Compiling multithread code with g++
C++LinuxUbuntuGccG++C++ Problem Overview
I have the easiest code ever:
#include <iostream>
#include <thread>
void worker()
{
std::cout << "another thread";
}
int main()
{
std::thread t(worker);
std::cout << "main thread" << std::endl;
t.join();
return 0;
}
though I still cannot compile it with g++ to run.
More details:
$ g++ --version
g++ (Ubuntu/Linaro 4.8.1-10ubuntu8) 4.8.1
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Command to compile:
$ g++ main.cpp -o main.out -pthread -std=c++11
Running:
$ ./main.out
terminate called after throwing an instance of 'std::system_error'
what(): Enable multithreading to use std::thread: Operation not permitted
Aborted (core dumped)
And now I'm in stuck. In every related thread over the internet it's recommended to add -pthread while I have it already.
What am I doing wrong?
PS: It's a brand new ubuntu 13.10 installation. Only g++ package was installed and minor things like chromium etc
PPS:
$ ldd ./a.out
linux-vdso.so.1 => (0x00007fff29fc1000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fb85397d000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fb853767000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb85339e000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fb85309a000)
/lib64/ld-linux-x86-64.so.2 (0x00007fb853c96000)
PPPS: with clang++ (v3.2) it compiles and runs fine
PPPPS: guys, it's not a duplicate of https://stackoverflow.com/questions/8649828/what-is-wrong-with-this-use-of-stdthread
PPPPPS:
$ dpkg --get-selections | grep 'libc.*dev'
libc-dev-bin install
libc6-dev:amd64 install
libclang-common-dev install
linux-libc-dev:amd64 install
C++ Solutions
Solution 1 - C++
The answer was provided by a kind member of SO C++ chat.
It looks like this behaviour is caused by a bug in gcc.
The workaround provided in the last comment of that bug discussion does work and solves the issue:
-Wl,--no-as-needed
Solution 2 - C++
Adding -lpthread fixed the identical problem for me:
g++ -std=c++11 foo.cpp -lpthread -o foo
Solution 3 - C++
I have slightly more advanced version (4.8.4 instead of 4.8.1), and I tested all three answers above. In fact:
-pthread alone works:
> g++ -std=c++11 -o main -pthread main.cpp
-Wl,--no-as-needed alone does not work.
-lpthread alone does not work.
-Wl,--no-as-needed and -lpthread together work:
> g++ -std=c++11 -o main -Wl,--no-as-needed main.cpp -lpthread
My version is "g++ (Ubuntu 4.8.4-2ubuntu1~14.04.1) 4.8.4".
Solution 4 - C++
answer already was made for qtcreator:
LIBS += -pthread
QMAKE_CXXFLAGS += -pthread
QMAKE_CXXFLAGS += -std=c++11
for console g++: here
g++ -c main.cpp -pthread -std=c++11 // generate target object file
g++ main.o -o main.out -pthread -std=c++11 // link to target binary