[Committed]: Update Gprof manual re thread-safe counting functions

[Nick Clifton <nickc at redhat dot com>]

Hi Guys,

  I am applying the patch below to add a note to the Gprof manual that
  the call counts and basic block counts are only reliable in a
  mutli-threaded program if the counting function is itself thread-safe.
  This is an issue because the basic mcount function in glibc is not
  thread-safe.

Cheers
  Nick


gprof/ChangeLog
2010-06-08  Nick Clifton  <nickc@redhat.com>

	* gprof.texi (Sampling Error): Note that call counts and basic
	block counts are only reliable for multi-threaded applications if the
	counting function itself is thread safe.

Index: gprof/gprof.texi
===================================================================
RCS file: /cvs/src/src/gprof/gprof.texi,v
retrieving revision 1.31
diff -c -3 -p -r1.31 gprof.texi
*** gprof/gprof.texi	8 Jun 2010 10:30:55 -0000	1.31
--- gprof/gprof.texi	8 Jun 2010 10:36:18 -0000
*************** only a small amount of time, so that on 
*** 1615,1624 ****
  ought to catch that function in the act only once, there is a pretty good
  chance it will actually find that function zero times, or twice.
  
! By contrast, the number-of-calls and basic-block figures
! are derived by counting, not
! sampling.  They are completely accurate and will not vary from run to run
! if your program is deterministic.
  
  The @dfn{sampling period} that is printed at the beginning of the flat
  profile says how often samples are taken.  The rule of thumb is that a
--- 1615,1628 ----
  ought to catch that function in the act only once, there is a pretty good
  chance it will actually find that function zero times, or twice.
  
! By contrast, the number-of-calls and basic-block figures are derived
! by counting, not sampling.  They are completely accurate and will not
! vary from run to run if your program is deterministic and single
! threaded.  In multi-threaded applications, or single threaded
! applications that link with multi-threaded libraries, the counts are
! only deterministic if the counting function is thread-safe.  (Note:
! beware that the mcount counting function in glibc is @emph{not}
! thread-safe).  @xref{Implementation, ,Implementation of Profiling}.
  
  The @dfn{sampling period} that is printed at the beginning of the flat
  profile says how often samples are taken.  The rule of thumb is that a