std::future build issue g++ 4.9.3 ARM #8447

I think this started after #8421.

httpserver.cpp:440:19: error: aggregate 'std::future<bool> threadResult' has incomplete type and cannot be defined
 std::future<bool> threadResult;
                   ^
httpserver.cpp: In function 'bool StartHTTPServer()':
httpserver.cpp:447:67: error: variable 'std::packaged_task<bool(event_base*, evhttp*)> task' has initializer but incomplete type
     std::packaged_task<bool(event_base*, evhttp*)> task(ThreadHTTP);
                                                                   ^
Makefile:5022: recipe for target 'libbitcoin_server_a-httpserver.o' failed

$ arm-unknown-linux-gnueabihf-g++ --version
arm-unknown-linux-gnueabihf-g++ (crosstool-NG crosstool-ng-1.22.0-11-g0e85151) 4.9.3
Copyright (C) 2015 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.

@theuni any idea?

Edit: maybe this is false alarm and the g++ compiler produced by crosstool lacks some feature to support the c++11 threading primitives, or I've just forgot to pass some setting. The Travis build for ARM (using g++ 4.8, of all versions) seems to work fine after all.

Ok, seems to be an ARM specific g++ bug (or rather, missing feature): https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64735 I'll try with a newer compiler.

Same problem with g++ 5.3, unfortunately:

httpserver.cpp:440:19: error: aggregate 'std::future<bool> threadResult' has incomplete type and cannot be defined
 std::future<bool> threadResult;
                   ^
httpserver.cpp: In function 'bool StartHTTPServer()':
httpserver.cpp:447:67: error: variable 'std::packaged_task<bool(event_base*, evhttp*)> task' has initializer but incomplete type
     std::packaged_task<bool(event_base*, evhttp*)> task(ThreadHTTP);
                                                                   ^
Makefile:5022: recipe for target 'libbitcoin_server_a-httpserver.o' failed

$ arm-unknown-linux-gnueabihf-g++ --version
arm-unknown-linux-gnueabihf-g++ (crosstool-NG crosstool-ng-1.22.0-11-g0e85151) 5.3.0
Copyright (C) 2015 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.

Confirmed that the build goes fine with Trusty's gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4 I think I misconfigured the architecture, trying with explicitly setting Architecture level to armv7-a.

OK that did it. For anyone building their toolchain using crosstool-ng, make sure to set the architecture level correctly, so that the required atomic instructions are available:

Thanks for tracking it down.