I wanted to test some things with threads on my Macbook pro, but I can't get it to work.
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: x86_64-apple-darwin18.2.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
this is the Version of clang installed on my machine. I tried to code some vector of threads but that didn't work so I went back and copied an example from SO.
#include <string>
#include <iostream>
#include <thread>
using namespace std;
// The function we want to execute on the new thread.
void task1(string msg)
{
cout << "task1 says: " << msg;
}
int main()
{
// Constructs the new thread and runs it. Does not block execution.
thread t1(task1, "Hello");
// Do other things...
// Makes the main thread wait for the new thread to finish execution, therefore blocks its own execution.
t1.join();
}
But I am getting a compiler error..
error: no matching constructor for initialization of
'std::__1::thread'
thread t1(task1, "Hello");
I guess my machine is the problem, but why?
Somehow, you built your code as C++03, probably by not providing a standard revision flag explicitly. libc++, the LLVM implementation of the standard library allows using <thread> in C++03 code. The source has conditional compilation of the following sort:
#ifndef _LIBCPP_CXX03_LANG
template <class _Fp, class ..._Args,
class = typename enable_if
<
!is_same<typename __uncvref<_Fp>::type, thread>::value
>::type
>
_LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
explicit thread(_Fp&& __f, _Args&&... __args);
#else // _LIBCPP_CXX03_LANG
template <class _Fp>
_LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
explicit thread(_Fp __f);
#endif
In C++11 and higher, the constructor adheres to the C++11 standard. Otherwise, it accepts only a callable without additional arguments. I managed to reproduce your error by providing the C++03 standard revision flag. The error even mentions this candidate:
prog.cc:16:12: error: no matching constructor for initialization of 'std::__1::thread'
thread t1(task1, "Hello");
^ ~~~~~~~~~~~~~~
/opt/wandbox/clang-8.0.0/include/c++/v1/thread:408:9: note: candidate constructor template not viable: requires single argument '__f', but 2 arguments were provided
thread::thread(_Fp __f)
Related
I'm using the protoc-3.18.0-win32 version from here. After successfully compiling the .proto files, I get the following error in my QtCreator 5 (C++11) program:
C:\Users\MyName\MyProject\lib\include\google\protobuf\stubs\mutex.h:124: error: temporary of non-literal type 'google::protobuf::internal::CallOnceInitializedMutex<std::mutex>' in a constant expression
In file included from lib\include/google/protobuf/descriptor.h:66:0,
from lib\include/google/protobuf/message.h:121,
from lib\include/google/protobuf/generated_message_bases.h:42,
from src/protodata/myfile.pb.h:26,
from src/myfile/myfile.h:12,
from src\myclass/myclass.h:8,
from src\mywidget.cpp:2:
lib\include/google/protobuf/stubs/mutex.h: In constructor 'constexpr google::protobuf::internal::WrappedMutex::WrappedMutex()':
lib\include/google/protobuf/stubs/mutex.h:124:29: error: temporary of non-literal type 'google::protobuf::internal::CallOnceInitializedMutex<std::mutex>' in a constant expression
constexpr WrappedMutex() {}
^
lib\include/google/protobuf/stubs/mutex.h:98:7: note: 'google::protobuf::internal::CallOnceInitializedMutex<std::mutex>' is not literal because:
class CallOnceInitializedMutex {
^~~~~~~~~~~~~~~~~~~~~~~~
lib\include/google/protobuf/stubs/mutex.h:98:7: note: 'google::protobuf::internal::CallOnceInitializedMutex<std::mutex>' has a non-trivial destructor
where the erroneous lines of code are:
// Mutex is a natural type to wrap. As both google and other organization have
// specialized mutexes. gRPC also provides an injection mechanism for custom
// mutexes.
class GOOGLE_PROTOBUF_CAPABILITY("mutex") PROTOBUF_EXPORT WrappedMutex {
public:
#if defined(__QNX__)
constexpr WrappedMutex() = default;
#else
constexpr WrappedMutex() {} // <--- Error points here
#endif
I hit the same issue when trying to use protobuf version higher than 3.15.0 with gcc 7.3 and c++17. This turned out to be a gcc bug, see more in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82461.
After looking into the protobuf generated code, what i find is in version after 3.15, protobuf generated code container pervasive 'constexpr' which trigger the gcc bug.
Possible solution:
use higher version of gcc, the bug is fixed in 7.4 (preferred)
use '-std=c++14' instead of '-std=c++17', this works for me
use protobuf older than 3.15, 3.13 and 3.14 works for me.
In my case it was enough:
Go to your opencv folder, find the file \opencv\sources\3rdparty\protobuf\src\google\protobuf\stubs\mutex.h and delete the line after the first else at the WrappedMutex class,
class GOOGLE_PROTOBUF_CAPABILITY("mutex") PROTOBUF_EXPORT WrappedMutex {
audience:
#if defined(__QNX__)
constexpr WrappedMutex() = default;
#else
constexpr WrappedMutex() {} // **Delete this line**
#endif
#include <iostream>
#include <thread>
using namespace std;
void thread_c() {
for (int i = 0; i < 11; ++i) {
cout << i;
}
}
int main() {
thread t(thread_c);
t.join();
return 0;
}
Such simple example, but it doesn't work on my g++ (MinGW.org GCC-6.3.0-1) 6.3.0, Windows 8.1
Here's the error:
main.cpp: In function 'int main()':
main.cpp:13:5: error: 'thread' was not declared in this scope
thread t(thread_c);
^~~~~~
main.cpp:14:5: error: 't' was not declared in this scope
t.join();
^
*I've been working on a big project, and noticed about some compilation errors. I wrote this code for testing my compiler out
What's wrong with it?
