Can't use threads

[viliml]

Hello, I have a problem with multithreading.
I thried this minimal code:

#include <iostream>
#include <thread>

using namespace std;

int main ()
{
  	thread mythread([](){cout<<"Hello World!";});
	mythread.detach();
	mythread.join();
}

With MinGW 4.7.1 32-bit on the Orwell Dev-C++ 5.2.0.3 IDE, compiled with -std=c++11 -fpermissive -Wall -Wextra -pthread and it produced the following errors:

The compiler wrote:

C:\Users\Vilim\Desktop\New folder\Neimenovano2.cpp In function 'int main()':
8 4 C:\Users\Vilim\Desktop\New folder\Neimenovano2.cpp [Error] 'thread' was not declared in this scope
8 11 C:\Users\Vilim\Desktop\New folder\Neimenovano2.cpp [Error] expected ';' before 'mythread'
8 47 C:\Users\Vilim\Desktop\New folder\Neimenovano2.cpp [Error] expected primary-expression before ')' token
8 47 C:\Users\Vilim\Desktop\New folder\Neimenovano2.cpp [Error] expected ';' before ')' token
9 2 C:\Users\Vilim\Desktop\New folder\Neimenovano2.cpp [Error] 'mythread' was not declared in this scope

I read every thread tutorial I could find and I don't know what's causing this!

[steve9164]

Are you sure C++11 is properly compiling?
If you haven't used any of the C++11 features before try this code:

#include <vector>
#include <iostream>

int main()
{
    std::vector<int> intVector = {1,2,3,4,5,6,7,8,9}; // C++11 initialiser list
    for (auto& num: intVector) // auto & range based loop
        std::cout << num << std::endl;
    std::cin.get();
}

Otherwise I'm not really sure.

[viliml]

No, I used a LOT! Here's something that works for me:

#include <iostream>
#include <forward_list>
#include <array>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>

using namespace std;

struct foo
{
	foo(int)
	{}
	foo(foo&&)=default;
	foo(const foo&)=default;
};

int bar()=delete;

int main ()
{
  	vector<foo> a={1, 6, 9, 10, -2876};
  	for (const auto& x: a);
  	for_each(x.begin(), x.end(), [](decltype(*x.begin())){});
  	unordered_map<int, vector<double>> x;
  	unordered_set<bool> foobar;
  	cout<<alignof(foobar);
}

It's all perfect, no compile errors, no run-time rrors. But with theads...

[viliml]

The only 2 things I tired and don't work are alignas() and threads.

[Peter87]

Does MinGW 4.7.1 contain the same functionality as GCC 4.7.1?

The code in the first post compiles for me in GCC 4.7.1 but gives a runtime error.

terminate called after throwing an instance of 'std::system_error'
what(): Invalid argument
Hello World!Aborted

Probably because you use both detach() and join().

I doubt the code in your last post works for you because it contains a few errors.

[viliml]

You think that I can't use threads becouse I use MinGW instead of the original GCC?

[Peter87]

I don't know.

[viliml]

Should I download GCC and see if that works?

[JLBorges]

Depends on how MinGW was built. Check it out with:
> gcc -v

If the output shows either --enable-threads=win32 or Thread model: win32, there is no C++11 thread support.

If instead, it was built with the MinGW-w64 winpthreads library --enable-threads=winpthreads C++11 concurrency is supported to the extent that GCC supports it.

Haven't used it myself, but I'm told that this is one such build:
http://mingw-w64.sourceforge.net/
You need to link statically to libstdc++ with the -static switch, though.

AFAIK, the latest Microsoft C++ has better C++11 concurrency support than GNU.

[Peter87]

You will not be able to run GCC on Windows. MinGW is the windows port of GCC.

[viliml]

Heres what it outputs with -v:

My compiler wrote:

mingw32
../gcc-4.7.0/configure --enable-languages=c,c++,ada,fortran,objc,obj-c++ --disable-sjlj-exceptions --with-dwarf2 --enable-shared --enable-libgomp --disable-win32-registry --enable-libstdcxx-debug --disable-build-poststage1-with-cxx --enable-version-specific-runtime-libs --build=mingw32 --prefix=/mingw
win32
--param ggc-min-expand=100 --param ggc-min-heapsize=131072
--param ggc-min-expand=100 --param ggc-min-heapsize=131072
9fc40f37d31a03e5502141ce58bdf4c7

[viliml]

BTW I'm on a 32-bit computer, with a 32-bit processor and 32-bit OS and I'm SURE it's a 32-bit compiler.

[Peter87]

MinGW-w64 works with 32 bit too. At least they say so on their homepage.

[viliml]

OK, so I cna't use threads AT ALL with the regular 32-bit MinGW?

[JLBorges]

> Heres what it outputs with -v ...

That build does not seem to have any thread support (other than native win32 threads) at all. Check out these preprocessor defines:

_GLIBCXX_HAS_GTHREADS && (ATOMIC_INT_LOCK_FREE > 1)

[viliml]

_GLIBCXX_HAS_GTHREADS isn't defined and ATOMIC_INT_LOCK_FREE is 1.

(other than native win32 threads)

How to use those?

[JLBorges]

> How to use those?

Don't. Use Boost threads instead; a later transition to C++11 threads would then be painless.
http://www.boost.org/doc/libs/1_50_0/doc/html/thread.html
http://www.boost.org/doc/libs/1_50_0/doc/html/thread/compliance.html#thread.compliance.cpp11

[viliml]

And how to make that later transition ot C++11 threads?

[JLBorges]

> And how to make that later transition ot C++11 threads?

For the most part, by replacing boost::<whatever> with std::<whatever>

[viliml]

But, as I said, it doesn't work!