Re: [Hydrogen-devel] singleton pattern and Logger class

[Gabriel M. B. <ga...@te...>]

On Tue, 15 Dec 2009, Jérémy Zurcher wrote:

>> That said, if you have any ideas on how to get (or make) some
>> RT-safe dynamic strings... please share.  I'm interested in having
>> that for Composite as well... so that even when there's an error
>> we're RT-safe.
>>
> quick and dirty thoughts :
> do something like errno perror does,
> have a global or per class static index of error strings
> send only the error code (and an instance reference maybe ) to the logger,
> then let the well known logger thread fetch the string and output it.

Ah, but these wouldn't be /dynamic/ strings.  These would be 
fixed strings.  :-)

One way to go is to look into the implementation of QString 
and std::string and see if we can use the .reserve(N) method 
to accomplish our goals.  It's unlikely in both cases... 
because I think they always allocate space on the heap.

Possibly this can be fixed by using a different allocator.

However, a string class could be created that meets the 
requirement:

     template <typename CharT, size_t Max>
     class RtString
     {
     public:
 	typedef CharT value_type;
 	const size_t max_chars;
 	const size_t npos;

 	/* Formatting: "There are @ objects", where @
 	 * will be replaced through one of the arg()
 	 * functions.
 	 */
 	RtString(const CharT* msg);
 	~RtString() {}

 	RtString& arg(unsigned i);

 	// This should not be part of the final
 	// class...
 	CharT* ref() { return _data; }
 	operator CharT* () { return _data; }

 	size_t size() { return _size; }

     protected:
 	// Search for next '@' sequence.
 	size_t insertion_location();

 	// Shift everything over, discarding the @
 	void make_room(size_t pos, size_t n);

     private:
 	CharT _data[Max + 1];
 	size_t _size;
     };

     typedef RtString<char, 140> LogString;

Typical usage would be like this:

     ERRORLOG( LogString("There were @ cats").arg(125) );

Which would spit out:

     "There were 125 cats"

If you overflow your message buffer... we just truncate the 
message.

I put together a full proof-of-concept, with a ringbuffered 
logging thread, in here:

     http://gitorious.org/composite/composite-labs/trees/94ecd61eee5ab05b6dd427df12a890ee773de16b/200912-rtstring

Comments are welcome!

(I love little puzzles like this... :-))

Peace,
Gabriel