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Date: Thu, 28 Jan 2010 11:21:19 +0000
From: Andrew West <andrewwest AT gmail DOT com>
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To: cygwin AT cygwin DOT com
Subject: dlclose not calling destructors of static variables.
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I seem to be having a problem with dlclose not calling the destructors 
of statically declared variables. I've attached a simple test case which 
I compile as follows;

testlib.cpp
g++ -g -shared testlib.cpp -o testlib

testrunner.cpp
g++ -g testrunner.cpp -o testrunner -ldl

When running testrunner, I get the following output;

Running test_runner
testlib:: start
TestClass::TestClass()
Running test_lib
testlib:: stop
Segmentation fault (core dumped)

Compiling and running the same code on linux gives me the expected 
result of;

Running test_runner
testlib:: start
TestClass::TestClass()
Running test_lib
TestClass::~TestClass()
testlib:: stop

Digging through with gdb, __EntryPoint() registers the destructor of 
TestClass with atexit but dlclose doesn't call the atexit for the dll 
it's unloading leaving the TestClass destructor in the atexit list when 
the program exits even thou testlib.dll has been unloaded, hence the 
segfault.

I'm afraid I'm don't really know much about how the internals of 
cygwin/library loading and unloading works. Is this a simply a case of 
dll_list::detach needing to call __cxa_finalize with a reference to the 
dll being unloaded?

Andy

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 name="testrunner.cpp"
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#include <iostream>
#include <dlfcn.h>

typedef int ( *ENTRYFUNC )();

int main( int argc, char** argv )
{
  std::cout << "Running test_runner" << std::endl;

  void* dll = 0;

  dll = dlopen( "testlib.dll", RTLD_LAZY );

  if ( !dll )
  {
    std::cout << "Could not open library: " << dlerror() << "." << std::endl;
    return 0;
  }

  ENTRYFUNC dllFunc = ( ENTRYFUNC ) dlsym( dll, "__EntryPoint" );

  if ( !dllFunc )
  {
    std::cout << "Could not find library entry point" << std::endl;
    dlclose( dll );
    return 0;
  }

  dllFunc();

  if ( 0 != dlclose( dll ) )
  {
    std::cout << "Could not close library" << std::endl;
    return 0;
  }

  return 1;
}

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 name="testlib.cpp"
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 filename="testlib.cpp"

#include <iostream>
#include <cstdlib>

struct TestClass {
  TestClass()
  {
    std::cout << "TestClass::TestClass()" << std::endl;
  }
  ~TestClass()
  {
    std::cout << "TestClass::~TestClass()" << std::endl;
  }
};

static void start() __attribute__ ((constructor));
static void stop() __attribute__ ((destructor));

extern "C" void __EntryPoint()
{
  static TestClass t1;
  std::cout << "Running test_lib" << std::endl;
}

void start(void)
{
  std::cout << "testlib:: start" << std::endl;
}

void stop(void)
{
  std::cout << "testlib:: stop" << std::endl;
}


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