ENH: unify dlSym handling

- amalgamate dlSym() and dlSymFound() into a single dlSymFind() backend
  with optional 'required' argument. This makes it possible to
  query and assign at once.

src/OSspecific/POSIX/POSIX.C

@@ -1701,27 +1701,38 @@ bool Foam::dlClose(void* handle)
 }
 
 
-void* Foam::dlSym(void* handle, const std::string& symbol)
+void* Foam::dlSymFind(void* handle, const std::string& symbol, bool required)
 {
+    if (!required && (!handle || symbol.empty()))
+    {
+        return nullptr;
+    }
+
     if (POSIX::debug)
     {
         std::cout
-            << "dlSym(void*, const std::string&)"
+            << "dlSymFind(void*, const std::string&, bool)"
             << " : dlsym of " << symbol << std::endl;
     }
-    // clear any old errors - see manpage dlopen
+
+    // Clear any old errors - see manpage dlopen
     (void) ::dlerror();
 
-    // get address of symbol
+    // Get address of symbol
     void* fun = ::dlsym(handle, symbol.c_str());
 
-    // find error (if any)
-    char *error = ::dlerror();
+    // Any error?
+    char *err = ::dlerror();
 
-    if (error)
+    if (err)
     {
+        if (!required)
+        {
+            return nullptr;
+        }
+
         WarningInFunction
-            << "Cannot lookup symbol " << symbol << " : " << error
+            << "Cannot lookup symbol " << symbol << " : " << err
             << endl;
     }
 
@@ -1729,31 +1740,6 @@ void* Foam::dlSym(void* handle, const std::string& symbol)
 }
 
 
-bool Foam::dlSymFound(void* handle, const std::string& symbol)
-{
-    if (handle && !symbol.empty())
-    {
-        if (POSIX::debug)
-        {
-            std::cout
-                << "dlSymFound(void*, const std::string&)"
-                << " : dlsym of " << symbol << std::endl;
-        }
-
-        // clear any old errors - see manpage dlopen
-        (void) ::dlerror();
-
-        // get address of symbol
-        (void) ::dlsym(handle, symbol.c_str());
-
-        // symbol can be found if there was no error
-        return !::dlerror();
-    }
-
-    return false;
-}
-
-
 #ifndef __APPLE__
 static int collectLibsCallback
 (

src/OpenFOAM/include/OSspecific.H

@@ -160,7 +160,7 @@ time_t lastModified(const fileName& name, const bool followLink=true);
 
 //- Return time of last file modification
 //  Using an empty name is a no-op and always returns 0.
-double highResLastModified(const fileName&, const bool followLink = true);
+double highResLastModified(const fileName&, const bool followLink=true);
 
 //- Read a directory and return the entries as a fileName List.
 //  Using an empty directory name returns an empty list.
@@ -259,13 +259,30 @@ void* dlOpen(const fileName& lib, const bool check = true);
 //- Close a dlopened library using handle. Return true if successful
 bool dlClose(void* handle);
 
-//- Lookup a symbol in a dlopened library using handle to library
-void* dlSym(void* handle, const std::string& symbol);
 
-//- Report if symbol in a dlopened library could be found.
+//- Look for symbol in a dlopened library.
+//  If the symbol is not 'required', using a null handle or an empty symbol
+//  name is a no-op and returns nullptr without error.
+//
+//  \return the symbol or nullptr.
+void* dlSymFind(void* handle, const std::string& symbol, bool required=false);
+
+//- Lookup a symbol in a dlopened library using handle to library
+//  \return the symbol or nullptr.
+inline void* dlSym(void* handle, const std::string& symbol)
+{
+    return dlSymFind(handle, symbol, true);
+}
+
+//- Check for symbol in a dlopened library.
 //  Using a null handle or an empty symbol name is a no-op and always
-//  returns false.
-bool dlSymFound(void* handle, const std::string& symbol);
+//  returns nullptr.
+//  \return the symbol or nullptr.
+inline void* dlSymFound(void* handle, const std::string& symbol)
+{
+    return dlSymFind(handle, symbol, false);
+}
+
 
 //- Return all loaded libraries
 fileNameList dlLoaded();