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dlclose() doesn't unload any .so that uses Boost
- From: J <j at jabster dot pl>
- To: binutils at sourceware dot org
- Date: Mon, 30 May 2011 15:18:52 +0200
- Subject: dlclose() doesn't unload any .so that uses Boost
Hi.
I've been told on the GCC mailing list to ask here. Please consider
the following code:
// host.cpp
// compile with: g++ -ldl host.cpp -o host
#include <stdio.h>
#include <dlfcn.h>
int main( int argc, char ** argv )
{
printf( "host: Loading libchild.so...\n" );
void * so = dlopen( "./libchild.so", RTLD_LOCAL | RTLD_NOW );
printf( "host: so = %p\n", so );
if( so == 0 ) return 1;
printf( "host: Unloading libchild.so...\n" );
if( dlclose( so ) != 0 )
{
printf( "host: Error: %s\n", dlerror() );
return 1;
}
printf( "host: Unloaded.\n" );
printf( "host: %p\n", dlopen( "./libchild.so", RTLD_NOLOAD ) );
return 0;
}
// child.cpp
// compile with: g++ -lboost_signals child.cpp -shared -fPIC -o libchild.so
#include <stdio.h>
#include <boost/signals.hpp>
struct foobar_t
{
boost :: signal< void () > signal;
};
void __attribute__ ( ( constructor ) ) ctor()
{
foobar_t foobar;
printf( "child: Constructor\n" );
}
void __attribute__ ( ( destructor ) ) dtor()
{
printf( "child: Destructor\n" );
}
This is the output I get:
host: Loading libchild.so...
child: Constructor
host: so = 0x94b6020
host: Unloading libchild.so...
host: Unloaded.
host: (nil)
child: Destructor
As you can see, dlclose() doesn't properly unload the .so, even though
it claims that it has done so. If you'll remove this line:
boost :: signal< void () > signal;
it works properly:
host: Loading libchild.so...
child: Constructor
host: so = 0x8f6f020
host: Unloading libchild.so...
child: Destructor
host: Unloaded.
host: (nil)
It took me a while to track this down. Now, my question is - is this a
bug? If so, in what? In GCC? (I tried this with both 4.5 and 4.6) In
the dynamic linker? In Boost? If not - why? And how would I fix this?
Any insight in greatly appreciated.
Thanks.