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The rope extension uses a volatile variable for its reference count. This is not only unnecessary for correctness (volatile provides neither atomicity nor memory visibility, and the variable is only modified while a lock is held) but it now causes deprecated warnings with -Wsystem-headers due to the use of ++ and -- operators. It would be possible to use __gnu_cxx::__exchange_and_add in _M_incr and _M_decr when __atomic_is_lock_free(sizeof(_RC_t), &_M_ref_count) is true, rather than locking a mutex. That would probably be a significant improvement for multi-threaded and single-threaded code (because __exchange_and_add will use non-atomic ops when possible, and even in MT code it should be faster than the mutex lock/unlock pair). However, mixing objects compiled with the old and new code would result in inconsistent synchronization being used for the reference count. libstdc++-v3/ChangeLog: * include/ext/rope (_Refcount_Base::_M_ref_count): Remove volatile qualifier. (_Refcount_Base::_M_decr()): Likewise. |
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| .. | ||
| config | ||
| doc | ||
| include | ||
| libsupc++ | ||
| po | ||
| python | ||
| scripts | ||
| src | ||
| testsuite | ||
| acinclude.m4 | ||
| aclocal.m4 | ||
| ChangeLog | ||
| ChangeLog-1998 | ||
| ChangeLog-1999 | ||
| ChangeLog-2000 | ||
| ChangeLog-2001 | ||
| ChangeLog-2002 | ||
| ChangeLog-2003 | ||
| ChangeLog-2004 | ||
| ChangeLog-2005 | ||
| ChangeLog-2006 | ||
| ChangeLog-2007 | ||
| ChangeLog-2008 | ||
| ChangeLog-2009 | ||
| ChangeLog-2010 | ||
| ChangeLog-2011 | ||
| ChangeLog-2012 | ||
| ChangeLog-2013 | ||
| ChangeLog-2014 | ||
| ChangeLog-2015 | ||
| ChangeLog-2016 | ||
| ChangeLog-2017 | ||
| ChangeLog-2018 | ||
| ChangeLog-2019 | ||
| config.h.in | ||
| configure | ||
| configure.ac | ||
| configure.host | ||
| crossconfig.m4 | ||
| fragment.am | ||
| linkage.m4 | ||
| Makefile.am | ||
| Makefile.in | ||
| README | ||
file: libstdc++-v3/README New users may wish to point their web browsers to the file index.html in the 'doc/html' subdirectory. It contains brief building instructions and notes on how to configure the library in interesting ways.