StackThreads/MP: version 0.77 User's Guide
StackThreads/MP: version 0.77 User's Guide
The problem occurs when you are using a C++ header file that uses
#pragma interface. When multiple C++ sources include such a
header file and they are linked together, you observe a lot of erros
saying symbols are duplicated. Symbols are names of member functions
defined in the header file. This is probably a gcc bug (that exists at
least in ver 2.7.2.1 on Solaris. I don't know situations in other
platforms and on other versions of gcc), but I describe it here because
the problem occurs faily often (most importantly when you use
iostream.h that comes with g++).
stgcc command gives -fno-default-inline to
gcc. When gcc compiles a C++ source that includes a header
file that uses #pragma interface, it generates all the symbols
defined in the header as global symbols, rather than file-scope
or weak symbols. If multiple sources include such headers, they result
in a link error. This is purely a gcc bug, I believe.
The problem does not occur without -fno-default-inline, in which
case definitions of these symbols are not generated. The problem does
not occurs without #pragma interface either, in which case
symbols are defined as weak symbols. The manual of gcc says the
specification about this pragma is in transition.
It would be nice if you would not encounter this problem unless you use
this pragma. Unfortunately, however, library header files that come with
gcc extensively use them! Most importantly, iostream.h
uses it. A possible work around is to give --default_inline_is_ok
to stgcc, which instructs stgcc not to pass
-fno-default-inline. But then, you must make sure that gcc
never inlines member function calls that appear in
ST_THREAD_CREATE. You can achieve this by, for example, never
calling member functions by ST_THREAD_CREATE. see Possible Slowdown by Disabling Inline for more details about
--default_inline_is_ok.