable across various OS and environments, it would be very difficult to not to consider Java. And they are very similar to C# so it be a very easy transition.
Unless you want to pull out your ninja scalpel and wanting to make your code extremely efficient, I would say java over VC++ or C++.
I am familiar with concurrent programming in Java which provides a lot of tools for this. However, C++ concurrent programming isn't so easy to start using.
What is the best way to start programming concurrently on C++? Are there any nice libraries which wrap concurrent programming primitives and provide you with more high-level constructs?
I tried QtConcurrent which provides you with nice MapReduce functionality but it is heavily biased towards concurrent computation using Qt so it's not a good choice if you don't want to use Qt.
Are there any other similar libraries? What do people use here?
Thanks for your help in advance,
sneg
There are several choices:
ACE which provides some concurrency constructs
Intel Threading Building Blocks
boost::threads
OpenMP
Qt Threading libraries
Morendil's suggestion (CSP - communicating sequential processes) is truly interesting to take a look at - it's a very different view of threading and one that works well once you wrap your head around it. I first encountered it in the rather esoteric Occam language for Transputers, but the idea has stuck with me.
A more conventional idea: boost::threads work quite well for building thread-based concurrent programs. It's quite low level though.
OpenMP is at a higher level than threads and also quite well-supported.
You could look at CSP, which has a C++ implementation. Way different from Java's threading primitives, though.
This question along with the answers can probably help you a little bit.
Intel's Threading Building Blocks is great for introducing concurrency at the level of individual data-parallel loops, and it takes care of managing threads and allocating work automagically. It can be used in similar ways to OpenMP, but without the need for explicit compiler support.