c++ - packaged_task operator() get exception -

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#include <future> #include <iostream> #include <thread>  int simple_task(int i) { return i*3; }  int main() {     std::packaged_task<int(int)> task(simple_task);      auto fut = task.get_future();      try {         task(10); // why ???? got exception ??     } catch (std::exception& e) {         std::cout << "exception caught: " << e.what() << std::endl;         return 0;     }      std::cout << "triple 10 " << fut.get() << std::endl; }

output:

exception caught: unknown error -1

am using in wrong way ? want test operator() function. know how use std::thread.

ubuntu 15.04

g++ -v using built-in specs. collect_gcc=g++ collect_lto_wrapper=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper target: x86_64-linux-gnu configured with: ../src/configure -v --with-pkgversion='ubuntu 4.9.2-    10ubuntu13' --with-bugurl=file:///usr/share/doc/gcc-4.9/readme.bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.9 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu thread model: posix gcc version 4.9.2 (ubuntu 4.9.2-10ubuntu13


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