[patch, libgfortran] PR47694 [4.3/4.4/4.5/4.6 Regression] Fortran read from named pipe fails

[Jerry DeLisle]

Hi folks,

The problem here is that when a read from a named pipe reads more than one line 
worth, the formatted IO buffer holds onto the data.  When fbuf_read is 
subsequently invoked, a sread is dutifully called and it waits for the next read 
completion.  In the meantime, the next line of data is already in the buffer so 
the read waits for another "enter".  The reads get out of sync.  The problem 
does not occur with regular files because there is either always data available 
from the file to read or an EOF occurs and in both those cases sread returns.

The patch fixes this by scanning the buffer under certain conditions looking for 
an End-of-Line (or EOR). If EOR is found, there is no need to sread again from 
the pipe.  This patch does add a little overhead from the tight scan loop, but 
will save some system calls.

Regression tested on x86-64.  I would appreciate others testing please. I do not 
know how to create a specific named pipe test in the test suite. See the PR for 
the original test.

OK for trunk?

Jerry

2011-02-18  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

	PR libgfortran/47694
	* io/fbuf.c (fbuf_read): Scan the buffer for end-of-record and if
	found, do not call sread unnecessarily.
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