On Sat, Oct 23, 2010 at 6:46 PM, Jeffrey Walton <noloader@xxxxxxxxx> wrote: > I have a few questions regarding ABI, ODR, and the Runtime Link-Loader. > > Here's the scenario that Crypto++ was taking bug reports on when > maintainers decided to start packaging Crypto++ as a DSO. > > ========== > > > +----- Some Plugin/DSO 1 -----\ > | \ > apache -----+ +----- Crytpo++ DSO > | / > +----- Some Plugin/DSO 2 -----/ > > * (best viewed with fixed font) > > ========== > > Crypto++ DSO declares a global C++ class which has a destructor. Call > it g_Global. g_Global is declared once in Crypto++, and storage is > allocated for it > Crypto++ DSO . > > Apache, Some Plugin/DSO 1, and Some Plugin/DSO 2 do not > declare it and do not provide a storage allocation for it. > > [SNIP] > > ========== > > Apache unloads Some Plugin/DSO 1. The destructor for g_Global > *IS* executed. > Apache unloads Some Plugin/DSO 2. The destructor for g_Global > *IS* executed. <== Crash* I've familiarized myself with ISO/IEC 14882 [1] and section 3.5 Program and Linkage. If a variable (g_Global above) satisfies paragraph/clause (9) (ie, names using external linkage in different scopes denotes the same object), where is it stated that constructors and destructors will run multiple times? I have not found anywhere in the standard where an object's constructor and destructors should be executed multiple times (cf, Section 12 Special member functions, Subsection 1, Constructors). In addition, I don't believe this is a violation of ODR. Section 3.5 specifies that the named variable is the same object, which brings me back to, "Why are constructors and destructors running multiple times?". > ========== > > Apache loads Some Plugin/DSO 1. The constructor for g_Global > is executed. > Apache loads Some Plugin/DSO 2. The constructor for g_Global > *IS NOT* executed. This was probably incorrect - constructors are probably running multiple times. It has not caused a crash, so it its probably causing a leak at worst (as someone else pointed out). Jeff [1] Free version, http://www-d0.fnal.gov/~dladams/cxx_standard.pdf