Loking at your code and the compiler results I see the following:
#include <thread> is not including a file that defines thread as your code expects
GCC 6.3.0 is very old (current is 10.2.0), and chances are it was built without POSIX thread support (and probably only support for Windows threads)
I always recommend using MinGW-w64 instead of MinGW as it is more up to date and supports both 32-bit and 64-bit Windows.
When I build your example with the MinGW-w64 from http://winlibs.com/ (which has POSIX thread support) I get no errors and the example works (output is 012345678910).
I was working on this thread swap c++ map objects in multithreaded environment
However,
#include <memory>
#include <thread>
#include <chrono>
#include <atomic>
#include <iostream>
using namespace std;
shared_ptr<std::string> the_string;
int main()
{
atomic_store(&the_string, std::make_shared<std::string>("first string"));
}
gives a compile time error
error: no matching function for call to 'atomic_store'
atomic_store(&the_string, std::make_shared<std::string>("first string"));
^~~~~~~~~~~~
/Library/Developer/CommandLineTools/usr/include/c++/v1/atomic:1165:1: note: candidate template ignored: could not match 'atomic' against 'shared_ptr'
atomic_store(volatile atomic<_Tp>* __o, _Tp __d) _NOEXCEPT
I did see a few threads on this problem and understand that it could be related to C++ version I have /usr/include/c++/4.2.1/ and /usr/include/c++/4.8.5/ on another box, both give the same issue. Should I upgrade the C++ version?
I resolved this issue by passing -std=c++11 flag.
I resolved this issue by passing the flag -std=c++11
It compiles fine here with GCC 8.3 and Clang 8.0, so yes, you should upgrade your compiler.
The following example program uses a thread local template variable, and instantiates it using a type inside an anonymous namespace. This produces a linker error in gcc. In clang it actually compiles but does not run correctly.
#include <stdio.h>
template<typename T>
struct container {
container() { printf("construct: %p\n", this); }
~container() { printf("destruct: %p\n", this); }
};
template<typename T>
thread_local container<T> storage;
namespace {
struct bar {};
}
int main() {
auto& ref1 = storage<bar>;
auto& ref2 = storage<bar>;
}
On gcc this fails with a link error:
a.cpp:6:2: warning: ‘container<T>::~container() noexcept [with T = {anonymous}::bar]’ used but never defined
~container() { printf("destruct: %p\n", this); }
^
/tmp/ccgh0P15.o: In function `__tls_init':
a.cpp:(.text+0xa9): undefined reference to `container<(anonymous namespace)::bar>::~container()'
With clang the program compiles but produces very troubling output:
construct: 0x7fb8d1c003d0
construct: 0x7fb8d1c003d0
destruct: 0x7fb8d1c003d0
destruct: 0x7fb8d1c003d0
Are there some rough edges surrounding thread_local/templated variables that I am running into here? I am unclear why this would ever produce a link error (the link error disappears if I remove thread_local). In the case of clang how could a double destroy of an object with static storage duration be anything but a compiler bug? In clang the issue disappears if I remove the anonymous namespace OR the thread_local specification, OR by removing one of the references in main().
Can anyone shed some light on this, I am mainly just curious if I am misunderstanding something. Thanks!
EDIT:
clang++ -v
Apple LLVM version 10.0.0 (clang-1000.11.45.5)
g++ -v
gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
I am trying to start a thread t:
#include <iostream>
#include <fstream>
#include <string>
#include <thread>
void function(int p1, int p2, int p3){
std::cout<<p1<<p2<<p3<<std::endl;
}
int main(int argc, char const *argv[]) {
std::cout<<"starting"<<std::endl;
std::thread t(function, 1, 2, 3);
std::cout<<"created thread"<<std::endl;
t.join();
std::cout<<"end"<<std::endl;
return 0;
}
My compiler tells me this:
doesntwork.cpp:12:15: error: no matching constructor for
initialization of 'std::thread'
std::thread t(function, 1, 2, 3);
^ ~~~~~~~~~~~~~~~~~
/Library/Developer/CommandLineTools/usr/include/c++/v1/thread:408:9: note:
candidate constructor template not viable: requires single
argument '__f', but 4 arguments were provided
thread::thread(_Fp __f)
^
/Library/Developer/CommandLineTools/usr/include/c++/v1/thread:289:5: note:
candidate constructor not viable: requires 1 argument, but 4
were provided
thread(const thread&);
^
/Library/Developer/CommandLineTools/usr/include/c++/v1/thread:296:5: note:
candidate constructor not viable: requires 0 arguments, but
4 were provided
thread() _NOEXCEPT : __t_(_LIBCPP_NULL_THREAD) {}
^
1 error generated.
In the first case it tells me that for the thread t, there is no constructor that can use more than 1 parameter, while if I just remove the arguments (p1, p2, p3) it doesn't work either because I am not passing any argmuent....
Compiler information:
Configured with: --prefix=/Library/Developer/CommandLineTools/usr
--with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.10.44.2)
Target: x86_64-apple-darwin17.7.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
built command used: g++ doesntwork.cpp -o doesntwork.out
Is there something different you have to do when compiling with threads? Am I missing something very obvious?
On macOS, g++ (from Xcode: Version 10.0 (10A255)) is aliased to clang which by default does not work with c++11 threads. To solve the problem you have to use the -std=c++11 switch.
Example:
g++ -std=c++11 fileToCompile.cpp -o outputFile.out
This should let you compile c++ code using c++11 threads.
Thank you to #M.M for providing the answer above in the comments.