[Bug c++/78184] New: std::call_once freezes on second execution if the callable threw an exception on first execution

[simon.heybrock at esss dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78184

            Bug ID: 78184
           Summary: std::call_once freezes on second execution if the
                    callable threw an exception on first execution
           Product: gcc
           Version: 5.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simon.heybrock at esss dot se
  Target Milestone: ---

=== Overview ===

If the callable in std::call_once throws an exception, a subsequent execution
of std::call_once causes a freeze.

Error observed with:
- gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.2)
- g++ (GCC) 6.2.1 20160830

Works with:
- g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4)


=== Example 1 ===

Compiled with: g++ --std=c++11 -fopenmp


#include <iostream>
#include <mutex>
#include <stdexcept>

struct Cache {
  mutable std::once_flag flag;
  void cache() const {
    std::cout << "caching...\n";
    throw std::runtime_error("error");
  }
  void freeze() const {
    std::cout << "freeze?\n";
    std::call_once(flag, &Cache::cache, this);
  }
};

int main() {
  Cache cache;
  try {
    cache.freeze();
  } catch (std::runtime_error &) {
  }
  try {
    cache.freeze();
  } catch (std::runtime_error &) {
  }
}


# Expected output:
freeze?
caching...
freeze?
caching...

# Actual output:
freeze?
caching...
freeze?
^C


=== Example 2 ===

A similar, slightly longer example can be found at
http://en.cppreference.com/w/cpp/thread/call_once.

# Expected output:
Simple example: called once
throw: call_once will retry
throw: call_once will retry
Didn't throw, call_once will not attempt again

# Actual output:
Simple example: called once
throw: call_once will retry
^C


=== Details ===

$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.4.0-6ubuntu1~16.04.2' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --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-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-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