clang++ caught bug - we need to first call lt_dlinit. Also add better error output based on returns from dladvise functions and simplify compile flag

SConstruct

@@ -61,12 +61,16 @@ def call(cmd, silent=False):
     elif not silent:
         color_print(1,'Problem encounted with SCons scripts, please post bug report to: http://trac.mapnik.org\nError was: %s' % stderr)
 
-def get_libtool_version():
+def get_libtool_major_version():
+    """libtool >= 2.1b support lt_dlopenadvise and the previous
+    release appears to be 1.9f (based on NEWS) so checking for 
+    >= 2 seems adequate.
+    """
     cmd = 'libtool'
     if platform.uname()[0] == "Darwin":
         cmd = 'glibtool'
-    fallback_version = 2
     version = None
+    fallback_version = 2
     pattern = r'(.*[^\S])(\d{1}\.\d+\.?\d?)(.*[^\S])'
     ret = os.popen('%s --version' % cmd).read()
     match = re.match(pattern,ret)
@@ -394,7 +398,7 @@ pickle_store = [# Scons internal variables
         'HAS_CAIRO',
         'HAS_PYCAIRO',
         'HAS_LIBXML2',
-        'LIBTOOL_MAJOR_VERSION'
+        'LIBTOOL_SUPPORTS_ADVISE'
         ]
 
 # Add all other user configurable options to pickle pickle_store
@@ -791,7 +795,7 @@ if not preconfigured:
     env['PLATFORM'] = platform.uname()[0]
     color_print(4,"Configuring on %s in *%s*..." % (env['PLATFORM'],mode))
     
-    env['LIBTOOL_MAJOR_VERSION'] = get_libtool_version()
+    env['LIBTOOL_SUPPORTS_ADVISE'] = get_libtool_major_version() >= 2
 
     env['MISSING_DEPS'] = []
     env['SKIPPED_DEPS'] = []

src/SConscript

@@ -141,10 +141,13 @@ source = Split(
     )
 
 
-# add the datasource_cache.cpp with custom LIBTOOL flag
+# add the datasource_cache.cpp with custom LIBTOOL flag if needed
-env3 = lib_env.Clone()
+if env['LIBTOOL_SUPPORTS_ADVISE']:
-env3.Append(CXXFLAGS='-DLIBTOOL_MAJOR_VERSION=%s' % env['LIBTOOL_MAJOR_VERSION'])
+    env3 = lib_env.Clone()
-source.insert(0,env3.SharedObject('datasource_cache.cpp'))
+    env3.Append(CXXFLAGS='-DLIBTOOL_SUPPORTS_ADVISE')
+    source.insert(0,env3.SharedObject('datasource_cache.cpp'))
+else:
+    source.insert(0,'datasource_cache.cpp')
 
 if env['JPEG']:
     source += Split(

src/datasource_cache.cpp

@@ -154,17 +154,35 @@ void datasource_cache::register_datasources(const std::string& str)
             {
                 try 
                 {
-                    // clear errors
+#ifdef LIBTOOL_SUPPORTS_ADVISE
-                    lt_dlerror();
+                    // with ltdl >=2.2 we can actually pass RTDL_GLOBAL to dlopen via the
-#if LIBTOOL_MAJOR_VERSION >= 2
-                    // with ltdl >=2 we can actually pass RTDL_GLOBAL to dlopen via the
                     // ltdl advise trick which is required on linux unless plugins are directly
                     // linked to libmapnik (and deps) at build time. The only other approach is to
                     // set the dlopen flags in the calling process (like in the python bindings)
+
+                    // clear errors
+                    lt_dlerror();
+
+                    lt_dlhandle module = 0;
                     lt_dladvise advise;
-                    lt_dladvise_init(&advise);
+                    int ret;
-                    lt_dladvise_global(&advise);
+                
-                    lt_dlhandle module = lt_dlopenadvise(itr->string().c_str(), advise);
+                    ret = lt_dlinit();
+                    if (ret != 0) {
+                        std::clog << "Datasource loader: could not intialize dynamic loading: " << lt_dlerror() << "\n";
+                    }
+                
+                    ret = lt_dladvise_init(&advise);
+                    if (ret != 0) {
+                        std::clog << "Datasource loader: could not intialize dynamic loading: " << lt_dlerror() << "\n";
+                    }
+                
+                    ret = lt_dladvise_global(&advise);
+                    if (ret != 0) {
+                        std::clog << "Datasource loader: could not intialize dynamic loading of global symbols: " << lt_dlerror() << "\n";
+                    }
+                    
+                    module = lt_dlopenadvise (itr->string().c_str(), advise);
                     lt_dladvise_destroy(&advise);
 #else
                     lt_dlhandle module = lt_dlopen(itr->string().c_str());
@@ -176,7 +194,7 @@ void datasource_cache::register_datasources(const std::string& str)
                         if (ds_name && insert(ds_name(),module))
                         {            
 #ifdef MAPNIK_DEBUG
-                            std::clog << "registered datasource : " << ds_name() << std::endl;
+                            std::clog << "Datasource loader: registered: " << ds_name() << std::endl;
 #endif 
                             registered_=true;
                         }