CODEWITHSUNDEEP
c++c++11g++pthreads
Recker
Recker

Reputation: 1975

In g++ is C++ 11 thread model using pthreads in the background?

I am just trying my hands on g++ 4.6 and C++11 features. Every time I compile a simple threading code using -std=c++0x flag, either it crashes with segmentation fault or it just throws some weird exception.

I read some questions related to C++11 threads and I realized that, I also need to use -pthread flag to compile the code properly. Using -pthread worked fine and I was able to run the threaded code.

My question is, whether the C++11 multi-threading model uses Pthreads in the background? Or is it written from the scratch?

I don't know if any of the members are gcc contributors but I am just curious.

Upvotes: 14

Views: 9635

Answers (3)

Mark Lakata
Mark Lakata

Reputation: 20878

The reason that it crashes is that if you do not specify -pthreads or -lpthreads, a number of weakly defined pthreads stub functions from libc are linked. These stub functions are enough to get your program to link without error. However, actually creating a pthread requires the full on libpthread.a library, and when the dynamic linker (dl) tries to resolve those missing functions, you get a segmentation violation.

Upvotes: 2

user1157391
user1157391

Reputation:

C++ doesn't specify how threads are implemented. In practice C++ threads are generally implemented as thin wrappers over pre-existing system thread libraries (like pthreads or windows threads). There is even a provision to access the underlying thread object with std::thread::native_handle().

Upvotes: 9

Chris Dodd
Chris Dodd

Reputation: 126378

If you run g++ -v it will give you a bunch of information about how it was configured. One of those things will generally be a line that looks like

Thread model: posix

which means that it was configured to use pthreads for its threading library (std::thread in libstdc++), and which means you also need to use any flags that might be required for pthreads on your system (-pthread on Linux).

This has nothing specific to do with the standard, its just a detail of how the standard is implemented by g++

Upvotes: 23

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