On 05/08/15 17:47, Jeffrey Walton wrote: > I'm catching an intermittent failure due to initialization order > across translation units. The code is for a C++ library that offers > both a static archive and a shared object. > > My first thought was to provide an accessor function and make the > global a static local. That did not work because the order of > construction and destruction was not right. It resulted in a crash in > a destructor because an object disappeared too soon. My second thought > was init_priotrity and __attribute__ (constructor) (and friends), but > I know from experience that does not work across translation units. > > My third though was a linker script, and then I came across "Replace > .ctors/.dtors with .init_array/.fini_array on targets supporting them" > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46770#c96) and "collect2 > breaks link order control" > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53068). If I am reading > the reports correctly, then a linker script is not the tool for the > job. > > We also thought about adding a global.cpp file, but we are not sure it > will meet goals because of third party programs, the static archive, > and the interactions during linking. > > The static archive seems to be the trickiest case because of the > interaction with third party programs. The shared object seems to be > an easier problem because its fully linked, and does not interact with > program linking. (Open question: does LTO affect this?). > > Are there any methods to specify initialization order across > translation units? If so, what is it (or are they)? init_priority (priority) In Standard C++, objects defined at namespace scope are guaranteed to be initialized in an order in strict accordance with that of their definitions in a given translation unit. No guarantee is made for initializations across translation units. However, GNU C++ allows users to control the order of initialization of objects defined at namespace scope with the init_priority attribute by specifying a relative priority, a constant integral expression currently bounded between 101 and 65535 inclusive. Lower numbers indicate a higher priority. In the following example, A would normally be created before B, but the init_priority attribute reverses that order: Some_Class A __attribute__ ((init_priority (2000))); Some_Class B __attribute__ ((init_priority (543))); Note that the particular values of priority do not matter; only their relative ordering. Andrew.
