[LLVMdev] [PATCH] Circular Buffered Debug Stream

[David Greene]

On Monday 21 December 2009 13:40, Chris Lattner wrote:

> >> Now that I understand the model :) I don't see why you need to fiddle
> >> with the underlying buffering of TheStream.  In the dbgs() use case,
> >> the underlying stream will be errs() which is already unbuffered.
> >
> > Might circular_raw_ostream be used with other streams at some point?
>
> In that case, setting the underlying stream to unbuffered seems even more
> dangerous.    The client who sets up the buffers has both the power and the
> knowledge to set the streams up correctly when the streams are created.

Fair enough.  I'll make the change.  I was simply following what we did
for formatted_raw_ostream.  It seems a bit wasteful to do buffering on
both streams.

> > +    /// flushBuffer - Dump the contents of the buffer to Stream.
> > +    ///
> > +    void flushBuffer(void) {
> > +      // Write the older portion of the buffer.
> > +      TheStream->write(Cur, BufferArray + BufferSize - Cur);
> > +      // Write the newer portion of the buffer.
> > +      TheStream->write(BufferArray, Cur - BufferArray);
> > +      Cur = BufferArray;
> > +    }
>
> Is this correct in the case when the circular buffer hasn't completely
> filled yet?

Hmm...Depends on what's "correct."  :)  You'll get a bunch of garbage
output but I don't think it should fault or anything.  I don't think 
there's a way of knowing whether the buffer got filled all the way to 
the end unless we add another member variable.  In practice, it will 
almost always be filled.

> > +void circular_raw_ostream::flushBufferWithBanner(void) {
> > +  if (BufferSize != 0) {
> > +    // Write out the buffer
> > +    const char *msg = "*** Log Output ***\n";
>
> This is not generic.  If you really want something like this, the string to
> print should be provided to the ctor.

Ok.

Attached an updated patch.

                                  -Dave
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